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

On Fri, 26 Nov 2004 15:05:00 GMT, "io"
wrote:

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


I have a bad amp too, but haven't had time yet to troubleshoot it. I
suspect mine has a bad I.C. amplifier. I would be interested in
knowing what eventually is found wrong on your amp.

-Format C:
Happily Destroying data one drive at a time...

OK but seems very hard to find out some informations about this damned amp.

Frank.

"Format C:" ha scritto nel messaggio
...
On Fri, 26 Nov 2004 15:05:00 GMT, "io"
wrote:

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


I have a bad amp too, but haven't had time yet to troubleshoot it. I
suspect mine has a bad I.C. amplifier. I would be interested in
knowing what eventually is found wrong on your amp.

-Format C:
Happily Destroying data one drive at a time...

"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



Have you checked the output transistors or IC's? Likely the protection
circuit is detecting a fault and shutting off the amp.

io wrote:
OK but seems very hard to find out some informations about this damned amp.

Frank.

"Format C:" ha scritto nel messaggio
...

On Fri, 26 Nov 2004 15:05:00 GMT, "io"
wrote:


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


I have a bad amp too, but haven't had time yet to troubleshoot it. I
suspect mine has a bad I.C. amplifier. I would be interested in
knowing what eventually is found wrong on your amp.

-Format C:
Happily Destroying data one drive at a time...




It sounds likely that some sort of protection circuit is activating.

Check for DC on the output -- often that's one thing amps check for --
another is overheating.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

io wrote:

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


I assume it may have a relay in the PS to prevent DC rush to the speakers.
check that relay and make sure it is staying on.

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

all the DC voltages are ok. +/-55 +/-5 +/-12 V
the protection ralay that cuts the 220 to the trasformer is driven directly
by a microcomputer M37478M4.

Frank.

It sounds likely that some sort of protection circuit is activating.

Check for DC on the output -- often that's one thing amps check for --
another is overheating.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

"io" wrote in message
...
all the DC voltages are ok. +/-55 +/-5 +/-12 V
the protection ralay that cuts the 220 to the trasformer is driven
directly by a microcomputer M37478M4.

Frank.

Are you saying this means the protect circuit isn't shutting the thing down?

It is.

I have lots of experience with Yamaha shut-down problems.

The PDF is about 13.3 meg. I'm not positive my mail server handles anything
over 10 meg, but I could try sending you the PDF - since you are able to
read voltages etc I will assume you aren't clueless.

Mark Z.
(Authorized Yamaha servicer)

Hi Mark.

I would appreciate if you can send me the PDF. I have a DSL connection,then
for me there are no probs to receive 13Megs.

Frank.

"Mark D. Zacharias" ha scritto nel messaggio
...
"io" wrote in message
...
all the DC voltages are ok. +/-55 +/-5 +/-12 V
the protection ralay that cuts the 220 to the trasformer is driven
directly by a microcomputer M37478M4.

Frank.

Are you saying this means the protect circuit isn't shutting the thing
down?

It is.

I have lots of experience with Yamaha shut-down problems.

The PDF is about 13.3 meg. I'm not positive my mail server handles
anything over 10 meg, but I could try sending you the PDF - since you are
able to read voltages etc I will assume you aren't clueless.

Mark Z.
(Authorized Yamaha servicer)

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

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

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

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

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

OK, I will purchase and replace those transistors.
Stay tuned.
Thanks a lot.

Frank.

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

Hi Mark.

I'm waiting for the spare parts.In the meantime I did some voltage
measurement.
When I give power to the amplifier, on both transistors (Q503 and Q504) the
voltage goes to 19,xx volts on all the three pin.
What does it mean?

Bye.

"io" ha scritto nel messaggio
...
OK, I will purchase and replace those transistors.
Stay tuned.
Thanks a lot.

Frank.

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

19,xx volts on all the three pin.

Not at all sure what this means.

Nineteen volts at the base doesn't sound right, and there should be no
voltage at the emitter or collector. -2.5 is specified to "unmute" and
full-on muting would run about .7 volts, I would think.

Mark Z.


"io" wrote in message
news
Hi Mark.

I'm waiting for the spare parts.In the meantime I did some voltage
measurement.
When I give power to the amplifier, on both transistors (Q503 and Q504)
the voltage goes to 19,xx volts on all the three pin.
What does it mean?

Bye.

"io" ha scritto nel messaggio
...
OK, I will purchase and replace those transistors.
Stay tuned.
Thanks a lot.

Frank.

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

I just replaced the transistor with the same type but the amplifier does not
work at all.
The voltage readings at base emitter and collector are the same.(around
19V).
Do you have any ideas?

Frank.

"Mark D. Zacharias" ha scritto nel messaggio
...
19,xx volts on all the three pin.

Not at all sure what this means.

Nineteen volts at the base doesn't sound right, and there should be no
voltage at the emitter or collector. -2.5 is specified to "unmute" and
full-on muting would run about .7 volts, I would think.

Mark Z.


"io" wrote in message
news
Hi Mark.

I'm waiting for the spare parts.In the meantime I did some voltage
measurement.
When I give power to the amplifier, on both transistors (Q503 and Q504)
the voltage goes to 19,xx volts on all the three pin.
What does it mean?

Bye.

"io" ha scritto nel messaggio
...
OK, I will purchase and replace those transistors.
Stay tuned.
Thanks a lot.

Frank.

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