[Denis]

Hi guys

one of my 2 5176 is very quiet. it is right behind my 573 and if i crank the gain up around +20db in comparison to my working 5176 it sounds as the other.
I think either Q1 or Q2 is having an issue but Id like to hear from someone who knows what is going on When I use line level 100mVAC to calibrate even at max input and max output it almost does not compress where the working one compresses.

Here my measurements:
DC: everything is fine. the "broken" unit and the working one are the same. Resister values are fine. Specifically all around Q1 are fine. C3 C4 and C7 seemed to be fine. I measured C7 and both fine. I could not measure C3 and C4 but resistance is the same on both units.
AC:here are some differences.

When I the same signal on both units, lets say the calibration 100mVAC I have at tp1 around 60mVAC on both. I have good signal on tp2, I think it was .5mVAC or something but on the broken one it was way less. something around 10mVAC+-.
I checked around Q1 and I have looking at the round side from left to right measured to 0V 60mVAC, 30mVAC and 45mVAC. on the broken one it is 0.0mVAC  0.0mVAC and 25mVAC.



It was working at some point. I dont know what happend. No damage is noticeable. Anything else I can measure to find the broken part?

I would just replace Q1 but I found that the BF245 has different pin outs? I found 2 different variants called the same. Or is it maybe some different part?

EDIT:
On the working unit I have with 60mVAC on tp1 and output at 100% I have 1.1VAC on tp2, on the broken unit I have 14mVAC on tp2

Thanks a lot!
Denis

[JPK]

Try removing Q1 on the broken unit. If the sound is back then Q1 is the culprit.

[Denis]

Try removing Q1 on the broken unit. If the sound is back then Q1 is the culprit.

Hi Jean-Pierre

I changed Q1 but that was not the issue..any ideas what it can be? I dont want to swap out all pre stage
I see that R56 and R57 changed color a little. A little burned the resistance is correct and they are just for power right? But that cannot be an issue?
I swapped the SK25 and the front assembly with no effect either. 
Do you think it might be transistor or capacitor? I would swap the caps out first.

Thanks
Denis

[JPK]

I changed Q1 but that was not the issue
Did the sound return when Q1 was disconnected?

I see that R56 and R57 changed color a little.
This means you have a short circuit somewhere. Are they getting hot? 

A little burned the resistance is correct and they are just for power right? But that cannot be an issue?
You can check their value with your ohmmeter (in circuit).

Do you think it might be transistor or capacitor?
Not a capacitor. Neither a transistor if you got the DC voltages right in the picture here.