Technics amp repair

Thread Starter

Bruno2016

Joined Dec 13, 2020
8
Hi
I’m trying to repair a technics su-v2 amplifier.
On the main board, both stk8040 ((ic301 and 302) and the an6552f (ic303) are faulty => i removed them
I disconnected the source input board from the main board as well (5 pin connector)
Afterwards, i measured voltages :
All power lines are OK but i found that voltage on the ground line (pin D or 4 on the connector between the source input board and the main board) is not zero
Is this normal ? Which value should i find ?
Thanks for your help
 

AlbertHall

Joined Jun 4, 2014
10,769
As far as I can see, those two points are not connected together - there is a capacitor (C351 I think it is named) between them.
I can't see how any voltage between them is determined.
 

Thread Starter

Bruno2016

Joined Dec 13, 2020
8
Actually, they must be connected via the transistor circuitry (the 2 blocks Right and Left containing Q301 to Q318) but I can’t figure out how
 

R!f@@

Joined Apr 2, 2009
9,740
Those grounds are connected via chassis screws on RCA Jacks.
Solder a wire from main GND to RCA GND and check
 

Thread Starter

Bruno2016

Joined Dec 13, 2020
8
I finalement found out the connection between those 2 lines (a missing screw between PCB and chassis).
After putting it back, I resumed my measurements : many voltages are not correct at transistor (Q301 to Q318 , Q601 to Q604) pins.
I don’t know where to start with ... maybe test points :
TP 601 = 0.2 V (0 normally)
TP 301 and 302 = 0 V , OK
TP 303 and 304 = 1 V (0 normally)
What can be wrong with this ?
All measurements were done without the 2 STK8040 (I removed them earlier).
 
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