QW-MS3010D 30V 10A Variable PSU Blown MOSFET

[RukyCon]

Re: QW-MS3010D 30V 10A Variable PSU Blown MOSFET

So i decided to try swapping the MOSFETS with what i have for testing (which in this case, were 2 K3568's (which i know may not be ideal in this thing)) and the PSU almost worked, the only issue is that it only outputs 500mV max (which is roughly 29.5V short of its rated max output). So i'm wondering now is it still the control chip or do i need to get the right MOSFETS and this thing will work fine?

A couple of things to note: the voltage control knobs were able the control the output (but due to the low max voltage, it wasn't any major change), and i was testing this thing in series with a 53W halogen bulb, but the bulb did not glow for most of the testing.

[RukyCon]

Re: QW-MS3010D 30V 10A Variable PSU Blown MOSFET

I guess i'll add a replacement driver chip to the shopping cart, just in case, will a KA7500C do as Digikey will only sell KA7500B chips in cases of 1500 (from what i can tell, the C variant is just a newer design of the same thing).

Between the chip and MOSFET appears to be 4 pairs of 1K resistors (in two parallel pairs), 4 pairs of 22 Ohm resistors (in two parallel pairs) 2 J3Y NPN Transistors, 2 2TY PNP Transistors, and 4 Diodes (and a transformer).

I'm very aware of the incandescent bulb trick and have used it in the past for testing.

[CapLeaker]

Re: QW-MS3010D 30V 10A Variable PSU Blown MOSFET

Because you get full power shorted to gate pin. The gate drive can't handle that kind of power. The PWM doesn't have to necessarily blow up, but it could be dead, or stuck on. If it is stuck on, well it will short out the new mosfet. There could be other devices in the gate drive circuit that could be bad.

Specifically for testing power supplies there is this "60W or 100W incandescent light bulb in series trick"

https://www.badcaps.net/forum/showthread.php?t=32748

[RukyCon]

Re: QW-MS3010D 30V 10A Variable PSU Blown MOSFET

It does appear the gate and drain pins are shorted, out of curiosity, how does this kill the chip?, as i'm looking at this thing and it looks like the chip is driving the MOSFETs through T1, which i would think would isolate the chip and MOSFET.

On top of that, could i use a different MOSFET/Transistor for testing this thing, I have a ton of salvaged MOSFETs from PSUs over the years. So if i install a used one and the chip kills it, then i will know if the driver is bad?

[R_J]

Re: QW-MS3010D 30V 10A Variable PSU Blown MOSFET

If you don't have a scope to check the ic output, then replace the mosfets and hope they don't blow up, or replace the driver ic along with the mosfets.

[RukyCon]

Re: QW-MS3010D 30V 10A Variable PSU Blown MOSFET

How do i test the drive circuitry? as it appears the drive circuitry is driven off its own separate power supply.

The main driver IC is a KA7500B (U4), the other two chips are LM324N (low power OP-AMP) (U6) and DK112 (low power SMPS driver)(U1).

[R_J]

Re: QW-MS3010D 30V 10A Variable PSU Blown MOSFET

Many times when a mosfet blows it shorts Drain to gate, this can damage the gate drive components and the drive ic. I would get the power supply working before replacing any caps. Once the power supply is operational, then replace the caps a few at a time, checking operation between replacing caps.

[RukyCon]

Re: QW-MS3010D 30V 10A Variable PSU Blown MOSFET

I was hoping for a bit of help, but i guess i'll try fixing it on my own. I think i'm going to replace both MOSFETs with IRF840BPBF parts, on top of that, i think i'm going to do a recap because, why not, as all of the caps are generic crap anyway (and doing this will also give me more parts to throw into the Digikey order so that most of the cost isn't shipping).

[RukyCon]

Hello again, I have this cheap 30v 10A variable power supply that died about a year ago, the issue with it is that one of the MOSFETs (IRF840) Blew its guts. Now despite this thing being cheap, the design may have saved the control electronics from being blown up, as they appear to be in good shape.

I may also replace some other components while at it and fix some of the bodge jobs so this thing looks nicer.

Being that this is my first time replacing a blown MOSFET, I may need a bit of help, so any help will be appreciated.
And hopefully, i don't make a dumbass out of myself again.