[bobh123]

Bob… I never had to have my 2Cherry repaired. Because I live in Florida with lots of lightening, I never leave the system powered on, so almost no chance for shorting. As for the sleeves, I’ve used those on and off over the years depending on the binding posts of the amp I had at the time… and when I kept reading about Cherries shorting out, it seemed like posting this idea might help others.

Hi Ron:  I misunderstood because one of your earlier postings said something like that's what happened to mine, which I inferred to mean that you had a failure.  Sorry for confusion.  Bob

[RonN5]

I'm pretty sure you could start a side business repairing these amps for people if you wanted to do so!

[FL Guy]

Excellent info, thank you @bobh123 - and congrats on the successful repair, and restoring your amp to operational.

I went through quite a process to match MOSFET's both for current and voltage to less than 1%.  I selected a pair and replaced the shorted pair of MOSFET's; I did not replace the functional pair.  The amp works and sounds great.

If you have what sounds like a small relay clicking, that's likely an overcurrent protection in case a channel shorts out.  You can easily check by unplugging the AC power plug, removing the top cover and using a DVM to check resistance between the 3 leads on the FET; for my shorted channel, all 3 combos of lead pairs showed a short so was easy to confirm.

If someone needs pair(s) for a channel, I can match more and sell them to you.

For those wanting to repair a unit, realize the MOSFET's are challenging to gently remove without damaging the PC board traces.  I may entertain replacing MOSFET's on cards that have known shorted MOSFET's; shipping the card costs less than shipping the whole amp.  Most other repairs will be harder without a schematic.  Seems to be an FPGA or similar on the board.

Bob

[bobh123]

I would be interested to know where to get DAC amps repaired as well. Last fall, I purchased a pair of 3 King Cherry amps for vertically tri-amping a speaker that was being built for me. I did not have a way to test the amps during the wait time, as my other system is fully active with built in Hypex amps. My new speakers finally arrived this past Friday and I hooked everything up. One of the amps is having an issue. It will play for 10 minutes or so, then completely shut off for about 10 seconds, then will come back on. Obviously disappointing, and I would like to get it fixed. I do have other amps and configurations I can use, so it is not keeping me from listening. Sadly, Tommy is gone and I would like to find someone that can do the repair. It may be something simple, but I am not sure. I do hear some switching in the amp so I am wondering if it has something to do with the automatic idle used. Just guessing.

Hi csmgolf:  See my recent postings on successfully repairing one of my Cherry Amp cards by replacing MOSFET's.  I have more FET's.  Bob

[bobh123]

Yes Bob, the sound is like what you described, a relay clicking. If there is no fuse, the situation I thought is even worse. The thing is I live in Turkey, so difficult to find someone who understands class d amps... If there is a failed card issue, I'll need all the help. Shorting from a touch of speaker cables is more common. But taking out XLR cable is what I did in all my previous amps. Nothing happened. A disturbing sound from speakers came at most. And I'm seriously thinking about selling it... Considering even sending to somewhere else, all repair, transportation and the extra VAT reduced price...

See my recent postings about finding MOSFET's and repairing one of my channels.  Bob

[bobh123]

Thanks for the reply. I hope it works and you can help others out. Mine will hopefully be done this week.

Thank You,
Ron

Hi Ron:  Where did you have your amp fixed and what needed to be repaired?  See recent postings on getting MOSFET's & fixing mine. Bob

[GregC]

Hi Ron:  Where did you have your amp fixed and what needed to be repaired?  See recent postings on getting MOSFET's & fixing mine. Bob

Bob, Thanks for sharing your findings regarding the amp repairs.  It is encouraging to know the amps can be repaired in the event of a short.   

I am curious to know where Ron sent his amp to be repaired.

[orchardaudio]

For those that my be interested, I have used this company to repair boards, they do good work:
https://circuitrework.com/

My contact:
aprice@circuitrework.com

[GregC]

For those that my be interested, I have used this company to repair boards, they do good work:
https://circuitrework.com/

My contact:
aprice@circuitrework.com

Thanks for the contact information.

[FL Guy]

+1 @GregC. Thanks @orchardaudio.

[rhale64l7]

Sorry folks forgot about this thread. My amp finally got repaired. It took a while. It was the fets as everyone else has mentioned. It was done at Protech repair in Cuyahoga Falls Ohio. Phone number is 330-879-8974. Just mention that it is one of them small amps with the Fets. The only problem is he is getting ready to retire so is taking a lot of vacations. Lol So the person on here might be a good choice also. If you need more help PM me. Or I will try to remember and check back. He would have to order the Fets from China also.

[rhale64l7]

Also Bob it would be nice if you could do it. If you have any questions please feel free to ask either on here or in PM

[bobh123]

I bought 100 of the FETs, have 90 left, and can match sets of 4.  $40 per set plus $9 shipping.

Bob

[GregC]

Hi Bob,

Are 4 FETS needed to repair a single mono amp?  Thanks for your contributions to help owners keep these amazing amps!

Greg

[bobh123]

Hi Greg:

I've repaired my 4-Cherry and one Stereo Maraschino.  Both have 4 FET's for each channel.  Since you're asking about a mono amp, I presume it's a Maraschino and likely has 4 output FET's.  If you're game to open the chassis and access the board you can confirm if you have AO B416 FET's; that's what my amp uses.

When losing a channel, seems that only one pair goes out.  Matching is important in two areas:
* Balancing source current between a pair of FET's that are in parallel.  This is more critical in amps with many more parallel FET's.
* Matching Vgs of the FET pair on one side with the pair on the other side.  For some amp designs, this is important to adjust crossover distortion to a desirable value; I don't know if that's critical for Tommy's Class D amps.  Presumably it is because of a posting I ran across (I think from Tommy) that talked about the extensive work involved in matching FET's in a channel; no specifics about how well matched or the consequences if not matched.  Part of his secret sauce  !!! 

Nelson Pass posted a great article in 1993 about how to match FET's; he advocated that MOSFET's P's and N's don't need to be matched.  I matched mine for Isource of a few hundred mA's to within a few mA and Vgs to 20mV or less.

I'm suggesting a set of 4 FET's for those that want to replace all 4 in a channel, or want to have spares on hand if another channel fails; can save time hunting for more FET's in the future.  The manufacturer no longer makes the parts or has inventory; I found inventory at 2-3 distributors in China and decided to order 100 to give a better chance of matching and to help other Cherry Amp owners in a situation similar to me.  I chose to only replace the shorted pair on one side of the one failed channel of my 4-Cherry. My aged, tinnitus-affected ears can likely not detect the last few hundredths of a % of distortion.   

For those that don't need matching or want to do their own matching, I'll sell to each amp owner up to 8 FET's for $2 each plus $9 shipping.

Bob

[GregC]

Hi Bob,

Thanks for the detailed response.  I have all Cherry amplification in my setup.

Mains: 2 Golden Cherry mono amps with very rare linear PSUs that Tommy fit into his 60v cases.  Mine has blue LEDs and the no sleep feature.

1 King Cherry mono amp with a 60v supply (Tommy disconnected the LED because the amp is under my center channel stand that sits below the TV in direct line of sight).
 
1 King Cherry STM MK2 with 60v supply for surrounds.

I have not had a short in awhile.  I take extra care to use banana plugs and be careful to not let the end bridge between the metal speaker posts.

I am thinking about buying some FETs in case I need them in the future.  I do not have the skill to replace them myself if I ever have an amp short out but having the parts may come in handy.

[rhale64l7]

Bob it seems I need some of those Fets. Don't ask how I did it. I am going to PM you. Also can someone confirm on the 60volt power supply I have a 8Amp small but are they fast or slo blow? I have the SMPS800RS and it is one that has two outputs.

Thank you,
Ron Hale

[bobh123]

Greg C:  Let me know how FET's and whether matched or not.

Bob

[bobh123]

Hi Ron:

We won't ask 

If you're game to remove the cover, you can check if the fuse is blown with a DVM.  My guess is that it is a slow blow given current of 8A; the current surge to charge the filter caps could be hefty.  You might be able to read some fine print on the fuse.  The 2 amps I've repaired have relays in them; I hear relays clicking some seconds after power on, and again at power down.

Bob

[rhale64l7]

Yeah I blew the fuse also. It is a slow blow I believe. I ordered one. 8 amp is not common. And the relay kicks then it kicks off within a second. Se problem with the other amp I had.