MTX Terminator TN250/1 blowing fuses

[cmarkell2001]

i have just the same issue, tn250/1 blowing fuses as soon as +B touches, no speakers connected, no rca's, not even the remote turn on. so I started following the bcae1 guides as well (which are excellent, next 50 bucks to land in my paypal account is yours/theirs) and am stuck.

the FET's failed the resistance tests between their leads, so I ordered and installed replacements, along with the dual rectifiers between each pair. also R111 (2.2 ohm 1%) was cooked so i replaced it and what i hope to be it's twin at R112.

I'm not positive i got the right replacement transistors either, but here's whats installed now:
IRF540 = FET600, FET601
FEP16DTA = REC103, REC104
IRF9540 = FET100, FET101

I tested them before and after installing them, and they appear to be ok, i think.

so, result.... same exact issue. i'm putting a 2 ohm 50w resistor (as per bcae1 guides, thank you bcae1) and have a 10w fuse instead of the 25w one the amp calls for.

the resistor gets hot FAST, and is dropping ~9v across it, measuring with my mutlimeter on DCV, black to GND and red to B+ (remote disconnected) i get the remaining ~3v.

(i actually f'd up and this is second time i've replaced the FET's, first time i misread the color code and put a 1k ohm 10% in at R111 and didn't replace the REC's, dropped full B+ on it like a dummy, and yes something went kabluey, spark and light smoke, could swear it was near Q101 but it looks ok).

don't suppose anyone knows what exactly to go after next? i can't find any more obvious damage....

I'd really appreciate any advice, I'm stumped.

[Perry Babin]

Please post at least one good quality photo of the inside of the amp.

[cmarkell2001]

I can get close ups if needed, I may have something new of use, for some reason i'm measuring 22.4 ohms across FET101 from gate (pin 1) to the drain (pin 3) and the same for FET100, these are the IRF9540 devices....

thank for all your help!

[Perry Babin]

I'm not really familiar with this amp but I'd expect to see all N-channel FETs. Are you sure that the original FETs were 9540s?

What happened to the original FETs that were in the amp?

Have you removed them from the circuit to see if they read 22 ohms out of the circuit?

Are you sure it's 22.4 ohms and not 22.4k ohms?

[cmarkell2001]

you were right, i had the wrong parts in FET101 and FET601. I had P-Channel's when they should have been N-Channels. Duh right =)

It's been a long time and I guess I was thinking BJT class a-b amps maybe.

Anyway, I finally got the new transistors in the mail and installed them, and bench tested the amp.... 12v accross the power terminals, let go 10 minutes.... Power resistor staying cool and happy.

This damn thing just might work! Gonna put in my truck and see tonight.