aleph5: only 3 irfp240 warms up

[fheanor]

Hello all:

Well, i have a problem with an Aleph5 pcb (kristian's pcb)...
when i power it up, only 3 output mosfets (T6, T7, T8) get hot
... while the others remain cold

I have replaced the mpsa18 and all the irfp240, but no luck.

Any idea of what is happening, guys??

Thanks in advance!!

PD: Sorry about my english skill !

[wuffwaff]

Hi,

I suppose the current source fets are getting hot?

Do you know how much current is flowing? Measure the voltage over the source resistors. If this is the normal 0,5-0,7volts then you somehow shorted the active current source to ground but at least the current source is working.

Measure the resistance after the source resistors to ground. If this is lower than 5k something is wrong!

Can you tell us the output voltage (DC)?

Check the wiring of the output boards.

Hope this helps,

William

[fheanor]

Thanks a lot for your help wuffwaff.

I've touched the source current fets, and only 2 of them were warm (less than 50ºC), so i decided to check them using the voltimeter diode test-range. At least they were not short-circuited. Anyway, I replaced them, and the result is that no one of the irfp240 are getting hot anymore .

When i was measuring the other parameters, i have accidentally short-circuited some components of the pcb , and now i am waiting for the replacement parts so in 3 or 4 days i'll be working again on the amp...


Ximo