I ran my amplifier off a switch mode power supply. one of my friends moved
it and the mains power of my flat tripped. when I got to the amp I noticed
that there is a burn mark on the metal casing in which it is built. This
casing is connected to the ground. I could not find the other place (I
presume it should be on the switch mode PSU) where the amp touched when this
happened.

When I turn on the amp the power led lights up and then fades slowely.
Neither of the 2 30Amp fuses blew out.

Also I opened the amp and noticed that one of the resistors is burnt black.

Any idea where I should start in repairing the amp?

Could it be one of the diodes?

OK first off Im no electronics expert, but have repaired simple circuits
before around the car/house.

Its possible you fird a diode in there too, and that may be whats
causing the overload on the fried resistor. If you can get a schematic
that would be helpful IMHO. I would test all the componets up stream
and down stream of that fried resistor. Check all the diodes around
that resistor. A diode should flow current in one direction only, if
you get current flow in both directions the diode is no good.

Check for other burnt components and do similar checks on that area of
the PCB. Do any of the PCB layer traces or fab look burnt or over
heated?....

Hope this helps, and repair gurus please correct me if I am wrong.


Garrett



Johan Wagener wrote:
I ran my amplifier off a switch mode power supply. one of my friends moved
it and the mains power of my flat tripped. when I got to the amp I noticed
that there is a burn mark on the metal casing in which it is built. This
casing is connected to the ground. I could not find the other place (I
presume it should be on the switch mode PSU) where the amp touched when this
happened.

When I turn on the amp the power led lights up and then fades slowely.
Neither of the 2 30Amp fuses blew out.

Also I opened the amp and noticed that one of the resistors is burnt black.

Any idea where I should start in repairing the amp?

Could it be one of the diodes?

A lot of amps separate the primary side ground of the internal switching
power supply from the secondary ground side with a power resistor. This way
they can reference each other.

Start by replacing the burnt resistor. It may have went open circuit and
allows the secondary side side voltage to float out of control.

Just a note. The case of most amplifiers is tied to the secondary
"floating" side ground. You may have shorted this to the primary side
ground.


--
Ge0
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Main & rear fill amp = a/d/s/ P840.2
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"Johan Wagener" wrote in message
...
I ran my amplifier off a switch mode power supply. one of my friends moved
it and the mains power of my flat tripped. when I got to the amp I noticed
that there is a burn mark on the metal casing in which it is built. This
casing is connected to the ground. I could not find the other place (I
presume it should be on the switch mode PSU) where the amp touched when
this
happened.

When I turn on the amp the power led lights up and then fades slowely.
Neither of the 2 30Amp fuses blew out.

Also I opened the amp and noticed that one of the resistors is burnt
black.

Any idea where I should start in repairing the amp?

Could it be one of the diodes?

Was the burned resistor rather large? Oh, say .200" dia. x .700" L. Was it
near the Power supply section?

Sounds like a power GND/Signal GND isolation resistor. But, there is
something else wrong as well. Believe it or not,
some amplifiers will operate with this resistor completely burned up. My
guess is that you have an output transistor shorted as well.

Probe both sides of the burned resistor. Can you still get a resistance
measurement? Say, less than 300 Ohms?
Look at all the PS capacitors. Do any look bulged or vented? Can you feel
any oily residue on any of these caps?
If so, they are probably bad due to excessive ripple current. Likely due to
running the amplifier on a SMPS. Not the best idea unless the +12V SMPS
output is **heavily** filtered. Could get ripple current from the sum and
difference switching
frequencies of the two SMPS.
Probe the Collector to Emitter resistance on all your output transistors.
Should be much greater than zero Ohms. If any is at or near zero Ohms, then
one could suspect that the device is bad.

Can you obtain a schematic?

Good Luck,

John Andreen
"Johan Wagener" wrote in message
...
I ran my amplifier off a switch mode power supply. one of my friends moved
it and the mains power of my flat tripped. when I got to the amp I noticed
that there is a burn mark on the metal casing in which it is built. This
casing is connected to the ground. I could not find the other place (I
presume it should be on the switch mode PSU) where the amp touched when
this
happened.

When I turn on the amp the power led lights up and then fades slowely.
Neither of the 2 30Amp fuses blew out.

Also I opened the amp and noticed that one of the resistors is burnt
black.

Any idea where I should start in repairing the amp?

Could it be one of the diodes?