Power Supply issue (ROAL 064)

[skynyrd]

Hello, I got a old IBM AS/400 with a ROAL 064 power supply (480W). This unit had been sitting for awhile, but when we fired it up, there was a loud pop, and smoke, that I have seen many times when a power supply goes bad. There is no power coming from the power supply now.

I would look for another one of these power supplies, but they are going for $500 used, and this machine isn't worth that much to me... but I would like to get it running again.

I have attached some pictures of the board. I don't see any capacitors bulging or discolored, but I did see a coil or transformer? that looks like it was melted. I talked to a electronics person where I work, and he said that likely was another component that was failing, causing the coil to get too hot.

Anyone got any ideas on whether this coil can be replaced? Should I try to replace that and go from there? Sorry, I am definitely as shadetree as they come with Electronics.. But I want to give this machine one more try before I scrap it. Thanks for any help anyone can give.

[ben7]

Re: Power Supply issue (ROAL 064)

Yeah, I think you might be out of luck, that transformer doesn't look healthy!

Could you desolder it so we can get a better look at it and the components next to it?

[skynyrd]

Re: Power Supply issue (ROAL 064)

Yea, I was afraid of that. I am thinking that transformer was a specialty part?

I don't have access to a soldering iron right now, but I did remove the board from it's casing to get some closer pics. The other components look OK around it, but the transformer is definitely burnt up.

[ben7]

Re: Power Supply issue (ROAL 064)

WOAH that is a very sad looking transformer!

[skynyrd]

Re: Power Supply issue (ROAL 064)

Anyone know of a place I could order a replacement transformer? Or could I rebuild this one (the base looks like its melted so bad I doubt it could be rebuilt). or would it be more trouble than it's worth?

[momaka]

Re: Power Supply issue (ROAL 064)

Looks more like a common-mode choke than a transformer. If that's what it really is, this would be a very easy fix (at least getting it replaced). Now, weather or not something else down the line has burned causing this transformer to burn - that is another issue. But I guess we will see.

Although you did provide quite a few pictures (and with good quality), I still can't see too well how the traces are connected on the board. Therefore, I would suggest you remove/desolder the transformer and take some pictures of the board again (top and bottom side, looking straight into the board and at a slight angle to reveal the traces).

Also, check the fuse on the input board (that board that connects to the AC receptacle and has the black and white wires coming out of it and going where that melted transformer is). It's probably blown now.

[ben7]

Re: Power Supply issue (ROAL 064)

Looks more like a common-mode choke than a transformer. If that's what it really is, this would be a very easy fix (at least getting it replaced). Now, weather or not something else down the line has burned causing this transformer to burn - that is another issue. But I guess we will see.

Although you did provide quite a few pictures (and with good quality), I still can't see too well how the traces are connected on the board. Therefore, I would suggest you remove/desolder the transformer and take some pictures of the board again (top and bottom side, looking straight into the board and at a slight angle to reveal the traces).

Also, check the fuse on the input board (that board that connects to the AC receptacle and has the black and white wires coming out of it and going where that melted transformer is). It's probably blown now.

It looks to be put after the bridge rectifier (bottom right of the board, it has a small U shaped heatsink on it), it might be part of a PFC circuit.

But, yes, the only way to tell is to look at how it's wired up, on the PCB.

[everell]

Re: Power Supply issue (ROAL 064)

I agree with Momoka........looks more like the booster choke in a PFC circuit. If so, you probably also have a blown (shorted) switching FET transistor in the PFC circuit, possibly the large diode in the PFC circuit, and a blown open fuse. Shorted booster chokes in PFC circuits is a common problem.

If this is the PFC choke that is burned up, you might be able to replace it with a toroid style booster choke - if there is enough room.

[momaka]

Re: Power Supply issue (ROAL 064)

It looks to be put after the bridge rectifier (bottom right of the board, it has a small U shaped heatsink on it), it might be part of a PFC circuit.

Yeah, now that I look at it, I think you are right. The core also appears to be a little bit too big for a common-mode choke.

Either way, it still shouldn't be too hard to fix. Worst case, you disable the PFC and run the PSU without it (and if this is in a region with 120 VAC, maybe add/convert the circuit to have a voltage doubler).