Got 0.0 vdc at collectors of Q7512 and Q7514
Emitter and base voltages -50,0 vdc on Q7514
Emitter and base voltages 50.2 and 50.4 vdcon Q7512

 

NTE36 is equivalent to 2SN3181N and NTE37 equivalent to 2SA1264N.
Should I remove the 2 original Q7511 and Q7513.
The 2 I installed are not touching the chassis. Shoulds I bend the leads to make them touch. The only thermal dissapate is the little silicone shields that come with the transistors. I managed to get enough of the old paste to stick the shields to the back of the transistors.

Do I need to get some thermal paste before i proceed?

 

NTE36 is equivalent to 2SN3181N and NTE37 equivalent to 2SA1264N.
Should I remove the 2 original Q7511 and Q7513.
The 2 I installed are not touching the chassis. Shoulds I bend the leads to make them touch. The only thermal dissapate is the little silicone shields that come with the transistors. I managed to get enough of the old paste to stick the shields to the back of the transistors.

Do I need to get some thermal paste before i proceed?

I am out of power again, will respond tomorrow.

 

Ok. Thanks. Hope your power returns soon. Talk tomorrow.

 

We are only testing the RIGHT CHANNEL for now. Leave Q7511 and Q7513 installed. With the +B1 and -B1 jumpers lifted there should be no power to the LEFT CHANNEL.

If the NTE36/NTE37 came with silicone pads then that is all you need. Normally you only need a very thin film of heatsink compound. We will not be doing any tests at full power for now. You are ok the way it is.

Do not connect any loudspeakers.

What we need to check are all the voltages at B, C, E at each of the four transistors when we apply power.
The voltage at C must be close to 0V.

Also we want to see the light bulb dim and not bright. This means that the amplifier is drawing low idle current.

 

Q7512
Base = 50.4 vdc
Collector = 0.00 vdc
Emitter =50.4 vdc

Q7514
Base = -50.8 vdc
Collector = -0.01 vdc
Emitter = -50.8 vdc

Q7511
Base = 0.0 vdc
Collector = 0.0 vdc
Emitter = 0.0 vdc

Q7513
Base = -0.01 vdc
Collector = 0.00 vdc
Emitter = 0.00 vdc

When power supplied via switch, bulb goes half bright quickly down to barely seeing the filament lit.

 

Just did a retest. Bulb barely lights. Voltages still the same.

 

All voltages appear to be in the expected ranges.
The initial power surge is because of the storage capacitors in the power supply circuit charging up.

We can either do a sound check on the RIGHT CHANNEL or we can leave it alone and move on to the LEFT CHANNEL.
I will leave the decision up to you.

 

I would like to move to the left channel if that's ok with you.

 

I would like to move to the left channel if that's ok with you.

Ok. Reconnect the +B1 and -B1 jumpers.
Observe the brightness of the lamp with power on.

How good are you at reading and interpreting circuit digrams?
Measure and compare voltage readings between the LEFT and RIGHT channels.
Start with:
LEFT === RIGHT
Q7511 = Q7512
Q7513 = Q7514

Also measure voltages at:
Q7603

 

Q7603 is a driver right? I can understand the circuit diagrams I think. I am reconnecting the B1+ and - right now will report to you shortly. What if the light stays bright? Keep on with the measurements. Do Q7603 first? It's output should be -52.2 volts vdc?

 

Light buld stays bright and I get a hum of sorts, i think from the speakers. speakers are hard wired to the board. Should I disconnect them? No smoke , just the hum. Afraid to go any further until I hear from you.

 

It's difficult to manuever the power board so that I can get to the solder connections for the speakers. Can I cut them and re splice or put connectors on the wires when done?

 

I got it in a position to unsolder them now. Let me know if I should proceed. I missed the post where you said not to connect the speakers. Now I find they are hard wired. I will wait to hear from you. Thanks.

 

Is there any way of disconnecting the speakers?
There is a danger of blowing the speakers before we get the amp working properly.
It would be safer to cut the wires and splice them back later.

Q7603 is a power shunt and its function is to blow the fuse if there is a fault detected.
The voltages on Q7603 will tell us if it is in fault mode.

 

I will cut the wires and splice later. I didn't want to bother you becasue it's the weekend. I will either do this tonight or tomorrow and send you the results.

 

Q7603 with speaker wires cut
Base= -2.43 vdc
Collector =-0.025 vdc
Emitter = -2.41 vdc

 

Please remove the two power transistors in the LEFT CHANNEL:

Q7511
Q7513

Set them aside in a marked envelope so that you remember where they belong.

Do the power on test with voltage measurements at all four power transistors.
LEFT === RIGHT
Q7511 = Q7512
Q7513 = Q7514

 

I messed up this morning. I removed Q7511 and 13. Started the voltage measurements. I iaccidentally shorted something when my magnifying glasses slipped. Everything started out good on Q7511 here are the readings
B =49. 7 vdc
C = 0.00 vdv
E = 48.9 vdc

Now the problem. I struck something on the board that caused a short. Now the readings are:
Q7511
Base = 50.4 vdc
Collector = 0.00 vdc
Emitter =-47.9 vdc

Q7513
Base = --0.00 vdc
Collector = -1.63 vdc
Emitter = -48.0 vdc

Q7512
Base = - 48.3 vdc
Collector = - 0.3 vdc
Emitter = - 48.2 vdc

Q7514
Base = - 48.0 vdc
Collector = - 48.1 vdc
Emitter = - 48.1 vdc

Looks like I am screwing up more than fixing. I thank you so much for your time. I am so frustrated with this. Looks like I am making more mistakes with this thing.

 

Things like this happen. Not to worry.

Remove all four transistors:
LEFT === RIGHT
Q7511 = Q7512
Q7513 = Q7514

Make sure the speakers are disconnected.

This is the standard power on test you will need to repeat.
Do the power on test and measure all voltages as before.
Report the brightness of the test lamp.