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

[CapLeaker]

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

Yes, they are all controlled by IC 11 on page 2 D2. It's just named "shutdown" but all the others are marked like boost, trim, xfer... etc. This same IC also has an AC detect pin. I suppose something is wrong with the AC detect, it wont turn on neither. Hm. I guess this isn't going to get fixed yesterday, but I keep working on it off and on.

If someone has the same model SUA UPS, I'd like to know what happens if you turn it off, unplug in from AC mains and short press the ON button. There should be a beep and a short flash with all the LED's on (at least it is like that in normal operation). Mine does the beep, but the LED's stay off.

[petehall347]

he starts pressing buttons at 3 minutes in . hope it helps .
https://www.google.co.uk/search?sca_...k_5YwbWLg,st:0

[sam_sam_sam]

he starts pressing buttons at 3 minutes in . hope it helps .
https://www.google.co.uk/search?sca_...k_5YwbWLg,st:0

This what is supposed to happen when you press the button when you do not have the mains connection but you should have the battery indicator should show something if the battery voltage is high enough

I just recently was going to buy a newer version of a 1500 watt battery backup it went to the off line function but it showed the battery level was zero but I knew better because I had this battery in one of my other 1000 watt battery backup and it showed it was about 80% charged so needless to say that I did not purchase this one because I did not have time to figure out what the issue was and $35.00 was too much money for something that does not work correctly

[CapLeaker]

I had a bit more time to work on this and verify the relay drive Q1 and Q2 transistors and they are fine. IC 11 is that socketed main IC. I hope that isn't blown, but i reseated it anyway. I also checked protection diode D52 for the relay coil on the trim and boost relays and that is fine as well. T1 and T2 are sense transformers and they aren't open. I also retested all the relays with my bench PSU and all relays work good and make proper contact. So what gives?

[petehall347]

any voltage on that AC detect pin ? or does that only detect when AC present on output ?

[redwire]

Applying external power to a relay on a board can damage the driver transistor, watch that it's not the best way to test them. Even then I have had carbonized relay contacts sorta give a good continuity reading but they failed under any load. Had me confused, I took the relay apart and the contracts were arced to death but still tryin.

I'm assuming the UPS can't or won't connect mains to the output.
Is the AVR autotransformer working, not open circuit?
I'm assuming it fails the self-check and goes into a coma, because the opto gives feedback if mains is present after the transfer relays, it knows there is a problem. You would think it would give an error message.

I would follow mains with a LowZ multimeter, see if it is making it through the path.
It's two transfer relays (one on line, other on neutral) then the (two) autotransformer tap change relays, and then one more output relay, as I understand.

[CapLeaker]

Applying external power to a relay on a board can damage the driver transistor, watch that it's not the best way to test them. Even then I have had carbonized relay contacts sorta give a good continuity reading but they failed under any load. Had me confused, I took the relay apart and the contracts were arced to death but still tryin.

I'm assuming the UPS can't or won't connect mains to the output.
Is the AVR autotransformer working, not open circuit?
I'm assuming it fails the self-check and goes into a coma, because the opto gives feedback if mains is present after the transfer relays, it knows there is a problem. You would think it would give an error message.

I would follow mains with a LowZ multimeter, see if it is making it through the path.
It's two transfer relays (one on line, other on neutral) then the (two) autotransformer tap change relays, and then one more output relay, as I understand.

This UPS behaves almost dead when on AC mains. The batteries do charge, I also hear the relay click when on AC and I can force the inverter on no problem. But that’s where it all stops. The UPS just doesn’t see that it is plugged into power mains. I did find a blown dual diode on RY3 that enables the power to the plugs in the back. Most of the relays are controlled by IC11 which is the main IC in that socket. It kinda acts like something is blown or a voltage is missing on the board. I didn’t check the AVR transformer, but I did have AC on one side of the output relay RY3. The sense transformers are good too.

[CapLeaker]

any voltage on that AC detect pin ? or does that only detect when AC present on output ?

Dunno yet, I have to put that thing together again.

[redwire]

I did see 640-7732H schematic at Elektrotanya, your board is the 640-7732D.
Is it close enough? To see what signals the MCU gets from incoming mains. The sch looks quite close and to tell the major blocks.

I'm wrong about the opto-coupler, it is only for SITE-FAULT detect, supposed to light an LED on the front panel? C109 is a filter cap for the bad site ground detect.

There are two little transformers (T1, T2) as PT's or voltage-sense step-downs. T2 pickoff is from mains input, T1 pickoff is the transfer bus.
T2 AC-IN2 detects mains input present to the MCU through Q10. T2 AC-IN1 detects mains input in range as AC-OK.

[CapLeaker]

I did see 640-7732H schematic at Elektrotanya, your board is the 640-7732D.
Is it close enough? To see what signals the MCU gets from incoming mains. The sch looks quite close and to tell the major blocks.

I'm wrong about the opto-coupler, it is only for SITE-FAULT detect, supposed to light an LED on the front panel? C109 is a filter cap for the bad site ground detect.

There are two little transformers (T1, T2) as PT's or voltage-sense step-downs. T2 pickoff is from mains input, T1 pickoff is the transfer bus.
T2 AC-IN2 detects mains input present to the MCU through Q10. T2 AC-IN1 detects mains input in range as AC-OK.

Your schematic find is the same as mine in post #15, less the water mark. Yes, so far this schematic has been accurate. The site fault LED is on the back of the UPS and I think this circuit works ok.

I did get as far as checking the two sense transformer windings for not being open. I compared the primary and secondary resistance to each other and they are the same. Basically post 24 is my latest on it. The unit is on my bench at work. I'll poke around on it with whatever time I have...

[sam_sam_sam]

The site fault LED is on the back of the UPS and I think this circuit works ok.

Dose anyone know what this fault really means because where I work there are several battery backup to have the site wiring light is on I actually have a battery backup has that light on to and it would not stop beeping so I put it out of service for the time being but I am not familiar with this issue to know where to start checking and what to check it on my work bench for now for when I do not have anything better to do

[CapLeaker]

Dose anyone know what this fault really means because where I work there are several battery backup to have the site wiring light is on I actually have a battery backup has that light on to and it would not stop beeping so I put it out of service for the time being but I am not familiar with this issue to know where to start checking and what to check it on my work bench for now for when I do not have anything better to do

Verify your wiring with a circuit tester. If it sez it’s good and the APC sez you got a wiring fault, there is something wrong with that detection circuit inside the UPS. The site wiring fault LED on this APC i am repairing (or trying to) is not on. Anyway that’s how I would go about it.

[redwire]

Using the schematic, SITE-FAULT activates if over 20VAC is seen between PE GND (chassis ground) and Neutral.
The LED is powered separately, from mains-in instead of the SMPS/battery etc.- so it can light even if the UPS is totally dead/blown.

[sam_sam_sam]

Verify your wiring with a circuit tester. If it sez it’s good and the APC sez you got a wiring fault, there is something wrong with that detection circuit inside the UPS. The site wiring fault LED on this APC i am repairing (or trying to) is not on. Anyway that’s how I would go about it.

Yes it is a APC brand I not sure exactly what the model number is at the moment

[CapLeaker]

redwire
I checked components R72, Q10 and D14; D18 and D28 are O.k. That's all I got for today. I miss my microscope at home.

[CapLeaker]

Went on this again today and chased things around checking diodes, transistors, fets and the transformer. I couldn't complete the AC-OK cirquit as there are a couple of IC involved, so I have to put this thing back together hook it up and check it from the backside.

[redwire]

I usually follow signal verses testing parts when I'm kinda lost what is not working.

The MCU gets these signals (that I can see):
SITE-FLT is ground-fault, but I don't think it matters the UPS works anyway?

Analogs:
AC-IN is mains from voltage sense transformer T1.
AC-OUT is transfer bus from from voltage sense transformer T2.
I-OUT is load current from CT2.
I-CAP is PFC capacitor current from CT1.

I would put a small load like 25W lamp on it and plug it into mains and trace the AC path with a multimeter. It might be an open relay and they can carbonize and test good... but they aren't. Or the autotransformer is open for BOOST/TRIM etc.
Is the 12V rail ok, IC2 will stop it from transfer relay from activating I think. This thing has so many permissive signals. Some relays have a permissive on each coil wire, so like an AND gate both have to approve before the coil pulls in.

[CapLeaker]

I usually follow signal verses testing parts when I'm kinda lost what is not working.

The MCU gets these signals (that I can see):
SITE-FLT is ground-fault, but I don't think it matters the UPS works anyway?

Analogs:
AC-IN is mains from voltage sense transformer T1.
AC-OUT is transfer bus from from voltage sense transformer T2.
I-OUT is load current from CT2.
I-CAP is PFC capacitor current from CT1.

I would put a small load like 25W lamp on it and plug it into mains and trace the AC path with a multimeter. It might be an open relay and they can carbonize and test good... but they aren't. Or the autotransformer is open for BOOST/TRIM etc.
Is the 12V rail ok, IC2 will stop it from transfer relay from activating I think. This thing has so many permissive signals. Some relays have a permissive on each coil wire, so like an AND gate both have to approve before the coil pulls in.

I am not concerned about the site fault, even at that mine works correctly as I had tested it at some point before,
the transformer should be good, as it isn’t open. I had another look at this schematic and it always takes me a while to wrap my head around it. Since I can’t work on it every day at work, I might put it back together and bring it home next week.

I do understand what you’re saying with the 12v rail and all the permissive jazz. That’s why it is such a pain to work on after a few days, as I have to go through the schematic again. For sure I am at the end with it in this state and have to get it back together in order to power it up. The cables are too short to power it up while being apart. I can’t connect the transformer like that.

I have always one thing going through my head: Why is it that there is a small beep when I short press the power button and absolutely no LED is working on the panel and the 120v sockets on the are disabled. Why is there nothing on that front display. I mean if it has a fault, it should display it. At the other end, the 12v should be OK because I can turn the inverter on and it works fine as kind, with display and all. Why no LEDs when on AC?

[redwire]

With mains present, I think the MCU is seeing something the firmware can't understand, undefined, or a safety-circuit has activated. Or it is a legal department reaction...

UPS auto-destruct is when mains is present yet the inverter starts up. That is very bad, if it were to do that backfeed into the inverter would blow it up. It would burn grandma's house down. I don't see fuses for that situation.

So to protect against that happening, I see it uses two transfer relays- one on Line RY5, other on Neutral RY7. It seems to be a redundant scheme so if one relay had welded contacts, it would not blow up.
Also the signals for the transfer relay coils has an extra safety circuit. XFR-GATE is an analog permissive that can override the MCU IC11.
It might be not permitting the line transfer relay (Line) to engage, the MCU sees this and shuts off. Or the H-FLT, ALL-EN2 are asserted?
"SMKLS" could mean smoke less lol.

You'll have to poke around and see which permissive saying no to the party.

[sam_sam_sam]

Or the sensing circuit has some kind of issue or the MCU has a issue that could be causing the issue but how to troubleshoot the issue is the real question I not even sure where to begin if I were doing this repair this is the reason I paying close attention to this post to see if he can figure out what wrong with it

I have always one thing going through my head: Why is it that there is a small beep when I short press the power button and absolutely no LED is working on the panel and the 120v sockets on the are disabled. Why is there nothing on that front display. I mean if it has a fault, it should display it. At the other end, the 12v should be

( I do not understand this part to why it would display the status when you do this part and not the other function )


OK because I can turn the inverter on and it works fine as kind, with display and all. Why no LEDs when on AC?

This is reason I have to wonder if the MCU is dead and this is reason why you have no response on the LED light status panel but like I said earlier I am not sure how you determine if the MCU is dead or the sensing circuit is dead in a section not letting it power up or something short out and destroy it

One question I have dose it charge up the battery because if it does then this really does not make sense at all unless it is a sensing issue or something wrong with the MCU programming issue or it corrupted some how

This might not be the same thing but we had a machine at work that it would boot up but it would not respond to switch commands or touch screen functions and come to find out from technical support they said that the Erom chip was corrupted somehow and once it was replaced and the parameters were reinstalled it was functioning again so I have to wonder if it could be something similar

if it does not charge up the battery then I would lean more to charging circuit issues

Dose this battery backup have the cue function on where you can see the status of the device and adjust settings and what not does this function correctly this might be one way to know if the MCU is functioning at all

Just keep in mind that I just thinking out loud and this is how I play out in my mind how and what to check sometimes I am on the right track and sometimes I just going down a rabbit hole and going nowhere and probably going nuts as well

I hope this helps you