APC Smart UPS 6000 Repair [FIXED]

[Jaxey]

Hi, new to the forum and hoping someone can help out...

I recently bought a ~10 year old 6kVA/4200W APC SMART UPS secondhand online and it appears to be dead-on-arrival. While I may be able to get back what I paid for it from the vendor (wasn't actually that much), with freight costs to return it I'd still be several hundred dollars out of pocket so trying I'd rather try and repair it (or have it repaired locally).

Symptoms: With or without power connected attempting to turn it on results in the green 'online' LED lighting very briefly, then goes out and a red 'Fault' LED comes on. When this happens the battery indicator lights the lower 2 (out of 5) segments. According to the APC documentation this appears to be an 'Inverter Error'.

The battery packs both appear to be fine, and the batteries are reading ~184V combined (about 92V each) which although low seems to be within the APC quoted minimums (nominal is 96V for the 8x12V Lead Acid cells in each of the 2 packs).

The UPS logic board appears to be working fine - when mains is applied the fan in the front of the unit comes on, buttons on the front panel work and the APC network management card works (I can connect to this from a web browser after figuring out the weird APC DHCP option required to give it an IP address on my home network). I don't know the 'apc' user password, but the secondary 'device' login was fortunately still set to the default password and I can use this. The web UI also shows an 'inverter error'.

I opened up the unit to see if I could spot anything that had obviously blown up or overheated, but all appears to be fine visually. Based on another thread here I tested what I believe is the inverter output capacitor (marked as TMPP 206K/400V) (it's the huge yellow capacitor that had obviously self-destructed in the other thread and was 10uF - but that was for a 1kVA model and not the 6kVA one I have). Anyway, the in-circuit capacitance from my trusty EEVblog 121GW meter is showing this capacitor as only 0.25uF.

So a few questions:

• Is this capacitor meant to be 20uF? I can't find any schematics for this model of UPS and although I have managed to google the service manual, it doesn't include part values. The '206' on the markings suggests 20uF to me(?)
• Should I try and desolder the capacitor and check it again out-of-circuit or just assume it's bad and replace it? It's going to be a bit of a mission to get the main board out of the unit but guess I'm going to have to do that anyway for any sort of repair/replacement.
• Is something like this this a suitable replacement part?
• Any other suggestions to get this up and running? I'm in Christchurch NZ and shipping this thing around is not very practical due to the size & weight, but if there's anyone local experienced with this type of repair I'd be keen to find them.

Would really like to get this working if at all possible, thanks in advance for any assistance!

[elecdonia]

Catastrophic visible failure doesn’t always take place. The capacitor may look fine externally. Measurement of uF is the standard way to test these large metallized-film capacitors.

It isn’t possible to measure uF accurately with the capacitor “in-circuit.” Unsolder one end of the large yellow inverter capacitor and then test it for proper uF. Make sure capacitor is discharged before connecting meter.

This type of capacitor, known as “metallized film,” tends to gradually lose uF as it ages. A loss of more than 10% indicates it should be replaced. Example: A 20uF capacitor should measure >18uF.

[bdunham7]

So a few questions:

• Is this capacitor meant to be 20uF? I can't find any schematics for this model of UPS and although I have managed to google the service manual, it doesn't include part values. The '206' on the markings suggests 20uF to me(?)
• Should I try and desolder the capacitor and check it again out-of-circuit or just assume it's bad and replace it? It's going to be a bit of a mission to get the main board out of the unit but guess I'm going to have to do that anyway for any sort of repair/replacement.
• Is something like this this a suitable replacement part?
• Any other suggestions to get this up and running? I'm in Christchurch NZ and shipping this thing around is not very practical due to the size & weight, but if there's anyone local experienced with this type of repair I'd be keen to find them.

Yes, based on other similar products I've worked on and the '206K' markings it is likely 20uF, with that value not being very critical--it would likely operate with 15, 20, 22 or 27uF.  It probably also operates a bit noisily with even lower values.  This is a metallized PP capacitor that is 'self-healing', meaning if there is a dielectric failure it internally discharges a bit of energy that melts it in a way that heals the failure at the cost of losing that area's capacitance--sort of like a scar.  If that happens enough, the value of the capacitor drops.  In 230V-land, this capacitor is very marginally specified and it is very possible that this is what has happened.

Yes, you should absolutely remove the board and capacitor and test it both for capacitance and leakage (ohms).  If you find it to be bad as you suspect, you likely have found both the problem and the solution.

Yes, the general type of part you show is appropriate.  It seems to be very difficult to find exact replacements for these and the large low-voltage capacitor found in the 24V inverters, the biggest problem being that most good replacements are physically larger.  I think APC got them specially made at low-ish cost and while they do typically work for quite a while, they seem to be just the bare minimum for the job.  You can't use just any capacitor here, it has to be very low dissipation and metallized PP is one of the few types that can meet the specs and not be excessively large.  If you have room to put in a larger unit with a higher voltage rating, that might be a good idea.  Perhaps look for welder inverter capacitors.

https://www.aliexpress.us/item/3256803884287671.html

My only other thought is that you need to be very careful with this unit.  It's pretty easy to blow them up or even hurt yourself with that high battery voltage.

[Jaxey]

Thanks both for the responses, looks like next step is to remove the main power board and desolder at least one end of the cap and check it again out of circuit.

And @bdunham7 appreciate the warning, I'm only a hobbyist but well aware of the risks around these types of boards and have already checked & discharged all the large caps on the board (and obviously being very careful around these until proven discharged). Luckily on these models it's very easy to disconnect the mains & batteries and make sure the 192V from them and the +/-400V from the inverter isn't present.

There probably is some room for a physically larger capacitor like the one you linked (but would have to run appropriate leads to the board from it), will consider that if/when the existing one is confirmed dead.

[bdunham7]

There probably is some room for a physically larger capacitor like the one you linked (but would have to run appropriate leads to the board from it)

Is there something in the way just above the board?  It would be best if you kept the lead length to a minimum.

Also, what is the exact APC model number of this unit?

[Jaxey]

There is a bracket (already removed in the picture I uploaded) which mounts the connectors for extended runtime battery packs above the capacitor but may still be enough room for something larger, will do some measurements.

The model number as far as I can work out is a 'Smart UPS RT 6,000VA' (SURT6000) using a 'Lynx2' power board (APC part number 0P7516 according to the service guide), but I'm not entirely clear since this is an IBM badged version of the APC 6KVA unit.

The board has a silkscreen part code of '640-0751K_REV11' and is marked 'APC POWER BD, LYNX II, 6KVA (c)2009'.

Edit: There's also a part number on the front of the unit under the cover that says 'SURT6000XLIX547' and 'Made in Philippines (Cavite)' and has a serial number 'QS1246250299'

[Jaxey]

Ok, that was a bit of a pain to get the main power board out, figured it out eventually (you have to slide forward to clear the power feed wires at the rear of the board and then tilt sideways up and out from the middle of the case to clear - not much room). Desoldering the suspect inverter capacitor wasn't actually too bad - just added some fresh solder and a solder pump made quick work of getting both legs free cleanly.

Unfortunately (or maybe fortunately if replacing it fixes the unit), looks like the capacitor is definitely bad - should be 20uF based on markings and everything known so far and is testing at the same 0.25uF as it was in-circuit (pic attached). Will now be ordering something to replace it - tempted by the Aliexpress one that @bdunham7 linked, but that will likely take 4+ weeks to make it to NZ so will probably order the Digikey one I linked above to try first and see if that fixes the unit before deciding on the 'permanent' replacement.

Will update when the new cap arrives & is installed - keeping fingers crossed and thanks all for the help so far.

[Jaxey]

After some more advice, Digikey want to ship a part from the US, but Mouser NZ appear to have a suitable part available locally: https://nz.mouser.com/datasheet/2/212/1/Kemet_F3131_R53B_X2_350_002-2944605.pdf

Specifically looking at part code: R53BY52000000K which looks like it will fit into the gap from the removed cap, but may have to mount 'upside down' and run patch leads from the pins to the PCB as the existing PCB holes are ~65mm apart and this part has pins at 52.5mm spacing.

Would this be suitable? I can't find any mention of 'pulse rating', 'maximum ripple current' or 'peak pulse current' in the datasheet, and the graph at the bottom of page 8 in the datasheet shows around 9A@1kHz and ~12A@10kHz which makes me a little nervous that this may not be suitable (if I'm understanding the requirement for withstanding high current pulses correctly).

[5U4GB]

Will now be ordering something to replace it - tempted by the Aliexpress one that @bdunham7 linked, but that will likely take 4+ weeks to make it to NZ so will probably order the Digikey one I linked above to try first and see if that fixes the unit before deciding on the 'permanent' replacement.

It may not be nearly that bad, if you select Aliexpress Standard Shipping instead of China Post (you have to click and scroll a bit in the shipping options) it can get to NZ in as little as a week.  That one also has nice lugs on it which you could attach via flying leads to wherever it needs to go if there's not enough space there.

[bdunham7]

Would this be suitable? I can't find any mention of 'pulse rating', 'maximum ripple current' or 'peak pulse current' in the datasheet, and the graph at the bottom of page 8 in the datasheet shows around 9A@1kHz and ~12A@10kHz which makes me a little nervous that this may not be suitable (if I'm understanding the requirement for withstanding high current pulses correctly).

I saw that part and had the same concerns.  I think the original oval custom APC unit is probably specified for lower ESR and more current,  perhaps 18-20A.  I don't know the exact topology and parameters of these units but I'm assuming the ripple current rating should be most or all of the output current at PF=1.  Or something like that.  What I would do, if there is room, is to stack 2 of the 10µF models of the PP capacitor that you originally linked.  If you can fit in a pair of the 10µF @600VDC/330VAC units, I think you'd have a good solution and an improvement over the original.  Is there any space underneath, on the back side of the board?  You could put one on each side if that were the case. 

Also, since you said you weren't all that experienced, be very careful soldering these.  Plan ahead, be quick and don't solder very close to the body of the capacitor even if it might look neater when stacking them.

Edit:  2 of these is also a good possibility, I don't know what their availibility to you is:  https://nz.mouser.com/ProductDetail/KEMET/C4GAHUD5100AA3J?qs=pqRVuuzkf6bzGYEJY4dRNw%3D%3D

[Jaxey]

Decided that I'd rather do this once/properly and since I haven't been able to find anything locally that matches the Aliexpress welder inverter capacitor that @bdunham7 originally linked so have ordered that - hopefully won't take too long (I did the 'Aliexpress standard shipping' that @5U4GB suggested so we'll see).

This also has the advantage that I can solder short wires with spade terminals to the board and then just plug it in rather than soldering directly to the cap - some of the datasheet soldering times are a bit scary.

Thanks all (again!), will update when it's arrived & fitted

[Jaxey]

Latest update:

Still waiting on the AliExpress welding inverter cap, but in the meantime from @bdunham7's suggestion I'd also ordered 2 x 10uF @600VDC caps from Mouser which turned up today - so I 'piggybacked' them and tried them out (picture). Was very careful soldering and used 'heat shunt' clips on the leads to try and make sure too much heat didn't go up the legs into the caps.

Just tried it out and UPS appears to be working fine(!) Passes self test, no warnings/errors in logs or on front panel and seems to be charging up the batteries fine \o/

Thanks all for the help & advice in here, first time I've attempted a repair on something like this and VERY happy to have an apparently functional unit at the end.

[bdunham7]

Thats great!  However, a quick note about those zip-ties--I wouldn't let them be directly in contact with the capacitors like that and I would be very careful to use low force when tightening them.  Perhaps a pieice of plastic or something under the zip tie where it contacts the curved surface would do it.  The reason is that these wound film capacitors can be damaged by physical distortion as they don't really have a case.  Doing it like  you have is probably not extremely bad, but it isn't ideal.

[Jaxey]

Thanks - and good to know, the previous cap had a zip-tie around it quite tightly onto the board (there's are 2 gel-like cushioning pads on the board under the bottom cap) so I've made the new ties 'firm' to hold the caps in place, but not particularly tight. Will make sure they're not too tight to deform the caps though and maybe put some soft plastic around the top one to keep the zip-tie away from the 'case'. Thanks again for all the help & advice