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[email protected] a6mech@rocketmail.com is offline
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Default TFM-35 Problem

Hi All,

I've had my Carver TFM-35 for 10 years or so, with never a problem.
Recently the speaker protection relay began cycling now and then. Now
it cycles almost constantly. Does not matter which set of speakers are
coupled up. Also, the front panel lights for the VU meters are out.

Any ideas?

Thanks,

Ernst

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Default TFM-35 Problem

Tim,

I appreciate the reply; however, I'd like to fix the problem rather
than patch it up. I got inside the cabinet and the only thing obvious
I found was a swollen filter cap. These caps seem to have four
terminals instead of the customary two. Seems like the first thing to
do is replace both of the filter caps (the other can't be far behind).

Regards,

Ernst

TimPerry wrote:
wrote:
Hi All,

I've had my Carver TFM-35 for 10 years or so, with never a problem.
Recently the speaker protection relay began cycling now and then. Now
it cycles almost constantly. Does not matter which set of speakers
are coupled up. Also, the front panel lights for the VU meters are
out.

Any ideas?

Thanks,

Ernst


add a capacitor across the relay coil to act as a time delay. this will
preserve the function of the circuit, just slow it down a little. size is
dependand on relay coil current. i might start off with a 100 uF / 35V. this
is assuming that the relay itself is ok.


replace VU lights as desired. no problem with leaving them dark.


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Tim Schwartz Tim Schwartz is offline
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Posts: 62
Default TFM-35 Problem

wrote:
Hi All,

I've had my Carver TFM-35 for 10 years or so, with never a problem.
Recently the speaker protection relay began cycling now and then. Now
it cycles almost constantly. Does not matter which set of speakers are
coupled up. Also, the front panel lights for the VU meters are out.

Any ideas?

Thanks,

Ernst

Ernst,

I'd agree with your idea of repairing and not patching the problem.
Take a close look at the swollen caps, they may be regular caps with
extra lugs just for mounting, or they could be 2 section caps. In the
case of a Carver amp I'd think they are just mounting, but look at the
foils and see how many of the leads actually connect, and look at the
markings on the capacitors.

Carver's switching supplies can be very fussy about caps, so I would
use the same value caps as the originals, though higher voltage is OK,
and if you can find ones with a 105 degree C rating, all the better.
If you can't find ones with the extra mounting lugs, you can use a dab
of caulk at the edge of the cap to glue it to the board to make the
mounting stronger. Don't use too much in case you ever have to do this
again.

Also, if you've never done this before, BE CAREFUL, as
polarity is critical. Please also note that I DON'T know your model amp
specifically, and there could be other problems in the amp. I'd also
look for overheated solder connections.

Regards,
Tim Schwartz
Bristol Electronics
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TimPerry TimPerry is offline
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Default TFM-35 Problem

wrote:
Tim,

I appreciate the reply; however, I'd like to fix the problem rather
than patch it up.


in making a recommendation one must make quite a few assumptions based upon
incomplete data.

my first assumption is that if you are qualified to troubleshoot and repair
electronic equipment or you were inclined to take it to qualified personnel
you would have already done so.
my second assumption based on your post was aside from the 2 issues
mentioned al else was fine.
conclusion: problem in the protection circuit. possibly a weak or magnetized
relay. maybe worn, pitted, intermittent contacts. finding exact parts or
even reasonably close these days can be a real challenge.

if on the other hand the prot circuit is just doing its job by all means fix
the real problem.

i must confess that i did not look up the TFM-35 and assumed it was a low
power consumer stereo. at 350 WPC you can get into serious trouble with this
thing.
please refer servicing to qualified personel.


I got inside the cabinet and the only thing obvious
I found was a swollen filter cap. These caps seem to have four
terminals instead of the customary two.


you can read about 4 pole capacitors here
http://www.jensencapacitors.com/audi...ctrolytic.html


Seems like the first thing to
do is replace both of the filter caps (the other can't be far behind).


maybe, as a service tech i never felt it was in the customers best interest
to change out parts that test good.
in commercial/industrial equipment there is more budget for repair, however
for example one box with 50 to 100 v-mos output FETs at $60 each means you
either be ready to swear every one was bad or be real persuasive as to why
you needed to change all of them.

in the case of old caps its a judgment call. much audio gear from the 60's
and earlier often needs to be recapped to achieve spec performance. 70's
and newer, evaluate on an individual bases.




Regards,

Ernst

TimPerry wrote:
wrote:
Hi All,

I've had my Carver TFM-35 for 10 years or so, with never a problem.
Recently the speaker protection relay began cycling now and then.
Now it cycles almost constantly. Does not matter which set of
speakers are coupled up. Also, the front panel lights for the VU
meters are out.

Any ideas?

Thanks,

Ernst


add a capacitor across the relay coil to act as a time delay. this
will preserve the function of the circuit, just slow it down a
little. size is dependand on relay coil current. i might start off
with a 100 uF / 35V. this is assuming that the relay itself is ok.


replace VU lights as desired. no problem with leaving them dark.





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Default TFM-35 Problem

TimPerry wrote:

my first assumption is that if you are qualified to troubleshoot and repair
electronic equipment or you were inclined to take it to qualified personnel
you would have already done so.


Well, sort of. I'm actually a jet mech by training; although I
completed a Cleaveland Institute of Electronics course and have been
tinkering with electronics for 30 years or so. I actually was employed
as an "Electro-Mechanical Technician" in a manufacturing environment
(PLC's, mechanical fab and repair) for a while between contracts.

my second assumption based on your post was aside from the 2 issues
mentioned al else was fine.


That's correct.

conclusion: problem in the protection circuit.


I agree. Truth is, I don't have alot of experience with protection
circuits, and no servicing data to follow. It seems to me that there
exists some sort of imbalance that is causing the protection to trip
(or more acurately, to cycle); and the only obvious defect is the
filter cap. At least if it is not the cause, I know it has to be
replaced anyway.

Keep in mind that I have owned the unit since it was new, so I at least
have the full history. It's very rarely pushed hard, has never
overheated, or tripped protection as a result of a shorted (or really
low impedance) output load. It has been subjected to vibration at
least during a fairly recent move (MS to TX). I say this because one
of the panel lamps has a detached filament. Not popped like a
burnt-out lamp, just detached. I checked really close for cracked
solder joints, loose components and such.

maybe, as a service tech i never felt it was in the customers best interest
to change out parts that test good.
in commercial/industrial equipment there is more budget for repair, however
for example one box with 50 to 100 v-mos output FETs at $60 each means you
either be ready to swear every one was bad or be real persuasive as to why
you needed to change all of them.


With that sort of expense, I would concur. But since I have two of the
same part, of the same age, operating in the same environment.... I'm
willing to fork over the extra $25.00 to change the second cap just for
the sake of preventative maintenance.

I'm not too proud to send the amp in for service. I'm just too cheap.
There's only one place I know of that works on this gear. They are
very, very good, and their prices reflect it. Before I spend that kind
of bucks on this amp, I'll sell it for parts and look for a
replacement.


Ernst

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Default TFM-35 Problem

TimPerry wrote:

my first assumption is that if you are qualified to troubleshoot and repair
electronic equipment or you were inclined to take it to qualified personnel
you would have already done so.


Well, sort of. I'm actually a jet mech by training; although I
completed a Cleaveland Institute of Electronics course and have been
tinkering with electronics for 30 years or so. I actually was employed
as an "Electro-Mechanical Technician" in a manufacturing environment
(PLC's, mechanical fab and repair) for a while between contracts.

my second assumption based on your post was aside from the 2 issues
mentioned al else was fine.


That's correct.

conclusion: problem in the protection circuit.


I agree. Truth is, I don't have alot of experience with protection
circuits, and no servicing data to follow. It seems to me that there
exists some sort of imbalance that is causing the protection to trip
(or more acurately, to cycle); and the only obvious defect is the
filter cap. At least if it is not the cause, I know it has to be
replaced anyway.

Keep in mind that I have owned the unit since it was new, so I at least
have the full history. It's very rarely pushed hard, has never
overheated, or tripped protection as a result of a shorted (or really
low impedance) output load. It has been subjected to vibration at
least during a fairly recent move (MS to TX). I say this because one
of the panel lamps has a detached filament. Not popped like a
burnt-out lamp, just detached. I checked really close for cracked
solder joints, loose components and such.

maybe, as a service tech i never felt it was in the customers best interest
to change out parts that test good.
in commercial/industrial equipment there is more budget for repair, however
for example one box with 50 to 100 v-mos output FETs at $60 each means you
either be ready to swear every one was bad or be real persuasive as to why
you needed to change all of them.


With that sort of expense, I would concur. But since I have two of the
same part, of the same age, operating in the same environment.... I'm
willing to fork over the extra $25.00 to change the second cap just for
the sake of preventative maintenance.

I'm not too proud to send the amp in for service. I'm just too cheap.
There's only one place I know of that works on this gear. They are
very, very good, and their prices reflect it. Before I spend that kind
of bucks on this amp, I'll sell it for parts and look for a
replacement.


Ernst

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TimPerry TimPerry is offline
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Posts: 129
Default TFM-35 Problem

wrote:
TimPerry wrote:

my first assumption is that if you are qualified to troubleshoot and
repair electronic equipment or you were inclined to take it to
qualified personnel you would have already done so.


Well, sort of. I'm actually a jet mech by training; although I
completed a Cleaveland Institute of Electronics course and have been
tinkering with electronics for 30 years or so. I actually was
employed as an "Electro-Mechanical Technician" in a manufacturing
environment (PLC's, mechanical fab and repair) for a while between
contracts.

my second assumption based on your post was aside from the 2 issues
mentioned al else was fine.


That's correct.

conclusion: problem in the protection circuit.


I agree. Truth is, I don't have alot of experience with protection
circuits, and no servicing data to follow. It seems to me that there
exists some sort of imbalance that is causing the protection to trip
(or more acurately, to cycle); and the only obvious defect is the
filter cap. At least if it is not the cause, I know it has to be
replaced anyway.


could be that one power supply rail is flaky, possibly creating a DC offset
at he output.

i don't know for sure but this could be a class G or H amplifier. if one
rail fails to switch up as needed that will mess things up.

please exorcise extreme care when working on switching supplies.


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