Electronics > Beginners
Help Fixing receiver
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AngraMelo:
Hey guys, how are you doing?
I have been studying electronics for about 2 years now. Mainly trying to fix some equipment and slowly understanding the theory behing them.
The issue in question is a receiver Sony Legato Linear.
Ive been struggling to find the problem with no success.

What I do know is that D803 is conducting (and I dont think it is supposed to, it seems like a fail safe diode of some sorts), it is bringing the ground to around -15V. Also, the voltage on the + and - of the bridge rec is around 24V and -55V. Which is really weird and I have no idea how that can happen.

When I remove D803 the voltages on the Bridge Rec stabilizes and become around 39V and -39V.

The Transistor Q803 is showing 0.5V on its base so it is not letting the collector to open.

I already changed D803 and Q803 with no success.

I tested all the resistors coming from the positive rail up to the base of Q803 and they are all fine, which is insaly weird for me because I dont understand how can almos no Voltage get to the base of Q803 if its not the resistors fault.


Can anyony help me?
My main question is, why would D803 start conducting? and is it his fault that the rails are messed up and not equal?

 Im uploading the whole schematics but the components Im talking about are on the first page (if I uploaded correctly)


Thank you so much for your time, please let me know if you want me to make any tests or probe something.

AngraMelo:
Here goes the other pages.

Also, please note the original post is talking about the file numbered 03
Dukov Ahzrukhal:
It looks like D803 and Q803 are making up some form of voltage regulator, and D803 is being used as a voltage reference. can you find the part number of D803? could you remove it and test it?
AngraMelo:
I already removed and changed D803 and Q803. Still the same situation.
AngraMelo:

--- Quote from: Dukov Ahzrukhal on June 08, 2018, 02:11:33 am ---It looks like D803 and Q803 are making up some form of voltage regulator, and D803 is being used as a voltage reference. can you find the part number of D803? could you remove it and test it?

--- End quote ---
To be exact, the 803 part number is EQA01-16R it is a 16V zener, which I already changed. appears to be working because it is conducting 15.5V at this moment.
Q803 is a 2SD880 which was also replaced today.
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