AcBel PowerMac G4 PSU

[Scenic]

i just got the innards of a Powermac G4 Gigabit Ethernet (400MHz) yesterday.
board + cpu + PSU..

a friend of mine bought a defective Powermac G4 on ebay because he wanted the case for modding reasons (build a x86 PC into it).
i then bought the "rest" of it for a few bucks..

the PSU is a failure prone AcBel API-9841-291 Rev. B made in 2000.
there's no wattage written on the label for some reason.. (searching on the net it turned out to be a 338 (?) watt unit)

reason i'd like to fix this one: it's a non-standard PSU for those macs :/
instead of a 5V standby line this one has a whopping 28V standby (which is also used to power the firewire devices and Apple displays via ADC (through the gfx card with a propritary connector) when powered up.

well.. that 28V standby line is completely dead. 0V.
so you cant turn the PC on even if all other lines would be OK (dunno if they are).

first thing i noticed when i opened it up is a resistor that got *really* hot
managed to damage the trace on the solder side and wasn't connected to it anymore..
i checked that resistor and it seems to be ok, so i rewired the trace and put the resistor more close to the fan, so it should run a lot cooler...

however.. that alone didn't fix it. still no go at all..
fuse is OK and it seems to get the input voltage (at least it gets to the primary caps).

a pic of that resistor (before i did anything to that PSU)




unfortunately i can't take pics ATM (battery of my cam is empty..)

has anyone of you guys already fixed one of those...!?

getting a replacement is not an option, as they want 100€ ( = about 133USD) for a repair or a repaired PSU... i could get a whole (working!) powermac G4 for that price WTF :O

[KeriJane]

Re: AcBel PowerMac G4 PSU

Hi Scenic.

Eek! a 28v standby?

All I can suggest is to see if you can't find the Mac service manuals.

Here's one I found..... it basically says if you have no 28v trickle that you're out of luck. But the Pinout is nice.
http://docs.info.apple.com/article.html?artnum=95064

Maybe you could follow the 28v trickle trace and see where it ends up?

Feeling lucky that my G5 uses a 5v trickle and it only has a 24V circuit for the display.

Have Fun,
Keri

[Scenic]

Re: AcBel PowerMac G4 PSU

yep.. 28V ..



ATM i'm rewiring a standard ATX PSU for this thingy to test if the logic board still works.. (if not i don't need to fix that PSU..)

http://www.atxg4.com/gige-da.html

just got some diodes out of that "520W" gutless wonder (psu pic thread)... lol

[Krankshaft]

Re: AcBel PowerMac G4 PSU

You will have to first find the standby switching transistor check to see if there is voltage at the source pin. If so power the PSU down and check to make sure that the switching FET isn't shorted.

If it's not trace back from it's gate pin to the standby PWM it can either be an IC, set of discrete components, or a TOP IC. Which is my personal favorite PWM and FET all in one .

The PSU can't power up without the voltage from the standby. You could probably inject an external voltage into it to try to get the main supply to turn over but that would probably do more harm than good.

Be careful when working on the primary (non isolated) side with it plugged in this is where I'm glad that I use an isolation transformer now .

[Scenic]

Re: AcBel PowerMac G4 PSU

okay.. i rewired an old 250W ATX PSU for use on that thing.
after 15minutes of being puzzled where the hell the 2 pins for the power button are it turned on and made the apple gong thingy, so i assume it's ok..

what i didn't think about: this thing has AGP. however.. you need special mac-compatible cards (or mainly a mac compatible bios on that card) for it to show up something...

i tried reflashing a GeForce 4MX 440 AGP with a mac bios ( http://themacelite.wikidot.com/wikidownloads2 ) and it sort of worked.. but the picture is scrambled (like a gfx card with bad memory chips)..

guess its a timing problem in that mac gfx card bios because my card differs from the reference layout..

anyways.. i'm gonna try to check that acbel PSU later on..

[KeriJane]

Re: AcBel PowerMac G4 PSU

Hi Scenic

Trying to get a PC videocard to work in a Mac can be a real trick. At first the firmware was different, but now Mac cards have a whole different ROM chip.

I feel that "older is better" in your quest for Mac video. That old GeForce is probably your best bet. Or something like it.

Here's another ROM page if you haven't been there already..
http://xenomorph.net/?page_id=575

Also, try to see what happens after boot- either into a hard drive or an installation CD. On the newer cards, part of that different ROM chip is merely for the Pre Boot environment and post-boot works OK from drivers.

Want to have a giggle?
Rent the WALL-E movie.... You'll hear the Apple Startup Chime no fewer than Three times!

Have Fun!
Keri
PS. My favorite WALL-E character-
E.V.E. (Extra-terrestrial Vegetation Evaluator)

[Scenic]

Re: AcBel PowerMac G4 PSU

problem solved already...

for some reason, a noname (?) GF2 MX400 AGP card (marked "MVGA-NVG11AM(400) 64MB" .. sort-of low profile with s-video out) works fine without reflashing it at all...

so this card works in PCs and macs without flashing it.. yay

i took the HDD out of my old half-dead iMac G3 233 and it booted OS X 10.2.8 just fine..

now i'm not quite sure why i should fix the original PSU.. as it works fine with the reworked ATX PSU.. lol

just bought a Powermac G4 case on ebay for 10€ (= about 13USD) because it would be a PITA to mount it into a standard ATX case (not even a single mounting hole fits the ATX ones..)
has a dead board in it (random freezing) and the PSU fan is rattling really bad.. (no optical drives, no RAM, no HDD, no gfx card, but case is in good condition)

maybe its just the same dumb AcBel PSU thats just about to die (flaky voltages, causing the freezes..)

if so, i've got a spare board + cpu and a PSU to compare parts between my already dead one..

i've been a little bit busy over the last days.. so i haven't had the time to play around with that AcBel PSU yet.. maybe i'll have some time on this weekend..

[Escort Eagle]

Re: AcBel PowerMac G4 PSU

Hi, Badcaps Forum .