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

[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

[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.

[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.

[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]

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...

[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]

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.

[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.

[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.

[petehall347]

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

[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?

[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

[petehall347]

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

[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.

[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

[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]

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]

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?

[petehall347]

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

[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.