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

I used my MK-328 transistor tester, it just says unknown or damaged part.

But using my DMM it measures like this:

Red probe to B
Black to E: 457 mV
Black to C: 490 mV

Black probe to B
Red to E: 480 mV
Red to C: 1820 mV

Red to E
Black to C: 493 mV

Black to E
Red to C: 1664 mV


I have already placed an order on a new one, but it might go a week before it's here..

 

I finally got the replacement transistor for Q418 !

I installed it and it may look like a success, the unit can now be turned on, without any overheating of the small heatsink.

So, next step will now be to replace the 21W bulbs at R505 and R506 with 6.8 ohm resistors ?

 

Congratulations!
Now your next steps are to add the remaining components:

1) Install R505 and R506.
2) Install remaining power transistors.
3) Adjust VR401, VR402, VR403, VR404 as per instructions.

Apply music you like listening to and enjoy a nice cold beer!

 

So i installed R505 and R506. Tried power on again, all good.
Then i installed the remaining four power transistors.

Power on again, all was still good!
Then i removed the dim light bulb tester and plugged it in the wall socket.
Stable! Oh my!

It might come some questions about the adjustments.. i will try now

 

Seems we're not finish yet...

I have two DMM's as you know.
Connected one to LEFT 401 and the other to RIGHT TP401
Speaker switch at OFF, and volume knob all down.

In the manual adjustment are listed as 1,2,3, and this is nr.1 so i guess this is the first adjustment..

So it says to adjust the channels to 25mV

Turning VR401 (LEFT), at first i didn't reach 25mV even at full turn.. but after a while i did.. still on full turn...

Turning VR402 (RIGHT) ..it reaches 25mV very easy... had to be veery careful, it was up in over 100mV a split second.... so i turned both down again.

And then we have the four transistors, Q652,Q654 and Q651,Q653 .. these usually gets hot, as i can see on the PCB, but when should these really get hot?
Even at just idling?
Starting to burn my fingers after a minute or two, just at idling now, even with the VR's all down.

Seems like the heat they produce accelerated a lot when i removed the dim light bulb tester...

 

These are the +17.8V and -17.8V regulators.
Can you post photos of that section where Q651-Q654 are located?

If possible, measure the voltages on each leg of the resistor:
R661
R662
R663
R664

This will tell us the input and output voltages and the current delivered by the regulators.
Expected voltages at R661 and R663
18.2V input on positive regulator
17.8V output

At R662 and R664
-18.2V input on negative regulator
-17.8v output

Current = 40mA

Transistor power dissipated = (38V - 18V) x 0.04A = 0.8W

 

Okey.. not a big current.... so that's what they do.. so basically, how the amp is driven has nothing to do with the load on these....they wil get just as hot at idling ?

They get hot normally, as i mentioned above you can see the pcb is almost burned, but now i believe it's going too much power through them, because i can't touch them after a short while and they start to smell warm, so i turn it off.

Measured resistors:

R661: +17.46 V / +17.20 V
R663: +17.58 V / +17.30 V

R662: -17.30 V / -17.06 V
R664: -17.39 V / -17.12 V

Not entirely as expected ...

Took some pictures....

 

Your voltages suggest that the transistors are supplying about 25mA, dissipating about ½W.
That should be ok.

Continue with the adjustments of VR401, VR402, VR403, VR404.

 

Your voltages suggest that the transistors are supplying about 25mA, dissipating about ½W.
That should be ok.

Continue with the adjustments of VR401, VR402, VR403, VR404.

Okey.......but i am afraid. hehehe

I tested now with a temp gun, after 5 minutes idling, Q652 reach 90 degrees celcius!
Seems too high temp for me...but what do i know..

I measured at the collector on the transistors, it they are fed with -45 Volt and +44 Volt a bit higher than 38..
Could this result in the heat ?

Transistor power dissipated = (45V - 18V) x 0.04A = 1,08 W ?

 

I just checked the resistors, R672,R674 and R676,R680 (330 ohm)
These measures all 164 Ohm... looking at the schematic, i measure two in parallel when checking them in circuit so they seem ok, right ?


I just checked 60 voltage at R505 and R506, it it +66 Volt / -66 Volt

Is this ok ?

 

Look on the rear panel of the amplifier for a voltage adjustment switch.
What is switch position, 230V or 240V?
Set it to 240V.

 

Look on the rear panel of the amplifier for a voltage adjustment switch.
What is switch position, 230V or 240V?
Set it to 240V.

It is set to 230.
Okey, i will try to switch it

 

Switched voltage adjuster to 240 Volt

Voltage at R505/R506 dropped to 63 Volts
Voltage at Q652 dropped to 42.2 Volts

 

I let it idle... it still get's those transistors stupid hot... 90 degrees celsius... will they survive that ?
It smells hot for sure.

As i mentioned earlier, when i was about to adjust at VR402 (RIGHT) .. voltage just flew up very early in the adjustment....
And i don't know if what i mention now could affect that... but sitting here with my IR temp gun measuring components when it's idling... Q416 was about 75 degrees after some minutes, Q412 were also almost 60 degrees, were the rest of the small transistors were around 40 degrees, i even pulled Q416 just to check it, it was ok, i even replaced it, it still gets hot.

So i have measured the voltages at the transistors Q412 and Q416, .. and compared to Q411 and Q415..

Q416 Base has -8.3 Volt versus Q415 Base has -7.8 Volt... 0.5 V difference.... it that ok?
Q412 Collector -8.3 Volt versus Q411 Collector -7.7 Volt .... just comparing the channels.. don't know if it's useful...

I'm just fooling around here now... any comment about the temperature at Q416.... or should we just leave it,...

 

These could all be separate issues.

1) Q651-Q654
2) Q412, Q416
3) VR401, VR402 adjustments

Don't fool around with it too much. I need to study these.

 

Instead of pulling components it would be better to get some data.

The first things we want to know is how much current is flowing. The simplest way to measure current is to measure the voltage across a known resistor.

For example, at Q412, we want to know the voltage across emitter resistor R424.
Measuring the voltage at the legs of R424 with respect to GND will give us two voltage readings, the supply voltage and the voltage at the emitter.

This is also safer since you are not poking two DMM probes into the circuit with two hands. The GND connection can be a clip on to a known GND (e.g. the chassis, if the chassis is known to be GND).

 

Okey,okey...

Measured R424: -61.9 Volt / -61.3 Volt

I still got one probe soldered to J401, as the GND connection.
So i'm just poking with the red one

 

1) Q651-Q654
Your measurements indicate a current of about 28mA.
With Q651-Q654 dropping about 25V, power dissipated is 0.7W. I am surprised that they get so hot (90°C).
I would expect around 50°C.
Is there room to clip on TO220 heatsinks?

2) Q412, Q416
Voltage across R424 is 0.6V. Current is 0.6 / 560 = 1mA
I cannot see why Q412 would be getting hot.

Measure resistance values of R423 and R424 while in-circuit, POWER OFF. Expected resistance is 560Ω.

If anything, RIGHT channel Q412 and Q416 voltages appear to match factory voltages,
It is LEFT channel Q411 and Q415 that appear to be off.

Can you measure voltages at R427, R429, R428, R430. Expected voltages approx. 7.8V and 1.3V

3) VR401, VR402 adjustments
Measure resistances R447, R448 in-circuit, POWER OFF. Expected resistance is 560Ω.
Measure voltages are R447, R448.

Also do same for R433, R434, 3.3kΩ
R437, R438, 680Ω

 

1) Q651-Q654

Strange, if the current is so low.
I was actually going to put heat sinks on these anyways... but i really didn't think they would get as hot as this without.
I have actually bought some small heat sinks, but there is almost no room between them, and i need to repair the PCB first, because of the heat they have dissipated earlier, the connections are a little loose on them. I've seen a picture online of a guy who mounted these on their own little heat sink, with cables to the PCB, thinking about something like that maybe.

I use a FLUKE 62MAX+ IR thermometer, which confuses me a bit, a strange instrument i think... it has to laser points, and i measured the temperature between the spots.
But, if i tape over one of the lasers, it seems to measure the temp just fine with one, but sometimes i get silly readings, and i need to "reset" it by pressing the button on it.. it seems to help.

I let the amp idle for 15 minutes now, nothing blew, but pointing straight at Q654, it showed 90.5°C.
Using the two laser points, having Q654 and Q652 between them it showed 94°C.

I actually tested with one of the sinks on Q651, it still showed 79°C.
Using the two laser points it read about 50°C.

So i don't know..
Maybe it's just the way it is?

2) Q412, Q416

I must correct my statements... my IR Thermometer is a weird instrument, and it now shows Q412 to be 45°C after long time of idling, not too hot to touch, i tried, so it doesn't seem to be a problem.
But Q416 and Q414 are very hot and measuring the temperature on them they show around 74°C
Doing the same measurement on the left side, Q415 and Q413, it shows 59°C
So there is some difference between the channels in temperature...

If the LEFT channel is off, might be why i didn't reach 25mW at the adjustment...?

Measured resistance in circuit:
R423: 561 ohm
R424: 559 ohm

Measured Voltages:
R427: +1.21 Volt / +7.13 Volt
R429: -0.96 Volt / +7.28 Volt
R428: +1.18 Volt / +7.87 Volt
R430: -1.02 Volt / -7.87 Volt

3) VR401, VR402 adjustments

Measured resistance in circuit:
R447: 556 ohm
R448: 562 ohm
R433: 2.7 Kohm
R434: 2.71 Kohm
R437: 650 ohm
R438: 650 ohm

Measured voltages:
R433: +1.19 Volt / -0.39 Volt
R434: +1.17 Volt / -0.44 Volt
R437: -0.39 Volt / -0.71 Volt
R438: -0.44 Volt / -0.76 Volt

R447: +0.56 Volt / -0.34 Volt
R448: +0.54 Volt / -0.40 Volt

 

So far, nothing makes any sense.
According to your data Q651-Q654 are conducting 28mA as opposed to 40mA on the circuit schematics.
Just thinking, maybe the regulators are oscillating.

Can you look at the 17-18V lines at R661-R664 with your oscilloscope?