APC back-ups es 650 (BE650y-in) Dead

[DesperateDude]

I have an APC Back-UPS ES 650 (BE650Y-IN), Board Number: 640-0678 REV01.

Recently, there was a power cut. After power was restored, I turned the UPS on, but later noticed that it had shut down. After checking, I confirmed that the unit is completely dead.

I began troubleshooting, and initially, there was absolutely no sign of life.

I found that the large fusible resistors and the 10Ω resistor between the relays were open, so I replaced them. However, this did not resolve the issue. (The main fusible resistors were originally 2.9K since I couldn't find the exact value I replaced them with 3.3K)

Next, I noticed that the three large resistors near the optocoupler (4N25) were getting extremely hot, along with the nearby MPSA42 transistor.

If I remove the transistor, the heating stops completely. If I remove the optocoupler instead, the heating is significantly reduced and appears closer to normal operating levels.

Symptoms:

• No signs of life at all
• No relay clicks
• No voltage present after the optocoupler

I then replaced:

• The optocoupler
• The MPSA42 transistor
• All small electrolytic capacitors (22µF, 16V), as they had very high ESR (one measured around 140Ω)

Despite this, the issue remains unchanged.

To investigate further, I injected 12V directly into the VCC of the LM358 IC. With this, the UPS appears to come to life, although the resistors still heat up.

However, even with this external voltage injection:

• When AC power is removed, the UPS beeps and LEDs flash, but it does not switch to battery mode
• The LEDs flash green and amber, indicating “Shutdown by Software”

I have tested most of the components, and nothing appears to be shorted or open.

With the battery connected: (Positive side of the battery goes via the transformer not directly to the circuit)

• I get 12V at one of the 330µF capacitors (Top one near IC), but not the other
• All Mosfet drains get 12V
• Transformer black and white cables which connect next to Mosfets get 12V
• The 47µF capacitor near the buzzer also receives 12V

This behavior is quite confusing, and I’m currently stuck. I could potentially use the UPS with external voltage injection and remove the overheating resistors, but since it does not switch to battery mode, it’s not usable.

Could anyone help me diagnose this issue?


A few years ago, I received great help here fixing a faulty PSU with similar strange behavior.


I’ve attached photos of the board, using backlighting so that both sides of the traces are visible.




Thank you.

[CapLeaker]

First you gotta get the primary side problem fixed. You plug it in and you get still nothing. So something is still open somewhere or an IC is dead. So follow along the primary, how it gets rectified and what needs to happen to turn the PSU on to supply DC voltage to the smaller components. Maybe it is a no go effort due to parts. Also could be that the relay coil is ope, the relay contacts are welded together or burnt off everything needs to be checked. The solder on the relays look like total @$$.

The last APC UPS I tried to fix, had a problem with not detecting when plugged into AC. Took me a while to figure out that on a little transformer the primary winding was open. No replacement available. Now I use it for parts. The small tiny UPS’s go straight in the bin if it isn’t something simple to fix, since they are cheap or free for the taking to find.

Maybe you want to learn how this works, so I suggest you download available APC UPS schematics (640-xxxx) and maybe that gives you an idea how these work.

[DesperateDude]

First you gotta get the primary side problem fixed. You plug it in and you get still nothing. So something is still open somewhere or an IC is dead. So follow along the primary, how it gets rectified and what needs to happen to turn the PSU on to supply DC voltage to the smaller components. Maybe it is a no go effort due to parts. Also could be that the relay coil is ope, the relay contacts are welded together or burnt off everything needs to be checked. The solder on the relays look like total @$$.

The last APC UPS I tried to fix, had a problem with not detecting when plugged into AC. Took me a while to figure out that on a little transformer the primary winding was open. No replacement available. Now I use it for parts. The small tiny UPS’s go straight in the bin if it isn’t something simple to fix, since they are cheap or free for the taking to find.

Maybe you want to learn how this works, so I suggest you download available APC UPS schematics (640-xxxx) and maybe that gives you an idea how these work.

Thank you for the reply. Yes solder is total @$$ because my iron is @$$ 😁 I knew someone would notice that.

I couldn't find any schematic for this UPS.

Also this UPS design is so weird. It just feeds the Opto and transistor here and nothing else. Opto directly connects to the main relay. I checked almost all parts here but didn't find any problem. I mostly had to check components on board without removing them, actually. I mean the SMD ones. The ones which were possible I removed and tested.

Yes this UPS is so old and not worth the try, but in our country all currently available models are cheap Chinese garbage and don't even have the even basic quality these ancient UPSes have. That's why I am trying to get this fixed, not because these are cheap, but because these are the only things worth using, and I am not so sure about the latest APC UPSes we have here in the market.

[redwire]

Check the Picofuse F4 I think rated 5A.

[CapLeaker]

Well, I couldn’t find schematic for this exact UPS neither, but some older versions are available.

First things first. Re-establish power. Reassemble the UPS somewhat, plug it in and start measuring the primary over to the secondary towards the main chip. There has to be some sort of a standby power circuit and some other voltage rails. If I remember, there is 12v, 5v for sure. Maybe even more and lower voltage rails. The are some older APC UPS’s need a battery for it to be able to turn on.

[DesperateDude]

Check the Picofuse F4 I think rated 5A.

Thank you. I already checked that first. It is OK.In-fact all the fuses are OK.

[DesperateDude]

Well, I couldn’t find schematic for this exact UPS neither, but some older versions are available.

First things first. Re-establish power. Reassemble the UPS somewhat, plug it in and start measuring the primary over to the secondary towards the main chip. There has to be some sort of a standby power circuit and some other voltage rails. If I remember, there is 12v, 5v for sure. Maybe even more and lower voltage rails. The are some older APC UPS’s need a battery for it to be able to turn on.

I tried with battery on and both AC on. As I said unfortunately there is no power at all to the secondary and when the battery is there is 12V in some places but nothing comes to any IC. Only manual voltage injection worked but even with that resistors heat up and once AC is off UPS doesn't switch to the battery power.

Also from AC side the power doesn't go anywhere. Only for the transistor and to the opto. Also very little voltage to the resistor chains below.

Already replaced the opto and transistor but still the same problem.

This is very strange and I no longer have almost anything to check in primary side.

[CapLeaker]

I have a APC BE550G that I opened up and had a quick look inside. Mine has a PWM LNK364PN on the board. Usually these are the culprits that blow or play dead etc. Given yours is a more fancier model maybe? There is only one relay in mine. lol.

[redwire]

The older APC UPS used a big power transformer, no SMPS. This transformer should be energized with mains to provide the low voltage AC for charging the battery, powering the MCU etc.
If the transformer is dead and the fuses are OK then that leaves the relays. With power off, you can beat them up a little bit, tap then, then see if they get unstuck. The contacts do arc and wear out too.

What happens I believe is the big transformer power flow gets reversed when the UPS is running - two power mosfets pulsing 12V battery into the secondary and the primary gets transferred to the load.
Not sure why all the extra relays, it must be doing tap switching for brownouts or something.

[DesperateDude]

I have a APC BE550G that I opened up and had a quick look inside. Mine has a PWM LNK364PN on the board. Usually these are the culprits that blow or play dead etc. Given yours is a more fancier model maybe? There is only one relay in mine. lol.

Yeah these things are crazy 😁

[DesperateDude]

The older APC UPS used a big power transformer, no SMPS. This transformer should be energized with mains to provide the low voltage AC for charging the battery, powering the MCU etc.
If the transformer is dead and the fuses are OK then that leaves the relays. With power off, you can beat them up a little bit, tap then, then see if they get unstuck. The contacts do arc and wear out too.

What happens I believe is the big transformer power flow gets reversed when the UPS is running - two power mosfets pulsing 12V battery into the secondary and the primary gets transferred to the load.
Not sure why all the extra relays, it must be doing tap switching for brownouts or something.

Thank you for the explanation. I even removed all the relays and checked. All of them work.

The optocoupler pin 5 is directly connects to the main relay.

With voltage injecting to the IC LM358, All logic seem to work except it doesn't switch to battery power when AC is off.

Also all these LM358 ICs' VCC is directly connected. Multi-meter continuity mode proves that.

Tested the transformer windings and they are all OK.

Also I remember with voltage injection, the battery was also getting charging voltage.

[CapLeaker]

This isn’t an exact schematic of yours, but bits and pieces are similar. It also has a PWM in the primary. If one of there 10 ohm resistors blew next to the relay, the relay is probably junk. There was some arcing going on inside the relay as it cycled trough the boost, trim whatever.
By injecting only 12V, things aren’t running yet. You need also to inject at least 5V and maybe another voltage.

2 relays are for brown outs, one for boost, the other for buck. The 10 ohm resistor is used in conjunction with a capacitor to stop arcing when switching around. If that resistor is blown, there was some arcing going on inside the relay contacts.

[DesperateDude]

This isn’t an exact schematic of yours, but bits and pieces are similar. It also has a PWM in the primary. If one of there 10 ohm resistors blew next to the relay, the relay is probably junk. There was some arcing going on inside the relay as it cycled trough the boost, trim whatever.
By injecting only 12V, things aren’t running yet. You need also to inject at least 5V and maybe another voltage.

2 relays are for brown outs, one for boost, the other for buck. The 10 ohm resistor is used in conjunction with a capacitor to stop arcing when switching around. If that resistor is blown, there was some arcing going on inside the relay contacts.

Thank you for the document. My problem is so confusing as nothing is flowing without voltage injection so even to check any relays are arching or not there is no voltage. Anyway I tested the relays by removing and energizing them too they worked.

Thank you again. I'll check more.

PS: Unfortunately I can't download the document as it asks me to subscribe.

[DesperateDude]

This isn’t an exact schematic of yours, but bits and pieces are similar. It also has a PWM in the primary. If one of there 10 ohm resistors blew next to the relay, the relay is probably junk. There was some arcing going on inside the relay as it cycled trough the boost, trim whatever.
By injecting only 12V, things aren’t running yet. You need also to inject at least 5V and maybe another voltage.

2 relays are for brown outs, one for boost, the other for buck. The 10 ohm resistor is used in conjunction with a capacitor to stop arcing when switching around. If that resistor is blown, there was some arcing going on inside the relay contacts.

Thank you. Some quick Googling with your given file name gave me the document.

[CapLeaker]

The relay clicking doesn't mean the contacts are not burnt off... you have to test them too or swap the relay around.

[DesperateDude]

The relay clicking doesn't mean the contacts are not burnt off... you have to test them too or swap the relay around.

I checked if the relays switch and they did and also correctly switched between contacts. Multimeter in continuity mode proved it once the replayed energized with an external power source. I even checked them this way out of the circuit too.

[stj]

small electrolytic caps are always a good place to start when something is dead.

[DesperateDude]

small electrolytic caps are always a good place to start when something is dead.

Thank you for the reply. I already replaced all of the small 22uf ones with new tested ones because all old caps had very high ESR.

The only ones which I didn't replace are the big 4 and I tested them and had normal ESR and capacitance.