M500T Carver help?

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And again thank you for your help. I do electronic diagnostics and repairs on a lot of automated machinery but never did much audio. So some of this is beyond my paygrade.
But thank you again.
I feel like a bull in a china shop with just enough smarts and strength to be dangerous.
 
Are you sure about R182? It should be the same as R180 or close to it. The left channel shows more current thru R179/181 but that's normal as the left channel is also the supply for the Zeners and opamp.

So you have the same voltage on the bases of Q101/103 but different voltages on the collectors along with very minor difference on the emitter, why? If R123 and R127 check out Q101 might be the cause. It all starts going downhill at Q101 and after.

Have you ever checked the DC offset on the output of the amplifier?

Craig
 
Checking again
R180 = -.13vdc
R182 = +56.0vdc
(Not questioning your expertise because I am the student here but, on my amp circuit board and on my schematic, 180 and 182 are not even on the same end of the board. And not the same size resistors. The only compliment to R182 that I can find is R183. It measures +57.3vdc. Are you thinking R178? R178 = +.14vdc.) Or am I confusing this?

Vb Q101 = +2.2vdc
Vb Q103 = -2.2vdc

Vc Q101 = +70.4vdc
Vc Q103 = -71.1vdc

R123 = 1.10vdc
R127 = 1.66vdc

DC offset = 1.1mv
 
I am guessing that at 1.13vdc R123 does not check out? I am basing that on what you said about the three using .6vdc each. Can I surmise that R123 should have been more like 1.7vdc? Would this also support your suggestion that possibly Q101 is a problem?

Or did I just confuse the whole thing?

Ok I have tried to pay close attention to everything you are helping me with and I have tried not to interject things I have seen and observed because I did not want to mess up your train of thought. So not I am going to ask a question based on something I observed and maybe this will help and maybe it won't but hey I will never know if I don't ask so here goes; While comparing voltages from left channel to right I observed that the collector voltages of Q105 wasn't even close to it's right channel equal. Q107 was spot on. Could this be a problem OR was it just more evidence of what you suspect is the problem?

Thanks again ........ I am eventually going to ask for your address so I will know where to send your birthday present.
 
Back on post #16 you confirmed that the voltage drops across R123 and R131 were low compared to the negative half. This means that both Q101 and Q105 are not conducting enough current. Q105 is supposed to do what Q101 tells it to do. Since the voltage drop across R123 is too low then Q101's collector voltage must be too high to make Q105 conduct properly and causing Q105's collector voltage to be low. Q101 is biased by the opamp's Zenered supply. What's the voltage drop across R119 and R121? Also when you find a difference across resistors make sure the resistors are the correct Ohms.

Craig
 
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Hi Terry,
Can you do a quick check for me? Put the common lead from your meter into the bad channel's speaker output terminal. Then measure to the output emitters and then the base connections. Repeat for the drivers. The reason your common lead is in the speaker hot output is so that you can get a true measurement of these voltage drops. You will notice that your readings are more stable. OF course, your readings are taken with no signal at all and no load connected.
R123 = .04vdc
R125 = .06vdc
R131 = .04vdc
R133 = .06vdc
I noticed that your readings were useless. You need to be able to measure at least to 0.1 mV in order to be able to set the bias current. What meter are you using? Do you have the manual, or just the schematic?

Now, when you look at the sine wave output with your 'scope, what does it look like? Can you attach a picture of the screen?

I know this is all basic stuff, but I'd like to have a clear idea of what is going on in that output circuit.

-Best, Chris
 
Q123e = .01mvdc
Q125e = .01mvdc
Q123b = 0mvdc
Q135b = 0mvdc

Q121e = 0mvdc
Q119e = .1mvdc

Q121b = 144.6mvdc
Q119b = 144.5mvdc

I am using the schematic.

There is no place for me to attach any images. On the scope nothing looks any different on the left channel than it does on the good channel at any setting. The only time there is a difference is when there is actual audio. Sorry. Thanks again for your help.

Terry
 
Lets see what happens with this attached image.
 

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This is the image I got with the scope set to the lowest voltage possible. The other channel has the exact same pattern. the noise is only present when I am actually playing audio and as I said only on the left channel. Another observation I made; I ran a 1khz signal through both channels and turned the input up until I reached 100 watts output on the vu meter for the good channel. The bad channel(left) only shows about 80 watts. Doubt this is much of a clue to anything but thought I would throw that in.
 
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