We had identified trouble at D409 and D411 back at page 22 post #435.
Replace:
D409
D411
Q413

Don't forget that J121 and J219 are cut.

 

We had identified trouble at D409 and D411 back at page 22 post #435.
Replace:
D409
D411
Q413

Don't forget that J121 and J219 are cut.

In order to complete the X4 circuits for the non powered test JoeJester described, i will just install the rest of the missing components?

I have now replaced:

D409
D411
Q413
Q415
Q407
R415

What's still left out is:

Q427
Q429
Q423
Q425
C425
C426
IC401

Proceed?

 

I am inclined to leave the LEFT channel inactive for now and just work with the RIGHT channel.

Since you have identified trouble in X3-- section we should try and resolve that before moving on.

@JoeJester has suggested using an audio source to trace the signal path from the input onwards. This is a good idea now that you have a DSO138 oscilloscope. I need to go back and analyze what you have discovered with regards to X3-- section.

 

Okey. I will leave the LEFT X4 circuit for now and look at the X3 section.

Here's what i found in X3 section, also found an earlier hot spot in the X2 section, but all these components; D153,D153,R296,R295,R294,R291,R292,R293 measures okey in circuit.
And the earlier smoke from the front panel didn't came from this side.
So i believe this hot spot must have been from something earlier...

At X3 section. R328,R330,R332 and Q336 have been hot.
Looking at the schematic i also need to pull Q338 to check it if i'm right..

 

Remove the four jumpers you have connected at J401 to
J222
J223
J224
J225

Clip
J222
J224

Leave out Q336, Q338, R330, R332 for now.
Install R328 820Ω if you have one.
If the unit powers up and everything is stable, measure the voltage at the following (compare with the voltages in the schematic)
R327 (0.5V and -0.7V)
R329 (0V)
R331 (0V)

R328 (0.5V and -0.7V)

 

Okey... i'll do that test, but i actually don't have the 820Ω resistor, a value i've not used until now.

I might just have to order some parts earlier found defective as well.

But about that, the thermistor at TH501 and TH502 ERTD22HL104T, what part should i order for that one.. can't find that part number other than in other Technics service manuals online...

 

What is the closest to 820Ω you have? 680Ω will do for now just to test.
Did you check Q332 and Q334?

As for the thermistor, what is its measured resistance at what temperature? (with one leg lifted).
Look at the chart on post #587. Nominal value is 100kΩ at 25°C. Use these numbers as a guide only. They may not be the same for your thermistor.
15°C - 180kΩ
20°C - 135kΩ
25°C - 100kΩ

 

I did remove Q336 and Q338, they were dead, i have not looked at Q332 and Q334 yet, i'm checking now.
Will also test the thermistors lifted.

With a closer look, R324 is also burned.

I do have 680 ohm resistors.

EDIT: Q334 is shot. Q332 is good.

Checked thermistors TH501,TH502 with one leg lifted, 15 degrees in my workplace, they both show 140 K ohm, also got a lamp shining on the board might made a little heat... can't be too bad, they are also very equal...

Continue with the test you described, even if Q334 is defective?

 

Don't do power test yet.
You will have to check Q324, Q326, Q328, Q330.

Make a note for your shopping list. You may want to get replacements for
Q332, Q336 = 2SC2631
Q334, Q338 = 2SC1123
Check and see what you already have in stock.

 

Don't do power test yet.
You will have to check Q324, Q326, Q328, Q330.

Make a note for your shopping list. You may want to get replacements for
Q332, Q336 = 2SC2631
Q334, Q338 = 2SC1123
Check and see what you already have in stock.

I do have 4 of 2SC2631 and 10 of 2SC1123 by the moment, so i have enough to replace what i've found

Lifted and checked
Q324
Q326
Q328
Q330

They were all ok.
I also by mistake desoldered Q308, just tested it, were ok as well

 

Looks like a lot of heat generated by R291-R296. I cannot find these in the schematics.

If you have removed
Q324
Q326
Q328
Q330
I would leave these out for now. If they are installed that's ok.

I would also leave out
Q332
Q334
Q336
Q338

If one or two transistors are already on board, that's ok too.

We will set aside this section for now (RIGHT CHANNEL?).
Make sure that you have removed the jumpers at J401 and J222-J225.

I would do the following steps, proceeding to each next step if each step is deemed ok.

1) Apply power. Check for smoke.
2) Measure DC voltage at R329 and R331. Expecting 0V.
3) Input stereo sound source (or LEFT CHANNEL?) into AUX INPUT?
Use DSO138 scope, DC input, start at 1V/DIV + x10 probe and look for sound waveform at R329 and/or R331.
You may have to set INPUT selector and adjust VOLUME control.

If you can see audio waveforms balanced around 0VDC, pat yourself on the back and have a drink!

 

Looks like a lot of heat generated by R291-R296. I cannot find these in the schematics.

If you have removed
Q324
Q326
Q328
Q330
I would leave these out for now. If they are installed that's ok.

I would also leave out
Q332
Q334
Q336
Q338

If one or two transistors are already on board, that's ok too.

We will set aside this section for now (RIGHT CHANNEL?).
Make sure that you have removed the jumpers at J401 and J222-J225.

I would do the following steps, proceeding to each next step if each step is deemed ok.

1) Apply power. Check for smoke.
2) Measure DC voltage at R329 and R331. Expecting 0V.
3) Input stereo sound source (or LEFT CHANNEL?) into AUX INPUT?
Use DSO138 scope, DC input, start at 1V/DIV + x10 probe and look for sound waveform at R329 and/or R331.
You may have to set INPUT selector and adjust VOLUME control.

If you can see audio waveforms balanced around 0VDC, pat yourself on the back and have a drink!

On the board it's only Q334, Q336 and Q338 that aren't present.
I soldered back the ones that measured ok... i can remove Q332 if it's the best to do.

one more question before proceeding, about X4 circuit, C425 and C426 are not in place, in the schematic i can see C426 belongs to LEFT channel, but i can't even see C425, but it should belong to RIGHT channel which is our focus now, so i guess i should put in a new one before testing?

 

If Q334, Q336 and Q338 are out you can leave Q332 where it is.

Since we are only testing x3 LEFT channel for now we can ignore C425 and C426 for now.
These are+60V and -60V power supply filters for both LEFT and RIGHT channels. C425 is just to the right of T401 in the schematics.

 

Sorry for not following.. i thought with the no power signal test, desribed earlier by JoeJester, we tested RIGHT channel X4, but this is another powered test , to check LEFT X3 circuit.. okey!
Edit: yes you said we would focus on the X3 circuit.. my bad.
I will try.. excited

 

I have put it together somehow now, with the front board open for measurement.

But just one thing before applying power.

In post #605 you wrote clip J222 and J224
Now in post #611 you mentioned to clip J222 and J225
What's correct?

Also light bulbs at R505 and R506 are not present, but i guess that's not needed now we don't have any power to LEFT X4 circuit.. right..

 

I have put it together somehow now, with the front board open for measurement.

But just one thing before applying power.

In post #605 you wrote clip J222 and J224
Now in post #611 you mentioned to clip J222 and J225
What's correct?

Also light bulbs at R505 and R506 are not present, but i guess that's not needed now we don't have any power to LEFT X4 circuit.. right..

Sorry my statements are correct but not clearly understood
You had connected hookup probes to J222, J223, J224, J225 (that is what I mean by writing J222-J225) and all connected to J401. Remove the hook up probes.

Clip wire jumpers J222 and J224 in order to prevent signals from x3 section to reach x4.

Since you are applying power, all sections will receive power. We still want the lamps in place instead of R505 and R506.

 

Sorry my statements are correct but not clearly understood
You had connected hookup probes to J222, J223, J224, J225 (that is what I mean by writing J222-J225) and all connected to J401. Remove the hook up probes.

Clip wire jumpers J222 and J224 in order to prevent signals from x3 section to reach x4.

Since you are applying power, all sections will receive power. We still want the lamps in place instead of R505 and R506.

ok. Yes i misunderstood..again.
Removed the hook ups, and clipped J222 and J224.

I will connect the bulbs again before applying power.
when looking for signal at R330/R329.. i will connect the probe clip to ground, correct?

 

ok. Yes i misunderstood..again.
Removed the hook ups, and clipped J222 and J224.

I will connect the bulbs again before applying power.
when looking for signal at R330/R329.. i will connect the probe clip to ground, correct?

Correct.

 

Okey, so i installed the 21W bulbs at R505 and R506.

Power ON.

No smoke or power draw, seems stable.

Measured voltage:
R329: 0 V one leg, +0.06 V on the other
R331: 0 V one leg, -0.06 V on the other

Put signal 1Khz in at AUX, also made sure the input board was set at AUX

Hooked up oscilloscope, set at DC and 1 Volt

The picture and video are measured at R329, got the same visual signal at R331.
It increased/decreased with the volume knob, see video link.
Signal disappears when i turn power off, or stopped the audio signal, so it's working doesn't it?

 

Congratulations! Well done.
Now replace the parts removed from x3 right channel with new components and repeat the test on the right channel.
The important test is looking for 0V at R330 and R332.