On the main amp board, on the side of the board nearest the front of the
unit, there are two signal sized transistors on either side of connector
W501, a 7-pin connector. The transistors are Q503 and Q504. They can both be
replaced cheaply enough, ever though only one is likely bad.

Mark Z.


"io" wrote in message
...
Can you tell me number of the transistor on the PCB?
It's impossible to find it simply following the copper tracks on the
board.

Frank.

"Mark D. Zacharias" ha scritto nel messaggio
...
P.S.

Use only the original type 2SD1915F or a 2SC2878. Regular signal types
won't do.

The PDF is on it's way.

Mark Z.


"Mark D. Zacharias" wrote in message
...
Look to see which amp channnel spikes negative at the instant that
channel should "unmute". The muting transistor associated with that
channel is faulty.

Mark Z.


"io" wrote in message
...
I injected an sine wave on both channels and with the oscilloscope I was
able to see the output.
Since the power amplifier works,I'm not sure about the behaviour of the
microcontroller witch drives the POWER ON relay.
I need to know from witch components it receives the data.

Frank.

"Mark D. Zacharias" ha scritto nel messaggio
...
Assuming an amp channel isn't "blown" which would likely give an
instant shut-down, the most likely scenario is a bad muting
transistor. At the precise moment the speaker relay should come on, a
negative bias is applied to shut off the muting transistor. If the
transistor is leaky, it passes the DC to the input of the power amp,
and this triggers the shut-down. One of Yamaha's "red-flag" repairs,
quite common. It might be a surface-mount type transistor.

Are you a technician or otherwise able to read a schematic?

Mark Z.


"io" wrote in message
...
Hi all.

I have a problem on a Yamaha AX-496 amplifier.
When I press the POWER ON button, it will turn on but only for 3-4
seconds.
I already checked the fuses and all the voltages +/-55 +/-12 +/-5 V
are OK
what can I do?

thanks.

Frank