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View Full Version : Acoustic model 125, schem needed please

JC@
08-04-2006, 02:23 AM
Here I am, asking for a schem, again. Sorry.
Where can I obtain a schematic for this amp?
Thank you.

JC
amplover
08-04-2006, 04:41 AM
Is that a Fender?
Enzo
08-04-2006, 07:20 AM
No, it's an Acoustic.

What part are you servicing? WHich power amp card is in it, 170074 or 170080? Are the preamp and EQ cards 170078 and 170076 respectively?
JC@
08-04-2006, 05:22 PM
No, it's an Acoustic.

What part are you servicing? WHich power amp card is in it, 170074 or 170080? Are the preamp and EQ cards 170078 and 170076 respectively?

Enzo,
I don't know yet. It had a cold and broken solder joint where the power transistor's card meets the rest on the power card, and a loose cable in the preamp card, but the amp still doesn´t work.
The amp powers up and there's little hum coming out from the speaker, that's all for the moment.

serial number: 12501554

Power amp card: 170080
Preamp card: 170078A
EQ card: 170076A

JC
JC@
08-04-2006, 05:58 PM
It's in the power amp or around it I belive. I get a good signal in the headphones that responds to the EQ pots, from the preamp out jack.

There is very little sound coming out from the speaker when I plug the signal generator in the power amp input jack, but only when the generator output level is sent to it's maximum level.
JC@
08-08-2006, 01:37 PM
The fault is in the power amp board.

I have a transistor that is gone, a 40409 RCA, so I will replace it's companion too, the 40410. I'm guessing these are the drivers, but a schem would help for sure. There is a little component placed between these two transistors that looks like a diode, with a white case and no marks, that I don't know what it is or what it does in the circuit.

I've been searching for a schem with no luck. Maybe someone from you have serviced one of these amps and remember what part of the amp I'm talking about. I'm trying to avoid changing all the transistors in the board.

One of the power transistor's collector from one side had a broken solder point and the 40409 belongs to that side of the power amp section.
JC@
08-09-2006, 01:48 AM
It's fixed.
I just wonder if a cold solder joint in a power transistor's collector may blow it's driver.

żIs this possible?
Enzo
08-09-2006, 01:52 AM
Depends. If the output rail tries to draw all its current through the base of the output device, which the driver tries to provide.

Do you no longer need drawings? Send an email to tmenzo at msn dot com if you do, and I will scan it in.
JC@
08-09-2006, 02:23 AM
No, it's ok Enzo, truly.
Thank you very much.
eddybruce
03-04-2008, 11:49 PM
Greetings,
I have a guitar in need of pre amp ... please advise
Thanks,
Bruce

480-516-2455
bew1@cox.net
bwashbur@insight.com
Don Moose
03-05-2008, 01:14 AM
e-b, I think you need to start a new thread on this topic - maybe in one of the guitar tech forums.

Here, at the end of a non-related thread, it's not likely to get much useful attention.

Hope this helps!