AcBel PSU / Quicksilver

[ssp3]

indibil, take a look here: http://macos9lives.com/smforum/index.php?topic=5341.msg39045#msg39045

[aBc]

Yes, for more in-depth, related info read through that entire thread beginning here:
http://macos9lives.com/smforum/index.php?topic=5341.0

[Jacques]

You may have a dead mainboard / motherboard...it's a possibility.

Have a look at this YT vid, similar symptoms and Nick found the issue was the mainboard.

https://youtu.be/vAi-L6KWwZs?si=xhVaLR-qMScBJQU2

[aBc]

You may have a dead mainboard / motherboard...it's a possibility.

Have a look at this YT vid, similar symptoms and Nick found the issue was the mainboard.

https://youtu.be/vAi-L6KWwZs?si=xhVaLR-qMScBJQU2

Interesting video.

And after watching through it a few times I’m uncertain as to whether or not he actually replaced the original mobo with a different one in the end - OR if he actually put the original mobo back in, making certain to properly seat all of the mounting screws? (Especially that one screw that was not Apple original.) And that one in particular is important screw for the CPU daughtercard circuit. No stable, solid connection there? Then no power up. So yes, definitely DO check ALL mounting screws and Molex connectors. No complete circuit power through the CPU = no boot and shut down.

Also… not a CUDA button. But instead… a PMU reset button. They are different and PMU needs only a fraction of a second to be depressed for a reset. I often confuse this terminology too, coming from older Macs with a CUDA button.

AND no new heatsink paste applied, nor any anti-static procedures followed?

[indibil]

I'm testing the power supply outside the QS, bridging green wire with black.

I have replaced several capacitors, checked several suspicious tracks, checked the 4A thermofuse... and it still doesn't work. It doesn't seem like a capacitor problem, I think there is a short circuit in some component but I can't detect it with the naked eye.

[aBc]

While I seem to be on a posting binge today…

After indibil’s comment that his PSU was like the one that Jacques shows, I noticed that Jacques’ sub board (“Fan control board”?) looked amazingly like mine. And while the bottom of Jacques’ main board seemed a bit different, his noted locations of the capacitors on his main board were very similar.

D’oh! Same API number and same Apple P/N number.



So, compared some other AcBel’s noted in this thread and came up with the following.

AcBel,  API1PC12. APPLE P/N:  614-0157     aBc         QS xxx

AcBel,  AP10PC24. APPLE P/N:  614-0146    gert79     QS 933

AcBel,  API1PC12.  APPLE P/N:  614-0157    ovalking  QS 800

AcBel,  API0PC24.  APPLE P/N:  xxx-xxxx     ovalking   QS 933

AcBel,  API1PC12.  APPLE P/N:  614-0157    Jacques   QS 867

AcBel,  API1xxxxx. APPLE P/N:  614-0157     indibil      QS 800

Would like internal images of gert79 and ovalking’s QS 933’s.
[AP10PC24 or API0PC24 PSUs.]

[Jacques]

For your reference table, mine is a QS 867Mhz.

In my PSU I noticed the resistor with the sleeve next to the one capacitor had actually caused that capacitor to discolour from heat as it had been touching. This is also the one that had bulged the most, surely this is not great design?

[aBc]

Thanks Jacques.
Have updated the reference table and changed your API number too.

And if referring to the same resistor, may note greater signs of heat on mine.
(Red dots on the resistors in the last image above.) R44

Likely result of sporadic power surges due to poor solder joint on mine, over time.
(As opposed instead to close proximity to failed (or failing) nearby capacitor.)
But that’s just my theory. And no… not a great design, all considered.

Having difficulty remembering and locating that exact PSU I recapped, now
over four years ago to determine just what all I did replace to correct it.

Do please keep us posted of your progress. Thanks.

[robespierre]

The large resistor is a 3 W power rated load resistor for the 12 V output. They are part of the design because when there are no hard disks installed, there might not be any consumer of 12 VDC power. The supply needs a minimum load (minimum power consumption) in order to keep the output regulated. So that resistor burns power all the time just to supply the minimum load.
They are typically 50 Ω in value (since P = V^2/R, or (12*12)/50 ≈ 3) and are scorching hot. If you always have 12 VDC consumers attached you can just cut the resistor out. If the PSU is run with no 12 VDC consumer, regulation may fail on the 12 V rail which could damage the fan operating at that voltage.

[aBc]

Thanks @robespierre for the detailed explanation of the R44’s intended role and its scorching hot operational nature.

With the latter in mind perhaps as Jacques intimated, its location and close proximity to that sub-board and especially to C29, with less than adequate heat shielding (if any at all) it could possibly have contributed greatly to the baking, swelling and possible failure of that single capacitor over time. And with that in mind… somewhat a poor design referring to the PSU’s internal layout and lack of heat shielding?




The black rubber / composite(?) shroud noted here above on Jacques’ R44 was nearly 75% degraded (melted away) on mine and perhaps more interesting… is that the PSU continued to function for six months before total failure, after I had supplied supplemental power directly to the PSU fan from an independent outside power source. The fan had stopped working beforehand. Perhaps the damage had already been done.

Also, given the scorching hot nature… also perhaps a contributor to why my R44 seemed to have a loose, poor solder joint? Weakened perhaps over countless working hours and at those scorching temps?

If you always have 12 VDC consumers attached you can just cut the resistor out.

You’re not suggesting that by not having the 12 VDC demand of a conventional hard drive alone present, that this could lead to the eventual failure of R44 and the PSU? Especially when considering all other 12V demands on the PSU (like mobo, other internal 12V components and the case fan, etc.)? Or, just a warning about powering on a PSU outside of the machine, unloaded?

If the former - then perhaps that does not bode well for SSDs, mSATA and/or other likewise “power-adapted” storage media actually requiring less than 12 VDC?

[ssp3]

If you always have 12 VDC consumers attached you can just cut the resistor out.

Don't mess around with original design, unless you know 100% why any particular component is there!!!

First Google hit gives you the correct answer:  https://tinyurl.com/2czp2yff

Typical minimum loads for switching supplies are 10% of the maximum load current and usually one ampere, or less. Some supplies have internal resistors to provide the minimum loading; however, they will only work when the loading is slightly above this internal load.

EDIT. Almost every component inside computer is a variable load. Their current consumption at any given time is unpredictable. Constant loads, such as resistors, are put in there for a reason.

@aBc - iment what I ment.

[robespierre]

The colored stripes indicate a 69 Ω resistor with 5% tolerance. (12*12)/69 ≈ 2.1 W.
Hard drives may not present a load on 12V all of the time; when they sleep by spinning down, they stop drawing power. But case fans operate consistently whenever power is on. It doesn't take too many case fans to add up to 2.1 W.
The stability of regulation can be tested using an instrument called a DC Electronic Load, which would be required to "check out" any modification.
It's also worth pointing out that some computers use the 12V rail to run the CPU, through a "point of load" (POL) buck regulator next to it.