Hey all,
I really need some guidance with this, so I would greatly appreciate any input you have.
I recently bought an Marantz SM80U power amplifier off ebay, cost me $300AUD. After plugging in my DAC/Preamp and connecting the speakers, i turned it on. The lights come on, but no sound is being outputted to the speakers.
After inspecting the internals, vacuuming all the dust and carbon, i replug it in and turn it on. I notice that a very strange almost ceramic smell start ommiting from the amplifier (not sure specifically from where).
Inspecting all the modules, i noticed that a few of the BJT transistors on the board had burnt the PCB surrounding them. Same goes for some FETs adjacent.
After taking the module out, i immediately notice that the underside of the board is quite burnt!
Quite annoyed that the ebayer has sold me a faulty item, I've demanded a partial refund because I think I may be able to fix this.
The module after consulting the service manual for the SM-80U:
Service Manual
Is the Power Supply Regulator for the power amplifier.
The interesting thing is that there are two fuses protecting the module from exactly this damage.
USA/Japan it specifies: 630mA 250V
Europe it specifies: 400mA 250V.
Im in Australia and our mains are 230V (which i think is the same as Europe), which means that these fuses should be rated at 400mA, because this burning has taken place, something tells me they are clearly not.
Looking at the circuit diagram, the LED's power bypass a majority of this module (only the rectifier is really used), which gives explanation that the LED's turn on when I power up the amp.
If this module isnt outputting the correct voltage, then I would expect that the power amplifier itself wouldnt be able to work, hence the output voltage isnt been conducted.
Is this an appropriate assumption?
This is my first repair Job and I can find the transistor parts in the service manual, but should I repaire ALL the transistors, including the mosfets etc?
Should I test each transistor seperately to see if its damaged, (all i have is a multi with a diode test on it). If the BJT's have broken down, the diode test on the BJT's base and collector/emitter shouldnt work, yes?
How can I test the FETs?
If you where me, what would you test first, output voltages etc? What would you do in this situation?
Thanks!!
I really need some guidance with this, so I would greatly appreciate any input you have.
I recently bought an Marantz SM80U power amplifier off ebay, cost me $300AUD. After plugging in my DAC/Preamp and connecting the speakers, i turned it on. The lights come on, but no sound is being outputted to the speakers.
After inspecting the internals, vacuuming all the dust and carbon, i replug it in and turn it on. I notice that a very strange almost ceramic smell start ommiting from the amplifier (not sure specifically from where).
Inspecting all the modules, i noticed that a few of the BJT transistors on the board had burnt the PCB surrounding them. Same goes for some FETs adjacent.
After taking the module out, i immediately notice that the underside of the board is quite burnt!
Quite annoyed that the ebayer has sold me a faulty item, I've demanded a partial refund because I think I may be able to fix this.
The module after consulting the service manual for the SM-80U:
Service Manual
Is the Power Supply Regulator for the power amplifier.
The interesting thing is that there are two fuses protecting the module from exactly this damage.
USA/Japan it specifies: 630mA 250V
Europe it specifies: 400mA 250V.
Im in Australia and our mains are 230V (which i think is the same as Europe), which means that these fuses should be rated at 400mA, because this burning has taken place, something tells me they are clearly not.
Looking at the circuit diagram, the LED's power bypass a majority of this module (only the rectifier is really used), which gives explanation that the LED's turn on when I power up the amp.
If this module isnt outputting the correct voltage, then I would expect that the power amplifier itself wouldnt be able to work, hence the output voltage isnt been conducted.
Is this an appropriate assumption?
This is my first repair Job and I can find the transistor parts in the service manual, but should I repaire ALL the transistors, including the mosfets etc?
Should I test each transistor seperately to see if its damaged, (all i have is a multi with a diode test on it). If the BJT's have broken down, the diode test on the BJT's base and collector/emitter shouldnt work, yes?
How can I test the FETs?
If you where me, what would you test first, output voltages etc? What would you do in this situation?
Thanks!!
Last edited:
Those are 400mA medium blow fuses, see http://www.ue-soft.de/oilfield/techtabs/electric/fuses001.pdf for a colour code table
Hey thanks for the replies,
I spent the last few hours examining the circuit "P851" which is the circuit power regulator (images above) from the schematic and testing the PCB.
There is a -35v output from transistor Q859, which should actually be -23.7V according to the schematic. This excess voltage is caused by the -62V rail actually being -95V.
Below i have highlighted the break down of analysis, the -80 -> -62 Module is damaged.
The scary thing now is that both this -95V and -35V has been conducted through the main circuit board. Unsure about the transistor ratings, this is a potential catastrophe..
Considering that no sound comes from this (at all), what would your initial thoughts be?
Should I attempt a full-refund?
I spent the last few hours examining the circuit "P851" which is the circuit power regulator (images above) from the schematic and testing the PCB.
There is a -35v output from transistor Q859, which should actually be -23.7V according to the schematic. This excess voltage is caused by the -62V rail actually being -95V.
Below i have highlighted the break down of analysis, the -80 -> -62 Module is damaged.
The scary thing now is that both this -95V and -35V has been conducted through the main circuit board. Unsure about the transistor ratings, this is a potential catastrophe..
Considering that no sound comes from this (at all), what would your initial thoughts be?
Should I attempt a full-refund?
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.