Hello All
Thought I might try my luck here with a problem amp. Picked a Denon PMA 2000 IVr for nowt the other day. Obviously was because it dont work. It looks very well built and well worth spending some time on.
Symptoms are : Straight into protection mode... flashing light . The service manual is on hifi engine so I dived in . Apart from the white chalky appearance to the ceramic ? caps everything looks fine. No bulging caps or cracked pcbs nor blackened burnt resistors.
So I start looking around and identify the protection circuit. now I dont know how these things work but I thought I might try removing the connections from it to other pcbs to narrow down the fault . I ended up with no connections to it at all apart from its own connection to a 12v ac and regulated supply that comes off the mains in. on this multi pin is a link to a relay that is marked p on off . I am thinking this is a relay to supply the ac power to the main power supply.
Being the case that when the amp goes into protection mode the main + - supplies to the power amp shuts off.
If I am correct , the protection circuit is cutting the supply even without sensing from any other pcbs . In my simple thought process this either means , the lack off connections to the other pcbs alone triggers the relay or the protection circuit is malfunctioning itself and closing the relay.
What would people advise ? pursue the protection circuit or another area...
cheers
Dave
Thought I might try my luck here with a problem amp. Picked a Denon PMA 2000 IVr for nowt the other day. Obviously was because it dont work. It looks very well built and well worth spending some time on.
Symptoms are : Straight into protection mode... flashing light . The service manual is on hifi engine so I dived in . Apart from the white chalky appearance to the ceramic ? caps everything looks fine. No bulging caps or cracked pcbs nor blackened burnt resistors.
So I start looking around and identify the protection circuit. now I dont know how these things work but I thought I might try removing the connections from it to other pcbs to narrow down the fault . I ended up with no connections to it at all apart from its own connection to a 12v ac and regulated supply that comes off the mains in. on this multi pin is a link to a relay that is marked p on off . I am thinking this is a relay to supply the ac power to the main power supply.
Being the case that when the amp goes into protection mode the main + - supplies to the power amp shuts off.
If I am correct , the protection circuit is cutting the supply even without sensing from any other pcbs . In my simple thought process this either means , the lack off connections to the other pcbs alone triggers the relay or the protection circuit is malfunctioning itself and closing the relay.
What would people advise ? pursue the protection circuit or another area...
cheers
Dave
Hi,
I very much doubt the fault lies with the protection circuit.
Disconnecting boards and powering stuff up is not a good idea.
rgds, sreten.
I very much doubt the fault lies with the protection circuit.
Disconnecting boards and powering stuff up is not a good idea.
rgds, sreten.
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Dave your methodology is wrong
Your assumptions about what relays do are also wrong
So you may choose what to do from here and then if you think that you have what it takes, down under there will be some help if not look for expert help.
There is a standby circuit always on after plugged ready to take your remote control command and power up the amplifier ( stand by circuit most of times supply also some parts of the brain of the amp )
Push on the one relay will click and will power up the amplifier while no more than 10 seconds there will be 2 more clicks from the protection relays that control the output of the amplifier ( not the power of the amp) ...That is the sequence
So if the amplifier powers up at the first stage one click but stays on protection it means that amp is powered up properly at all stages but protection will not allow led to stay on and output to come to the speakers for a number of reasons .
Most common amplifier is toasted and there is DC in the output ( measurable with a DVM no more than 2 seconds )
If outputs are at 0V before the relay then there is a small chance that you have a protection issue and this will be ( most common ) a few small capacitors around the protection IC
Another common failure for this protection circuit is a malfunction of the AC loss detection circuit usually a resistor of a few K connected before the main rectifier sensing if AC is present information that is critical to the protection circuit
Common also is some failure in the "logic" circuit PSU of the amplifier which means that you need to trace the +5V line and make sure that all capacitors there are OK regarding capacitance and ESR
If these sound Greek to you then seek expert help its a nice amp to throw away or to destroy by lifting connectors that might provide a very critical ground to some of the boards
Kind regards
Sakis
Your assumptions about what relays do are also wrong
So you may choose what to do from here and then if you think that you have what it takes, down under there will be some help if not look for expert help.
There is a standby circuit always on after plugged ready to take your remote control command and power up the amplifier ( stand by circuit most of times supply also some parts of the brain of the amp )
Push on the one relay will click and will power up the amplifier while no more than 10 seconds there will be 2 more clicks from the protection relays that control the output of the amplifier ( not the power of the amp) ...That is the sequence
So if the amplifier powers up at the first stage one click but stays on protection it means that amp is powered up properly at all stages but protection will not allow led to stay on and output to come to the speakers for a number of reasons .
Most common amplifier is toasted and there is DC in the output ( measurable with a DVM no more than 2 seconds )
If outputs are at 0V before the relay then there is a small chance that you have a protection issue and this will be ( most common ) a few small capacitors around the protection IC
Another common failure for this protection circuit is a malfunction of the AC loss detection circuit usually a resistor of a few K connected before the main rectifier sensing if AC is present information that is critical to the protection circuit
Common also is some failure in the "logic" circuit PSU of the amplifier which means that you need to trace the +5V line and make sure that all capacitors there are OK regarding capacitance and ESR
If these sound Greek to you then seek expert help its a nice amp to throw away or to destroy by lifting connectors that might provide a very critical ground to some of the boards
Kind regards
Sakis
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Ok chaps, thanks for the reply.
So I checked the output transistors and found one channel has both shorted. I have some on the way. The problem is, what killed them.... Nothing on the channel looks damaged or burnt etc. Is there anything people would advice in checking before powering up after replacement ? I would hope it was perhaps a shorted speaker terminal that caused them to die ( I don't know the history as I recently acquired it ) I checked the other transistors on the channel for shorts and no others gone. There are no shorted zeners either.
Regards
Dave
So I checked the output transistors and found one channel has both shorted. I have some on the way. The problem is, what killed them.... Nothing on the channel looks damaged or burnt etc. Is there anything people would advice in checking before powering up after replacement ? I would hope it was perhaps a shorted speaker terminal that caused them to die ( I don't know the history as I recently acquired it ) I checked the other transistors on the channel for shorts and no others gone. There are no shorted zeners either.
Regards
Dave
Blowing outputs is quiet common finding out why not always easy
Install new ones and power up is a guaranteed explosion
Use a bulb tester
Much better if a variac exists
Monitor bias while increasing mains voltage
Make sure that you didn't get fake replacements
Make sure that drivers and peripherals are not blown
measuring semis with a DVM is only an indication semis often fail only under voltage
Best of luck !
Install new ones and power up is a guaranteed explosion
Use a bulb tester
Much better if a variac exists
Monitor bias while increasing mains voltage
Make sure that you didn't get fake replacements
Make sure that drivers and peripherals are not blown
measuring semis with a DVM is only an indication semis often fail only under voltage
Best of luck !
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