Its in a very difficult place for me to test that C51. I would have to flip the board. I tried looking for another solution but the transistors it goes to has a heatsink and also difficult to measure!
That's a further indication of life in that channel. But no sign of audio at speaker terminals? I recall an earlier post indicating amp output voltage was only a few mV, another good sign? Any way you can confirm input signal to R49 in left PA?
Yup even took it as far as the first input caps on both channels and its good. Just testing phono really not the real input tester LOL
Yup DC on right channel is -18 and 4mv on other working channel
Yup DC on right channel is -18 and 4mv on other working channel
Hi dj,
I'm sorry this is so frustrating.
I'm guessing you don't have an oscilloscope and audio generator. As a test aid, I suggest injecting some DC into the amp to generate an expected DC output from the amp. Disconnect your speakers for this test. Tack in about 300K from R71/base Q5 to -Vcc rail. This will/should generate about +10VDC on amp output (i.e. ~ -1/4 of applied voltage). If you switch the resistor supply to the +Vcc rail, you'll get about -10VDC at output. And of course, this technique should do the same on the other channel.
I'm sorry this is so frustrating.
I'm guessing you don't have an oscilloscope and audio generator. As a test aid, I suggest injecting some DC into the amp to generate an expected DC output from the amp. Disconnect your speakers for this test. Tack in about 300K from R71/base Q5 to -Vcc rail. This will/should generate about +10VDC on amp output (i.e. ~ -1/4 of applied voltage). If you switch the resistor supply to the +Vcc rail, you'll get about -10VDC at output. And of course, this technique should do the same on the other channel.
Dont get me wrong I greatly appreciate your help! And your time but mostly your teaching. I do have a scope too. Only took 10 years! Been a member since 2004!
Its a Rigol DS1054. And I have almost no knowledge on how to use it LOL. I just press the auto button and it works 80% of the time. Might as well learn Chinese, might be easier LOL
I'm extremely hestitant to do any DC experiments. Here what I know/think correct me please:
Left channel working fine but no audio output
Right channel not working and no audio output
Both channels seem to be affected, is it a shared component?
On power off both channels work
No blown output drivers, no blown drivers
fuses intact
1,Heres what I plan to do just as a side experiment, Remove resistors that power phono stage and try for audio output.
2,try to measure voltage on base of Q5 on both channels. Just to see if there is signal. Might even try feed it a 1khz signal with my computer and see if my scope can pick it up at Q5 (Q6 right channel)
If 1 fixes fault I will be be very happy but not holding my breath. Not sure on experiment 2 and what it may conclude. I'm already predicting no voltage at Q5 on faulty channel (Q6 right channel).
Its a Rigol DS1054. And I have almost no knowledge on how to use it LOL. I just press the auto button and it works 80% of the time. Might as well learn Chinese, might be easier LOL
I'm extremely hestitant to do any DC experiments. Here what I know/think correct me please:
Left channel working fine but no audio output
Right channel not working and no audio output
Both channels seem to be affected, is it a shared component?
On power off both channels work
No blown output drivers, no blown drivers
fuses intact
1,Heres what I plan to do just as a side experiment, Remove resistors that power phono stage and try for audio output.
2,try to measure voltage on base of Q5 on both channels. Just to see if there is signal. Might even try feed it a 1khz signal with my computer and see if my scope can pick it up at Q5 (Q6 right channel)
If 1 fixes fault I will be be very happy but not holding my breath. Not sure on experiment 2 and what it may conclude. I'm already predicting no voltage at Q5 on faulty channel (Q6 right channel).
I sure do not intend to pressure you into something you're not comfortable with trying. And since you have a scope, that's the much preferred tool anyway. I don't understand the need to disable the phono stage; why not apply a source from any of the of the other passive inputs--- eg. Tape In, Video, Tuner, CD? BTW, your amp has relatively large gain--- about 101 v/v or about 40dB.
Good luck!
Good luck!
Sorry been under the weather recently. I'm going to have another fiddle with this hopefully tomorrow. Experiencing muscle pains currently