I thought I would share this hoping that other people who have also damaged their supplies could share the information they have or what they learned while repairing it so we could have a compilation of repair data in one compact thread.

I just blew up my Mastech HY3010E-3 a few days ago and it made me sick cause it was my stupidity that blew it up and I had no idea how much it would cost to fix it and the worst part was that I thought I would have to wait for at least a couple of months to have someone repair it.

Here's what I did. I got the polarity reversed while plugging in the battery. In short, I induced over 50 volts of reverse polarity dc power to the output while in the series mode. There was no smoke from the power supply nor did I see any burnt components inside. There wasn't even any hint of odor normally associated with electrical burn. The voltage meters on both channels read 0 no matter where the knob was set and the amp meters read .3 amps when I cranked up the amp knobs.

Here's the email I got from Sean at Africa Inc.:

Hello,

thanks for your note. sorry to hear the bad news. one thing you may
check is that there is a diode that's right inside the unit, connected
between the outputs. it is possible that the diode is damaged and there
is a chance that the unit might still work after you replace the diode.
you can verify that the diode is damage by measuring the resistance
between the positive and negative when the unit is turned off, if the
diode is damaged, it should be the same either direction and it should
be small.

Best regards,

Sean
Acifica, Inc. - Innovative products at compelling price.

Sure enough both channels had bad diodes and read a dead short both ways. I checked some diodes that I had sitting around and they were the exact same ones, so I replaced them and the power supply works perfectly. The diodes were attached to the small sub circuit board that holds the output terminals (not visible till the bottom panel is removed, front panel detached and the small terminal board removed).

I got lucky, this was an easy one and my downtime was only 4 days.

Please lets not let this thread get sidetracked by "should've been using protection on the putput line via fuses and diodes". That has been well covered on other threads.
If we can compile enough repair info here, then maybe we wont have to bother Sean all the time.

My Mastech HY5020E doorstop is fixed and regulates like a new one now (no longer a doorstop, will have to find something else for this purpose).

John Mardock (john4648) contacted me from the thread I started on rcu and through me was able to pinpoint the problem by checking for voltage at various points. The symptoms were a totally dead supply with no display and no obvious blown fuses. So he started at the control board. This is a modular board located near the on/off switch. (see picture) The motherboard supplies this modular board with 340v dc, so be careful as it will kill you. With the dead supply turned on, it was getting 340v dc to the board. Next to check for output voltage, the lower three pins of the molex connector should have +/- 5v with the bottom pin as common. (see picture) My dead supply had nothing here and this is where the display gets its power so with no voltage then no display, aaaahaa. He then suspected the pulse width controller (TOP223) had gone bad since there was no ouput from the control board. So I mailed him this modular board, he confirmed the bad part, replaced it, and mailed it back. After I put the board back in, the supply turned on the first time. I checked output voltage at the terminals and tried various loads and it regulates just fine.

The part cost a little over $3 and with priority mail postage turn around time was six days from the day he contacted me. Can't beat that with a stick.

This of course is only a solution to the specific problem of my power supply, which we now believe to have been caused by a power surge. However, he said one of his mastech 's burned up when he connected a 7s pack when it was set for a 4s pack and caused a lot more damage than just the pulse width controller. (reverse current?) But he was still able to repair it. Said it blew the diode across the output, a dual diode on the right hand heatsink (looks like a mosfet), and a couple of gate resistors to the main switching fets. He said he didn't find the gate resistors until he replaced the dual diode and discovered it wouldn't regulate properly. Then after replacing the bad gate resistors everything was back to normal.

He also said that if anyone else wanted help in repairing their mastech to send an e-mail, but warned if the problem was any of the transformers inside it could be nearly impossible to fix since they are unique to this power supply and getting a replacement from the manufacturer isn't easy. The good news is that the transformers rarely get messed up.

I've learned a bunch from this.

Oh yeah, the schematic for the HY5020E.

I've blown the output-shorting diodes of my Mastech several times. The output binder posts have holes drilled through them.

I found it to be easier to replace the diodes by clipping one lead of the blown diode and threading the replacement diodes trough the holes than it is to remove the blown diodes and solder the replacement in its original position on a small PC board behind the front panel.

Originally Posted by RD Blakeslee

I've blown the output-shorting diodes of my Mastech several times. The output binder posts have holes drilled through them.

I found it to be easier to replace the diodes by clipping one lead of the blown diode and threading the replacement diodes trough the holes than it is to remove the blown diodes and solder the replacement in its original position on a small PC board behind the front panel.

Thanks for the tip. Was it reverse polarity that blew your diodes each time?

Yes.

Logged on!

How To Use And Protect A Mastech Power Supply: https://www.rcgroups.com/forums/showthread.php?t=833118

I'll join that list, I hooked up a 10s1p A123 backwards last month. Blew the output diode and the fuse/strap on the "dewalt" made pack. Fixed it this week after KAR's report. Thanks for the lead, and CH for the schematic.
Did I mention I bought a new Mastech last week, I guess I'll sell it at SEFF!

James

You're welcome JESbond. I'm glad someone was able to benefit from this thread already. and also thanks Carlyle Harper for your post.

FYI

“How a switching power supply works”

http://www.hardwaresecrets.com/article/327/1

http://en.wikipedia.org/wiki/Switched-mode_power_supply

http://www.howstuffworks.com/power-supply.htm

One of the capacitors in my HY3010E-3 just blew its top with a loud bang. Anyone seen this before? I noticed a burning smell at the field last time I used the power supply and it seemed to be working well but one channel was putting out slightly more amperage. Today when I turned it on it was on the fritz. The whole display was flashing on and off. Then it stayed on and the voltage would only go to 20v per side instead of the normal 30. When I put a load on it, it would not provide the full 10 amps at first but about 8. Then it gradually went up to 10.3 amps. Just as I was turning the amp knob down it went bang. Hopefully it is just the capacitor that is damaged so I will try replacing it and see what happens. If anyone has any words of wisdom I would be happy hear them.

Sorry to hear about this K.A.R.!

How did power it at the field?

Cheap $99 two stroke gas generator.

Do you think the gen surged in some way to cause the cap to fail; or just a cap failure?

I don't know. I'm hoping just a cap failure. A lot of other people are using the same type of generator as I am and I haven't heard any complaints. I already ordered a couple of caps. I think I found the exact replacement at Digikey:

http://search.digikey.com/scripts/Dk...me=565-2976-ND

The one in the Mastech says Nippon Chimi-con, also known as United Chimi-con in case someone else blows a cap and is looking for one of these.