Perhaps there is a simple explanation after all.
Let us assume that turning VR402 was not such a good idea (even though it is one of the steps described in the service manual).
Let us assume that at this point some components were damaged in both LEFT and RIGHT channels.
R401 and R402 blew only when the hook-up jumpers were in place. This makes absolute sense because there is nothing else connected to the input side of R401 and R402.

Leave your hook-up jumpers installed where they are.
Remove R401 and R402. Do not replace.
Replace Q423, 2SC2631

Power ON and check for smoke (as always, of course).

Measure voltages at:
C401
C402

 

Okey.

Leaved hook-up jumpers installed

Removed R401 and R402
Replaced Q423

Power on!
No smoke.

Measured:

C401: 64.2 Volt / 0 volt
C402: 64.5 Volt / 0 volt

One leg with 64 volt and the other leg with no voltage.

 

That must mean that there is a low resistance path newly developed between +60V supply rail and R401 and R402.

Possible suspects are Q401 and Q405 on the LEFT channel, and Q402 and Q406 on the RIGHT channel.

Can you do resistance check on those transistors while in-circuit (as if you were testing the transistors out of circuit)?

If not, you will have to pull them and test.

 

So i removed all the four transistors you are mentioning Q401,Q402,Q405 and Q406 and tested them out of circuit.


Q401:
Black to B:
Red to E: 856
Red to C: 822
Other readings are open circuit. So this is ok.

Q402:
Black to B:
Red to E: 845
Red to C: 814
Other readings are open circuit. So this is ok.

Q405:
Red to B:
Black to E: 798
Black to C: 777
Other readings are open circuit. So this is ok.

Q406:
Red to B:
Black to E: 735
Black to C: 735

Black to B:
Red to E: 1118

Red to E:
Black to C: 984
Other readings are open circuit.


So as i understand... Q406 has gone bad again !?

 

Thanks. There are two of us working in the background trying to analyze what is happening.
This recent failure is more of a mystery and hence it is taking us longer than usual to plan our next line of attack.
If Q406 is bad, it doesn't tell us what is still wrong with the LEFT channel.

 

Thanks. There are two of us working in the background trying to analyze what is happening.
This recent failure is more of a mystery and hence it is taking us longer than usual to plan our next line of attack.
If Q406 is bad, it doesn't tell us what is still wrong with the LEFT channel.

Thank you guys for that!
As i thought about Q406... since it belongs to the RIGHT channel.

 

I believe you have 100, 330, 560, 680Ω resistors.
What is the largest value resistor you have on hand, anything like 1k, 10k, 100kΩ?

 

Now that you have Q401 and Q405 removed, I want you to label these and put them aside.
Do the same for Q402 and Q406.
Remove Q408, label and set aside.

Connect hook-up jumper to the leg of R414 that is closest to R416 (or to J124, which ever is easier).

(Check for continuity, should be almost 0Ω between J124 and the leg of R414 as above.)

You are going to connect the largest resistor that you have between this jumper wire and GND (perhaps J401).

Turn ON power.

Measure voltages at:
R414
R416
R426
D410
D412
R428
R430
TP401 (1)
TP401 (2)
TP401 (3)
TP401 (4)
+TP502
-TP502

 

I believe you have 100, 330, 560, 680Ω resistors.
What is the largest value resistor you have on hand, anything like 1k, 10k, 100kΩ?

I stopped at the local repair shop yesterday and got a 1k Ω and a 100kΩ
So i will use the 100kΩ then for testing..

I'm away for some days but will get to it as soon as i'm home.

 

Soo i labeled and put aside Q401, Q405, Q402 and Q406.
Removed Q408, labeled and put aside.

I then measured the resistance between R414 (leg closest R416) and J124, it was 0Ω.

Then i took a hook-up jumper connected to J124, and a hook-up jumper and connected to J401(GND).. between the hook-up jumpers i put the 100KΩ resistor.

Then i turned Power On!

Voltage measurements:

R414: +62.7 / +62.7 V
R416: +62.7 / +62.7 V
R426: +58 / +64 V
D410: +62.4 / +62.2 V
D412: +63.7 / +62.9 V
R428: +63.7 / +63.3 V
R430: +63.9 / +64.4 V
TP401 (1): +64.7 V
TP401 (2): 64,6 V
TP401 (3): +63.5 V
TP401 (4): +63.4 V
+TP502: +62.8 V
-TP502: +63.3 V



EDIT:
I forgot to put my hook-up jumpers
J222
J223
J224
J225
to J401

i guess that would make a difference? I must put them on and measure again..?




EDIT 2:
I put on the hook-up jumpers i forgot above.
Readings are the same! Not a difference.

 

Houston, we have a major problem here!

or is it...

Ground Control to Major Tom.

Measure voltage at
R423
R424
C426 (pads)
R506

 

hehe... what could have gone so wrong suddenly...it's like it's 60 everywhere

R423: +64 / +64 Volt
R424: +64 / +64 Volt
C426: +64 / 0 Volt
R506: -64 / +64 Volt

 

R506 is blown.

Remove R506 and measure its resistance.

Order R506 and some spares, 6.8Ω ¼W.

 

Ok.
I guess the local shop have 6.8Ω ¼W in storage. i will check tomorrow

 

Ok.
I guess the local shop have 6.8Ω ¼W in storage. i will check tomorrow

It doesn't have to be exact. Even 10Ω, ¼W or ½W will do.

 

So i removed R506, measured, it is open circuit...

I actually have a replacement, i believe it is a 6.8Ω ¼W, i bought two when i earlier replaced R505

See picture.

 

Keep that in mind next time you need to get more parts.
Replace R506.

Repeat voltage measurements:

R414
R416
R426
D410
D412
R428
R430
TP401 (1)
TP401 (2)
TP401 (3)
TP401 (4)
+TP502
-TP502

 

Okey.
Shall i let my hook-up jumpers between J124, and J401 with a 100kΩ remain installed?

 

Okey.
Shall i let my hook-up jumpers between J124, and J401 with a 100kΩ remain installed?

Yes, hook-up J124 to J401 via 100kΩ.

 

Ok i leaved the hook-up with 100kΩ installed.
So i replaced R506 with my replacement 6.8Ω ¼W.

Power on!

R506 fried instantly.... so i did not do any measurements..