Tested Old Mosfets
I ran that test as described above on the four old mosfets taken out of the amp. Multi-metre set to 2000.
Black terminal to middle, red to right:-
683/675/673/675
Red terminal to middle, black to right:-
1/1/1/1
I ran that test as described above on the four old mosfets taken out of the amp. Multi-metre set to 2000.
Black terminal to middle, red to right:-
683/675/673/675
Red terminal to middle, black to right:-
1/1/1/1
that "1" is probably the meter showing "open circuit", so the original MOSFETs werent the problem. Nevertheless something is causing a hard power supply short. My next suspect would be the rectifier diodes D201-D204
I cannot see how the mentioned LM393 would cause the fuse to blow.
I cannot see how the mentioned LM393 would cause the fuse to blow.
Yes, 1 is what it reads before i do anything.
I reckon it's the diodes. Think I'll order a pack. Pretty cheap.
Cheers
I reckon it's the diodes. Think I'll order a pack. Pretty cheap.
Cheers
Ah - having looked at the pictures again - were there insulating washers between the heatsinks and the MOSFETs ?
The original ones had a sheet of material between them and the heatsink. Maybe a silicon pad. I have used thermal paste for the new ones.
You have possibly created a short from +ve to -ve supply through the metal pads of the MOSFET's. You need to use insulating washers. The silicone pads wouldve functioned as insulating washers as well as heat transfer.
Are you sure they don't have to be insulated from the heatsink? It depends on the package, some do, some don't. If it has a metal back it needs insulating
They have metal on the rear. I can reuse the silicon sheet i guess. Still think there is something else wrong. The original MOSFETs seem to be ok (see above) and they were insulated by the pad.
I'll need to check out on line as to how to do that. I haven't yet understood how it works. I will have all the necessary parts I'm sure
Have a look at the picture in post #10 http://www.diyaudio.com/forums/power-supplies/167579-light-bulb-tester.html
It really is that simple 😀
Mooly's explanation of how it works was very comprehensive
It really is that simple 😀
Mooly's explanation of how it works was very comprehensive
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Ok, cool. Saw this too. Powering Your Radio Safely With a Dim-bulb Tester
Sounds very simple. See what i can do tomorrow night. Switching off now.
Sounds very simple. See what i can do tomorrow night. Switching off now.
OK, so it looks like I should put back the insulating sheet between mosfets and heatsink. I thought thermal past was enough (Ceramique 2 by Arctic Silver). Hopefully not damaged them.
I still think that something else is wrong. I have also ordered 10x ST BYW98-200 diodes from France which are in post. Only £6.49 inc p&p.
I still think that something else is wrong. I have also ordered 10x ST BYW98-200 diodes from France which are in post. Only £6.49 inc p&p.
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