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Well, my newly delivered amp from China lasted all of two days before a problem ocurred. It was sounding pretty good too. The power switch has a LED which cycles through colors while warming up, and then glows steady when the speaker relay closes. Last night, I was listening and noticed that the LED started cyclying the colors while the amp was playing. (I thought,"well, this is annoying", and didn't think about it again until this morning when I turned it back on. No closing of the relay. No sound. Everything looks normal with the tubes, so I'm guessing it's not a protection issue. The amp is a Music Angel XD800MkIII. I would like to ask for some help with diagnosing and fixing this. I'm handy with a soldering iron and am getting better a reading a schematic. Any ideas where I should go with this besides back to China ;)? TIA, Craig
Follow Ups:
I wanted to follow up and let you know how things turned out. It's repaired, I was able to find someone locally. I dropped it off, expecting to pick it up in a week and he called me 2 hours later!
It turned out to be the 555 timer chip.
I'm listening to it now to give it a few monthes to burn in to see how it sounds before I start messing with it. I've already got all new coupling caps, NOS Amperex ECC85's and a matched quartet of the Genelex reissues from Jim McShane. The seller refunded the repair charge to me also.
Thanks Jim and thank you Gary of Pro Audio Repair of Sarasota!
The seller contacted me and told me that the factory thinks it's a failed relay and is going to send one to me. I suggested that maybe he could send a replacement set of KT88's in case the problem lies there. We'll see what happens there. Thanks for the help. I'm going to check the voltage on the relay Uncle Mike, and let you know. Should I pull the power tubes also?
Should I pull the power tubes also?
I don't think there is a need it will be a short test and the tubes conducting may trigger the relay.
Craig,
I have played around with quite a few of the chinese made amps, from music angel, bewitch Yakin, etc.
I have the soldering job on most leaves a lot to be desired. I think the first thing I would do is reflow all the soldered connections and see if the problem disappears.
I have had a few of the Chinese amps red plate on me. Found a cracked solder joint between the socket and board in each case.
Once you get the amp going again, try some better coupling caps. your angel will sound much better.
best.
J
"No closing of the relay. No sound."
I might suggest two things to look at:
1- the connections at the relay coil to be sure you have continuity to pull it in.
2- Make sure the relay coil is energizing. You can check, with a voltmeter, the connections of the relay coil. If you see voltage and nothing happens then you should suspect the relay coil is open and not pulling in the contacts. If there is no voltage to the coil, get the schematic and see what should be upstream pulling it in.
Because you say the LED was cycling I suspect the relay was failing.
Edits: 07/06/16 07/06/16 07/06/16
How long did you have the amp on, before it started cycling? If it was awhile --- could have overheating issues. If the cycling occur soon after startup --- prolly short somewhere.
Check the idle bias of those KT-88 tubes? You have another set that you can try? Or tube tester --- to test for shorts?
Try removing all connections and restart (including the speaker) --- cycling stop? Check speaker wires for shorts or poor connections. Could be short within the speakers. You have another set of speakers that you can try out?
If the cycling still happens with all external connections pulled --- it's most prolly within the amp. You need to contact seller and see about warranty.
BTW... the main fuse never blew?
I also forgot to mention that I did power it up on the Variac at 90VAC, and there was no change.
Here's a shot of the whole underside:
On the right side board, it looks like the bottom cap is not loaded. The top cap seems to have only one lead soldered. Whats happening there? I dont think that is your problem, but it looks odd.
Thank you for the suggestions. I opened it up and could see no obvious signs of broken contacts, loose/miss wires, or arcing. I looked at the undersign of the power supply board, nothing there. I had just assumed that the relay was the symptom and cause of the problem. That looks fine.
Would it go into protect mode and keep playing? It kept playing when the LED went back to cycling through the warm-up colors. I also did hear a pop while I was listening to it but that wasn't at the same time the LED started cycling. The speaker connection look fine. I've soldered spades on the speaker side and banana plugs on the amp side. I ordered a NOS set of Amperex 6AQ8's which are Chinese in the amp now and I have plenty of 12AU7's. The 12AU7's that were shipped with the amp look like old stock western tubes. That leaves the KT88's. Nothing visually wrong with them except that one's envelope is significantly larger and one is slightly smaller. There is a warranty, but I assume I will be paying return shipping, ($175.00). I also payed with paypal, so I assume I have some buyer protection there as well. I would like to keep it if possible. I can ask the seller to send a new set of KT88's as well.
That's actually a true dual mono amp and the iron is made in Eastern Europe even tho the amp is built in China.There are a couple things can be an issue..One is,the units that are sent to the US and Canada are converted by request when you buy these amps.They don't have an actual 120vac primary a lot of times but they have a 110 volt primary which may or may not work in all cases. The other issue may be speaker impedance issues.There is a delay circuit in the Music Angel amps but if you have a variac,try running the amp at 100v setting on your variac `just to see if it starts running.You can also have a bad tube.Being this is a dual channel amp,you need to pop the bottom off and look for any obvious signs.Try the variac first tho and lets start at 90vac and go up until it comes on if it comes on.Something caused it to go into protection.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Is there any support or warrantee with that amp?
However recheck all your connections. Check to make sure the speaker wires are not touching or shorting anywhere.
Unhook everything and rehook it up again and retry. post your findings
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