Marshall Valvestate vs100 Problem

[Mars Amp Repair]

Hey Kid,
the heatsink MUST be isolated from the chassis as it is hot. Meaning, there are as I recall 4 insulating washers that keep the heatsink from electrically connecting with the chassis. you have put them in the wrong position thereby letting the heatsink become connected with the chassis.
the version of the amp in the prior posts is different from yours. His has a discrete power stage where yours is a single IC....glen
glen

[quazcha]

MG100HDFX 2 fan mounting scenarios

I have 2 MG100HDFX's one circa 2005 and the other 2006. the 2005 had the earlier fan style. The earlier marshall MG100HDFX fans were mounted to the heatsink by 4 screws insulated (from the chassis) at the head end by the same type of TO220 "transistor mounting screw" insulators. The later ones have a plastic fan shroud that mounts to the chassis and the heatsink mounts to the other side of the shroud the screws are offset as not to touch each other to provide insulation. The heatsink is electrically live (i believe +48vdc) and must be insulated.
I replaced it with a thicker computer fan/heatsink (40mm x 40mm x20mm thick) and was able to find a heatsink with the fan mount locked onto the heatsink and then used short sheet metal screws to mount the fan to the chassis. before you power up, use an ohm meter and measure the resistance from the chassis to the heatsink it should be in the megohms or you will bow to the TDA7293 replacement gremlins once again...