Hello
This is my fist time doing a post so hope i am doing correctly and in the correct place. See correspondence from a Teck. i have used for years that is suggesting i get someone with experience with these amps to look at it .He did the usual things that old amps. need but then ran into this issue below .My problem is that Georgetown [ if one was interested in looking at it ] is along way from Ottawa and this amp. is heavy to ship.
Any suggestions
Cheers
"Hi David,
Further research on possible causes of the observed power supply issues suggested that the transistor Q1 (MPSA93) might be faulty (it is close to the part of the board which had the overheating resistors). However, replacing the MPSA93 did not solve the intermittent power supply issues.
The Carver M1.5 does not use a typical linear power supply; it has a "tracking" power supply that varies the B+ and B- rails to follow the input music signal. Although reputed to be an excellent design, troubleshooting faults is a complicated process (see pages 18-21 of the attached service manual). The problem may very well be with the leaky/failing dual capacitors (C13/C14) that I mentioned in my earlier message. And as discussed in the linked AK thread in the earlier message as well as the M1.5 Service Bulletin (included in Service Manual), their replacement requires an adapter board since dual can capacitors are no longer available. I do not know of any local source for the adapter board, but it is available from after-market sellers on eBay, e.g., https://www.ebay.com/itm/220766804156?hash=item3366ba18bc:g:GjcAAOSwUuFWxmds.
At this point, I think it would be best to have your unit looked at by a tech that is familiar with Carver amplifiers rather than me since I lack specific knowledge/experience with this type of design. I know of a former Carver Authorized Service Centre/Distributor with an excellent reputation that might be able to help; he is an Administrator at DIYAudio (https://www.diyaudio.com/community/members/anatech.12165/ ) and is located in Georgetown, ON."
This is my fist time doing a post so hope i am doing correctly and in the correct place. See correspondence from a Teck. i have used for years that is suggesting i get someone with experience with these amps to look at it .He did the usual things that old amps. need but then ran into this issue below .My problem is that Georgetown [ if one was interested in looking at it ] is along way from Ottawa and this amp. is heavy to ship.
Any suggestions
Cheers
"Hi David,
Further research on possible causes of the observed power supply issues suggested that the transistor Q1 (MPSA93) might be faulty (it is close to the part of the board which had the overheating resistors). However, replacing the MPSA93 did not solve the intermittent power supply issues.
The Carver M1.5 does not use a typical linear power supply; it has a "tracking" power supply that varies the B+ and B- rails to follow the input music signal. Although reputed to be an excellent design, troubleshooting faults is a complicated process (see pages 18-21 of the attached service manual). The problem may very well be with the leaky/failing dual capacitors (C13/C14) that I mentioned in my earlier message. And as discussed in the linked AK thread in the earlier message as well as the M1.5 Service Bulletin (included in Service Manual), their replacement requires an adapter board since dual can capacitors are no longer available. I do not know of any local source for the adapter board, but it is available from after-market sellers on eBay, e.g., https://www.ebay.com/itm/220766804156?hash=item3366ba18bc:g:GjcAAOSwUuFWxmds.
At this point, I think it would be best to have your unit looked at by a tech that is familiar with Carver amplifiers rather than me since I lack specific knowledge/experience with this type of design. I know of a former Carver Authorized Service Centre/Distributor with an excellent reputation that might be able to help; he is an Administrator at DIYAudio (https://www.diyaudio.com/community/members/anatech.12165/ ) and is located in Georgetown, ON."
This is not an amp to learn do it yourself repair on. Too complicated, too many things to go wrong. Pay the tech, pay the freight, or move on. If you ship it put lots of foam peanuts or bubblewrap in the box to prevent bent aluminum or broken connectors & knobs. If <70 lb might ship by royal post. Above, UPS & FedEx only.
I repair used peavey QSC or or crown PA amps. Fairly straightforwards and easy to get schematics & part numbers for. .1% or lower HD in the post 1988 models. M-2600 & MMA-875t & MMA-8150 & 180MA don't have fans. The mma & 180MA are monaural & very cheap. dynaco & parasound amps are nice but the used prices are outrageous.
I repair used peavey QSC or or crown PA amps. Fairly straightforwards and easy to get schematics & part numbers for. .1% or lower HD in the post 1988 models. M-2600 & MMA-875t & MMA-8150 & 180MA don't have fans. The mma & 180MA are monaural & very cheap. dynaco & parasound amps are nice but the used prices are outrageous.
I believe (don’t quote me) it was anandtech that had mentioned once that he’d never repair another one of these that would need to be shipped, since the fine calibration of the power supply is easily corrupted by shock and vibration. I recall something about having a successful repair followed by a month on the test bench, working fine, only to have it fail after having been delivered, and used by the owner.
I was listening to one some 30 years ago that just unexpectedly blew up at low volume.
The owner wasn’t present, and to this day probably thinks I was abusing it. The device had just been moved in a trailer up the west coast. This was one that had been acquired for the cost of parts through a contact at the factory back when these were new.
The actual amp is run, by design, very close to the maximum voltage of the transistors. The power supply is very touchy to adjust, and is prone to drift.
Winning combination, not so much, although a novel concept in it’s time.
There are in fact hundreds of other amps out there that will likely give a better return on the dollar, and that is a factor for many on this forum, who also spend a lot on this hobby.
I was listening to one some 30 years ago that just unexpectedly blew up at low volume.
The owner wasn’t present, and to this day probably thinks I was abusing it. The device had just been moved in a trailer up the west coast. This was one that had been acquired for the cost of parts through a contact at the factory back when these were new.
The actual amp is run, by design, very close to the maximum voltage of the transistors. The power supply is very touchy to adjust, and is prone to drift.
Winning combination, not so much, although a novel concept in it’s time.
There are in fact hundreds of other amps out there that will likely give a better return on the dollar, and that is a factor for many on this forum, who also spend a lot on this hobby.