Pioneer SA-9500 No sound one phono channel

[yaka24]

Hi All,

I'm working on a pioneer SA-9500 and one of the phono channels does not work.

I scoped the signal and it stops right at Q2, so I'm assuming its not activating.

Here's what I know / have done.

- Q2, Q4 have been replaced and test good
- I measure around .2 v by those transistors. It's suppose to be .6 as per schematic / other channel
- R10, R12, R14 all test good with 1 lead removed from circuit
- C3, C7, C5, C6 have all been changed
- I measure the proper 23.8 V before r10/r12

Any help greatly appreciated! thank you

 

[JonSnell Electronic]

R10 open circuit?

 

[yaka24]

R10 measures within tolerance of schematic.. I have 23.8 v before it and around .2 after

 

[JonSnell Electronic]

C13 leaky?

 

[sgrossklass]

R30 is OK? Q6 isn't shorted or leaky or anything? What sort of DC voltage do you get across C11?

I would assume C12/13 to be pretty much done at this point.

BTW, in one of these DC-coupled feedback circuits you always need to look at the entire loop, from input to output and back. If the input pair is out of balance (check voltage between Q2/Q4 bases), something has broken the loop, and you need to investigate what that something is.

 

[JonSnell Electronic]

If you measure the voltages on all components from the good to the bad side, it will soon become apparent where the fault is. Be methodical.

 

[yaka24]

thanks

thanks everyone for your help.. the 24v trace that goes to Q7 was broken.. I must of accidentally done this while replacing something else. After fixing that everything works.

I didn't really understand how that was affecting the voltage going to Q2 so i wasn't looking in that area.

thanks again!