APC Smart UPS SUA1500 does not detect AC / doesn't turn on

[CapLeaker]

Sooo... I have an interesting victim today. Our special on the menu is a APC Smart UPS SUA1500. Looks like it's got Alzheimer or isn't smart anymore (dead, dumb as f@ck), but at the same time it isn't.
Battery is about a year old and they are good at a resting voltage of 26.5VDC. If I press the on button for 3 seconds it does turn the inverter on and I get 120VAC no problem at the back and the battery shows full. So it isn't the battery. It also charges the battery no problem when plugged in add that as a twist!
However if I plug it in with the battery attached it won't do squat. I (short) press the power button, get a short beep and nothing on the LED's. I do hear a delayed click from a relay, but that is about it. When on AC, there is no way in any shape or form that I get more than 1.5VAC out of the AC sockets on the back, but at the same time it does charge the batteries.
The main filter cap tested good, I don't see anything burnt, or leaked, the over load fuse is o.k. (otherwise it wouldn't charge the battery), battery is o.k., battery connections are good, so WTF am I missing? It's like the UPS doesn't see any AC input power. I've repaired a stack of UPS's but this is something I haven't come across. Maybe a relay?
Anyone seen a strange behaviour on an SUA like that before?

[CapLeaker]

OK. not sure what went on here (it probably didn't help working on this only on certain days when I had time), but I verified T1 against T2 transformer again. T1 is making this sizzling sound and the I measure 1.7kOhm across the primary winding. It's game over with this, as I don't have a replacement transformer.

[petehall347]

reading through this might help
https://community.se.com/t5/APC-UPS-...er/td-p/301697

[CapLeaker]

reading through this might help
https://community.se.com/t5/APC-UPS-...er/td-p/301697

Thanks, but nothing there that I didn't try. He ended up buying another one from fleabay.

[redwire]

I had the same problem with my Powerchute UPS. It's like it refused to go online, acted dead yet worked off battery if I hit the power button and it was charging ok.
A while back I'd replaced just the larger electrolytic capacitors, and this time when I went in it was a small 22uF cap that went low value, it was across the relay coil or in the circuit for a relay.
Must be the transfer relay. I think the relay pulse went too short for it to pull in or something. So replacing all the small caps I did.
These are a nice UPS because of the metal enclosure.

[CapLeaker]

I had the same problem with my Powerchute UPS. It's like it refused to go online, acted dead yet worked off battery if I hit the power button and it was charging ok.
A while back I'd replaced just the larger electrolytic capacitors, and this time when I went in it was a small 22uF cap that went low value, it was across the relay coil or in the circuit for a relay.
Must be the transfer relay. I think the relay pulse went too short for it to pull in or something. So replacing all the small caps I did.
These are a nice UPS because of the metal enclosure.

This is a picture of the same version board I have (mine is at work). I went through the obvious yesterday and so far I came up with squat. The only thing I didn't do is was using powerchute and connect the UPS to my computer. I do realize this thing is 20 years old, but I do want to put it back in service.
The whole board got only like a dozen electrolytic capacitors. Would be easy enough to change them. I did press that chip with the firmware firm in its socket, no change.

[redwire]

It looks good, worth checking some of the small caps at the 23 year mark.
Check Elektrotanya if there is a schematic for it. Your board marking is APC 640-7732D Rev. 5 but I did not see if with all the confusing bullshit names, model numbers then there are different power versions using same board, which products use it.

Usually, two relays for voltage tap change, one for load disconnect, two for transfer. I don't know what the 20uF 150VAC cap is doing, but that relay must get beat up, contacts roast.
I have seen they do a self-check where on power up, the load is disconnected from mains, UPS runs for a second it looks for output voltage, then is either good to go (connects mains to load) or it sits there like a zombie if it saw ACV before running, which means the transfer relay is stuck and it would go boom if it ran.
Check C109 for the "transfer relay contact weld detect" with that opto IC20, and a few caps around there.

[sam_sam_sam]

It looks good, worth checking some of the small caps at the 23 year mark.
Usually, two relays for voltage tap change, one for load disconnect, two for transfer. I don't know what the 20uF 150VAC cap is doing, but that relay must get beat up, contacts roast.

I have seen they do a self-check where on power up, the load is disconnected from mains, UPS runs for a second it looks for output voltage, then is either good to go (connects mains to load) or it sits there like a zombie if it saw ACV before running, which means the transfer relay is stuck and it would go boom if it ran.
Check C109 for the "transfer relay contact weld detect" with that opto IC20, and a few caps around there.

I was thinking the same thing about what to check I would not necessarily trust a ESR meter for a definitive answer to weather or not a small value UF capacitor has become I have ran into case where the ESR readings were not that far off of a new one but for some reason after recapping the device it started working again and I really do not have an answer for this

[redwire]

A new 22uF 50V is rated say ESR 1.0Ω but the old one measures 2.0Ω Does that pass your criteria? It's 2x rated but looks close sorta.
It depends on what the cap is doing - say a time delay or mains filtering is low stress compared to filtering power for an SMPS IC, it's a big difference in the stress on it and ESR needed for the circuit to work.

I find the small, low value electrolytics, under 47uF don't last, they seem to dry out fast or the seal is worse. In production, if the reflow/wave solder was a bit hot and cooked parts, the caps would last maybe 2-3 years only. It does affect the bung.
So some products you'll see the same brand of caps failing early.

[CapLeaker]

I was thinking the same thing about what to check I would not necessarily trust a ESR meter for a definitive answer to weather or not a small value UF capacitor has become I have ran into case where the ESR readings were not that far off of a new one but for some reason after recapping the device it started working again and I really do not have an answer for this

That depends on the ESR meter. Good ESR meters can set the frequency. Better ESR meters can set like 4 testing frequencies and you use them depending on cap size. Larger caps use low frequency like 100 hz. Small caps use 100khz. That's why some of them are so darn expensive. At the end you get what you pay for. I didn't run into such problems with my handheld Agilent LCR meter.
The biggest problem are the high voltage capacitors. They can show good ESR but yet leaking voltage. Look at my plasma cutter thread.

[CapLeaker]

Replaced C75 and C109 de to high ESR values (but showed capacitance all right). Hooked up the battery pack and plugged it in. Hear a couple of relay clicks, press the on button and the unit goes beep. nothing happens on the display. If I press the on button for 3 seconds, the unit will go on battery and supply power o.k. Basically same thing what it was before. No bueno...

[CapLeaker]

O.k. I think I am getting somewhere. I started to go the reverse way and concentrated on why I am not getting any power on the outlets when on AC. Sure and behold I came on RY3. That is the relay on the very top right on the picture. I tried to energize it with my bench PSU and got nothing, but yet it consumed all the power that I had preset (200ma). Sure enough I got a 75 Ohm short across the coil? Well no wonder that doesn't work! Relay out she goes and??? Relay works fine but I got still a 75 Ohm short across the pads where the relay coil is. Traced it to an SMD diode D13. Took that diode out and short disappeared. I guess I need a new diode for now.

Diode marking A4 with a sideways "c" probably something 75V to 100V dual diode in some config.

[CapLeaker]

I found an SOT23 diode marking A4 with a sideways "F" and it is a dual diode, common cathode. I actually wonder what that sideways printed letter business is... If that shitty lil diode makes the whole UPS not work... man...

[CapLeaker]

So I put my replacement common cathode diode in. Now the pads measure up correctly and I see 27VDC on the relay coil. Yet, I am still sitting in the same boat, no progress. Exact same thing as before. Inverter works, but while on AC, nothing is on the front panel and doesn't "see" any incoming AC and no AC under normal operations on the rear ports. Damn.

[valvashon]

Have you independently checked to make sure the relay isn't "welded"? I repaired a MiddleAtlantic unit recently that suffered from a relay weld for what I think would be the equivalent relay.

[CapLeaker]

Have you independently checked to make sure the relay isn't "welded"? I repaired a MiddleAtlantic unit recently that suffered from a relay weld for what I think would be the equivalent relay.

RY3 is not welded. Works fine as kind out of circuit. I found this schematic… quite complicated thing. I was right with the 75v-100v common cathode diode across the coil of RY3.

[petehall347]

what tells the relay to switch on ? i take it that it isnt switching .

[CapLeaker]

what tells the relay to switch on ? i take it that it isnt switching .

That's how I found the blown diode after that it was like crazy tracing with via's and didn't come up with much. I do know that there is 27vdc on that relay coil now, but it is in the off position, which suggest the NPN is either blown or the IC doesn't want the relay to turn on. Through this schematic I posted, the coil drive are a couple of NPN transistors. Following that further back, it goes to an IC. The problem is that this RY3 just puts the AC power to the plugs on the back, I do understand that if this protection diode across the coil blows or isn't there it will damage the coils drive. Not sure, but there may be much more damage, since the UPS doesn't see that it is connected to AC mains. This is a complicated bugger, I guess I have to figure out, how this thing knows that there is AC mains present. Unless someone has a better idea?

[sam_sam_sam]

This is one of hardest wiring diagram to follow that I seem in a long time what I do not like about this wiring diagram is that it does not have the terminal marked very well and it is hard to tell exactly what it connects with another part of the circuit

Here is a case in point it shows the battery positive but it does not show the battery negative at all but it does show the charging negative but it does not show how it is connected to the battery negative really this is crap

But if my guess is right relays 4 and 5 seems to play a role in weather or not it could get power to charging circuit but it is not clear exactly what control it really

Dose relay 3 coil have 24 volts to it if not I agree with you about what controls it but what controls relay 4 and 5 also

[CapLeaker]

sam_sam_sam I think this is partly due that one gets sent between pages back and forth like stupid. To figure out RY3, the relay drive back to the IC I had to go through 3 pages of crap.

All the relays always have 27VDC laying across the coil once the UPS is plugged into AC mains.. They are switching the ground in and out for the coil to complete the circuit and fire up the relay.

[sam_sam_sam]

I just realized that that there are two more pages I did not keep scrolling to the edge of the first page because on this tablet you have to scroll down a little bit further but sometimes when you do this close the page this is why I did not see the other two pages if I have time later on today when I get home from work I will look at it some more because I have a battery backup that does not want to turn on either do know if it charges the battery or not I have not had time when I have nothing better to do but begin pulling my hair what little bit I still have

sam_sam_sam I think this is partly due that one gets sent between pages back and forth like stupid. To figure out RY3, the relay drive back to the IC I had to go through 3 pages of crap.

I have seen this type of wiring manuals and before I despise them all because they are the most difficult to follow and the time consuming process which does not need to be the way if they are broken up for functionality this a lot easier to follow and understand

[USER="38202"]All the relays always have 27VDC laying across the coil once the UPS is plugged into AC mains.. They are switching the ground in and out for the coil to complete the circuit and fire up the relay.

I have seen this before where the negative side of the circuit is the control side of the individual relay circuits which is not very common so you have get your mind out of what is the usual way which the positive side of power rail

Question is the relay circuits controlled by one ic chip or are they individually controlled by individual circuits