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.
Waleed Rishmawi
November 16, 2024 at 3:30 pm
Mark: you are most welcome. I hope you will be able to get the device up and running. we are not miracle workers, we do what we can to get things going otherwise we learn from the situation and we move on. have a blessed day
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!
Waleed Rishmawi
November 16, 2024 at 3:31 pm
Parasuraman: very true statements. I thank you for your comments. have a blessed day.
Anwar Yunas Shiekh
November 16, 2024 at 4:08 pm
A Dead UPS Device Was Brought Back To Life
?
Waleed Rishmawi
November 17, 2024 at 3:14 am
it was brought to life half way but most important I have learned a lot from this experience although it was not fixed the way it should be. have a blessed day
Yogesh Panchal
November 16, 2024 at 5:40 pm
Right approach for arrangement of parts from the customer when equipment is non predictable. so that customer is also aware for what he is paying for. yes off course with repair attempt Fees for the time & other expenses you invest for troubleshooting his equipment.
Waleed Rishmawi
November 17, 2024 at 3:15 am
Yogesh: yea I was not sure of the outcome of this repair because it seems complicated so I made that arrangement with the customer. have a blessed day
Albert van Bemmelen
November 16, 2024 at 8:22 pm
That indeed was a wasted time in trying to help a customer who kept blowing up devices multiple times over! Who even after been warned not to, inserted new fuses again!
Waleed Rishmawi
November 17, 2024 at 3:17 am
Albert: sad to say customer alway think that replacing a fuse would bring the machine back to life. in this case it was fully destoryed and was not back to life. have a blessed day
Mark J
November 17, 2024 at 4:16 am
Waleed you did what you could. You still did a good job.
Waleed Rishmawi
November 17, 2024 at 1:22 pm
Mark: thanks man I appreciate the encouragement. Have a blessed day
Hollis LuQuette
November 17, 2024 at 2:40 pm
Fuses are there for different reasons, hooking up a radio backwards in a car for instance , it will blow the fuse... Replace the fuse and connect the radio to the correct polarity and the radio will work .....The fuse did it's job..... Voltage spikes from a power outage when the grid comes back on. The fuse blows or the breaker in the mains panel flips, reset the breaker, air conditioner works again ......
Waleed Rishmawi
November 18, 2024 at 2:40 pm
Hollis: in my case the fuse did not protect the device and it was shorted in more than one spot in the device where no fuse to protect. have a blessed day
James McElhannon
November 19, 2024 at 8:30 pm
I would guess a shorted turn or fault in the transformer or inductors. On heavy traces that are missing, desolder braid works well as a repair bridge, and maintains current carrying capacity.
PHILIP
November 19, 2024 at 10:56 pm
The moment voltage is applied to a mosfet/transistor and it blows right away, then, the voltage may be exess or the switching signal for the transistor may be inefficient or the transistors circuit associated components like capacitors, resistors or diodes may have failed. Transistors regulating circuit also could be faulty. In this case study, the 20 ampere fuse blew when the transistor(s) developed a short circuit due to what i suspect was caused by the transistors voltage regulator failure, or circuit component failure that brought about a high current draw through the transistor in the circuit. This is open to correction or addups.
Waleed Rishmawi
November 23, 2024 at 2:33 pm
philip: in this case I am not really sure what happened due to the fact that there are lots of boards in that device developed shorts because the customer kept replacing the fuse. there are also IC's on these boards can not be checked except by replacing them then turn on and try so it was a big hassle and I gave up on it. sometime we as tech's should have the common sense when to stop and move on. I appreciate your input have a blessed day