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January 30, 2008 11:51 AM

Categories: Receivers and Audio Components

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zapdbf

Expert
Joined: 09/14/2007

Hey does anybody know where i can find this manual Yamaha AV-50  (stereo amp)- if you have it, thinks, but even if you can just point me to a place that has it, i tried the usual haunts but no joy. Any help, Thanks 

Doug

Discussion:    Add a Comment | Comments 1-13 of 13 | Latest Comment

Generic Member Avatar
Expert
January 30, 2008 12:14 PM

What is the problem with the unit?  I don't have that specific manual, but I'veworked on many Yamahas.

Dan

zapdbf Avatar
Expert
January 30, 2008 12:35 PM

i have a dc balance issue on one channel, replaced both outputs and preamps. it is a -52 volt offset.

Thanks for your help

zapdbf Avatar
Expert
January 30, 2008 12:40 PM

I don't get that many amps any more. i usually just focus on tv's but every once in a while i get one in to fix.

Generic Member Avatar
Expert
January 30, 2008 1:22 PM

You have an open resistor and the whole output section is shifted.  Many of the Yamaha designs send the B+ and B- through "current limiting" resistors.  These are usually 22-47 Ohms and are flameproof.  Check any low ohm resistors first.  I'll try and get the service manual to get you more specifics.

Dan

zapdbf Avatar
Expert
January 30, 2008 2:35 PM

found an open 220 ohm resistor, it is allot better but i have a -20 volt dc balance on both channels now ??

zapdbf Avatar
Expert
January 30, 2008 3:14 PM

found an open cap, but still have -20 on each channel,

Generic Member Avatar
Expert
January 30, 2008 6:47 PM

How many stages back from the outputs did you go?  You stated that you changed both the output and preamp.  Are these the drivers?  The next stage back from the outputs?  There shouldbe a set of dif-amps back a stage from the drivers.  These may be 5 pin "transistors".  One sode of those could be open.

Dan

zapdbf Avatar
Expert
January 31, 2008 9:15 AM

Not far enough :) i found two more transistors back in further that were bad, but i really don't know what circuit they were in. There were 6 transistors in the small signal end that  i pulled out and just checked. It looks like 3 per channel. No 5 legged ones, i have seen the 5 legged ones before in fisher i think the emitters are tied together.  Oh ! the carnage, when one of these blows.

Generic Member Avatar
Expert
January 31, 2008 12:50 PM

I'm still waiting for the manual, but one more thing to check.  There should be a low voltage supply for the front end as well.  If you have lost 1/2 of that, you will get the symptom your describe.  Unfortunately, Yamaha designs are not hte most straightforward designs.

Dan

zapdbf Avatar
Expert
February 1, 2008 1:05 PM

i replaced the bad transistors i mentioned above, and now i have a -55 volts offset on both channels.

zapdbf Avatar
Expert
February 1, 2008 1:29 PM

i tested all transistors got one bad one left, but there is no number on the part, and the same part on the other channel is also missing it's part number, board location q123 the other is q124.

can you help with this number.

zapdbf Avatar
Expert
February 4, 2008 1:30 PM

bump, still having issues, any idea on the part numbers Dan. Thanks

Generic Member Avatar
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  • member since: 04/21/2008
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April 21, 2008 6:38 PM

zapdbf,

   This is completely off topic but just wanted to thank you for the article you wrote on the Sony Convergence problem, the thread is closed so I could not post there. My Sony KP-43HT20 developed the convergence problem yesterdat and now it looks as good or even better than when it was new. I replaced the bad STK392-560s with the STK392-570s version (no body around here carries the 560 version anymore) and one of the 5A pico fuses on the G board. Since I was in there I also cleaned up the lenses and the mirror.

 Thanks Again,

DZ 

Discussion:    Add a Comment | Back to Top | Comments 1-13 of 13 | Latest Comment

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