QW-MS3010D 30V 10A Variable PSU Blown MOSFET

[RukyCon]

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

The thing is, the PSU isn't going into constant current mode when this happens, and i've triple checked it just to make sure.

[CapLeaker]

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

So the CC isn’t working properly? Maybe look at the sensing circuit.

[RukyCon]

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

Well, the power supply is back on the healing bench, as the voltage regulation has gone out the window, especially at lower voltages, the main transformer also makes this awful and inconsistent hissing sound, The unit also seems to shut down randomly at voltages below 6v, and only restarts after the voltage drops to 0v. I did swap a few caps on the control side of the circuit, but stopped since it wasn't making any visible change to the condition of the unit. I also checked the primary caps, and they seem fine, so i'm not quite sure what to do next.

[pc7fan]

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

The PSU design itself is OK, it's the parts that are not adequate for its rating, but after doing my modifications, it can deliver its full 300W and can short it without breaking anything. It was built down to cost but as a basic bench PSU, it's fine as long you know its limitations (there are many). In stock form, I wouldn't run the supply or any of its variants over 150W continuous.

[sam_sam_sam]

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

Yes, it is. Yes, you can put them in series. However unground the outputs.

Another common problem with these power supplies is the P75NF75 linear regulator FET fails D-S. (makes the supply lose regulation and mashes the output at 100% power)

These supplies are alright after you know their quirks...

The way you can cause that FET to fail is...

1. When you short the output when you set the voltage too high, hence dumping the supply's cap into the linear regulator FET, shorting drain-source.

2. Disconnect the load (esp. if an inductive load) while the supply is on. This scenario can cause inductive spiking, can cause the FET to short.

When this happens, the supply popped the output caps once on me. Mine had 2x 63V 330u caps, those vented, installed 1x 330u 100V and 2x 150u 100V. All Rubycon ZLHs. And I've got a few spare FETs.

Try to not do the two scenarios and your supply should do you well.

If this is true what you have here then correct me if I am wrong but this to me is poorly designed switching power supply

[pc7fan]

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

Yes, it is. Yes, you can put them in series. However unground the outputs.

Another common problem with these power supplies is the P75NF75 linear regulator FET fails D-S. (makes the supply lose regulation and mashes the output at 100% power)

These supplies are alright after you know their quirks...

The way you can cause that FET to fail is...

1. When you short the output when you set the voltage too high, hence dumping the supply's cap into the linear regulator FET, shorting drain-source.

2. Disconnect the load (esp. if an inductive load) while the supply is on. This scenario can cause inductive spiking, can cause the FET to short.

When this happens, the supply popped the output caps once on me. Mine had 2x 63V 330u caps, those vented, installed 1x 330u 100V and 2x 150u 100V. All Rubycon ZLHs. And I've got a few spare FETs.

Try to not do the two scenarios and your supply should do you well.

[RukyCon]

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

Isn't the MS605D the 60V 5A version? I'm also wondering if i could use this in series with another identical power supply to get a higher voltage (i have two of these things, the second one was a free replacement for the first), IIRC the owners manual said they could be used in series, but to contact the supplier, but i don't remember who i got them from (and eBay seems to have also forgotten).

I did a burn-in test and it seems to work fine.

[pc7fan]

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

I have an QW-MS605D (same basic circuit as the 3010D except for a few components) the IRF840s in mine failed while running a 200W load. While it failed, it took out Q4, Q5, Q6 and Q7 - as well as the gate resistors. They are 47 ohms as well. The KA7500 was unharmed, and used some salvaged 2SK2915s from an old Delta PSU instead of more IRF840s. It now can do its full 300W without the primary FETs failing.

[RukyCon]

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

How long did you have them in storage because I have had some that I have bought at least 5 years or more and have had no issues using them I have values from 0.47UF to 47000UF

One thing that I do power on the device at low load and leave it powered on for hours to at least 24 hours before turning the device off

Then use the device normally after this

It's not how long i had them in storage, it's how long the store (that i bought them from) had them in storage. But i reformed them (according to the instructions i found online) and they seem to work fine.

I'll plug a small load into it tomorrow and leave it plugged in and see if it holds up.

[sam_sam_sam]

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

I also found some 470uf 50v KZEs that i plan to put on the output, but i think they're NOS so i may have to reform them first (they still test within spec).

How long did you have them in storage because I have had some that I have bought at least 5 years or more and have had no issues using them I have values from 0.47UF to 47000UF

One thing that I do power on the device at low load and leave it powered on for hours to at least 24 hours before turning the device off

Then use the device normally after this

[RukyCon]

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

Here are the final repair photos...

[RukyCon]

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

So i went and found some 51Ω resistors and some IRF840A's from the surplus store, threw them into the power supply, tested it, and it appears to be fully working as now when its set to full power it outputs 31V instead of 500mV. I also found some 470uf 50v KZEs that i plan to put on the output, but i think they're NOS so i may have to reform them first (they still test within spec).

Once i'm done with testing, i'll post photos of the repair

[RukyCon]

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

The resistors are both blown open, or at least have a resistance greater than 10MΩ. I'm going to see if my local electronic surplus store has any 47Ω SMD resistors and IRF840 MOSFETs (to replace the placeholder K3568's) today, if not, then i'll try ordering them from Digikey.

[R_J]

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

Well the mosfets won't work if the resistors are open, so will it work after? If the resistors are good, then that's not the problem.

[RukyCon]

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

If i were to replace both 47Ω resistors, will this thing start working again? As far as i can tell, they are the only components that are still blown. So if i were to replace both of them, this should work again, or is there anything else i should check?

[RukyCon]

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

R2 and R5 are likely 47Ω, they should be the same value. Check the voltage before Q2 (p75nf75), the output of the dual diode (STTH1602CT) or across C11,16 or 22

Tested, and it's roughly 500mV, or roughly the same voltage as i was able to get on the output with both IRF840's replaced (see post #9 for more info).

[R_J]

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

R2 and R5 are likely 47Ω, they should be the same value. Check the voltage before Q2 (p75nf75), the output of the dual diode (STTH1602CT) or across C11,16 or 22

[RukyCon]

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

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.

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.

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)

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.

[redwire]

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

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 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.

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.

[CapLeaker]

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

what is on the other side of the heat sink?