My long serving Sola UPS 325, the 750VA version, recently died on me. Having spent considerable time and effort, and some wasted money, on repairing it, I thought I'd post some notes about it here, so that they'll be archived on Google Groups, and someone may benefit from them.
Others might want to add some comments.
The symptoms were that the UPS was abruptly almost completely dead. No power was coming out of it, and the front panel was dark. The only reaction was that a relay would click when the mains power was applied or removed.
This seemed odd, in that even if its PSU part had failed, it has its own battery backup. Conversly, if the battery backup part had failed, it had a PSU. This conundrum was subsequently resolved by the realisation that it is impossible to power up this unit from the mains unless it has a battery connected with at least some charge in it. Without that, the internal relays are configured so that the mains power is not connected to anything useful.
I removed the cover. Before doing this, you should not only disconnect the mains, but, less obviously, the internal battery. This is because there is some possibility of shorting things out while removing the cover. You'll need a Torx 9 (or possibly 10) bit to remove the screws.
Removing the circuit board involves unplugging a lot of leads. It's best to note what goes where (or as I did, simply photograph it). Note that one of the leads is plugged into the centre of the board. This lead, together with one other plugged into the edge of the board, has a clip that needs to be pushed away from the plug to release it. Most of the other leads use spade connectors. You'll also need to thread the battery leads through the slot that gives them access to the battery compartment, since these leads are soldered to the board.
It was fairly quickly apparent that the 40A fuse has blown. (A 1000 Ah version may have a different fuse, or two of them). This fuse is of a type used in vehicles, and is easy to source, but is soldered directly to the board. Removing it is reasonably straight forward if one first cuts it in half (bit by bit, using wire cutters). When replacing the fuse, make sure you're generous with the solder - these joints have to carry a lot of current.
However, the fuse wasn't the only thing that had failed. I found that two of the four power FETS mounted on large heat sinks were short circuited, which certainly explained the failure of the fuse.
Removing the existing FETs is best achieved by cutting them off, so their leads can be removed individually. Also I found that clearing the holes so that new FETs could be fitted was best achieved by applying the soldering iron to one side of the board, and a solder sucker to the other. Knees are useful for holding the board.
Once the FETs have been removed (leaving the heat sinks in place), and the fuse replaced, and all the leads reconnected, you should be able to power up the unit on its batteries (by pressing the large button on the front panel). If it's connected to the mains, it should start up in its normal non-backup mode, otherwise you'll get a continuous beeb indicating an error. Wear protective eye gear while doing this - you don't want bits of liquified metal in your eyes if things go wrong.
With the mains connected, you may want to check that you have a reasonable AC voltage between the two thick leads connected to the heat sinks. Note that the peak to peak voltage is about 48V. This is potentially dangerous. And, of course, you've got mains voltages anyway on the board. So be careful! Note that these thick leads are so thick that you cannot get a meaningful resistance reading from them with a normal multimetre, so don't bother.
On the 750VA model it's about 32V AC RMS betwen the heat sinks. You can also check between each heat sink and the third thick wire from the transformer to the circuit bord, which on the 750VA model gives 16V AC RMS. The primary purpose of these tests is to verify the integrity of the transormer windings to which they're connected. If the transformer has shortcircuited (which would probably trip the circuit breaker), or open circuit, then it's certainly time for a visit to the tip.
The voltage across the larger two wire plug leading from the transformer was about 27V AC RMS.
The voltage across the smaller two wire plug leading from the transformer seems to be zero, despite the UPS functioning. It appears to be some sort of sense circuit.
If the unit powers up once the FETs have been removed, then replacing them should allow it to perform its inverter function again.
Now, this was where I made my biggest mistake. I replaced just the two that appeared to have failed, powered the unit up, and was rewarded by a flash of light, two new destroyed FETs and another fuse that I had to remove and replace. Indeed, the two FETs that had appeared OK were also now clearly damaged. Clearly, what I *should* have done was to replace all four. Doing that subsequently made the inverter part work.
You may want to backtrack from the circuits that supply the FET gates (through a resistor) to where there are two bipolar transistors that drive the gates, and check them. In my unit they were OK.
At this point, I thought I'd finished. But after I'd run down the battery while testing the inverter function until the unit turned itself off because of battery depletion, I discovered that it wasn't charging again. This turned out to be because the LM317T regulator attached to the third large heat sink had also failed. Presumably it was taken out either by the failure of the first two FETs, or by the more dramatic event when I tried it after replacing the two FETs.
However, replacing the LM317T regulator restore the unit to full service.
There's a large diode (looks a bit like a power transistor, but only has two terminals) near the heatsink for the LM317T regulator. It was OK in my unit, but it seemed to me that whatever took out the regulator could also take out that diode. It's worth checking.
So what caused the original failure? Maybe a surge from the mains, though the unit was connected through a surge protector, and nothing else in the house suffered.
Maybe just a chance failure of one of the FETs, the effects of which cascaded to take out the other components.
But there was one further possibility. Some of the leads to the transformer are held very tight against the transformer casing. Some abrasion may have compromised the insulation. You might want to add some more insulation in those places.
Good luck.
Sylvia.