SVT 3 Pro Issues

[yurka]

First time looking at one of these. Looks like a tube preamp, SS power section. The amp powers up, and plays fine for about 20-30 minutes, then the output dies. My only guess is the power mosfets probably overheating, improper heatsink placement, etc. Anyone else got any suggestions?

[teemuk]

Well, the amp has an overtemp shutdown circuit so it should be a pretty quick test to see if it's indeed operating. (See sheet 2 of the power amp schematic, if you don't have the schema a Google search will find one in a heartbeat).

Are you running the thing with at least the rated load? No clutter of wires or stuff in front of airtake holes? Fan working? No gobbles of dust inside...?

[selloutrr]

Common problem the heat compound dries out take off the heat sinks clean and reseat.

You may also need to replace any diodes or resistors in that section that lead directly to the safety as they might have tripped.

The parts are run rather hot so if the unit didn't get proper cooling it kills the heatsinks fast.

You may need to replace the mosfets just to be safe. As the heat sink stopped being effective they took on the heat before the safety kicked in.

[ampdoc1]

It sounds like it is heat related. Get a can of computer "dust remover" spray. Turn on the amp and when it dies, take the can, turn it upside down, and spray small areas one after another. With the can upside down the cold propellent (freon?) is sprayed instead of the normal contents.

Easiest way in the world to find most overheating problems.

a'doc1

[selloutrr]

great idea!

If the protection circuit is like the other Rackmount SVT models it requires the power being switched off/on to reset.