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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Audio amp won't stay on.
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 |
#2
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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... |
#3
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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... |
#4
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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 . |
#5
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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 . |
#6
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"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) |
#7
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"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. |
#8
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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. |
#9
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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 |
#10
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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 |
#11
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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 |
#12
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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 |
#13
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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 |
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