Ampeg SVT-7 Pro No Power On

[Jon Snell]

Just a simple test, if the Mos Fet output transistors, Q10 - 13 are OK, check the secondary diodes on the power supply board. If faulty, replace ONLY with the original type and specification.

[Jon Snell]

It is basically a Mackie 450Mk2 without the power factor corrector for more efficient use of power.
If you are not experienced with Switch Mode and Class D, take it to someone more qualified or you may kill it completely.

[glebert]

Do you have a schematic that is correct to your board? IMHO these things are dang near unserviceable (unless this is different than the one I had). I think most people just replace the main board if they can be purchased. There are cascaded SMPS power supplies, multiple protect modes that aren't really documented, and probing is dang near impossible because of the tight layout of the FETS, heatsinks, and caps.

I guess you could check for shorted output devices

[ca7922303]

Brought up voltage slowly with Variac. No fan or lights coming on at any point. Was able to get some DC voltage readings on main board of about (125vdc) on right side of main board facing front of amp. Left side no DC voltage.