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Old 30th June 2006, 04:40 AM   #1
ostie01 is offline ostie01  Canada
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Default Help me with my Denon POA1500(schem include)

Hi, I have a very nice denon POA1500, both channels were not working when I got it, now one channel works great and have troubles fix the other(right). Here is a link for some measurments I've made so if someone can help me resolve this problem.I can't get the +/- to be equal on the preamp side. Prior R11(-) and R9(+) it's ok(-7.26v,+7.24v) .After R9,R11, I measure 2.6v and -1.26v,both should be equal.
0v should be present and pin 7 of IC1 but the 1.34v is the difference between the 2.6v and the 1.26v.All power transistors are disconnected.But at connectors it's OK, +62.5v, -62.5v.D31 and D23 have only .2 to .3 voltage drop but I'm sure they're OK. IC3 is ok with +6.7v, -6.7v. Prior R41(2.7k 2w),62.5v and R57(2.7k 2w) -62.5v. Note that I have the same error at emitor of TR23 and TR27 which are connected to D23 and D31.Thanks for any help.

http://img49.imageshack.us/img49/413...poa15005qp.jpg
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Old 30th June 2006, 04:46 AM   #2
ostie01 is offline ostie01  Canada
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Just forgot to mention, all cap have been by-passed,C11, C13, C49, C15, C19, all electrolytique are new. All transistors are new
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Old 1st July 2006, 12:17 AM   #3
anatech is offline anatech  Canada
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Hi ostie01,
You would need to use diodes in place of the emitter base junctions of the power transistors for the circuit to "operate". Then you can get meaningful readings. TR7 seems to be on hard. Did you measure all the low value flame proof resistors yet? Darn things can be open and look just fine.

-Chris
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Old 1st July 2006, 01:05 AM   #4
ostie01 is offline ostie01  Canada
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Hi, thanks for the reply. Every components have been remove prior measurment. Both channels work when I put back power transistor but at the base, I measure only .1 at .2 volts, normally about .6v should be measured at this point. Every transistors have also been remove for measurment. Q5 and Q3 were not original but were replaced with originals parts. Can you explain a bit more about diode at emiter-base junctions or power transistors.Thanks a lot.
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Old 1st July 2006, 01:17 AM   #5
anatech is offline anatech  Canada
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Hi ostie01,
So you are saying your voltage measurments are with the power transistors connected?

The drivers need to have current flow to the output so the feedback works properly. A standard 1N4001 will provide close to the proper voltage drop. So just connect the diode in so it's forward biased if you don't want to have the outputs installed.

-Chris
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Old 1st July 2006, 01:20 AM   #6
ostie01 is offline ostie01  Canada
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Thanks a lot. Look like you're a very active guy on this forum and very helpful too. Just keep up the good work. We need you.
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