APC Back-UPS RS 800 VA (BR800I) overload LED

[Behemot]

Anybody familiar with these? Schematic attached. Usually small 22uF/10uF caps are bad but here it was almost not used so they are still OK. Overload LED with PWR LED are blinking, that usually means shortd transistors and indeed, Q3 and Q4 were bad. But no luck after replacement. I've also swapped all four relays from different ditched unit, no change. Other semiconductors measure fine.

I am thinking maybe shorted T1 transformer on the board? The iron transformer is not the problem, tried different one too.

[stj]

Re: APC Back-UPS RS 800 VA (BR800I) overload LED

i would try changing the op-amp's

[Behemot]

Re: APC Back-UPS RS 800 VA (BR800I) overload LED

All five of them?

[stj]

Re: APC Back-UPS RS 800 VA (BR800I) overload LED

the ones that seem related to monitoring the output.

[Behemot]

Re: APC Back-UPS RS 800 VA (BR800I) overload LED

Them all seem relevant all right

[Behemot]

Re: APC Back-UPS RS 800 VA (BR800I) overload LED

I 've tried removing transformer and measuring it with new ring tester, seemed OK. That unit was ditched.

Got another one with blasted transistors again, seems like somebody tried to repair this one but they have been still blasted (maybe for second time?). Replaced, nothing. Replaced those foru optocouplers, nothing. I am flying blind here…

[Christos K]

Re: APC Back-UPS RS 800 VA (BR800I) overload LED

Hi, i had the same problem twice...!!!
My battery was ok, everything was ok but
the beep keep going on, for overload...
Both times i fixed doing these steps...

- Turn off the unit
- Flip over the unit
- Open the battery-cap and turn the power on
- Green Light is flashing
- Try Now (with the green light flashing) to disconnect the battery...
- Now it should be ON with the Empty battery light on (Red light)
- Connect again the battery as it is...

Now it should be ok...!!!

Good Luck...

[Behemot]

Re: APC Back-UPS RS 800 VA (BR800I) overload LED

Not really, that's no fix for anything, it's just temporary hack, maybe, for some situations.

I've learned something about the Back-UPS BK650EI in the meantime which shares a bit of the same circuitry, plus I made the BR1500G explode and fixed it. In the end the FET driver was bad, and I also found similar condition as one of previous units showed: after turning it off, after a while all the LEDs started glowing. The problem is either in some of the small transistors arround the processor, or the processor itself. It should turn into low-power mode after 5-10 seconds, don't remember exactly. It seems that the CPU detects when it does not and shows fault.

So it is good to check the SMD transistors as some of them may be bad. Also when FETs explode check the PWM modulator SG3525A near the CPU, mine was shorted.

[Duckbill]

Re: APC Back-UPS RS 800 VA (BR800I) overload LED

I recently repaired my RS 800 which showed a variety of fault symptoms including overload until I finally was able to have it help me track down the fault (C60 in the -8V charge pump). Yup, a bad cap. I'll get to the details shortly.

The first APC overload issues I had were with XS 1500 and XS 1000 models. In both cases, it was the FET 'modified' sine wave switchers (34N20 or similar 20NQ20). I wrote an amazon.com review of these units years ago, link here: https://www.amazon.com/review/R26OF4E1QBAOUF

In the case of the RS 800, I suspected this type of failure again. The unit failed to provide backup, and with all load removed, on AC, pressing the 'on' button gave a momentary green light, followed by beeping and overload and replace battery LED's on, sometimes solid, usually flashing.

The unit had relatively new batteries, less than one year old, but pulling them out revealed that they were almost totally discharged. Swapping them out with known good batteries changed the behavior slightly, but overload and replace battery still came on, though now in intervals of a few seconds, and relay switching could clearly be heard.

I was able to gain some control manually using front panel button pushing sequence to lower unit sensitivity (this procedure can be found by google-ing). With low sensitivity, the several second switching changed to almost a buzz of the relays, but the overload and replace battery lights went out.

At this point, I connected a laptop to the unit's RJ45 port and installed APC's PowerChute software. The UPS was unloaded, the laptop independently powered. From there, I was able to lower the low voltage switching level to the lowest offered, 94V. This stopped the relay switching, and all lights went out except the green On-line. In the Current Status window, I was able to see the Input Voltage reading ranging between 99 and 121, even though an independent voltmeter (and oscilloscope) showed a solid 121V. This explained a lot, since the UPS had been set on high sensitivity and low over/under voltage tolerance. Due to its measured input voltage variation, it discharged the battery by rapidly switching off and on, never staying off long enough to recharge the battery.

So now, the question became why is the voltage reading incorrect? I'll shorten a long story, but first having a schematic is invaluable. If you don't have one for the RS 800, you can get it here:

It would have been possible for me to repair my UPC without an oscilloscope, but it was very valuable. I used a differential input to avoid as much common-mode noise as possible, with the battery negative terminal as the reference. The third terminal, Green wire utility ground is noisy and NOT the electronics ground. The circuit diagram referenced above shows a "Line Sense Circuit" and an "Output Line Sense Circuit". Output of the Line Sense Circuit was the expected sine wave but surprisingly full of hash. This hash noise was causing the measured voltage to fluctuate. By setting the UPC action low voltage lower than the hash noise induced variation, the unit was able to keep operating and charge the battery. I suspected a problem with the Line Sense Circuit, so looked at the Output Line Sense Circuit, expecting to see a good sine wave there, and providing a troubleshooting companion to the clearly malfunctioning Line Sense Circuit. To my surprise, I saw the same noisy variation there.

These circuits both use quad op-amp IC9, powered by +12 and -8V. The +12 terminal was clean, the -8V terminal was overwhelmed by the noise I saw on the Line Sense outputs.

This sent me to the "-8V Charge Pump" circuit, and from there immediately to output cap C60 (22uF, 16V). The hash noise was simply the charge pump oscillator signal feeding through. Temporarily bypassing C60 cleaned everything up, and replacing it fixed the problem for good.

Interestingly, the Current Sense circuits (needed for power calculation and overload) also use the -8V power supply. I've reasoned that the overload indication was due to these faulty voltage and current sense value (that coupled with a failing battery due to the incessant switching).

I hope this will be useful to someone ...

[Behemot]

Re: APC Back-UPS RS 800 VA (BR800I) overload LED

Interesting story But simply by measuring the caps with ESR Micro v4.0 I've learned ages ago that good start is usually to replace all the SMD crapacitors in these units, and than continue if there is something else

Thanks for the manual, I'll upload it here for backup. There is one question though. Can the unit handle long-life Chemi-Con LE? Their ESR is somewhat between standard and low-ESR, slightly closer to standard, according to my measurements. There are always GP craps in these APC units. I know that units like BExx0CP (FR) don't like these caps in most places (especially around opamps and all these other analog ICs), I could only use like 3 pieces there. What about here? After all, rated life of 10000 hours instead of 1000 hours is signifficant difference. Even though normal-sized GP 105°C caps, and also Chemi-Con, should still work much longer than the original craps, usually tiny 85°C. But still…

[Duckbill]

Re: APC Back-UPS RS 800 VA (BR800I) overload LED

Thanks for your reply Behemot! While I certainly agree with your rationale of simply replacing all the SMD caps, I do not have an inventory of components with which to make such a change. I must admit to having a bias for repair over replacement in general, even though it may not be economically sound -- I intensely disliked the notion of sending my UPS to a garbage dump. Considering only the replacement cost of batteries, after two replacement cycles, it is probably more cost effective to buy a new UPS than a third set -- nevertheless ...

As to your ESR consideration, you raise excellent points. I favor longer expected life over ESR in this application. To a significant extent, the built in surge protection mitigates ESR risk. Long duration heat exposure is a certainty, however. You may find it interesting that my failed SMT 22uF cap did not fail either open or shorted -- it still had a residual capacitance of 4.1UF. I replaced it with a normal sized GP 105° cap lying on its side, secured with a dab of adhesive.

My vocational work is largely theoretical and analytical, but I do have a reasonably wide understanding and knowledge of hardware from components to subsystems; I'm only able to work on hardware because I have a home 'lab' (workshop). I've always had an aptitude and interest in physical 'things', repairing electronics and machines for family and friends (and a little extra money decades ago when at graduate school). Lately, I've depended greatly on the kindness of strangers posting on the Internet to help me with these non-work interests. My post at badcaps is among my efforts to give back (and hopefully to get badcaps some 'clicks' if my post is interesting to others). By the way, I donated to elektrotanya.com via PayPal in appreciation to them for providing the schematic; I hope you can help them with a recognition of some sort.

[Behemot]

Re: APC Back-UPS RS 800 VA (BR800I) overload LED

Most of the new plastic UPS ppl buy are even way worse than this is, trust me.

Not sure bout Florida but I can get Panasonics quite cheap from distributor here. Usually higher capacity for half the price of APC-labeled Longs or similar cheap PoS. They do just this, take Longs, put APC sticker on them and sell it three times more expensive as RBC.

[Duckbill]

Re: APC Back-UPS RS 800 VA (BR800I) overload LED

By the way, I was thinking ESD, not ESR. At the frequencies in play in the UPS, I don't think really low ESR is necessary.

[Behemot]

Re: APC Back-UPS RS 800 VA (BR800I) overload LED

Does not matter if necessary or not, long-life caps always have lower ESR than GP caps.