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Old 06-04-2020, 09:14 PM   #12
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Default Re: QW-MS3010D 30V 10A Variable PSU Blown MOSFET

Originally Posted by CapLeaker View Post
what is on the other side of the heat sink?
On the other heatsink is a P75NF75 and an STTH1602CT, i haven't tested either of them since i don't think they would have been damaged.

Originally Posted by redwire View Post
The power supply is a half-bridge configuration with transformer drive to the power mosfets. So shorted mosfets cannot damage the KA7500 (TL494). But the gate-drive resistors, R2 50R? looks be blown and there is another for Q3's gate to check. They are the fuse sometimes. In-circuit you would read a short G-S due to the drive transformer to the IRFP840's.
I did not notice R2, but it's definitely blown, the first numbers on it appear to be 47, but the multiplier is missing, but i'm guessing it must be a fairly low value (maybe 47R).
Edit: appon closer inspection, i found another resistor (R5, or in your schematic, R203?) thats also blown, the resistors marking are still readable and say 47R3.

Originally Posted by redwire View Post
I have this Mastech HY3030E schematic which I believe is similar enough to understand the circuit.
PWM IC drives 4 transistors which drive the gate-drive transformer.
Okay, i'll take a look at it to help me figure this out (hopefully)

Originally Posted by redwire View Post
The low voltage SMPS IC DK112 looks discoloured, I wonder if it works and you have any low voltage DC present?
Note the (Mastech) power suplpy has an SCR which supplies power to the power mosfets only after the little SMPS turns it on.
It still works, as stuff like the voltage/current displays and controls still work, it also looks fine so it may have been poor lighting that made it look bad.

Last edited by RukyCon; 06-04-2020 at 09:38 PM..
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