Magic Capacitor

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Hello

I am repairing an old Marantz reciever. I have no gain coming out of the rt ch
1 st preamp xistor. I have determined that when I swap the cap from the other chanel (coming off the emiter47uf@50 v) I have gain. Here is the voodo. I replaced the cap and viola no gain. I replaced the same cap in the other ch with a new one -no gain. I only get gain when I use the original old raty cap. Any thoughts. I made certain the polarity is corect


conforzaled
 
?

The model is 2230 the cap in question is c 754. The circuit will lose gain in either ch unless the original cap is in circuit. I replaced the xistor in one ch but no difference, same same. I checked the print and it definately calls for a 47uf@50. I checked the polarity and it is as in the print.



Thanks
clueless
 
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Hi tenderland,
That cap is in a low impedance position. It would have to be awfully leaky to cause a problem, it is in your feedback loop as a coupling cap. If it were to open, your gain should go up.

Look at R754 and the foil around that area. I would install new caps in both positions if you don't have a cap checker and troubleshoot from there. I'm wondering if the high gain is a fault condition.

C753 and it's mate on the other channel should be checked. I have more trouble with the small 1 uF types. You may be further ahead to just simply replace all the electrolytic caps in the amplifier boards to be honest with you.

-Chris
 
victory

Thanks all who contributed to this thread.
Thanks Anatech and teemuk whos resonse put me on the corect path. Anatech , right on .The old cap created a fault condition. With all new caps gain ON THE OUTPUT is equal. I am a bit embarased I didnt figure it out.


Thanks again
Jeff
:spin:
 
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LOL
More than once!

There always seems to be something else. Mind you, I very rarely get units that someone else hasn't worked on first.

How about getting all the expensive parts and the 5 ¢ part is always backordered? No replacement. That's a killer when you are doing warranty service.

-Chris
 
Boy... can I relate to that! I used to have an auto shop. One of our first questions was usually, "What did you have fixed last?".

Somebody would need new wheel bearings after a brake job... because some knothead used an impact wrench on the adjusting nut... out of cotter pins I guess.

:(
 
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Hi poobah,
It really doesn't matter what industry you are in, does it?

Along the same vein, getting good techs. The customer always pays for the moron who works on their stuff. I am looking for another good auto mechanic in my area. Mine moved to a better paying dealership in a galaxy far, far away. :bawling:

-Chris
 
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