I'm new here and I just want to say thanks.
I'm a semi pro amp mechanic, converted over from antique radio collecting and restoration and a former aircraft engine mechanic and my first SVT came in as a referral from Professional Music here in central Iowa.
It was an ebay buy, ran pretty well for a year, and then started with the "Honey, I've got a headache. Find someone else to play with." red and green fault light routine.
I did the research and concluded that people are scared of these things, because they're heavy and everything looks expensive inside.
The first thing I did was remove the main board and the power tube board to visually inspect for burns and scorched resistors, tube sockets, bad solder joints and other defects. The two yellow leads from the power transformer to the main board came off in my hands because they hadn't been crimped properly. After reinstalling the boards and getting the ribbon connectors mixed up and straightened out (digital camera!) I was about ready to toss in the towel.
I advised the customer that the fault indicator was saying "maybe you need new tubes, maybe you don't" but that he could spend the money with no guarantee that would fix the problem.
Then I found this forum and found a thread from a couple years ago where a user described the exact same problem with the exact same amp. After a couple trips to the shop, an old TV repairman said "Yah. Problems like that are usually bad solder joints on the circuit boards." This user's service man pulled out the power input board, resoldered the connections and fixed the amp.
So before I tossed in the towel, I decided I was this far along, removed the power input board, resoldered all the joints especially around the relays and thermistor, and reinstalled.
I've just finished 2 long heat soak runs, fine tuned the bias, and played my shop mule strat clone through it for an hour and things look good. It'll go home tomorrow.
I did find loose hardware rattling around inside the amp and the power receptacle was attached to the board with glued on nuts, one of which had dropped into the works. I also redid the tube socket solder joints. The folks who make these over in Viet Nam could use a class in process improvement, because poorly crimped wiring and loose hardware could cause serious problems.
Fact is, I've got another one coming in Monday with much the same problem. It was a B stock amp that lasted all of four days before it quit.
So thanks for the help. This forum saved my reputation around here.
