A Dead UPS Device Was Brought Back To Life
A customer brought this to my shop after he called to make sure that I repair such devices. Once this device was on my bench, I realized this was a very complicated repair and I discussed that with the customer.
The customer explained the UPS is dead and he tried to revive it by adding two of the open blown fuses on board
and the result was disastrous because it caused more parts to blow; the customer said that he did that about four times and the fuses kept blowing.
The customer was talking about these two fuses at the input of the batteries; they are rated at 20 amps 250 volts and I when I checked them in the shop both were open even the customer suggested to put new fuses there to give it a try which drove me crazy.
That is the location of the shorted Mosfets that I found later on and next to them you could see the blown traces that were affected with the process.
I de soldered all these Mosfets off board and sure enough all the 6 Mosfets (FDA38N30) were had a dead short on them which was not a very good sign.
Click here to access the FDA38N30 Datasheet
I was expecting more shorted parts on board so I called the customer and explained that the repair of the UPS is not recommended and if the customer insists on this repair, he had to provide the right parts and I do not guarantee the outcome of this repair.
The customer agreed to this and I provided him with the part number; one month later the customer called and informed me that he has the parts and he will bring them over to me shop to be installed back on board.
Of course I checked as much as possible for any other shorted parts on that board but I could not check all of them because it has lots of IC’s and parts that that I was not familiar with.
Before installing the new parts I had to fix the broken traces on this side of the board; once these were done I proceeded with the soldering of the 6 shorted Mosfets after adding thermal paste and then screw them back on the heat sink provided.
It was not an easy job aligning all the pins of the six Mosfets to be fitted on board but once that was done I soldered all them on board.
I added a two new 20 amp fuses at the input of the batteries (batteries were not included with the device), and connected it to the current limiter and hoped for the best.
The output as seen in the photo was very low; it should have been at least 24 volts. The current limiter was flashing on and off and the main screen was flashing indicating a fault somewhere on board but sad to say I could not find the fault.
I called the customer and explained the situation that this device still have problems and cannot be repaired; for I have spent so many hours on it and no new outcome in sight.
As agreed with the customer he paid the fees of repair attempt; later on he called and told me that he powered on the device even though I told him not to; all the parts were shorted again and the device was dead again.
A sad result of a repair attempt that failed miserably but we keep up the good work, learn from mistakes and move on.
Mission Failed…
This article was prepared for you by Waleed Rishmawi, one of our ‘Master Authors’ and currently working in the Bethlehem area of Palestine repairing electrical and electronic equipment.
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Note: You can check his previous article on An LCD Computer Screen With A Delay In Powering On Repaired. Model: Mag MS-776K
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Mark
November 16, 2024 at 12:25 pm
A lot of uninformed people think that the first thing you do with a blown fuse is to replace it as if it is a magical, quick solution. However, we know that there is a reason for a fuse to blow and as in this case, more problems can be created by simply replacing a blown fuse.
I have a similar situation on my bench at the moment. A power supply/controller from a spa bath. It has done some strange damage including a blown inductor/filter and lifted tracks. However the Varistors are all OK! Lightning strike perhaps?
I have informed the customer that I am happy to attempt a repair, but no warranty will be given as I don't know what he has it plugged into that might cause the problem again........He is happy to go ahead as the controller costs over $800 AUD!
Thanks for sharing your experience Waleed.
Parasuraman S
November 16, 2024 at 1:39 pm
Yes, every failure is a stepping stone for success; we learn a lot more from failures than successes. Good attempt with experience gained! Thanks for sharing, dear friend!