Originally Posted by Rob Morse
It is difficult to diagnose based on your description there are a few possibilities, fortunately the electronics pack can be serviced on the component level by any audio repair center, Velodyne can provide the schematics for this model at no charge. You can request a pdf version by emailing your model and serial number to firstname.lastname@example.org
Here's what I've done to try to fix my VA1012 today:
1) It turns out the resistors at R42 and R43 (1.8K ohm) that were originally put on the circuit board from Velodyne were, in fact, 1-watt resistors. The schematic calls for 2-watt resistors in those spots, so I replaced them with 2-watt ones (same resistance with 2% tolerance). I do not know if the lower 1-watt resistors are what is responsible for the discoloration/burning that I see on the circuit board, but using 2-watt ones can't hurt.
2) I found a few references on the web from Velodyne owners that had the same problem (2A main power fuse blowing) and they traced the problem to a faulty bridge rectifier. Since bridge rectifiers are pretty cheap, I decided to invest $2.79 to get a replacement one when I purchased the resistors. The original rectifier was a KBU4D. I picked up an NTE5318, which cross references exactly to a KBU4D.
Replacing those did NOT fix the problem. The 2A fuse blows immediately upon turning on the power switch.
3) Next I decided to check the output voltage of the secondary winding on the transformer. I disconnected the secondary wires from the circuit board and, end to end, the secondary measured 67 volts AC. Center-tap to end, it measured 33.5 volts AC (I measured center tap to each end and both halves measured 33.5 volts).
I do not know if 67 volts is too high. I see references to 45 volts on the schematic but that is after the bridge rectifier and several other components that are probably stepping down the voltage. My "gut" again tells me the power transformer is okay, but I'd appreciate some confirmation if you can. I'd simply measure it along the circuit board, but I can't do that because the main power fuse (2A) blows immediately when the secondary windings are connected to the circuit board.
Again, the large capacitors all appear to be perfectly normal. Other than the discoloration around those two resistors, no component looks stressed or dull.
In lieu of you suggesting something else to try, I think the only other thing I can do is to go ahead and spend $20 to replace the Sanyo STK4040II power amplifier. If that doesn't fix it, I don't know where else to turn.