Apple iMac Power Supply Acbel API4PC47-290 Dead

[torgeson5kqs]

I have a fully re-capped Acbel PSU that when I went to test it after recapping, part of the silver metal plate (plug connector plate) touched the copper heatsink and shorted the unit and thus no power whatsoever. I've checked standby voltage and nothing. I've checked voltage across the main filter cap and nothing. My guess is that current went in through the out door on one of the diodes and thus fried it (just guessing). So I would imagine this narrows down the possibilities to just the "HOT" side. If anyone has some pointers or suggestions I'm all ears. I'll post a picture of the unit as well. Caps used are Samxon series GDM, GCM, and GFM not that it matters at this point.

In one of the pictures I show the metal plate and copper heat sink where the short happened. I've since added some black electrical tape to the underside and corner of the plate.

[Toasty]

Re: Apple iMac Power Supply Acbel API4PC47-290 Dead

You're all over the place, eh?

Check the fuse and bridge rectifier.

[torgeson5kqs]

Re: Apple iMac Power Supply Acbel API4PC47-290 Dead

Odd, but I can't find the fuse. There is nothing that resembles the standard type cylinder fuse either a slow blow (white) or a clear glass fuse. I've even tried looking for a SMD fuse which I've seen before. Don't most power supplies have a fuse?

[Toasty]

Re: Apple iMac Power Supply Acbel API4PC47-290 Dead

The fuse is vertical on the board and shrink-wrapped in black. It is a rectangular (brown) plastic device perhaps 8x4x10mm. Just to the left of the power connections on the other side of the 2 blue protection caps.

T4A / 250v - Time delay 4 amp (Slo-Blo)

You can use the same type or a standard 5x20mm pigtail type, mounted vertically. Be sure you insulate the long leg and then shrink wrap the whole affair. The short leg, input, or "down" leg should connect to the mains side. The long leg or "output" side of the fuse should connect to the rest of the supply.

Toast

PS: Slo-Blo is not indicated by the white ceramic fuses. They come in clear glass too. The ceramic are safety fuses and offer better protection as they don't shatter under certain types of circuit faults. I always use ceramics when repairing PSU's.

[torgeson5kqs]

Re: Apple iMac Power Supply Acbel API4PC47-290 Dead

Turns out it was the fuse also checked rectifier and it's good. I pulled another fuse from a spare supply I have, it was a 5 amp slow blow just to get the unit powered up. I have standby voltages at pin 9 (purple) 5v and pin 22 (brown) 23.8v. However, when I jumper the unit I have no voltages on any of the other pins.

[Toasty]

Re: Apple iMac Power Supply Acbel API4PC47-290 Dead

Q1

[torgeson5kqs]

Re: Apple iMac Power Supply Acbel API4PC47-290 Dead

Appearance of Q1 looked good checked in circuit with transistor tester. Pulled it out anyway tested it again good NPN. Replaced anyway. Also replaced 3845B since I know that sometimes one can render the other bad or vice versa. I really have no way of testing the 3845B and I always destroy them when I remove them from they board because of that adheasive under the chip. Conclusion, same problem still exists. Standby is good but no other voltages exist when jumpered on any other pins.

[Toasty]

Re: Apple iMac Power Supply Acbel API4PC47-290 Dead

https://www.badcaps.net/forum/showthread.php?t=8665

https://www.badcaps.net/forum/showthread.php?t=14273

https://www.badcaps.net/forum/showthread.php?t=8869

Go thru some of these and see if anything makes sense. Especially the one with voltage readings on Q1.

The last one that wouldn't be resolved ended up being a blown supervisor chip (WT7515) which I replaced off of another board. Those chips are no longer available.

Double check your cap soldering. Bad via connection can cause these problems too.

Toast

[torgeson5kqs]

Re: Apple iMac Power Supply Acbel API4PC47-290 Dead

I found good information on this thread

https://www.badcaps.net/forum/showthread.php?t=14273

I checked the TOP245YN (M6 on PCB) with my meter set to diode and it seems to be good (checked in circuit). However, I seem to have a short on R70 (continuity) is that normal? C41 I won't be able to check until my SMD Tweezers get here in the mail since I have no way of checking capacitance. As far as SFH615 at M7, M11, M4, and another I can't read. How do I correctly read the voltage off these? When you helped me with the PSU from the Power Mac G5 thread https://www.badcaps.net/forum/showthread.php?t=14628 on post #10 you mentioned having the negative probe on the anode of a diode and then checking pin 1 on these optoisolators, would something similar work in this case?

[Toasty]

Re: Apple iMac Power Supply Acbel API4PC47-290 Dead

Going by the questions in Post #2 in the other thread, what voltages show on Q1?

[torgeson5kqs]

Re: Apple iMac Power Supply Acbel API4PC47-290 Dead

Voltages are the same regardless if unit is in standby or on. From B,E, and C the voltages are either 0 or .1 to .2 with negative probe on common (black wires). However, when neg. probe is on pin 7 of 3845B the Collector reads between 13.8 to 14.3 and emiter reads about .5 V, base is 0. I actually replaced the Q1 and 3845B with brand new ones from mouser the other day so this test is with the new replaced chips.

[Toasty]

Re: Apple iMac Power Supply Acbel API4PC47-290 Dead

>>From B,E, and C the voltages are either 0 or .1 to .2 with negative probe on common (black wires).<<
FYI - That's the -output- side grounds. You're dealing with the input (HOT) side, so measuring from Pin 7 on M2 was the correct place for measurement.

Make sure you're jumpering the correct pin to output ground.

Double check all your cap replacements for top-to-bottom via connection continuity. I've seen a broken via that got pulled out of the hole and had this effect because there was no connection to the board topside trace.

If they check out, you might be facing a failed supervisory chip.

Toast