Tyco spi270f4b24 ATX supply repair tips (not starting)

[Dannyx]

Re: Tyco spi270f4b24 ATX supply repair tips (not starting)

v3.0 - replaced physical LM339 op-amp with individual internal op-amps

[momaka]

Re: Tyco spi270f4b24 ATX supply repair tips (not starting)

No offense, but I think you're wasting time replacing all the ICs, especially on the secondary side. If there's anything that's going to be popped or bad, it would likely be on the primary side. After all, you had something pop. So there's definitely going to be a bad component in there somewhere now. Only way to find it is to dig deeper with the multimeter and soldering iron.

You still haven't reported back if you actually checked all the primary-side parts and the output rectifiers too. So no point drawing a schematic really. Only thing I can tell from your schematic is that the 3.3V and 5V rails are mag-amp regulated. If their parts check out alright, it won't be them that's causing the trouble.

That being said, with the 3.3V and 5V rails being mag-amp regulated, this means you need to get the 12V rail loaded up to a minimum of 1-2 Amps while testing. Otherwise, the PSU may act up and not want to start.

Last but not least:

It's not fixed yet though because he's tested it through a series lighbulb on the mains which stays on constantly because of the PFC booster - it's not a defect, I've seen it happen many times on PFC circuits. The added current limit prevents the circuit from going up to 400v which forces the "pump" circuit to stay on to try to compensate, thus drawing a lot of current, but it works fined if you attempt a startup straight on the mains.

To get around testing APFC PSUs with a "dim bulb" tester circuit, you just need a more powerful light bulb. 200-400 Watts halogen or incandescent should do the trick. Maybe even 500W, if it's still acting up. Even with such a powerful bulb, the current will still be limited to about 2.2 Amps @ 230V AC line (note: this is not running current but rather short-circuit current if the PSU shorts somewhere. The running current will be limited to whatever makes the line voltage drop below 90V AC, as that's usually the lowest most APFC PSUs can handle).

[Dannyx]

Re: Tyco spi270f4b24 ATX supply repair tips (not starting)

I haven't actually replaced any ICs - just the PS224 with the PS223, which resulted in the aforementioned pop (which wasn't my idea to begin with ). Of course, I did some more digging in the meantime, removing the whole heatsink assembly on the secondary so I could get a better look down there, but again: nothing - just coils and jumpers, none of which appeared charred or burned. After all, the pop was rather small - not like what happens when something on the primary goes wrong for instance. It was more like a small spark with no smoke afterwards.

I also took this opportunity to measure the diodes on that heatsink out of circuit. All of them read good, with low Vf in one direction (forward biased) and no flow in the other direction. They're not identical - it's actually a cluster-f in there, with various types of diodes mixed together, so the results weren't consistent. One of them is actually a LM7912 regulator for the negative 12v bus, but that's ok too.

The pop was on the secondary side and it appeared to come from the area I pictured up close with the heatsink out. I thought that transistor or blue cap went, but that would mean no 5vSB which I AM getting, so those are fine. I also thought about those two TO-92 packages on the daughter board, but they show no sign of damage proportional to that spark (cracked case, unreadable serial number...). My only other idea is that one of those coils did it, like if the insulation on them gave in due to age and made contact with something it shouldn't...it might also explain why the PSU is now immediately shutting down. Just before the pop happened, the PSU came on and appeared to work fine, then there was the pop and now this (immediate shutdown) so my money is on a short somewhere in those coils.......but I can't find it. I doubt replacing the 224 will help, as it wasn't faulty to begin with....

The schematic is only for the daughter board. True, not that handy and it's a mess....doesn't really matter. It was more for proof of concept.

Mag-amps: I can indeed see some wires going THROUGH the big coil (the one with blue paint and reddish wire barely visible) and I believe it doesn't utilize series resistors for current sensing but instead these "mag-amp" things. There's only one actual shunt in there, on the 24v bus which I included in the schematic.

[Dannyx]

Re: Tyco spi270f4b24 ATX supply repair tips (not starting)

Just in case someone is still following along at home, this project has been on hold ever since and I decided to look into it some more, not wanting to give up.

I did some more research on mag-amps like previously suggested and found resources ranging from scientific articles to more practical explanations like this one. At least now I kinda know what to look for. This opens up the possibility of the mag-amp not running and the output "overshooting", tripping OVP on one of the outputs which the PS223 senses and shuts off the supply. According to that article, it's the 3.3v output that's most likely to be mag-amp regulated from the 5v supply, while the 12 and 24v outputs are not directly regulated. If so, our mag amp would consist of op-amp LM339, those transistors on the riser board and the largest coil most likely, since there are no other components around.

[lpraderi]

Re: Tyco spi270f4b24 ATX supply repair tips (not starting)

Hi Dannyx in case you still hold this dead creature, received today a Tyco/Elo Touch POS/Cashier with the same PSU (SPI270F4B24).
Customer wants to upgrade CPU/Ram, and only reuse monitor/touchscreen.
Tested complete system before upgrade, PSU works but after a couple of minutes shutoff with that "relay like" sound.
Finally put (outside case) standard ATX PSU with borrowed CN19 connector piggybacked to ATX connector (without 24V lines) from original PSU.
So long everything works OK.
Let me know if you need some pictures/ measure from partial working PSU unit.