Hartke 3500 Mosfet cuts out

ric3xrt · #1 07-24-2011, 02:33 PM

Bought this Mosfet 3500 yester day @ a Yard sale, girl at the sale said that it was her brothers back up amp and that its works when it feels like it.
Plug it in hooked it up , work fine for about 15 mins, the it would cut out, sounds like a relay is kicking in and out.
turn the volume down(around 2 with Pre's @ 5)plays or about 30 mins befre it cuts out.
Ran a Preamp in to the FX return, and it cuts out right off the bat every thing else seems to work.....

RickenBoogie · #2 07-24-2011, 03:32 PM

So, it needs to be bench tested, and repaired by a qualified amp technician. Find one, and take it in. I always consider a trip to the tech as part of the price when buying a used amp.

BassmanPaul · #3 07-24-2011, 03:56 PM

+1 to Rick's post.

There IS something that you can check for first and that is to see if the cooling tunnel is blocked with crud. Fans draw in a lost of dust during operation. With the amp unplugged, take the case off (or lid) and vacuum out any dust you find. Wear a mask while doing this for safety. An old tooth brush will help with the more stubborn stuff.

Kael · #4 07-24-2011, 04:14 PM

Classic bad solder joint. That is an issue on those amps. It is a massive PITA to track down which one is bad. Take it to a tech and tell him to redo every single solder point. That's the only way to be sure. I went through this same issue msyself.

It's worth getting that head fixed though. The older MOSFET heads were actually pretty nice heads. I used one for years. They were a little hissy, but if you engage the graphic and start dropping the highest fader (10kHz if I recall correctly) that hiss will disappear.

runmikeyrun · #5 07-24-2011, 07:57 PM

yeah I had one too, it was nice for what I was using it for at that time. Never had any problems with it.

ric3xrt · #6 07-26-2011, 06:55 PM

this after noon I swaped out the Power module with a parts amp one. played it for about an hour no issue. so tomorrow I'll pull this Module aprat and see if anythig jumps out.

Jerrold Tiers · #7 07-26-2011, 08:23 PM

If those are still made like similar ones were a while back, check the filter cap on the DC detector...... Found one like that that did just what you say......replaced bad cap, all well. mebbe they aren't made the same now.