Stumped this weird G4 power supply problem

[JOHNBOY]

Hi Folks. I'm trying to diagnose and repair a G4 MDD power supply problem. I checked the other thread here and my problem is totally different from the guy's who keeps on blowing his fuse.

My power supply will not start in the system but if I remove it and short the green and black the fans will spin up for a second. So it is not the same problem as the one that blows as soon as you replace the fuse and power it on, this one is actually the model without the glass fuse.

But here is the funny thing, if I take the paper clip and touch it on and voff really fast, like revving a motorcycle higher and higher, I can get it to start up. I have to do a wroom wroom with the paper clip about 10 times as the fans get faster and faster and eventually if I leave the clip on it remains on forever and works fine, however if I touch the pin once or twice and leave it on it does nothing.

Any idea on where to begin with this. I've done many board level repairs but I don't know where to start with this, I think its a simple problem with the switching part of the supply.

Thanks
JB

[seanc]

Re: Stumped this weird G4 power supply problem

What capacitors does this have - capxon? Tested any of them?

[JOHNBOY]

Re: Stumped this weird G4 power supply problem

I don't really know how to test for a bad cap. I have always done my cap tests by seeing if they bulge or leak.

It doesn't look like capxon, the big ones say SHOEI

[seanc]

Re: Stumped this weird G4 power supply problem

You'd need to remove them from the power supply and use an ESR meter.

Have you measured voltages at all?
What's on the 5VSB line?

[Toasty]

Re: Stumped this weird G4 power supply problem

Photos of internals?
Model (Apple P/N) and Manufacturer (Samsung, ACBel, Delta)?

Sounds like the 5vsb start-up is not working. Probably a 10 to 50uF/35 to 50v cap or two.

[JOHNBOY]

Re: Stumped this weird G4 power supply problem

I'll check out the 5V now.

The model is a ACBEL API1C36 400w

No components on the bottom

[JOHNBOY]

Re: Stumped this weird G4 power supply problem

The pics

[Scenic]

Re: Stumped this weird G4 power supply problem

looks like a bulging cap on the last pic (the topmost one)
plus the other caps look like teapos.. :|

[Toasty]

Re: Stumped this weird G4 power supply problem

Replace all "vent" style caps on the mainboard under the heatsink with the 2 slots. They are a mix-n-match of failures from unit to unit. 11 pieces total.

There is also a small cap at the end of that heat sink just before the optos that fails. C43 - 100uF @ 25v

BTW - The other thread is a Samsung unit. Very different beasty.

Toast

[JOHNBOY]

Re: Stumped this weird G4 power supply problem

Still trying to find some parts. The caps on these are small and narrow and I've exhausted all my local stores. I'm now on to ordering online, I just realized this site sells the caps. I need the last 3 which I couldn't get locally, 1000@10v 8mm , 2700@6.3v 10mm and 680@35v 10mm. I'll take 4 of each.

[JOHNBOY]

Re: Stumped this weird G4 power supply problem

Still trying to find some parts. The caps on these are small and narrow and I've exhausted all my local stores. I'm now on to ordering online, I just realized this site sells the caps. I need the last 3 which I couldn't get locally, 1000@10v 8mm , 2700@6.3v 10mm and 680@35v 10mm. I'll take 4 of each.

[JOHNBOY]

Re: Stumped this weird G4 power supply problem

Now I have even a bigger problem. I replaced most of the caps. Now when I turn it on I hear about 5 clicks a second. It just goes click click click and the fans barely move. I probed the lines and most of them are 4.25 .. I put my finger on the fans to stop them and eliminate that as the clicking and the power supply was still clicking. I can't isolate the part that is clicking because I'm tired of getting shocked. Any ideas. could it be the 1000uf 10V cap, that is the one I didn't replace and a couple of others. None of the local stores have these long narrow caps.

[Toasty]

Re: Stumped this weird G4 power supply problem

Replace C43?

Load it up. Needs it to run/start.

[JOHNBOY]

Re: Stumped this weird G4 power supply problem

I'll check it out.. As long as it isn't uner the heatsink. I don't think I can desolder all that, my hakko died and I'm using a $9.99 soldering iron.

[JOHNBOY]

Re: Stumped this weird G4 power supply problem

Interesting now it doesn't start. The same little click is only heard once, when I jump the power supply, but only 1 fan spins for a second and then it cuts out. The C43 was brand new in a bag so I know its good.

I guess I have to replace those last 3-4 caps

[cyclones]

Re: Stumped this weird G4 power supply problem

Yes replace them.

[Toasty]

Re: Stumped this weird G4 power supply problem

Are you loading the power supply as I mentioned?

[JOHNBOY]

Re: Stumped this weird G4 power supply problem

Are you loading the power supply as I mentioned?

I'm not sure what you mean by that .. I'm starting it by shorting out the green and black wires. What is loading ?

[Toasty]

Re: Stumped this weird G4 power supply problem

Hard drives, fans, motherboard, etc. These PSU's (typically) will not run unless they have sufficient loads on each output.

[JOHNBOY]

Re: Stumped this weird G4 power supply problem

I don't have anything plugged in the power supply. I have always turned on the good ones with the shorting method.

It gives the same result when I do it through the motherboard so I'm sure the problem isn't with how I start it.