Yes, go ahead and install Q501 and everything else that needs to be in place for LEFT channel.

The only items we are leaving out for now are the following:

C425
C426
R505
R506

Q515
Q517

(ignore RIGHT channel components for now)

 

Okey.
But i did install C426 and C425 earlier when i completed X4 circuit.
Should i remove them or let it be?
I have plenty new ones of that type.

 

Okey.
But i did install C426 and C425 earlier when i completed X4 circuit.
Should i remove them or let it be?
I have plenty new ones of that type.

I wake up to the sound of music... let It be.

 

okey

So i installed Q501.
Only missing in LEFT now is Q515 and Q517
And of course... R505/R506 which is bulbs.

Power ON!

No smoke or power draw, woow...


Measured
TP501+ : 0 Volt
TP501- : 0 Volt

 

Good. Now do the same thing on the RIGHT channel.
Leave out
Q516
Q518

Measure voltages at TP502.

 

Installed Q502, Q508 and Q510
Only components missing at RIGHT channel now is Q516/Q518

Power ON.

No smoke or draw.

Measured at TP502, 0 Volts at -/+

 

Ok. You're getting close but no cigars yet!
We still have some more tests to perform, final install, and tweaking to do.

Perform your sine wave tests and examine the signals with the oscilloscope on either terminals (+ or -) at TP501 and TP502.
In all live signal tests, do not drive the amp at full volume. Provide just enough signal to verify that the signal is reaching TP501 and TP502 and that the voltage is balanced about 0V.

After you have done that, turn the power OFF and ON and listen if the speaker relay is clicking in after a second or two.

 

Tested signal at both TP501 and TP502 +
Signal is fine at both and i don't have to turn so much on the volume knob before it's there, on the 1V setting.

Relay are clicking in after a second or two
Also, when powered on, when i choose speaker output, they click as they should.
When a+b is chosen, they both click, so they seem to work

 

Good. Now comes the live test.
Do one channel at a time. Connect a loud speaker to the speaker connection at the back of the amplifier.
Use a stereo sound source as your input. As stated before, keep the volume control low just enough to verify that the channel is working.

 

Feels like a breakthrough to me, it plays music on both channels on A and B
But.. after it has been on for a couple of minutes, it smells a little warm, and the little black heatsink with Q428, Q430, Q418, RIGHT channel was a bit hot.
Same heatsink on LEFT channel was ice cold.

 

Postpone the live testing for now.
Measure the voltages at the transistors, Q418, Q428, Q430.

 

Q418:
E: -1.36 Volt
C: +1.37 Volt
B: -1 Volt

Q428:
E: +0.06 Volt
C: +46 Volt
B: +0.7 Volt

Q430:
E: -0.08 Volt
C: -46.4 Volt
B: -0.7 Volt

Looking at the schematics i can't find anything being veery off?
Except maybe Q418 B ? which should be -0.6 Volt
The low 60 voltage, is it because of the dim bulb tester ?

 

See if you can identify by touch which of the three transistors, Q418, Q428, Q430 is getting hot.

Try the adjustments on page 10 of the service manual as follows:
Measure voltage difference between + and - for RIGHT channel at TP401, essentially from emitter of Q428 to emitter of Q430.
Adjust VR402 so that the voltage is 0.025V, i.e. 25mV.
See if the heat sink is not so hot.

Don't do any other adjustments until we can complete the rest of the install and tests.

 

I have an IR temp tester, hard to tell when they all were into the heat sink, i removed the screw and got them off the heatsink, yes i was careful watching the temperature..

Q418 generates most of the heat, but also the two others are making quite a bit,
When Q418 reaches 50 degrees, Q428,Q430 are around 32 degrees and rising, so it's not Q418 that makes all the heat alone...

I will check difference tomorrow.

 

Have not adjusted anything.
I have to put the meter to mV to get a reading on two of the measurements as you see...

Measured:

TP401+ to Q428E: -0.4 mV
TP401- to Q428E: -200 mV after about 20 seconds... voltage is increasing the whole time it is turned on

TP401+ to Q430E: +190 mV after about 20 seconds... increasing while it's turned on
TP401- to Q430E: +0.4 mV

 

Maybe you misunderstood what I wrote in post #653.

TP401 + is connected to Q428 E. Hence voltage reading between these two points ought to be 0mV.
TP401 - is connected to Q430 E. Hence voltage reading between these two points ought to be 0mV.

What we are looking to find is the voltage reading between TP401 + and TP401 - (for RIGHT channel only).
Adjust VR402 and see if you can bring the voltage to between 0mV and 25mV.
The reading you observe of about 200mV is too high which is probably why the transistors are running hot.

(You cannot touch the DMM probes to TP401 and do the adjustment at the same time unless you have three hands. Use the grabber hooks connected to the DMM probes in order to free up both hands. Make the connections with the POWER OFF. Careful not to create a short. At a later stage you will have to make adjustments to the other three trimmers.)

 

Yes, then i misunderstood.
But i understand now.

Connected minigrabbers to TP401 +/- RIGHT

Power ON!

VR402 were from earlier turned all the way down.
So the only way i can turn it is "up", i turned it all the way, it does not affect the voltage measured, it just keep increasing when it's on....to about 200 mV after a while...then i turn off..... it does not increase faster or slower how i put VR402

 

I cannot see anything obvious. At this point, remove the two small lamps and install
R505 6.8Ω
R506 6.8Ω

Install
C425
C426

With the power off measure R447 and R448 while in-circuit.

Power ON and repeat the test, i.e. measure TP401 + to - for each channel LEFT and RIGHT.
Measure voltages at Q428 and Q430.

 

So i took out the pcb again to install resistors R505/R06...

When i had it out, i thought of Q418, it has never been out of circuit earlier, so i removed it and checked it,
And my transistor tester says it's bad!

Then i removed Q417 on the other small heat sink just to compare, and this tests fine.

I also tested Q428 and Q430 just to be sure, and both these were fine.

So i might have found the culprit for this heat... just luck something else didn't blew, are the bulbs saving me?

 

Good find.
What did your tests on Q418 indicate?
I presume that you have to order replacements for Q418?