Magic Smoke from a 1U Backup UPS (Trippelite Smart1500) - Page 1
Forum section: electronics / repair

author: kml183
author_rank: Contributor
timestamp: September 01, 2023, 04:32:47 am
content: Hello!I bought a used smart1500 backup ups for my server rack on facebook marketplace. Before I purchased it, I double-checked that It would boot up and that the battery was detected. When I got back to my place, I took it apart and noticed that some magic smoke was definitely released around the transistors that are used in the inversion circuitry from 12VDC to 120VAC. Also C25 on PCB was so hot it desoldered. See the attached images. I can see a little hole on one of the transistors attached to the heat sink. Is it reasonable to fix something like this so that I could actually rely on it? I would like to leave it on while I travel.Thanks

author: fmashockie
author_rank: Frequent Contributor
timestamp: September 01, 2023, 05:03:30 am
content: I can't really tell from your photos which components you are referring to. Are you saying you left it on when you went away, and then came back and the unit had failed? I'm not too familiar with this make/model, though Tripp-Lite generally makes quality surge protectors. If you are able to fully resolve the issue with this unit, and thoroughly test it, there's no reason why you shouldn't be able to rely on it. I would also test the batteries. If you don't have the ability to thoroughly test them, and they came with the unit you bought used, it would be a good practice just to buy new ones for it. Bad batteries are what reeks the most havoc on UPSs.

author: kml183
author_rank: Contributor
timestamp: September 01, 2023, 06:22:19 am
content: I have not seen the unit fail. I have plugged it in and it seems to work.The burnt components are the transistors that are connected to the aluminum heat sinks.

author: fmashockie
author_rank: Frequent Contributor
timestamp: September 01, 2023, 03:28:12 pm
content: I can't really see that they are burnt from you photos. If they were damaged, the unit would not work. As you stated, they are part of the inverter circuit. Your unit would not be able to go into backup battery mode without these. It would likely trigger an error as well if they were shorted. These units typically have the ability to sense internal shorts. But if you can clearly see they look burnt, I would suggest replacing them. These MOSFETs can take a lot of abuse over time. They handle large amounts of current which is why they are adhered to such large heatsinks. But as I said, as long as you've resolved this potential issue, and gave the PCB a thorough inspection (replacing other potentially out of spec components like electrolytic caps) there's no reason why you shouldn't be able to rely on this for daily use. That being said, this is a more general statement. I am not too familiar with Tripp-Lite's UPSs. Do some research on this model. If there's a known failure mechanism (like I've ecountered with some APC UPS brands), then maybe switch to a different product.

author: kml183
author_rank: Contributor
timestamp: September 02, 2023, 06:11:35 am
content: Quote from: fmashockie on September 01, 2023, 03:28:12 pmMy mistake, I meant that the power distribution feature works, I never tried the battery. I took it apart further with the intention of fixing it. I definitely don't think I will be doing that now

author: fmashockie
author_rank: Frequent Contributor
timestamp: September 02, 2023, 01:11:16 pm
content: Oh wow!! I am sorry I completely missed that burn mark on top of that large heatsink in your first photos (I thought it was just dust or something). Yea something definitely realized the magic smoke!!And very violently at that. Definitely appears to be one or more of the inverter MOSFETs. I've seen these guys catastrophically release magic smoke when hooked up batteries. Especially when they are shorted - they draw so much current from those batteries.So I know this looks bad and you'd probably not want to put this back into service, but fixing it could still be in realm of possibility if you are interested. A lot of those burn marks are likely to clean off. Its hard to say how much damage has been done to components on the board. It could be just these MOSFETs, or it could be their pull-up and pull-down resistors (and additional smaller BJT transistors if its a sine-wave model) that get fried/shorted. I've seen both cases happen. This is not including the primary fault that caused the magic smoke to be released in the first place! Typically, the inverter/H-bridge MOSFETs failing is a secondary fault caused by some primary fault. Now on some APC UPS models, I've seen this happen due to internal breakdown of the large inverter low-frequency (50-60Hz) transformer. But in your case it could be something else. So you'd have to find that fault as well if you want to fix it.Working on these can be quite dangerous. I would suggest not using the battery during testing/troubleshooting since it can allow the unit to draw so much current during a short. I would use a DC supply with current limiting to emulate the battery. But if you're completely new to electronics, I would not suggest this be the first thing you work on to learn how due to the dangers involved.

author: kml183
author_rank: Contributor
timestamp: September 02, 2023, 06:40:32 pm
content: Quote from: fmashockie on September 02, 2023, 01:11:16 pmI might try and see if I can get it running again for fun, but ya definitely not going to put this in my server rack for long-term backup!Its not just burn marks the PCB Looks like it it completely burned through in that location. There is not much FR4 left around those mosfets.I tried to take a picture to illustrate this.Not sure how I will be able to figure out what mosfets are used there as they have a ton of holes along where the part number is. There is a 1n4001 burnt in that area and two high voltage caps.

author: fmashockie
author_rank: Frequent Contributor
timestamp: September 02, 2023, 07:17:32 pm
content: Yea on second thought the traces for this board are pretty trashed... Might have to skip the repair for this one like you said. But man, that must have been an epic release of the magic smoke!!Always good to keep older PCBs like that around for parts. Since a lot of those components are likely obsolete. I typically work on equipment thats 10-20 yrs old (or more) and sometimes finding replacement components can be very difficult.

author: Dinesh6252
author_rank: Contributor
timestamp: September 10, 2024, 06:12:17 pm
content: Quote from: fmashockie on September 02, 2023, 01:11:16 pmIt's a old post but still I think you can help me out with my APC 1000VA back-UPS pro in which one out of the four MOSFET got shorted when there was a power outage happened causing the battery fuse to burn. I replaced the fuse and the both mosfet of one phase. But its now throwing f09 fault which translates to "Internal Fault"