Do the test requested in post #257 and post the results. It would also be interesting to see how the removed Q29 behaves in the transistor tester.

Les.

 

Here is the transistor i removed from Q29 in the tester,
also the voltage between the new Q29 collector and emitter is 4.00vdc , bang on what you expected les

 

This does not make sense. The bias regulator now seems to be working correctly but the suspect transistor that you removed looks to be OK in the tester. When you did the voltage tests in post #190 you got 1.36 volts between the emitter and collector of Q29.
With no signal input on no load resistor connected to the output measure the following voltages.
Q23 base to Q40 base. (I expect this to be 4.17 volts.)

With the black lead from your DMM connected to T9 measure the voltages at the following points and present the results laid out as below. Include the polarity of the readings

Q23 base Q40 base
Q25 base Q37 base
Q26 base Q34 base
Q28 base Q36 base
Q28 emitter Q36 emitter
T10

What value of resistors have you fitted in place of the fuses ?

Les.

 

Q23 base = 0.753
Q40 base = --3.436
Q25 base = 0.433
Q37 base = --3.033
Q26 base = 0.432
Q34 base = 0.432
Q28 base = 0.027
Q36 base = 0.028
Q28 emitter = 0.027
Q36 emitter = 0.027
T10 = 0.027

Resister fuses mesure 39 ohms

 

This is how the resister fuses were build, apart from i used 2 led's in parallel and opposite polarity

 

Here are you readings laid out as I requested in post #263 so that it is easier to compare them.

Q23 base = 0.753 Q40 base = --3.436
Q25 base = 0.433 Q37 base = --3.033
Q26 base = 0.432 Q34 base = 0.432
Q28 base = 0.027 Q36 base = 0.028
Q28 emitter = 0.027 Q36 emitter = 0.027
T10 = 0.027

I think Q37 is base emitter open circuit. I suggest removing it and testing it in your transistor tester to check if I am right.

Les.

 

Here is Q37 removed and in the tester

 

Q 37 looks OK. Solder it back in the board and look for damage to the etch between Q37 collector and Q34 base and check the solder joint to Q34 base. That is all I can think of at the moment. I will have to try to think of another explanation.

Les.

 

Would it be possible to inject a signal into the r-in and bypass the pre amp, this could possibly show if the problem is further back in the circuit ?
Also do you think it could be the resister fuses limiting the current to the main amp ?

Just guessing here

 

You just seem to be going away from the problem. We know the present fault we are chasing is very close to Q37. I cant see any logic in your ideas. Now you gave soldered Q37 back in measure the resistance between Q37 emitter and Q34 base. When we fix the problem with the negative side emitter followers the 39 ohm resistors in place of the fused may have to be reduced as we don't know the designed value of the quiescent current for the output stage.

Les.

 

Q37 has been re installed, also Q40 has been replased as the pad it was soldered to has detached from the board and the old one would not go back through the holes, with my meter on Ω setting and the negative probe on Q37 emitter and positive on Q40 base i get 431.30KΩ, if i reverse the leads the reading slowly climbs

Pete

 

Can you explain the reason for the test you did in post #271 ?

Les.

 

Now you gave soldered Q37 back in measure the resistance between Q37 emitter and Q34 base.

 

Measuring the resistance between Q37 emitter and Q34 base was the test I requested. That was to try to identify why the seems to be a voltage drop of 3.465 volts between Q37 base and Q34 base when the transistor tester shows that the base emitter junction of Q37 is OK. It is the test between Q37 emitter and Q40 base that I don't understand.

Les.

 

Sorry my mistake, you did indeed say Q37 base not Q40 base,
For some reason i got that wrong

Would you still like me to do that test ?

 

Yes. And also repeat the test in post #263 AS REQUESTED. This is because you have replaced Q40 so this may have caused some changes.

Les.

 

I do t believe this amp!!,
I now have a new problem, turned it on tonight to complete the testing and the fan stopped and now i have no power lights on or anything, you can hear the transformers come on and hum, the + and --45v rails have power but the main board is dead, all fuses look to be ok, i checked the plug at connection 10 and have 56vAC relative to earth (chassis)

I swear this thing is cursed

 

Ok, sorted that , for some strange reason F8 and F9 630ma 250v decided to let go, i have just noticed that the amp will power up with eithe F8 or F9 in place , so its possible one of them had been blown for a long time, i will order some replacement and some for where the resistor fuses are for future

 

New fuses ordered, should be here by friday, then i will carry on with the test requested in post #263

 

Results ::
Measured relative to T9,
First test, Q29 collector to emitter =4.0vdc,

Q23B= 0.728 Q40B= --3.436
Q25B= 0.418 Q37B= --3.032
Q26B= 0.417 Q34B= 0.417
Q28B= 0.0264 Q36B= 0.0265
Q28E= 0.0264 Q36E= 0.0265
T10= 0.259,

Q37E to Q34B resistance = 0.930MΩ