Problem w/Concept CCD-2400 amp

[raljazz77]

Hello all,
1st time poster on this interesting forum.
I'm a tv repair tech (Boca Raton, Florida), and recently had someone bring me
a Concept Audio amp; the actual model number is no longer anywhere on unit, but noticed an earlier ad from [Mauquill], who had the exact same issue, which is there are 12 MOSFET (to-220) transistors dead shorted in this unit. Do not have the schematic, but proceeded to find all three 25A fuses were open, and with the before-mentioned shorted transistors. Performed resistance checks across all the output transistors and other solid-state devices including the caps, and found nothing else out of norm. Replaced the IRFZ44N transistors, with same value good transistors, and applied 12v to both 12 and REM, and transistors shorted ONCE again.
I would appreciate if anyone has the schematic/diagram, or at least confirm that these are the correct value transistors.
Thanks,
Ralf

[Perry Babin]

You need to be working through a current limiter. A 2 ohm 50-100 watt resistor is the most common. Using hte limiter and having the FETs clamped down when power is applied will virtually eliminate the chance of blowing any of the power semis.

If you don't have a limiter, at least insert a 10-15 amp fuse in the B+ line and clamp the FETs to protect them.

If you remove all of the FETs from the power supply, you will be able to check the gate drive signals. They should be square and the falling edge should be almost perfectly vertical down to at least 2v.

Did you confirm that all of the gate resistors were within tolerance?

I have a Lanzar Vibe schematic that should be virtually identical. Email me if you want it.
babin_perry@yahoo.com

[raljazz77]

Thanks Perry - Sent you a message to your yahoo address!