I’m lookin for a bit of help with an Mc2 Mc450 amplifier that won’t power up.
It was working fine until I cleaned it inside with a can of compressed air.
Now it won’t power up, no lights or anything. The fuses are ok and power is reaching the circuit board.
I’ve very little electronics knowledge, so would appreciate if anyone can point me in the right direction. I have the schematic, but don’t really know how to test if each component is ok.
Thanks
Matt
It was working fine until I cleaned it inside with a can of compressed air.
Now it won’t power up, no lights or anything. The fuses are ok and power is reaching the circuit board.
I’ve very little electronics knowledge, so would appreciate if anyone can point me in the right direction. I have the schematic, but don’t really know how to test if each component is ok.
Thanks
Matt
Please take some pictures about the inside of the amplifier, there can be some mechanical damage, due the air pressure.
Sajti
Sajti
Thanks for the reply. I will take pics later. Everything looks ok in the amp. I was wondering if I may have frozen a component with the spray and caused damage. Is this possible?
Thanks
Thanks
don't overlook simple things like mute and mode switches, even control positions.
the only way freeze spray would cause a problem is if the amp was on at the time of cleaning, was it?
the only way freeze spray would cause a problem is if the amp was on at the time of cleaning, was it?
The amp is digitally controlled, so none of the functions like mute and gain operate unless the amp is on.
The amp was off while cleaning.
I think I’ve found the problem, there’s a 2k7 resistor directly after where the neutral starts on the circuit board. It’s faulty, reading around 0.6ohm.
The amp was off while cleaning.
I think I’ve found the problem, there’s a 2k7 resistor directly after where the neutral starts on the circuit board. It’s faulty, reading around 0.6ohm.
i've only found a partial schematic of the supply and i am still trying to decipher the turn on sequence.
i would have expected a standby supply to be always on but not so...
can you PM me the schematics?
i would have expected a standby supply to be always on but not so...
can you PM me the schematics?
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Pm sent. I will bring the amp to an electronics repair today so they can check all the amp.
Thanks
Matt
Thanks
Matt
Thanks for the reply.
I brought the amplifier to an electronics repair and they managed to fix the amp, although it took them some time as each time they found a fault and repaired it, they would find another fault.
I don’t actually know what was broken in the end, but I suspect that the new fans I installed caused the problem due to the metal logo sticker in the centre of the fan touching positive and negative sides of the heat sink. I could see marks there on the heat sink where it had melted slightly from the arching.
Cheers
Matt
I brought the amplifier to an electronics repair and they managed to fix the amp, although it took them some time as each time they found a fault and repaired it, they would find another fault.
I don’t actually know what was broken in the end, but I suspect that the new fans I installed caused the problem due to the metal logo sticker in the centre of the fan touching positive and negative sides of the heat sink. I could see marks there on the heat sink where it had melted slightly from the arching.
Cheers
Matt
#H713
Hi,
I need help with a MC450 with an output of -108 / -165 mV DC offset. For analog input pcb 6023, I found a circuit diagram for 6025 but this is different from 6023.
Any idea where to adjust the DC offset? Or should I not deal with it?
THX! D '
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I don't have schematics for the 6023 PCB- just the 6025. Can you post a picture of the board? It may be very similar (or the same) as the 6025. Unfortunately, there were multiple revisions of some of the PCBs in these amps. Not all of them are in the service manual. This is common with amp manufacturers (Crest is AWFUL about this), but it does make service work a lot harder.
As far as I know, there is no adjustment for DC offset on these amplifiers- the op-amp takes care of that for you. 100 mV seems way high for one of these. Does it otherwise pass audio acceptably? If you can measure THD, what does it look like for this amp? You should be getting less than .01% at 1 kHz into a 4 ohm load.
Also, how much of the service manual do you have for this? Their service manual is fairly lousy, but it's better than nothing.
FWIW, the most common failures I've seen on these amps are the 5532s on the input board (usually it's the first one in the signal path), the PM7524 multiplying DAC and the Toshiba or NEC IO expander chips on the processor board.
This does not sound like a fault on the processor board to me.
Before anything else, check the power rails on the op-amps.
As far as I know, there is no adjustment for DC offset on these amplifiers- the op-amp takes care of that for you. 100 mV seems way high for one of these. Does it otherwise pass audio acceptably? If you can measure THD, what does it look like for this amp? You should be getting less than .01% at 1 kHz into a 4 ohm load.
Also, how much of the service manual do you have for this? Their service manual is fairly lousy, but it's better than nothing.
FWIW, the most common failures I've seen on these amps are the 5532s on the input board (usually it's the first one in the signal path), the PM7524 multiplying DAC and the Toshiba or NEC IO expander chips on the processor board.
This does not sound like a fault on the processor board to me.
Before anything else, check the power rails on the op-amps.
MC2 MC450
#H713
Thank you for the answare!
Here is the service manual MC2 450 650 Service Manual download, schematics, eeprom, repair info for electronics experts
pcb 6023 does not include VR5 trimmer
I cannot measure distortion in the absence of a suitable instrument.
The amplifier works perfectly well anyway, I just don't like the high DC offset 🙂
#H713
Thank you for the answare!
Here is the service manual MC2 450 650 Service Manual download, schematics, eeprom, repair info for electronics experts
pcb 6023 does not include VR5 trimmer
I cannot measure distortion in the absence of a suitable instrument.
The amplifier works perfectly well anyway, I just don't like the high DC offset 🙂
That looks to be the same revision as what I got from them a few years ago.
Look at the output of the 5532 (IC1A) to see what the DC offset is like there. I've never had to adjust VR5, though it does certainly look like a DC offset control. Interesting that the PCB6023 does not have it.
Essentially what I'm trying to determine here is whether the DC offset is caused by a maladjustment or a failed part.
Look at the output of the 5532 (IC1A) to see what the DC offset is like there. I've never had to adjust VR5, though it does certainly look like a DC offset control. Interesting that the PCB6023 does not have it.
Essentially what I'm trying to determine here is whether the DC offset is caused by a maladjustment or a failed part.