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For best performance TR602,3 should be hfe matched, better than +/-5. Don't get bogged down with trying to align all voltages to the schematic, eg. the +/-50 +/-B rails are never 50V. Not sure I follow. TP1,2 is about setting up a 1mA current source to feed the diff pair. If you can adjust...

As per the Getting Started Wiki/link above, depending on what you are measuring/doing

Haven't done any work on quasi-complementary so below would be a guess, happy to be corrected by those that know.

Under "Generators" select the bottom option FreqResponse, see https://github.com/QuantAsylum/QA40x/wiki/Getting-Started This will generate 1 trace for the amps tone settings. Would expect that you would repeat this 10 times for each "turn-over" freq 250Hz and 500Hz and then you would need to...

Haven't been following but looking at the schematic, yamaha has provided some good test points eg, Pin 1 (Preamp left in), 2(Rin) Pin 13(Power amp left in), 14(Rin), schematic has an error lables pin 12 as Rin Tracing at the base of driver transistors along with the wipers ov vol/bass/treble are...

It's just a frequency response with different tone settings. The shape is dependent on amp performance, ie, position of switches. Maybe the QA403 can overlay the 10 seperate traces???

Plots from another amp that only has the one corner frequency, the CA offers a choice of 3, none, 250Hz, 500Hz. The start point of the "divergance" moves depending on if 250/500Hz selected, likewise for treble. The point is to boost the low/high levels to make up in short comings of spkrs, room....

Hard to see 60V anywhere when amp has +46V rails. Note 60V+10V / 2 = 35V, make me think you have a grounding problem, suggest remeasure with black meter probe inserted into any black speaker connector/post. Emitters of output transistors should be at less that 100mV on both channels so 35V on...

I would have thought that a KR-7400 would be worth the effort... With no significant DC offset the relay should kick in, maybe a simple fault in the protection circuit. First up, verify no significant DC offset. Measure dc voltage at midpoint between the emitter resistors Rm41, Rm43(L) and...

Was TR605 "round face to heatsink"? Thinking TR602, consider replacing TR602,603 with a hfe matched pair. Possibly TR604 is in saturation so bs in = bs out pointing to TR602.

Guessing Q14 is breaking down under load. Headphones are an easier load to drive, typically 30-300ohms but speakers 8ohms demand higher current. By the numbers with scope test for distortion at Q12base (ok?) then at Q14b (notok?) Also check for distortion at Q8b and Q10b.

Pinout is ecb, round face to heat sink(I always get that wrong...)

Suggest replace. Odd size for a fusible, if they are supposed to be 1.2ohms then they should read ok in circuit.

Plz check if that is -50V or +50V at TR604c With +50V at TR605c would expect OUT to be +48.8V and you would have flagged that. Were you able to adjust VR602 for TP1, TP2 15V? Measure TR602 e/c/b voltages to GND.

Also take a look at the two black wires (marked in blue). They look a little strange as they appear to be jumpers on the same track. Has he cut the trace there also? Compare with other unit?

Image is not great but it looks like the tech cut the traces/tracks then worked out that wasn't the problem then resoldered the wires to jumper the cut, rather than using a solder bridge

Voltages appear mostly ok however Q12 Vbe=0.8V appears abnormally high. I'd be tempted to replace. Driver Vbe's appear ok.

The drivers see almost 50V Vce connected to the rail. Surprised if your tester tests at 50Vdc, more like 5-9Vdc General rule, if it tests ok then it still may be faulty. If it tests Notok then it is dead.

You think the hump at -130dB is significant but at 60Hz spike at -85dB where it was previously -95dB(?) is not

What were the driver and output base voltages. Use transistor designation, eg, Qxxxb or TRxxxb important, note the sign +/-. Also which parts burnt up and/or replaced. Need to work out the fault scenario to try and identify all failed parts.

Don't know the amp, does it have a relay/protection circuit. Reads like the relay contacts are welded closed so power up/down transients go to the speakers. The power up/down transients are normal but the relay should only connect after about 4 seconds of p-on, likewise the relay should...

"Workaround" is a better description. If the amp is not performing to spec then the problem should be investigated and resolved before it gets worse and possibly does further damage. Increasing the caps hides the issue for the time being. 60Hz peak at -85db might be due to measurement...

The 3150 uses a NE5532 opamp in the preamp stage(IC501). Carefully unsolder the IC, you may want to reuse it. Then solder in a socket so you can easily change(=roll) the opamp without soldering. See pix below. From memory, NAD ran the NE5532 at +/-18.4Vdc, this voltage will fry other opamps...

Apples and oranges? Post #181 was on the filter board, retest this board and post results (with the changed psu caps) for direct comparison. The ripple depends on the load and ..., you've changed the load and get different results, no surprise there but -95dB looks good.

First up, replace C647 (22uf) with a low ESR type like Nichicon UPW or UHE and see if that improved the relay click time.