Did you ever have to replace Q417 or Q418?
Do you have replacements, 2SD1761?

Replacing Q417 would be the next try, otherwise it is going to get tricky finding the fault.
Something in the Q417 to Q429 section is drawing too much current across the rails where Q417 collector and emitter are connected.

Without having a Q417 replacement readily at hand, here is what I would do.
Adjust VR402 and VR404 on the RIGHT channel according to the Service Manual.
That is, adjust VR402 for 25mV at TP401 and adjust VR404 for 3mV at TP502.

Attempt to adjust VR401 and VR403 on the LEFT channel in the similar fashion.

Measure all the voltages from Q417 to Q429 on the LEFT channel and compare with the similar voltages from Q418 to Q430 on the RIGHT channel. Look for any discrepancies between those and those on the schematic.

 

I had an earlier problem with Q418 getting hot, so i measured it and it was bad.

Then i purchased replacements (2SD1761 ) for Q418 and Q417.
Even if Q417 did test ok, i did replace both Q418 and Q417 with new ones!

I got more replacements, so i could always check it again... but i got the same problem with low voltage at LEFT channel before Q515 blew, so i don't think it's anything wrong with it now.

I will check voltages from Q417 to Q429 and compare with RIGHT channel......

 

If you have an extra 2SD1761 then try replacing Q417 and see if that fixes the problem.

 

If you have an extra 2SD1761 then try replacing Q417 and see if that fixes the problem.

I removed Q417, it measured ok.
Then i installed a new 2SD1761, power on and tried to adjust VR401, there was no difference from earlier


So next step would be to compare voltages.... RIGHT to LEFT channel then, Q417 -> Q429 and Q418 ->Q430 ....

 

I know you have two meters. Can you do two simple tests?

On the meter you normally use for testing with this problem, set it to the lowest ohms scale. With the other meter, measure the voltage across your red lead and the black lead. Then with the meter you just used to measure the voltage, switch to measure the current. I'd say start with the highest current scale and work down till you get the most accurate answer.

I found out my simulation program's ohm meters measured 1 V and then 1 A. That is NOT typical. I know a Fluke 287 has a short circuit of 1 mA.

These little differences really can mess up what we see. For instance, I saw a much different set of resistances than you did, however, if I know those two things about your meter, I can have something in place to improve information I relay to you.

I'm sorry I didn't realize this earlier on ....

 

@JoeJester

At lowest resistance range i measure:

2.54 Volt
0.74 A at "200m" setting at DMM

 

I took some comparison voltage measurements as MrChips told me to do earlier.
I have written in red the value it should be according to the schematic, on them who has the greatest deviation......


LEFT:

Q417:
E: -0.95 V (-1.3) C: +1.23 V B: -0.38 V (-0.6V)

Q421:
E: 0 V C: -0.35 V (-1.3) B: -0.35

Q425:
E: -0.29 V (-0.6) C: -63 V B: -0.94 V (-1.3)

Q429:
E: 0 V C: -63 V B: -0.3 V (-0.6)


RIGHT:

Q418:
E: -1.1 V C: +1.13 V B: -0.53 V

Q422:
E: 0 V C: -2.45 V (-1.3) B: -0.3 V

Q426:
E: -0.5 V C: -63 V B: -1.1 V

Q430:
E: 0 V C: -63 V B: -0.5 V

 

Bonsoir,

prendre des lectures de tension sur:

IC401 et IC402
Q501, Q503, Q505 et Q502, Q504, Q506

 

Bonsoir,

prendre des lectures de tension sur:

IC401 et IC402
Q501, Q503, Q505 et Q502, Q504, Q506

Merci pour votre conseil. Ceci est un site en anglais. Traduire en anglais, s'il vous plaît.

Take voltage readings on
IC401 and IC402
Q501, Q503, Q505 and Q502, Q504, Q506

 

I translated into English though, weird ...

 

Here are measurements

IC401:
Pin1: +0.45 V
Pin2: 0 V
Pin3: 0 V
Pin4: -7.19 V
Pin5: 0 V
Pin6: 0 V
Pin7: +1 V
Pin8: +7.1 V

IC402:
Pin1: +1 V
Pin2: 0 V
Pin3: 0 V
Pin4: -7.76 V
Pin5: 0 V
Pin6: 0 V
Pin7: +1.1 V
Pin8; +7.78 V

LEFT:

Q501:
E: -1.08 V C: +1 V B: -0.4 V

Q503:
E: +0.39 V C: +62.5 V B: +1 V

Q505:
E: -0.45 V C: -62.7 V B: -1.06 V

RIGHT:

Q502:
E: -1.1 V C: +1 V B: -0.42 V

Q504:
E: +0.39 V C: +62.5 V B: +1 V

Q506:
E: -0.47 V C: -62.8 V B: -1.07 V

 

Here are the readings compared to the technical manual listings (TM) with the percent error ---- disregarding the polarity of the error > 10 percent error has red backgrounds. Only one suspected polarity transcription error.

 

Damn it! Checked my notes, Q505 collector should of course be -62.70 Volt

i corrected post #771

 

Damn it! Checked my notes, Q505 collector should of course be -62.70 Volt

No biggie .... at least is was a clearly obvious error. That will bring it down to under 5% like the others.


I've assumed all the resistors to be about 10%.

 

To complete the post 771 results



A quick note about IC401/IC402 .... IC401(B) is the audio input amp in the Left channel of x4xx circuit while IC402(A) is the same circuit of the right channel of the x4xx circuit.

 

I am still trying to analyze the most recent voltage measurements.

Here is an idea. Use a thermal imaging camera and take a photo of the board with the objective of being able to compare the left and right channels on one photograph.

 

Hi,

Have sections Q401 to Q415 of the left way and Q402 to Q416 of the right way been compared?

Otherwise isolate the AMP board from the preamplifier by disconnecting CN302A and resume the settings ...

 

I'm pretty sure they were checked multiple times in the preceding 38 pages.

I'm more inclined to have him scope IC401(B) on the left channel and IC401(A) on the right channel. The left channel seems to vary as post 746 pin 1 at -0.15 and post 771 had it at -0.45

This latest round is generated by post 751 about the large discrepancy in the positioning of the x4xx ICQ adjustments of the left and right channel. The right channel is about mid-scale, which is consistent with good design. That discrepancy shows there are other problems not yet identified. The voltages indicate there are some problems as well.

I think most, if not all, of the active devices in x4xx and x5xx have been replaced at least once since the beginning of this thread 39 pages ago. I do not think the problem is with an active device, unless it was damaged by human intervention which is always a real possibility.

From post 751 .... "well........ i don't think we are any further than we were earlier when i was adjusting the VR's I have now removed all load lamps, and it seems stable to be plugged in the wall socket.. but i still need to turn VR401(LEFT) to max to almost reach the correct voltage...(25mV) VR402(RIGHT) increases voltage much faster and i don't need to turn it to max to get the correct value (25mV)
Similar as earlier."

 

However, we are missing some readings from the x4xx section .... the readings that are connected to the positive rails ....


Q419
Q420
Q423
Q424
Q427
Q428

 

Thanks for all effort you guys are putting in this, it would have fun to get it working, now when the circuit is complete i feel like there is only some small obstacles left... but what do i know..

@MrChips: I will try to let it idle for a while and take some photos with the thermal cam, but i don't feel like anything special is heating up except the same transistors as mentioned earlier on both channels.

Measurement:

Q419:
E: 0 V C: +2.78 V B: +0.28 V
Q420:
E: 0 V C: +2.47 V B: +0.28 V

Q423:
E: +0.57 V C: +61.5 V B: +1.21 V
Q424:
E: +0.58 V C: +61.7 V B: +1.11 V

Q427:
E: 0 V C: +61.6 V B: +0.57 V
Q428:
E: 0 V C: +61.7 V B: +0.58 V