TDA7294 - high current on stdby-gnd (pin1)

B

Bruno Willi

Guest
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
 
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 <bruno*nospamplease*@brunowilli.de> wrote in message
news:i2jutvk2iu0ebdjt1ls9j0tla8s44lif7d@4ax.com...
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
Click to expand...
 
.... actually, I don't know exactly, if they are the same; Thanx for
your tip, I'll let you know, if it worked.
Bruno

On Tue, 16 Dec 2003 20:51:22 -0500, "David" <dkuhajda@locl.net.spam>
wrote:

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 <bruno*nospamplease*@brunowilli.de> wrote in message
news:i2jutvk2iu0ebdjt1ls9j0tla8s44lif7d@4ax.com...
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
Click to expand...
 
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