Hey all;

I'm an unhappy camper this week. Electronics seem to explode as soon as
I walk in the same room as them.

Anyways...

One channel on my Hafler DH-200 amp quit working yesterday. The first
thing I wanted to check was the fuse at the back, but in the process of
moving the amp around, I just about burnt my hand--the right heat sink
(the channel that died) was HOT!!!! Not just warm like usual, but REALLY
hot!

So I let it cool down for half an hour or so, and then checked the fuse.
It was fine.

Tonight I'm going to pop the lid and check things inside, i.e. both fuses
on the circuit board, wires shorting, etc.

Does anyone have any suggestions here?

As an aside, I've had no tweeter on one speaker for the past week or so,
but this occurred on the opposite channel. I can't imagine a different
load one one channel seriously frying the other one like this.

Thanks all,
Colin

"Colin B." wrote in message
...
Hey all;

I'm an unhappy camper this week. Electronics seem to explode as soon as
I walk in the same room as them.

Anyways...

One channel on my Hafler DH-200 amp quit working yesterday. The first
thing I wanted to check was the fuse at the back, but in the process of
moving the amp around, I just about burnt my hand--the right heat sink
(the channel that died) was HOT!!!! Not just warm like usual, but REALLY
hot!

So I let it cool down for half an hour or so, and then checked the fuse.
It was fine.

Tonight I'm going to pop the lid and check things inside, i.e. both fuses
on the circuit board, wires shorting, etc.

Does anyone have any suggestions here?

That is a really tough amp. Rumored to withstand a direct short on the
outputs without damage.
Against that one must balance the reputation of the Hitachi MOSFETs as
having a higher failure rate due to internal defect, than bipolar output
transistors.

I would look at the MOSFETs, but you'll have to read up on how to test them.
Do NOT test them with a Lissajous box or other standard transistor curve
tracer.
The breakdown voltage of the gate oxide is about 15V, and standard
procedures would bust them.
These devices are far more sensitive to ESD than a typical MOS integrated
circuit, because they contain no input protection diodes.
Antistatic pad and wrist strap are mandatory.

"Colin B." wrote in message
...
Hey all;

I'm an unhappy camper this week. Electronics seem to explode as soon as
I walk in the same room as them.

Anyways...

One channel on my Hafler DH-200 amp quit working yesterday. The first
thing I wanted to check was the fuse at the back, but in the process of
moving the amp around, I just about burnt my hand--the right heat sink
(the channel that died) was HOT!!!! Not just warm like usual, but REALLY
hot!

So I let it cool down for half an hour or so, and then checked the fuse.
It was fine.

Tonight I'm going to pop the lid and check things inside, i.e. both fuses
on the circuit board, wires shorting, etc.

Does anyone have any suggestions here?

That is a really tough amp. Rumored to withstand a direct short on the
outputs without damage.
Against that one must balance the reputation of the Hitachi MOSFETs as
having a higher failure rate due to internal defect, than bipolar output
transistors.

I would look at the MOSFETs, but you'll have to read up on how to test them.
Do NOT test them with a Lissajous box or other standard transistor curve
tracer.
The breakdown voltage of the gate oxide is about 15V, and standard
procedures would bust them.
These devices are far more sensitive to ESD than a typical MOS integrated
circuit, because they contain no input protection diodes.
Antistatic pad and wrist strap are mandatory.

"Colin B." wrote in message
...
Hey all;

I'm an unhappy camper this week. Electronics seem to explode as soon as
I walk in the same room as them.

Anyways...

One channel on my Hafler DH-200 amp quit working yesterday. The first
thing I wanted to check was the fuse at the back, but in the process of
moving the amp around, I just about burnt my hand--the right heat sink
(the channel that died) was HOT!!!! Not just warm like usual, but REALLY
hot!

So I let it cool down for half an hour or so, and then checked the fuse.
It was fine.

Tonight I'm going to pop the lid and check things inside, i.e. both fuses
on the circuit board, wires shorting, etc.

Does anyone have any suggestions here?

That is a really tough amp. Rumored to withstand a direct short on the
outputs without damage.
Against that one must balance the reputation of the Hitachi MOSFETs as
having a higher failure rate due to internal defect, than bipolar output
transistors.

I would look at the MOSFETs, but you'll have to read up on how to test them.
Do NOT test them with a Lissajous box or other standard transistor curve
tracer.
The breakdown voltage of the gate oxide is about 15V, and standard
procedures would bust them.
These devices are far more sensitive to ESD than a typical MOS integrated
circuit, because they contain no input protection diodes.
Antistatic pad and wrist strap are mandatory.

"Colin B." wrote in message
...
Hey all;

I'm an unhappy camper this week. Electronics seem to explode as soon as
I walk in the same room as them.

Anyways...

One channel on my Hafler DH-200 amp quit working yesterday. The first
thing I wanted to check was the fuse at the back, but in the process of
moving the amp around, I just about burnt my hand--the right heat sink
(the channel that died) was HOT!!!! Not just warm like usual, but REALLY
hot!

So I let it cool down for half an hour or so, and then checked the fuse.
It was fine.

Tonight I'm going to pop the lid and check things inside, i.e. both fuses
on the circuit board, wires shorting, etc.

Does anyone have any suggestions here?

That is a really tough amp. Rumored to withstand a direct short on the
outputs without damage.
Against that one must balance the reputation of the Hitachi MOSFETs as
having a higher failure rate due to internal defect, than bipolar output
transistors.

I would look at the MOSFETs, but you'll have to read up on how to test them.
Do NOT test them with a Lissajous box or other standard transistor curve
tracer.
The breakdown voltage of the gate oxide is about 15V, and standard
procedures would bust them.
These devices are far more sensitive to ESD than a typical MOS integrated
circuit, because they contain no input protection diodes.
Antistatic pad and wrist strap are mandatory.

Does it still work but get very hot? ..... they have a nasty habit of
oscillating at VHF radio frequencies when the electrolytic dry up from old
age....

Also you could check the bias setting....

Rgds:
Eric


"Robert Morein" wrote in message
...

"Colin B." wrote in message
...
Hey all;

I'm an unhappy camper this week. Electronics seem to explode as soon as
I walk in the same room as them.

Anyways...

One channel on my Hafler DH-200 amp quit working yesterday. The first
thing I wanted to check was the fuse at the back, but in the process of
moving the amp around, I just about burnt my hand--the right heat sink
(the channel that died) was HOT!!!! Not just warm like usual, but REALLY
hot!

So I let it cool down for half an hour or so, and then checked the fuse.
It was fine.

Tonight I'm going to pop the lid and check things inside, i.e. both
fuses
on the circuit board, wires shorting, etc.

Does anyone have any suggestions here?

That is a really tough amp. Rumored to withstand a direct short on the
outputs without damage.
Against that one must balance the reputation of the Hitachi MOSFETs as
having a higher failure rate due to internal defect, than bipolar output
transistors.

I would look at the MOSFETs, but you'll have to read up on how to test
them.
Do NOT test them with a Lissajous box or other standard transistor curve
tracer.
The breakdown voltage of the gate oxide is about 15V, and standard
procedures would bust them.
These devices are far more sensitive to ESD than a typical MOS integrated
circuit, because they contain no input protection diodes.
Antistatic pad and wrist strap are mandatory.

Does it still work but get very hot? ..... they have a nasty habit of
oscillating at VHF radio frequencies when the electrolytic dry up from old
age....

Also you could check the bias setting....

Rgds:
Eric


"Robert Morein" wrote in message
...

"Colin B." wrote in message
...
Hey all;

I'm an unhappy camper this week. Electronics seem to explode as soon as
I walk in the same room as them.

Anyways...

One channel on my Hafler DH-200 amp quit working yesterday. The first
thing I wanted to check was the fuse at the back, but in the process of
moving the amp around, I just about burnt my hand--the right heat sink
(the channel that died) was HOT!!!! Not just warm like usual, but REALLY
hot!

So I let it cool down for half an hour or so, and then checked the fuse.
It was fine.

Tonight I'm going to pop the lid and check things inside, i.e. both
fuses
on the circuit board, wires shorting, etc.

Does anyone have any suggestions here?

That is a really tough amp. Rumored to withstand a direct short on the
outputs without damage.
Against that one must balance the reputation of the Hitachi MOSFETs as
having a higher failure rate due to internal defect, than bipolar output
transistors.

I would look at the MOSFETs, but you'll have to read up on how to test
them.
Do NOT test them with a Lissajous box or other standard transistor curve
tracer.
The breakdown voltage of the gate oxide is about 15V, and standard
procedures would bust them.
These devices are far more sensitive to ESD than a typical MOS integrated
circuit, because they contain no input protection diodes.
Antistatic pad and wrist strap are mandatory.

Does it still work but get very hot? ..... they have a nasty habit of
oscillating at VHF radio frequencies when the electrolytic dry up from old
age....

Also you could check the bias setting....

Rgds:
Eric


"Robert Morein" wrote in message
...

"Colin B." wrote in message
...
Hey all;

I'm an unhappy camper this week. Electronics seem to explode as soon as
I walk in the same room as them.

Anyways...

One channel on my Hafler DH-200 amp quit working yesterday. The first
thing I wanted to check was the fuse at the back, but in the process of
moving the amp around, I just about burnt my hand--the right heat sink
(the channel that died) was HOT!!!! Not just warm like usual, but REALLY
hot!

So I let it cool down for half an hour or so, and then checked the fuse.
It was fine.

Tonight I'm going to pop the lid and check things inside, i.e. both
fuses
on the circuit board, wires shorting, etc.

Does anyone have any suggestions here?

That is a really tough amp. Rumored to withstand a direct short on the
outputs without damage.
Against that one must balance the reputation of the Hitachi MOSFETs as
having a higher failure rate due to internal defect, than bipolar output
transistors.

I would look at the MOSFETs, but you'll have to read up on how to test
them.
Do NOT test them with a Lissajous box or other standard transistor curve
tracer.
The breakdown voltage of the gate oxide is about 15V, and standard
procedures would bust them.
These devices are far more sensitive to ESD than a typical MOS integrated
circuit, because they contain no input protection diodes.
Antistatic pad and wrist strap are mandatory.

Does it still work but get very hot? ..... they have a nasty habit of
oscillating at VHF radio frequencies when the electrolytic dry up from old
age....

Also you could check the bias setting....

Rgds:
Eric


"Robert Morein" wrote in message
...

"Colin B." wrote in message
...
Hey all;

I'm an unhappy camper this week. Electronics seem to explode as soon as
I walk in the same room as them.

Anyways...

One channel on my Hafler DH-200 amp quit working yesterday. The first
thing I wanted to check was the fuse at the back, but in the process of
moving the amp around, I just about burnt my hand--the right heat sink
(the channel that died) was HOT!!!! Not just warm like usual, but REALLY
hot!

So I let it cool down for half an hour or so, and then checked the fuse.
It was fine.

Tonight I'm going to pop the lid and check things inside, i.e. both
fuses
on the circuit board, wires shorting, etc.

Does anyone have any suggestions here?

That is a really tough amp. Rumored to withstand a direct short on the
outputs without damage.
Against that one must balance the reputation of the Hitachi MOSFETs as
having a higher failure rate due to internal defect, than bipolar output
transistors.

I would look at the MOSFETs, but you'll have to read up on how to test
them.
Do NOT test them with a Lissajous box or other standard transistor curve
tracer.
The breakdown voltage of the gate oxide is about 15V, and standard
procedures would bust them.
These devices are far more sensitive to ESD than a typical MOS integrated
circuit, because they contain no input protection diodes.
Antistatic pad and wrist strap are mandatory.

Eric K. Weber wrote:
Does it still work but get very hot? ..... they have a nasty habit of
oscillating at VHF radio frequencies when the electrolytic dry up from old
age....

Nope. The channel that gets hot doesn't work at all. No output, nada.

Also you could check the bias setting....

Just set it a few months back, to 250mA each side.

Colin

Eric K. Weber wrote:
Does it still work but get very hot? ..... they have a nasty habit of
oscillating at VHF radio frequencies when the electrolytic dry up from old
age....

Nope. The channel that gets hot doesn't work at all. No output, nada.

Also you could check the bias setting....

Just set it a few months back, to 250mA each side.

Colin

Eric K. Weber wrote:
Does it still work but get very hot? ..... they have a nasty habit of
oscillating at VHF radio frequencies when the electrolytic dry up from old
age....

Nope. The channel that gets hot doesn't work at all. No output, nada.

Also you could check the bias setting....

Just set it a few months back, to 250mA each side.

Colin

Eric K. Weber wrote:
Does it still work but get very hot? ..... they have a nasty habit of
oscillating at VHF radio frequencies when the electrolytic dry up from old
age....

Nope. The channel that gets hot doesn't work at all. No output, nada.

Also you could check the bias setting....

Just set it a few months back, to 250mA each side.

Colin

Robert Morein wrote:

"Colin B." wrote in message
...
Hey all;

I'm an unhappy camper this week. Electronics seem to explode as soon as
I walk in the same room as them.

Anyways...

One channel on my Hafler DH-200 amp quit working yesterday. The first
thing I wanted to check was the fuse at the back, but in the process of
moving the amp around, I just about burnt my hand--the right heat sink
(the channel that died) was HOT!!!! Not just warm like usual, but REALLY
hot!

So I let it cool down for half an hour or so, and then checked the fuse.
It was fine.

Tonight I'm going to pop the lid and check things inside, i.e. both fuses
on the circuit board, wires shorting, etc.

Does anyone have any suggestions here?

That is a really tough amp. Rumored to withstand a direct short on the
outputs without damage.
Against that one must balance the reputation of the Hitachi MOSFETs as
having a higher failure rate due to internal defect, than bipolar output
transistors.

Thanks for the info Robert.
If I had a (or some) blown output transistors, could the heat sink get
hotter? My generic idea of failed parts is: dead part = open circuit =
no current flowing.

I didn't get to crack it open last night, but I'm hoping to find a small
bit of loose wire shorting the outputs, and no damage when its removed.
I might be living in a fantasy, though.

Colin

Robert Morein wrote:

"Colin B." wrote in message
...
Hey all;

I'm an unhappy camper this week. Electronics seem to explode as soon as
I walk in the same room as them.

Anyways...

One channel on my Hafler DH-200 amp quit working yesterday. The first
thing I wanted to check was the fuse at the back, but in the process of
moving the amp around, I just about burnt my hand--the right heat sink
(the channel that died) was HOT!!!! Not just warm like usual, but REALLY
hot!

So I let it cool down for half an hour or so, and then checked the fuse.
It was fine.

Tonight I'm going to pop the lid and check things inside, i.e. both fuses
on the circuit board, wires shorting, etc.

Does anyone have any suggestions here?

That is a really tough amp. Rumored to withstand a direct short on the
outputs without damage.
Against that one must balance the reputation of the Hitachi MOSFETs as
having a higher failure rate due to internal defect, than bipolar output
transistors.

Thanks for the info Robert.
If I had a (or some) blown output transistors, could the heat sink get
hotter? My generic idea of failed parts is: dead part = open circuit =
no current flowing.

I didn't get to crack it open last night, but I'm hoping to find a small
bit of loose wire shorting the outputs, and no damage when its removed.
I might be living in a fantasy, though.

Colin

Robert Morein wrote:

"Colin B." wrote in message
...
Hey all;

I'm an unhappy camper this week. Electronics seem to explode as soon as
I walk in the same room as them.

Anyways...

One channel on my Hafler DH-200 amp quit working yesterday. The first
thing I wanted to check was the fuse at the back, but in the process of
moving the amp around, I just about burnt my hand--the right heat sink
(the channel that died) was HOT!!!! Not just warm like usual, but REALLY
hot!

So I let it cool down for half an hour or so, and then checked the fuse.
It was fine.

Tonight I'm going to pop the lid and check things inside, i.e. both fuses
on the circuit board, wires shorting, etc.

Does anyone have any suggestions here?

That is a really tough amp. Rumored to withstand a direct short on the
outputs without damage.
Against that one must balance the reputation of the Hitachi MOSFETs as
having a higher failure rate due to internal defect, than bipolar output
transistors.

Thanks for the info Robert.
If I had a (or some) blown output transistors, could the heat sink get
hotter? My generic idea of failed parts is: dead part = open circuit =
no current flowing.

I didn't get to crack it open last night, but I'm hoping to find a small
bit of loose wire shorting the outputs, and no damage when its removed.
I might be living in a fantasy, though.

Colin

Robert Morein wrote:

"Colin B." wrote in message
...
Hey all;

I'm an unhappy camper this week. Electronics seem to explode as soon as
I walk in the same room as them.

Anyways...

One channel on my Hafler DH-200 amp quit working yesterday. The first
thing I wanted to check was the fuse at the back, but in the process of
moving the amp around, I just about burnt my hand--the right heat sink
(the channel that died) was HOT!!!! Not just warm like usual, but REALLY
hot!

So I let it cool down for half an hour or so, and then checked the fuse.
It was fine.

Tonight I'm going to pop the lid and check things inside, i.e. both fuses
on the circuit board, wires shorting, etc.

Does anyone have any suggestions here?

That is a really tough amp. Rumored to withstand a direct short on the
outputs without damage.
Against that one must balance the reputation of the Hitachi MOSFETs as
having a higher failure rate due to internal defect, than bipolar output
transistors.

Thanks for the info Robert.
If I had a (or some) blown output transistors, could the heat sink get
hotter? My generic idea of failed parts is: dead part = open circuit =
no current flowing.

I didn't get to crack it open last night, but I'm hoping to find a small
bit of loose wire shorting the outputs, and no damage when its removed.
I might be living in a fantasy, though.

Colin

"Colin B." wrote in message
...
Robert Morein wrote:

"Colin B." wrote in message
...
Hey all;

I'm an unhappy camper this week. Electronics seem to explode as soon as
I walk in the same room as them.

Anyways...

One channel on my Hafler DH-200 amp quit working yesterday. The first
thing I wanted to check was the fuse at the back, but in the process of
moving the amp around, I just about burnt my hand--the right heat sink
(the channel that died) was HOT!!!! Not just warm like usual, but
REALLY
hot!

So I let it cool down for half an hour or so, and then checked the
fuse.
It was fine.

Tonight I'm going to pop the lid and check things inside, i.e. both
fuses
on the circuit board, wires shorting, etc.

Does anyone have any suggestions here?

That is a really tough amp. Rumored to withstand a direct short on the
outputs without damage.
Against that one must balance the reputation of the Hitachi MOSFETs as
having a higher failure rate due to internal defect, than bipolar output
transistors.

Thanks for the info Robert.
If I had a (or some) blown output transistors, could the heat sink get
hotter? My generic idea of failed parts is: dead part = open circuit =
no current flowing.

I didn't get to crack it open last night, but I'm hoping to find a small
bit of loose wire shorting the outputs, and no damage when its removed.
I might be living in a fantasy, though.

Colin

They can fail either way, though it is true that open circuit is somewhat
more common, and that would not cause it to heat up.

You'll want to remove each supply rail fuse separately, and connect an
ammeter or a current measuring shunt. You want 200 ma quiescent bias current
on each.
Once you find which side is hot, you have a choice: start testing MOSFETs,
or look at the voltage on the MOSFET gates. If there's something out of line
there, you may be able to excuse the MOSFETs and look for a defect in the
driver circuitry.

"Colin B." wrote in message
...
Robert Morein wrote:

"Colin B." wrote in message
...
Hey all;

I'm an unhappy camper this week. Electronics seem to explode as soon as
I walk in the same room as them.

Anyways...

One channel on my Hafler DH-200 amp quit working yesterday. The first
thing I wanted to check was the fuse at the back, but in the process of
moving the amp around, I just about burnt my hand--the right heat sink
(the channel that died) was HOT!!!! Not just warm like usual, but
REALLY
hot!

So I let it cool down for half an hour or so, and then checked the
fuse.
It was fine.

Tonight I'm going to pop the lid and check things inside, i.e. both
fuses
on the circuit board, wires shorting, etc.

Does anyone have any suggestions here?

That is a really tough amp. Rumored to withstand a direct short on the
outputs without damage.
Against that one must balance the reputation of the Hitachi MOSFETs as
having a higher failure rate due to internal defect, than bipolar output
transistors.

Thanks for the info Robert.
If I had a (or some) blown output transistors, could the heat sink get
hotter? My generic idea of failed parts is: dead part = open circuit =
no current flowing.

I didn't get to crack it open last night, but I'm hoping to find a small
bit of loose wire shorting the outputs, and no damage when its removed.
I might be living in a fantasy, though.

Colin

They can fail either way, though it is true that open circuit is somewhat
more common, and that would not cause it to heat up.

You'll want to remove each supply rail fuse separately, and connect an
ammeter or a current measuring shunt. You want 200 ma quiescent bias current
on each.
Once you find which side is hot, you have a choice: start testing MOSFETs,
or look at the voltage on the MOSFET gates. If there's something out of line
there, you may be able to excuse the MOSFETs and look for a defect in the
driver circuitry.

"Colin B." wrote in message
...
Robert Morein wrote:

"Colin B." wrote in message
...
Hey all;

I'm an unhappy camper this week. Electronics seem to explode as soon as
I walk in the same room as them.

Anyways...

One channel on my Hafler DH-200 amp quit working yesterday. The first
thing I wanted to check was the fuse at the back, but in the process of
moving the amp around, I just about burnt my hand--the right heat sink
(the channel that died) was HOT!!!! Not just warm like usual, but
REALLY
hot!

So I let it cool down for half an hour or so, and then checked the
fuse.
It was fine.

Tonight I'm going to pop the lid and check things inside, i.e. both
fuses
on the circuit board, wires shorting, etc.

Does anyone have any suggestions here?

That is a really tough amp. Rumored to withstand a direct short on the
outputs without damage.
Against that one must balance the reputation of the Hitachi MOSFETs as
having a higher failure rate due to internal defect, than bipolar output
transistors.

Thanks for the info Robert.
If I had a (or some) blown output transistors, could the heat sink get
hotter? My generic idea of failed parts is: dead part = open circuit =
no current flowing.

I didn't get to crack it open last night, but I'm hoping to find a small
bit of loose wire shorting the outputs, and no damage when its removed.
I might be living in a fantasy, though.

Colin

They can fail either way, though it is true that open circuit is somewhat
more common, and that would not cause it to heat up.

You'll want to remove each supply rail fuse separately, and connect an
ammeter or a current measuring shunt. You want 200 ma quiescent bias current
on each.
Once you find which side is hot, you have a choice: start testing MOSFETs,
or look at the voltage on the MOSFET gates. If there's something out of line
there, you may be able to excuse the MOSFETs and look for a defect in the
driver circuitry.

"Colin B." wrote in message
...
Robert Morein wrote:

"Colin B." wrote in message
...
Hey all;

I'm an unhappy camper this week. Electronics seem to explode as soon as
I walk in the same room as them.

Anyways...

One channel on my Hafler DH-200 amp quit working yesterday. The first
thing I wanted to check was the fuse at the back, but in the process of
moving the amp around, I just about burnt my hand--the right heat sink
(the channel that died) was HOT!!!! Not just warm like usual, but
REALLY
hot!

So I let it cool down for half an hour or so, and then checked the
fuse.
It was fine.

Tonight I'm going to pop the lid and check things inside, i.e. both
fuses
on the circuit board, wires shorting, etc.

Does anyone have any suggestions here?

That is a really tough amp. Rumored to withstand a direct short on the
outputs without damage.
Against that one must balance the reputation of the Hitachi MOSFETs as
having a higher failure rate due to internal defect, than bipolar output
transistors.

Thanks for the info Robert.
If I had a (or some) blown output transistors, could the heat sink get
hotter? My generic idea of failed parts is: dead part = open circuit =
no current flowing.

I didn't get to crack it open last night, but I'm hoping to find a small
bit of loose wire shorting the outputs, and no damage when its removed.
I might be living in a fantasy, though.

Colin

They can fail either way, though it is true that open circuit is somewhat
more common, and that would not cause it to heat up.

You'll want to remove each supply rail fuse separately, and connect an
ammeter or a current measuring shunt. You want 200 ma quiescent bias current
on each.
Once you find which side is hot, you have a choice: start testing MOSFETs,
or look at the voltage on the MOSFET gates. If there's something out of line
there, you may be able to excuse the MOSFETs and look for a defect in the
driver circuitry.

"Colin B." wrote in
:

Eric K. Weber wrote:
Does it still work but get very hot? ..... they have a nasty habit of
oscillating at VHF radio frequencies when the electrolytic dry up from
old
age....

Nope. The channel that gets hot doesn't work at all. No output, nada.

Also you could check the bias setting....

Just set it a few months back, to 250mA each side.

Colin


My guess is that a driver transistor failed and is driving the outputs
into DC coduction. Re-check your bias, I will be willing to bet it is way
off.

r


--
Nothing beats the bandwidth of a station wagon filled with DLT tapes.

"Colin B." wrote in
:

Eric K. Weber wrote:
Does it still work but get very hot? ..... they have a nasty habit of
oscillating at VHF radio frequencies when the electrolytic dry up from
old
age....

Nope. The channel that gets hot doesn't work at all. No output, nada.

Also you could check the bias setting....

Just set it a few months back, to 250mA each side.

Colin


My guess is that a driver transistor failed and is driving the outputs
into DC coduction. Re-check your bias, I will be willing to bet it is way
off.

r


--
Nothing beats the bandwidth of a station wagon filled with DLT tapes.

"Colin B." wrote in
:

Eric K. Weber wrote:
Does it still work but get very hot? ..... they have a nasty habit of
oscillating at VHF radio frequencies when the electrolytic dry up from
old
age....

Nope. The channel that gets hot doesn't work at all. No output, nada.

Also you could check the bias setting....

Just set it a few months back, to 250mA each side.

Colin


My guess is that a driver transistor failed and is driving the outputs
into DC coduction. Re-check your bias, I will be willing to bet it is way
off.

r


--
Nothing beats the bandwidth of a station wagon filled with DLT tapes.

"Colin B." wrote in
:

Eric K. Weber wrote:
Does it still work but get very hot? ..... they have a nasty habit of
oscillating at VHF radio frequencies when the electrolytic dry up from
old
age....

Nope. The channel that gets hot doesn't work at all. No output, nada.

Also you could check the bias setting....

Just set it a few months back, to 250mA each side.

Colin


My guess is that a driver transistor failed and is driving the outputs
into DC coduction. Re-check your bias, I will be willing to bet it is way
off.

r


--
Nothing beats the bandwidth of a station wagon filled with DLT tapes.

Rich Andrews. wrote:
"Colin B." wrote in
:

(One channel dead on Hafler power amp)

My guess is that a driver transistor failed and is driving the outputs
into DC coduction. Re-check your bias, I will be willing to bet it is way
off.

Well, here's the latest:

The good channel has a bias of about 30mA when stone cold! (should be
250mA when fully warmed up--ten times increase seems odd). The bad
channel though, has a bias of about 900mA when cold. Yikes!!!
With no load attached, nothing warms up on the bad channel at all.
With speakers attached, I hear a 60Hz hum on the bad channel, and the
2SJ49s get ferociously hot in a matter of seconds.

As an aside, I've got a feeling I fried the unfused (10A max) ammeter
in my DVM. :-( Somedays I think I should just bury myself away from
anything electronic.

Anyways, do I have a hope for this thing, or is it a matter of replacing
the transistors ($80 a set!) vs. junking it?

And what would have caused it to die so suddenly on me?

thanks all,
Colin

Rich Andrews. wrote:
"Colin B." wrote in
:

(One channel dead on Hafler power amp)

My guess is that a driver transistor failed and is driving the outputs
into DC coduction. Re-check your bias, I will be willing to bet it is way
off.

Well, here's the latest:

The good channel has a bias of about 30mA when stone cold! (should be
250mA when fully warmed up--ten times increase seems odd). The bad
channel though, has a bias of about 900mA when cold. Yikes!!!
With no load attached, nothing warms up on the bad channel at all.
With speakers attached, I hear a 60Hz hum on the bad channel, and the
2SJ49s get ferociously hot in a matter of seconds.

As an aside, I've got a feeling I fried the unfused (10A max) ammeter
in my DVM. :-( Somedays I think I should just bury myself away from
anything electronic.

Anyways, do I have a hope for this thing, or is it a matter of replacing
the transistors ($80 a set!) vs. junking it?

And what would have caused it to die so suddenly on me?

thanks all,
Colin

Rich Andrews. wrote:
"Colin B." wrote in
:

(One channel dead on Hafler power amp)

My guess is that a driver transistor failed and is driving the outputs
into DC coduction. Re-check your bias, I will be willing to bet it is way
off.

Well, here's the latest:

The good channel has a bias of about 30mA when stone cold! (should be
250mA when fully warmed up--ten times increase seems odd). The bad
channel though, has a bias of about 900mA when cold. Yikes!!!
With no load attached, nothing warms up on the bad channel at all.
With speakers attached, I hear a 60Hz hum on the bad channel, and the
2SJ49s get ferociously hot in a matter of seconds.

As an aside, I've got a feeling I fried the unfused (10A max) ammeter
in my DVM. :-( Somedays I think I should just bury myself away from
anything electronic.

Anyways, do I have a hope for this thing, or is it a matter of replacing
the transistors ($80 a set!) vs. junking it?

And what would have caused it to die so suddenly on me?

thanks all,
Colin

Rich Andrews. wrote:
"Colin B." wrote in
:

(One channel dead on Hafler power amp)

My guess is that a driver transistor failed and is driving the outputs
into DC coduction. Re-check your bias, I will be willing to bet it is way
off.

Well, here's the latest:

The good channel has a bias of about 30mA when stone cold! (should be
250mA when fully warmed up--ten times increase seems odd). The bad
channel though, has a bias of about 900mA when cold. Yikes!!!
With no load attached, nothing warms up on the bad channel at all.
With speakers attached, I hear a 60Hz hum on the bad channel, and the
2SJ49s get ferociously hot in a matter of seconds.

As an aside, I've got a feeling I fried the unfused (10A max) ammeter
in my DVM. :-( Somedays I think I should just bury myself away from
anything electronic.

Anyways, do I have a hope for this thing, or is it a matter of replacing
the transistors ($80 a set!) vs. junking it?

And what would have caused it to die so suddenly on me?

thanks all,
Colin

"Colin B." wrote:

Rich Andrews. wrote:
"Colin B." wrote in
:

(One channel dead on Hafler power amp)

My guess is that a driver transistor failed and is driving the outputs
into DC coduction. Re-check your bias, I will be willing to bet it is way
off.

Well, here's the latest:

The good channel has a bias of about 30mA when stone cold! (should be
250mA when fully warmed up--ten times increase seems odd). The bad
channel though, has a bias of about 900mA when cold. Yikes!!!
With no load attached, nothing warms up on the bad channel at all.
With speakers attached, I hear a 60Hz hum on the bad channel, and the
2SJ49s get ferociously hot in a matter of seconds.

Be careful: your amp has a heavy DC offset on the output of the bad
channel that could fry your speakers.

Anyways, do I have a hope for this thing, or is it a matter of replacing
the transistors ($80 a set!) vs. junking it?

Try disconnecting the driver transistors of the bad channel, and
measuring (with the DC Volts scale of your DMM) if there is DC on the
speaker terminals. If it's not, then probably the output transistors
are in good shape, and the trouble may be cheaper to repair.
---
Ing. Remberto Gomez-Meda
http://ingemeda.tripod.com/
INGE - Ingenieria Electronica.
Puerto Vallarta, Jalisco, Mexico.

"Colin B." wrote:

Rich Andrews. wrote:
"Colin B." wrote in
:

(One channel dead on Hafler power amp)

My guess is that a driver transistor failed and is driving the outputs
into DC coduction. Re-check your bias, I will be willing to bet it is way
off.

Well, here's the latest:

The good channel has a bias of about 30mA when stone cold! (should be
250mA when fully warmed up--ten times increase seems odd). The bad
channel though, has a bias of about 900mA when cold. Yikes!!!
With no load attached, nothing warms up on the bad channel at all.
With speakers attached, I hear a 60Hz hum on the bad channel, and the
2SJ49s get ferociously hot in a matter of seconds.

Be careful: your amp has a heavy DC offset on the output of the bad
channel that could fry your speakers.

Anyways, do I have a hope for this thing, or is it a matter of replacing
the transistors ($80 a set!) vs. junking it?

Try disconnecting the driver transistors of the bad channel, and
measuring (with the DC Volts scale of your DMM) if there is DC on the
speaker terminals. If it's not, then probably the output transistors
are in good shape, and the trouble may be cheaper to repair.
---
Ing. Remberto Gomez-Meda
http://ingemeda.tripod.com/
INGE - Ingenieria Electronica.
Puerto Vallarta, Jalisco, Mexico.

"Colin B." wrote:

Rich Andrews. wrote:
"Colin B." wrote in
:

(One channel dead on Hafler power amp)

My guess is that a driver transistor failed and is driving the outputs
into DC coduction. Re-check your bias, I will be willing to bet it is way
off.

Well, here's the latest:

The good channel has a bias of about 30mA when stone cold! (should be
250mA when fully warmed up--ten times increase seems odd). The bad
channel though, has a bias of about 900mA when cold. Yikes!!!
With no load attached, nothing warms up on the bad channel at all.
With speakers attached, I hear a 60Hz hum on the bad channel, and the
2SJ49s get ferociously hot in a matter of seconds.

Be careful: your amp has a heavy DC offset on the output of the bad
channel that could fry your speakers.

Anyways, do I have a hope for this thing, or is it a matter of replacing
the transistors ($80 a set!) vs. junking it?

Try disconnecting the driver transistors of the bad channel, and
measuring (with the DC Volts scale of your DMM) if there is DC on the
speaker terminals. If it's not, then probably the output transistors
are in good shape, and the trouble may be cheaper to repair.
---
Ing. Remberto Gomez-Meda
http://ingemeda.tripod.com/
INGE - Ingenieria Electronica.
Puerto Vallarta, Jalisco, Mexico.

"Colin B." wrote:

Rich Andrews. wrote:
"Colin B." wrote in
:

(One channel dead on Hafler power amp)

My guess is that a driver transistor failed and is driving the outputs
into DC coduction. Re-check your bias, I will be willing to bet it is way
off.

Well, here's the latest:

The good channel has a bias of about 30mA when stone cold! (should be
250mA when fully warmed up--ten times increase seems odd). The bad
channel though, has a bias of about 900mA when cold. Yikes!!!
With no load attached, nothing warms up on the bad channel at all.
With speakers attached, I hear a 60Hz hum on the bad channel, and the
2SJ49s get ferociously hot in a matter of seconds.

Be careful: your amp has a heavy DC offset on the output of the bad
channel that could fry your speakers.

Anyways, do I have a hope for this thing, or is it a matter of replacing
the transistors ($80 a set!) vs. junking it?

Try disconnecting the driver transistors of the bad channel, and
measuring (with the DC Volts scale of your DMM) if there is DC on the
speaker terminals. If it's not, then probably the output transistors
are in good shape, and the trouble may be cheaper to repair.
---
Ing. Remberto Gomez-Meda
http://ingemeda.tripod.com/
INGE - Ingenieria Electronica.
Puerto Vallarta, Jalisco, Mexico.

El Meda wrote:
"Colin B." wrote:

Rich Andrews. wrote:
"Colin B." wrote in
:

(One channel dead on Hafler power amp)

My guess is that a driver transistor failed and is driving the outputs
into DC coduction. Re-check your bias, I will be willing to bet it is way
off.

Well, here's the latest:

The good channel has a bias of about 30mA when stone cold! (should be
250mA when fully warmed up--ten times increase seems odd). The bad
channel though, has a bias of about 900mA when cold. Yikes!!!
With no load attached, nothing warms up on the bad channel at all.
With speakers attached, I hear a 60Hz hum on the bad channel, and the
2SJ49s get ferociously hot in a matter of seconds.

Be careful: your amp has a heavy DC offset on the output of the bad
channel that could fry your speakers.

Indeed it does! Luckily, the speakers are fine.

Try disconnecting the driver transistors of the bad channel, and
measuring (with the DC Volts scale of your DMM) if there is DC on the
speaker terminals. If it's not, then probably the output transistors
are in good shape, and the trouble may be cheaper to repair.

On the bad channel with no output transistors, I'm measuring -0.5VDC
output. That's pretty substantial. I measured the output with the
transistors in place, and it was sitting at -20VDC!

Next steps? It looks like the transistors might be OK.

Colin

El Meda wrote:
"Colin B." wrote:

Rich Andrews. wrote:
"Colin B." wrote in
:

(One channel dead on Hafler power amp)

My guess is that a driver transistor failed and is driving the outputs
into DC coduction. Re-check your bias, I will be willing to bet it is way
off.

Well, here's the latest:

The good channel has a bias of about 30mA when stone cold! (should be
250mA when fully warmed up--ten times increase seems odd). The bad
channel though, has a bias of about 900mA when cold. Yikes!!!
With no load attached, nothing warms up on the bad channel at all.
With speakers attached, I hear a 60Hz hum on the bad channel, and the
2SJ49s get ferociously hot in a matter of seconds.

Be careful: your amp has a heavy DC offset on the output of the bad
channel that could fry your speakers.

Indeed it does! Luckily, the speakers are fine.

Try disconnecting the driver transistors of the bad channel, and
measuring (with the DC Volts scale of your DMM) if there is DC on the
speaker terminals. If it's not, then probably the output transistors
are in good shape, and the trouble may be cheaper to repair.

On the bad channel with no output transistors, I'm measuring -0.5VDC
output. That's pretty substantial. I measured the output with the
transistors in place, and it was sitting at -20VDC!

Next steps? It looks like the transistors might be OK.

Colin

El Meda wrote:
"Colin B." wrote:

Rich Andrews. wrote:
"Colin B." wrote in
:

(One channel dead on Hafler power amp)

My guess is that a driver transistor failed and is driving the outputs
into DC coduction. Re-check your bias, I will be willing to bet it is way
off.

Well, here's the latest:

The good channel has a bias of about 30mA when stone cold! (should be
250mA when fully warmed up--ten times increase seems odd). The bad
channel though, has a bias of about 900mA when cold. Yikes!!!
With no load attached, nothing warms up on the bad channel at all.
With speakers attached, I hear a 60Hz hum on the bad channel, and the
2SJ49s get ferociously hot in a matter of seconds.

Be careful: your amp has a heavy DC offset on the output of the bad
channel that could fry your speakers.

Indeed it does! Luckily, the speakers are fine.

Try disconnecting the driver transistors of the bad channel, and
measuring (with the DC Volts scale of your DMM) if there is DC on the
speaker terminals. If it's not, then probably the output transistors
are in good shape, and the trouble may be cheaper to repair.

On the bad channel with no output transistors, I'm measuring -0.5VDC
output. That's pretty substantial. I measured the output with the
transistors in place, and it was sitting at -20VDC!

Next steps? It looks like the transistors might be OK.

Colin

El Meda wrote:
"Colin B." wrote:

Rich Andrews. wrote:
"Colin B." wrote in
:

(One channel dead on Hafler power amp)

My guess is that a driver transistor failed and is driving the outputs
into DC coduction. Re-check your bias, I will be willing to bet it is way
off.

Well, here's the latest:

The good channel has a bias of about 30mA when stone cold! (should be
250mA when fully warmed up--ten times increase seems odd). The bad
channel though, has a bias of about 900mA when cold. Yikes!!!
With no load attached, nothing warms up on the bad channel at all.
With speakers attached, I hear a 60Hz hum on the bad channel, and the
2SJ49s get ferociously hot in a matter of seconds.

Be careful: your amp has a heavy DC offset on the output of the bad
channel that could fry your speakers.

Indeed it does! Luckily, the speakers are fine.

Try disconnecting the driver transistors of the bad channel, and
measuring (with the DC Volts scale of your DMM) if there is DC on the
speaker terminals. If it's not, then probably the output transistors
are in good shape, and the trouble may be cheaper to repair.

On the bad channel with no output transistors, I'm measuring -0.5VDC
output. That's pretty substantial. I measured the output with the
transistors in place, and it was sitting at -20VDC!

Next steps? It looks like the transistors might be OK.

Colin

"Colin B." wrote:

Try disconnecting the driver transistors of the bad channel, and
measuring (with the DC Volts scale of your DMM) if there is DC on the
speaker terminals. If it's not, then probably the output transistors
are in good shape, and the trouble may be cheaper to repair.

On the bad channel with no output transistors, I'm measuring -0.5VDC
output. That's pretty substantial. I measured the output with the
transistors in place, and it was sitting at -20VDC!

Next steps? It looks like the transistors might be OK.

Colin

The driver transistors that I was talking about weren't the output
transistors, but the smaller transistors that are connected to them.

With the output transistors in place disconnect the smaller ones,
power on the amplifier, and check for DC on the speaker terminals. If
there is not DC, then the output transistors are probably OK.

Even If the output transistors are good, check the disconnected
drivers. Check in circuit (with the amplifier turned off) also every
diode and Zener on the bad channel, and every resistance of less than
1 Kohm. Check in circuit the even smaller transistors for short
circuits. Disconnect and test off-circuit everything suspicious.

Change the bad ones.
---
Ing. Remberto Gomez-Meda
http://ingemeda.tripod.com/
INGE - Ingenieria Electronica.
Puerto Vallarta, Jalisco, Mexico.

"Colin B." wrote:

Try disconnecting the driver transistors of the bad channel, and
measuring (with the DC Volts scale of your DMM) if there is DC on the
speaker terminals. If it's not, then probably the output transistors
are in good shape, and the trouble may be cheaper to repair.

On the bad channel with no output transistors, I'm measuring -0.5VDC
output. That's pretty substantial. I measured the output with the
transistors in place, and it was sitting at -20VDC!

Next steps? It looks like the transistors might be OK.

Colin

The driver transistors that I was talking about weren't the output
transistors, but the smaller transistors that are connected to them.

With the output transistors in place disconnect the smaller ones,
power on the amplifier, and check for DC on the speaker terminals. If
there is not DC, then the output transistors are probably OK.

Even If the output transistors are good, check the disconnected
drivers. Check in circuit (with the amplifier turned off) also every
diode and Zener on the bad channel, and every resistance of less than
1 Kohm. Check in circuit the even smaller transistors for short
circuits. Disconnect and test off-circuit everything suspicious.

Change the bad ones.
---
Ing. Remberto Gomez-Meda
http://ingemeda.tripod.com/
INGE - Ingenieria Electronica.
Puerto Vallarta, Jalisco, Mexico.

"Colin B." wrote:

Try disconnecting the driver transistors of the bad channel, and
measuring (with the DC Volts scale of your DMM) if there is DC on the
speaker terminals. If it's not, then probably the output transistors
are in good shape, and the trouble may be cheaper to repair.

On the bad channel with no output transistors, I'm measuring -0.5VDC
output. That's pretty substantial. I measured the output with the
transistors in place, and it was sitting at -20VDC!

Next steps? It looks like the transistors might be OK.

Colin

The driver transistors that I was talking about weren't the output
transistors, but the smaller transistors that are connected to them.

With the output transistors in place disconnect the smaller ones,
power on the amplifier, and check for DC on the speaker terminals. If
there is not DC, then the output transistors are probably OK.

Even If the output transistors are good, check the disconnected
drivers. Check in circuit (with the amplifier turned off) also every
diode and Zener on the bad channel, and every resistance of less than
1 Kohm. Check in circuit the even smaller transistors for short
circuits. Disconnect and test off-circuit everything suspicious.

Change the bad ones.
---
Ing. Remberto Gomez-Meda
http://ingemeda.tripod.com/
INGE - Ingenieria Electronica.
Puerto Vallarta, Jalisco, Mexico.