APC Smart-UPS SC1500 Service manual? - Page 1
Forum section: electronics / repair

author: cs.dk
author_rank: Unknown
timestamp: February 05, 2015, 02:58:55 pm
content: Hi,Can someone help with a service-manual to this unit? Google isn't my friend today. From frontplate: APC Smart-UPS SC1500, from the label at the back: SC1500II'll try to explain what happens:My friend disconnected the UPS about a year ago, because it started to beep, but no errors show via LED's on the frontpanel.We powered it up the other day, because he needed it now. The UPS set a battery-fault, and the "battery-warning" LED lights up red. Battery was sort of discharged, I charged up via a lab-PSU. The batterypack now measures 25,6V at idle, which is fine and dandy.However, it powers up, no fault-LED's are on - But the darn thing still beeps like crazy. Tested some basics, it only beeps when on mains; Some older APC could be programmed to match the actual input-voltage, this seems impossible on this unit. Earth-connection checked OK.Tried to disconnect it from mains, power it down, remove the batterypack, and let the caps be discharged. When i reconnected the battery, it blows the two 40A fuses, WTF??Anyway, I can replace the fuses - But another component is dead, probably a diode (picture attached) - The question is, was it blown before i reconnected the batterypack, and is it that thing that causes it to beep?

author: BradC
author_rank: Super Contributor
timestamp: February 06, 2015, 07:27:41 am
content: Yeah, looks like the diode has suffered some distress. The blowing of the fuses is characteristic of the switching mosfets failing. You won't have much luck with a circuit for that unit, APC hammered the russian site that had the best collection of manuals. Is this a newer generation unit with a totally HF switching supply, or does it have a massive transformer in it and 4 banks of MOSFET's ?This only applies to the big transformer based units, I have no experience on the really new ones.They won't power up properly if the battery is not connected. If you hold the power button down until it beeps, and then quickly release and re-press the button you can get it to spark up on battery with no mains, so that way you can hook it to a current limited bench PSU to get it going without smoking more parts,The common failure on these units are the MOSFET drivers which then take out the MOSFETS for the main transformer. If you can get it to a point where it switches on and no smoke comes out, connecting it to a linux-pc and running apcupsd will allow you to run the various tests and diagnostics on it without having to get familiar with the APC smart mode protocol (which is the incarnation of brain-damage).The only other issue I've seen is the main CPU losing its mind. This causes it to power up thinking its a completely different device (like a 110v 60hz unit) and that makes things go haywire. Getting back from that sort of failure is pretty difficult unless you have a copy of the existing calibration constants and firmware version.

author: cs.dk
author_rank: Unknown
timestamp: February 07, 2015, 10:39:48 am
content: Thanks alot for your reply.As said above, the unit powered up after charging the batteries. No fault-LEDS on. The fuses did blow when i attached the battery and the caps was bleed to 0V.Maybe the caps are charged via a resistor, when on mains? I don't know.Great idea to power it via a current limited supply, after the fuses are replaced.The transformer isn't that big. Not sure what type of PSU this is. (Picture attached)Does anyone have a clue, what type of diode that is blown?

author: cs.dk
author_rank: Unknown
timestamp: February 15, 2015, 12:49:43 pm
content: It seems impossible to find a servicemanual or schematic onlineAnyway, what can happen, worst case, if i bodge some 1N4007 or UF4004 in there? I don't have dual SMD diodes at hand.

author: BradC
author_rank: Super Contributor
timestamp: February 15, 2015, 03:30:53 pm
content: Quote from: cs.dk on February 15, 2015, 12:49:43 pmI reckon you'll be ok. I'd maybe look at 1n914's or 1n4148 rather than a 4007, but whatever you have on hand will probably work. I'd hazard a guess though that the diode did not go up in smoke on its own, and there is likely an underlying cause. Replacing the diode with something bigger or stronger may well just move the failure point to the next weakest component and let the smoke out of that too. Have you put a meter across it to see what you have on the pads?When I did my last SmartUPS 2200 it had a set of smoked switching mosfets. Those were killed by a failed resistor in the MOSFET driver stage which died and took the entire driver stage with it. The resistor failed because it's actually a badly designed circuit which runs the resistor in excess of its rating and eventual heat related failure.Always try to determine the cause of the failure before replacing the failed bits. A bit like don't replace the fuse until you figured out why it blew.Your UPS is one of the new SMPS designs, so unfortunately you are on your own, but if you think of it as a SMPS PSU coupled to an inverter you won't go far wrong. Use the same techniques you'd use repairing a complex SMPS and you'll be on the way. My most useful tool when working with UPS/SMPS is a hacked up extension cord with a bayonet cap batten holder in the active line allowing me to plug various wattages of bulb in series with the device. That way a shorted component won't go up in smoke, it'll just light the bulb. I usually start with about 12W and work up from there.

author: aspire737
author_rank: Newbie
timestamp: June 30, 2018, 08:05:08 am
content: Hello,I have the same diode blown in my APC RS1500. Does anyone have an idea of what type/number diode should be used as an replacement.Thanks in advance.Aspire737Edit: after a long day searching the internet I finally found the right schematics. The diode bridge is 4148SE that is practically 2 diodes from the type 1N4148 placed in series and I also changed out Cap C79 (560uF) that was at the point of blowing up. It all seems to work now. Load test not yet performed...

author: JoeO
author_rank: Frequent Contributor
timestamp: July 01, 2018, 01:50:08 am
content: Quote from: aspire737 on June 30, 2018, 08:05:08 amHow about a link to the schematics?TIA

author: aspire737
author_rank: Newbie
timestamp: July 01, 2018, 01:26:20 pm
content: Much Schematics for UPS:https://www.elektroda.pl/rtvforum/topic70072.htmlIt's in polish language, but with Google translate it is readable