Badcaps.net Forum
Go Back   Badcaps Forums > Troubleshooting Hardware & Devices and Electronics Theory > Troubleshooting Power Supplies and Power Supply Design
Register FAQ Calendar Search Today's Posts Mark Forums Read

 
Thread Tools Display Modes
Old 04-24-2020, 03:23 AM   #1
RukyCon
A Fake Rubycon
 
RukyCon's Avatar
 
Join Date: Jan 2017
City & State: Peoples Republic of California
My Country: USA
Line Voltage: 122.5VAC 59.9Hz
I'm a: Knowledge Seeker
Posts: 567
Default QW-MS3010D 30V 10A Variable PSU Blown MOSFET

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.
Attached Images
File Type: jpg 20200424_020515[1].jpg (2.63 MB, 39 views)
File Type: jpg IMG_20200424_021511[1].jpg (592.0 KB, 40 views)
File Type: jpg IMG_20200424_021525[1].jpg (613.0 KB, 31 views)

Last edited by RukyCon; 04-24-2020 at 03:33 AM..
RukyCon is offline   Reply With Quote
Old 05-01-2020, 10:08 PM   #2
RukyCon
A Fake Rubycon
 
RukyCon's Avatar
 
Join Date: Jan 2017
City & State: Peoples Republic of California
My Country: USA
Line Voltage: 122.5VAC 59.9Hz
I'm a: Knowledge Seeker
Posts: 567
Default 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 is offline   Reply With Quote
Old 05-01-2020, 10:17 PM   #3
R_J
Badcaps Veteran
 
Join Date: Jun 2012
City & State: ☻
My Country: Canada
I'm a: Professional Tech
Posts: 6,181
Default 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.

Last edited by R_J; 05-01-2020 at 10:20 PM..
R_J is offline   Reply With Quote
Old 05-02-2020, 12:29 AM   #4
RukyCon
A Fake Rubycon
 
RukyCon's Avatar
 
Join Date: Jan 2017
City & State: Peoples Republic of California
My Country: USA
Line Voltage: 122.5VAC 59.9Hz
I'm a: Knowledge Seeker
Posts: 567
Default 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).
RukyCon is offline   Reply With Quote
Old 05-02-2020, 09:12 PM   #5
R_J
Badcaps Veteran
 
Join Date: Jun 2012
City & State: ☻
My Country: Canada
I'm a: Professional Tech
Posts: 6,181
Default 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.
R_J is offline   Reply With Quote
Old 05-03-2020, 12:03 AM   #6
RukyCon
A Fake Rubycon
 
RukyCon's Avatar
 
Join Date: Jan 2017
City & State: Peoples Republic of California
My Country: USA
Line Voltage: 122.5VAC 59.9Hz
I'm a: Knowledge Seeker
Posts: 567
Default 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?
RukyCon is offline   Reply With Quote
Old 05-03-2020, 06:02 AM   #7
CapLeaker
Leaking Member
 
CapLeaker's Avatar
 
Join Date: Dec 2014
City & State: Atlantic Canada
My Country: Canada
Line Voltage: Ground, 0Hz
I'm a: Hobbyist Tech
Posts: 4,502
Default 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
CapLeaker is online now   Reply With Quote
Old 05-03-2020, 07:11 AM   #8
RukyCon
A Fake Rubycon
 
RukyCon's Avatar
 
Join Date: Jan 2017
City & State: Peoples Republic of California
My Country: USA
Line Voltage: 122.5VAC 59.9Hz
I'm a: Knowledge Seeker
Posts: 567
Default 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.
RukyCon is offline   Reply With Quote
Old 06-02-2020, 02:30 AM   #9
RukyCon
A Fake Rubycon
 
RukyCon's Avatar
 
Join Date: Jan 2017
City & State: Peoples Republic of California
My Country: USA
Line Voltage: 122.5VAC 59.9Hz
I'm a: Knowledge Seeker
Posts: 567
Default 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 is offline   Reply With Quote
Old 06-02-2020, 10:20 AM   #10
CapLeaker
Leaking Member
 
CapLeaker's Avatar
 
Join Date: Dec 2014
City & State: Atlantic Canada
My Country: Canada
Line Voltage: Ground, 0Hz
I'm a: Hobbyist Tech
Posts: 4,502
Default Re: QW-MS3010D 30V 10A Variable PSU Blown MOSFET

what is on the other side of the heat sink?
CapLeaker is online now   Reply With Quote
Old 06-02-2020, 10:28 PM   #11
redwire
Badcaps Veteran
 
Join Date: Dec 2010
City & State: Alberta
My Country: Canada
Posts: 1,745
Default 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.
Attached Files
File Type: pdf Mastech PSU HY3030E.pdf (68.4 KB, 7 views)

Last edited by redwire; 06-02-2020 at 10:32 PM..
redwire is offline   Reply With Quote
Old 06-04-2020, 09:14 PM   #12
RukyCon
A Fake Rubycon
 
RukyCon's Avatar
 
Join Date: Jan 2017
City & State: Peoples Republic of California
My Country: USA
Line Voltage: 122.5VAC 59.9Hz
I'm a: Knowledge Seeker
Posts: 567
Default Re: QW-MS3010D 30V 10A Variable PSU Blown MOSFET

Quote:
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.

Quote:
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.

Quote:
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)

Quote:
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..
RukyCon is offline   Reply With Quote
Old 06-04-2020, 09:54 PM   #13
R_J
Badcaps Veteran
 
Join Date: Jun 2012
City & State: ☻
My Country: Canada
I'm a: Professional Tech
Posts: 6,181
Default 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
R_J is offline   Reply With Quote
Old 06-05-2020, 01:22 AM   #14
RukyCon
A Fake Rubycon
 
RukyCon's Avatar
 
Join Date: Jan 2017
City & State: Peoples Republic of California
My Country: USA
Line Voltage: 122.5VAC 59.9Hz
I'm a: Knowledge Seeker
Posts: 567
Default Re: QW-MS3010D 30V 10A Variable PSU Blown MOSFET

Quote:
Originally Posted by R_J View Post
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).
RukyCon is offline   Reply With Quote
Old 06-05-2020, 10:18 PM   #15
RukyCon
A Fake Rubycon
 
RukyCon's Avatar
 
Join Date: Jan 2017
City & State: Peoples Republic of California
My Country: USA
Line Voltage: 122.5VAC 59.9Hz
I'm a: Knowledge Seeker
Posts: 567
Default 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 is offline   Reply With Quote
Old 06-06-2020, 09:54 AM   #16
R_J
Badcaps Veteran
 
Join Date: Jun 2012
City & State: ☻
My Country: Canada
I'm a: Professional Tech
Posts: 6,181
Default 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.
R_J is offline   Reply With Quote
Old 06-06-2020, 02:16 PM   #17
RukyCon
A Fake Rubycon
 
RukyCon's Avatar
 
Join Date: Jan 2017
City & State: Peoples Republic of California
My Country: USA
Line Voltage: 122.5VAC 59.9Hz
I'm a: Knowledge Seeker
Posts: 567
Default 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.
RukyCon is offline   Reply With Quote
Old 06-06-2020, 06:51 PM   #18
RukyCon
A Fake Rubycon
 
RukyCon's Avatar
 
Join Date: Jan 2017
City & State: Peoples Republic of California
My Country: USA
Line Voltage: 122.5VAC 59.9Hz
I'm a: Knowledge Seeker
Posts: 567
Default 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

Last edited by RukyCon; 06-06-2020 at 06:54 PM..
RukyCon is offline   Reply With Quote
Old 06-06-2020, 10:35 PM   #19
RukyCon
A Fake Rubycon
 
RukyCon's Avatar
 
Join Date: Jan 2017
City & State: Peoples Republic of California
My Country: USA
Line Voltage: 122.5VAC 59.9Hz
I'm a: Knowledge Seeker
Posts: 567
Default Re: QW-MS3010D 30V 10A Variable PSU Blown MOSFET

Here are the final repair photos...
Attached Images
File Type: jpg 20200606_210710[1].jpg (2.61 MB, 14 views)
File Type: jpg IMG_20200606_210845[1].jpg (593.9 KB, 8 views)
File Type: jpg IMG_20200606_171448[1].jpg (747.3 KB, 9 views)
RukyCon is offline   Reply With Quote
Old 06-07-2020, 06:32 AM   #20
sam_sam_sam
Badcaps Veteran
 
Join Date: Jul 2011
City & State: Sunny Jacksonville FL
My Country: USA
Line Voltage: 120 Volts 60 HZ
I'm a: Knowledge Seeker
Posts: 2,043
Default Re: QW-MS3010D 30V 10A Variable PSU Blown MOSFET

Quote:
Originally Posted by RukyCon View Post
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
__________________
9 PC LCD Monitor
6 LCD Flat Screen TV
30 Desk Top Switching Power Supply
10 Battery Charger Switching Power Supply for Power Tool
6 18v Lithium Battery Power Boards for Tool Battery Packs
1 XBox 360 Switching Power Supply and M Board
25 Servo Drives 220/460 3 Phase
6 De-soldering Station Switching Power Supply 1 Power Supply
1 Dell Mother Board
15 Computer Power Supply
1 HP Printer Supply & Control Board * lighting finished it *


These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
2 Hem Saw Computer Stack Board

All of these had CAPs POOF
All of the mosfet that are taken out by bad caps

Last edited by sam_sam_sam; 06-07-2020 at 06:38 AM..
sam_sam_sam is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



Badcaps.net Technical Forums 2003 - 2020
Powered by vBulletin ®
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
All times are GMT -6. The time now is 03:15 PM.
Did you find this forum helpful?