TDA7294 - high current on stdby-gnd (pin1)

[Bruno Willi]

Hi,

I'm stuck repairing a JVC compact system. Problem is the power-amp pcb
with a TDA7294; supply-voltages (pos and neg) seem to be ok; PIN1
(Stdby-Gnd) is connected via a R4.7 to ground; Stdby and Mute are
connected via a 47k to 20V;

When switching on the system, R4.7 (... and the TDA) is getting hot;
on the output are about 20V DC (... which isn't that good for the
speakers...)
I replaced the IC with a new one, but the same behaviour; I also
replaced the most surround caps. Nothing helped.
Maybe someone out there can tell me, what causes such behaviour; is
there a way to test this IC (maybe a characteristic input-resistance
or something like that.).

Bruno

 

[David]

Missing neg voltage supply, imbalanced + and - supply, problem in the
external resistors supplying the bias to the ic.

"supply-voltages (pos and neg) seem to be ok" Do you KNOW they are at the
correct voltage?

David

 

[Bruno Willi]

.... actually, I don't know exactly, if they are the same; Thanx for
your tip, I'll let you know, if it worked.
Bruno