What do you think the resistance between Q37 emitter and Q34 base should be ? You should be able to answer this question by looking at the schematic. I am trying to get you to follow the reasoning for these tests.

Les.

 

Looking at the schematic Q37E is directly connected to Q34B so about 1 to 2 Ω, i said this as this is what i get connecting the probes together, so basically i am getting the resistance or the PCB track

 

Good. So are you going to try to trace the cause of this fault yourself ? If you want us to try to identify it you will have to post VERY CLEAR pictures of the etch side of the board close to Q37 and Q34. ( See post #268. )

Les.

 

I have a question !,
So as far as i can work out this works on a balance of + and -- input relative to the 0v rail, my queation is if i have repaired a section of the PCB track, say with covering the track with solder or use a pice of wire to connect one componant to the next because some of the tracks are bad, would this difference in resistance effect the current flow and would i have to do the same for the opposite rail for it to still be (balanced) and yes i can take good photos if needed,

Pete

 

It is unlikely to make any significant difference in the resistance of the track. Even if it is just a hairline break in the track solder a suitable thickness wire across the break,(Don't just rely on a blob of solder.) There will probably be solder resist on the track which you will have to scrape off to be able to solder to it.

Les.

 

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

I will look at this again and resistance and continuity test each chanel and post my results

 

Just find the break in the track between Q37 emitter and Q34 base and repair it. The chance of having the same fault on the left hand channel is VERY small. You seem to be going off at a tangent again wanting to do tests that have no relevance to the fault.

Les.

 

I will look at this tonight, never crossed my mind that this could be a fault,

 

Hats off to you @LesJones , there is indeed a brake in the track where Q34 base connects to the etch, its connected on one side but not the emitter side of Q37,

Ok repaired that,
NOW!!! WE HAVE ONE SIDE WORKING, and sounds nice and clear, still have the resister fuses installed,
Whats my next steps?

 

A lot of the tracks are quite bad on this board, it dosent like to have componants changed, the tracks start to lift

 

Even though it seems to be working I suggest taking the voltage readings again and layout the results as I showed them in post#266. Now the transistors on the negative side are conducting it will change the readings on the positive. Post the results and also make a note of them as it may be useful when fault finding the left hand channel. Before you try the amplifier at higher output levels MAKE SURE that Q27 is in good thermal contact with the heat sink with the output transistors. (As I have not seen the amplifier I don't know how Q27 is secured to the heat sink.) If this is not done it is likely that the output stages will go into thermal runaway which could destroy the output transistors.

Les.

 

A lot of the tracks are quite bad on this board, it dosent like to have componants changed, the tracks start to lift

If copper traces on a PCB are lifting then your soldering iron is too hot and/or you are spending too much time heating up the joints.

 

@LesJones
The only outputs on the right side that are attached or close to the heatsynk are Q20, Q26,Q34 Q36, and Q28

 

Here are the results with the broken track fixed relative to T9, no resistors connected,

Q23B= 2.111 Q40B= -- 2.014
Q25B= 1.526 Q37B= -- 1.433
Q26B= 0.925 Q34B= -- 0.871
Q28B= 0.422 Q36B= -- 0.018
Q28E= 0.017 Q36E= 0.018



Pete

 

Q27 is not fitted along with the corresponding Q35, i am assuming you meant Q34, this is held to the heatsynk with a metal spring like clip ( not currently installed), once you are happy everything is good i will dismantle, clean and thermal paste everything,

Pete

 

When I said Q27 I should have said Q29 (The bias regulator) Sorry for the error.
Something is still not right around Q34 and Q36. Check the resistance between Q34 emitter and Q36 base.

Les.

 

On the side that works, you should look at the voltage across any of the last emitter resistors over time with no load and no signal. At least an hour.

 

@LesJones

You've done a nice job so far. I didn't realize we were also dealing with severe wiring (PCB) issues.

 

Hi kiss, I have no idea of the history of the amplifier so I had no hints at the sorts of faults it was likely to have. I did ask for the history of the amplifier but the question was not answered. Looking at the pictures of the etch side in post #289 it looks like someone that had never soldered before has had a go at it. I feel that Rookieme is just following instructions but not attempting to understand the reasoning behind the tests.

Les.

 

I feel that Rookieme is just following instructions but not attempting to understand the reasoning behind the tests.

I also concur.