SMT3000RM2U Fault Finding/Repair - Page 1
Forum section: electronics / repair

author: Black_Pete_The_Blackbeard
author_rank: Newbie
timestamp: August 02, 2020, 03:01:54 pm
content: Main board is marked with 2U3K 640-3080_REV04TL:DR - Does anyone have this board or the schematic and can tell me what SMD transistors should be at D13 and Q2?Thanks in advance to anyone willing to read through my story. As I'm also trying to determine if this is purely battery related faults, or is a sign of more issues to do with the UPS?I picked up an old 2U ups in an auction. Since it was second hand then the batteries in it were of course spent, but I plugged in a few pcs without a battery connected just to test the UPS. Alas I found that it would infrequently cut out and turn off the outputs with the log showing input over voltage errors, I read that it uses the battery in cases of over voltage, so thought that might just be a missing battery issue.After a bit more testing it started reporting an AVR relay weld error.So I tested the relays on it, without removing them from the board first, because I'm lazy... and an idiot.And when testing RY3 found it was sticking, I tested it with reversed polarity and got a lovely spark and smell of burning plastic, but it did then start switching properly?!I turned the board over and saw a telltale bubble on the Q2 transistor and the UPS would no longer turn on the outputs. Of course I couldn't read the markings on it any more because of the damage but decided I had nothing much to loose so forged ahead by salvaging a random transistor from another board and soldering that in place.The UPS then powered up the outputs, I tested it with a load but didn't want to test it with the PCs just in case it was still cutting out, so could only load it with to 5%. I also upgraded firmware (with the old battery in temporarily) and it stopped reporting over-voltages, but that might just have been a few days of my household voltage not actually going above 260ac as I have nothing else logging it.I also tried my hand at popping the seal on the sealed batteries that hadn't bulged and putting some distilled water in them. This did seem to get a bit more life out of them and I put them back in the UPS, it was an 8 battery pack but 5 of the cells hadn't budged so I put 4 of them back for half capacity.That lasted a few days before it reported a faulty battery, which is to be expected, and I mostly just wanted to test that the UPS was working, I knew I'd have to replace the battery if I wanted to use the UPS for something important, so I left it.But naturally, I had flooded the batteries! But I thought that would be a risk, and its at least a lesson learned.So about a week or so after that, after I had reconnected a 15% load, it cut off the outputs, reported a battery charger fault and would not turn the outputs back on.After cleaning up all the sulfur, that luckily hadn't reached the electronics, I found another battery that had bulged and read 7.8v and the other cells read 11.5v, so I gave up on the batteries and recycled them all.But the UPS still wouldn't turn on the outputs with the battery unplugged and still reported a battery charger error. And upon inspecting the board I found another telltale bubble had appeared on the D13 transistor, the one right next to the one I replaced (I believe it was marked as a 1P transistor, but I'm not sure).But since this UPS isn't currently essential in my setup, I thought it best I at least try and find out what transistors are supposed to be there this time.And try to determine if there's more at fault here than just the battery (and me)Because I'm guessing that all of these issues could just be battery related (aside from me melting a transistor obviously) but I have no other battery to test the UPS and a replacement battery would be £140 which I obviously wouldn't want to spend if it turns out something else is wrong with the UPS.So for anyone who made it this far, I'd appreciated any advice you can give.Thanks, Pete.

author: asis
author_rank: Frequent Contributor
timestamp: August 02, 2020, 11:42:19 pm
content: Hi PeteThe SMT1500RMI2U does this:

author: Black_Pete_The_Blackbeard
author_rank: Newbie
timestamp: August 03, 2020, 06:20:32 pm
content: ThanksSo I can still read Q1, and its marked as '702 U'. So I'm guessing Q1 and Q2 were 2N7002LT1G transistors?I'm not so sure about D13 though, but at least now I know its not a transistor!There are other 'A7W 26' chips on the board, was D13 likely to be the same?A google search says its a dual diode, and as best as I can see they function roughly the same as schottky diodes.And as best as I can see from their datasheets, these parts are all close enough that I could replace the parts with those in your schematic and it would work fine. (And no, I won't hold you responsible for the results if ya say yes)I'd replaced Q2 with a 'W1P 27' transistor, which I think is a PMBT2222A, whose datasheet looks similar to the MMBT2222A.But my donor board doesn't seem to any schottky or rectifier diodes, so I have to keep looking for a suitable replacement to D13.

author: asis
author_rank: Frequent Contributor
timestamp: August 03, 2020, 08:06:28 pm
content: Hi,I wrote a PCB model that I have, this is 640-3081J-001.You have a different PCB, so I don't exclude that Q1, Q2 are MOSFET's 2N7002 (marking code "702").Year of manufacture of your UPS in first SN digits (ASxxxx ..).If you want to get a working device, check all relays, all ECAPs, charger and install normal batteries, and do not be smart about anything, it can end badly.Vladimir.

author: Black_Pete_The_Blackbeard
author_rank: Newbie
timestamp: August 04, 2020, 01:51:58 am
content: So how exactly do you suggest I check a destroyed component?

author: asis
author_rank: Frequent Contributor
timestamp: August 05, 2020, 10:14:08 am
content: Hi,What are the values of resistors R5 and R6?What transistor Q1 is on your PCB?Does the diagram I gave you overlap in some way?

author: Black_Pete_The_Blackbeard
author_rank: Newbie
timestamp: August 07, 2020, 07:46:29 pm
content: I mentioned the value of Q1 in my first response to you.And playing a game of spot the difference to try and figure out what the components might be, isn't that trying to 'be smart'? I thought you told me not to do that?!Either way you have all ready managed to completely derail this thread, so thanks for that.I hope some one here is still willing to help me?

author: asis
author_rank: Frequent Contributor
timestamp: August 10, 2020, 01:27:20 pm
content: Hi,I didn’t mean to offend you in any way - believe me.I am trying to help you with what I have at the moment for UPS SMT / SMC / SMX series. Their schematic technique is very similar.You are unlikely to find schemes anywhere.Therefore, I asked you - what are the values of the resistors R5 and R6 to determine which transistors Q1, Q2 are installed - n-p-n or MOSFET n-ch.Sorry again!Vladimir.