Hifonics Olympus VII drawing tons of amps!

[marko]

one of my Olympus's has a power supply problem i can't resolve, all outputs check out fine but the ps end of things isn't when i bought it it had blown irfz44's, quick fix i thought so put 10 fresh fets in there but straight away drawing a very large amount of power, needless to say there is a short somewhere and hoping it's not the transformer but some of the new fets (irfz44n's now) are still ohming out fine but the rest are either open or low ohms..

any ideas? think i'll strip the ps down again and start from scratch but could use some tips on how to test the variable transformer to check for shorts.

Mark.

[gisewhcs]

Check the connection between the FETs and their gates.
Sometimes these tiny tracks break by age or due to disassemling when changing FETs.
Then the gates charge theirselves by whatever and the FETs become conductive.
A friend of mine had exactly that problem when I sent him my Gemini VII for benchmarking it...
When I had it on my desk everything was fine, but when he recieved it the PS was defective...
He found out that only one FET had no connection to the gate resistor.

[marko]

just been and taken all ps fets out and cleaned back everything again. i was getting some low voltage readings going from a couple of gate resistors to +V, resoldered the gates and got 12v again, not sure if this would have the sort of effect i was getting or not though. drivers seam ok too..

i need to know if there's anything i can check whilst all the ps fets are out. i'm getting +/- 12v and all gate resistors are spot on

[gisewhcs]

You can take out the rectifiers, then you can be sure to have the PS only.
If it still draws much current then, the fault is in the PS, if it's running fine then, put back in the rectifiers.
When it starts drawing that much current again you'll have to check the four channels.

[marko]

took the rectifiers out and started putting 1 fet back in at a time, started off with 1 and it drew .55A, ended up climbing the more i put in until it got to the 10th then went OTT again and blew a fet straight away.

think i've damaged my multimetre too, don't think it appreciated me puting 35amp through it

[807tubenut]

why would you let the meter climb to such a high amperage? I get weird if they pull more then 3 amps @ idle.

Check the gate drivers in the smps section, pull the rectifiers as suggested to get the audio section out of your current draw.

[marko]

Originally Posted by 807tubenut

Check the gate drivers in the smps section, pull the rectifiers as suggested to get the audio section out of your current draw.

already pulled rectifiers and it pulls more than 5amp with anymore than 2 fets in the ps

still looking on info on how to check for a shorted transformer but no such luck..

[Dr Zeus]

Are there any shorts between the pads of each individual fet?

[marko]

Originally Posted by unclemeaty

Are there any shorts between the pads of each individual fet?

looked very closely and didn't see any..

is it possible to run the amp with just a couple of ps fets? (just for testing purpose!)

all gate resistors check out at 220ohms ok too and i've been over the joints to check for any dry joints.

[Dr Zeus]

I meant to say test with your meter the resistance between the fet pads. Each fet should measure similarly but not near shorted.

I know I've tested amps with some fets missing. To me its cheap insurance and will only damage the parts youve installed. I've even run a larger amp with lots of fets at high power and it didnt cause any harm. I'd hate to have to buy more than 1 full set of fets. Your miledge may very.

If the fets start to get hot or draw too much current at idle make sure you have a quick trigger finger to pull the amp out of the oven.