iMAC G5 PSU (again.. sigh)!

[JEWilson]

Manu - AcBel
http://www.acbel.com.tw/eng
Model - API4PC46
Apple P/N - 614-0326

System unit stuck on LED1
Will not start
Removed PSU, recapped
Tested PSU out of unit post recap

On standby
1 : +0.028 VDC (Black)
2 : +0.028 VDC (Black)
3 : +0.000 VDC (Black)
4 : +0.009 VDC (Grey/Purple)
5 : +0.000 VDC (Black)
6 : +0.009 VDC (Grey/Purple)
7 : +0.000 VDC (Black)
8 : +0.000/1 VDC PG (Blue) - swings between these two values
9 : +5.196 VDC 5VSB (Purple)
10 : +0.025 VDC (Brown)
11 : +0.000 VDC (Black)
12 : +0.028 VDC (Black)
13 : +0.025 VDC (Brown)
14 : +0.000 VDC (Black)
15 : +5.196 VDC On/Off (Grey)
16 : +0.000 VDC (Black)
17 : +0.000 VDC (Black)
18 : +0.000 VDC (Black)
19 : +0.025 VDC (Brown)
20 : +0.009 VDC (Grey/Purple)
21 : +0.009 VDC (Grey/Purple)
22 : +20.42 VDC (Brown)

Jumpered 15-16
1 : +3.332 VDC (Black), ripple 4.7mV VAC
2 : +3.332 VDC (Black), ripple 4.7mV VAC
3 : +0.000 VDC (Black)
4 : +5.145 VDC (Grey/Purple), ripple 36.8mV VAC
5 : +0.000 VDC (Black)
6 : +5.145 VDC (Grey/Purple), ripple 36.9mV VAC
7 : +0.000 VDC (Black)
8 : +0.079 VDC PG (Blue), ripple 3.5mV VAC
9 : +5.196 VDC 5VSB (Purple), ripple 3.8mV VAC
10 : +11.970 VDC (Brown), ripple 149.9mV VAC
11 : +0.000 VDC (Black)
12 : +3.332 VDC (Black), ripple 4.5mV VAC
13 : +11.970 VDC (Brown), ripple 3.5mV VAC
14 : +0.000 VDC (Black)
15 : +0.000 VDC On/Off (Grey), ripple 3.5mV VAC
16 : +0.000 VDC (Black)
17 : +0.000 VDC (Black)
18 : +0.000 VDC (Black)
19 : +11.970 VDC (Brown), ripple 98.3mV VAC
20 : +5.135 VDC (Grey/Purple), ripple 32.6mV VAC
21 : +5.135 VDC (Grey/Purple), ripple 32.8mV VAC
22 : +23.530 VDC (Brown), ripple 270mV VAC

Is PG 8 correct for this type of PSU?
Anyway, put PSU back in the unit.
Same problem, still only LED.
Unit logic board has 1 domed 6.3V 1800uF Nichicon on the VRM O/P.
Took the PSU out again.
Now cannot get the PSU (15-16) to start again.
Odd...

Suggestions...
Q1 on the PSU? Why would it just let go?
Are there TopSwitches in these?
Advice appreciated.

Thx

[Toasty]

Re: iMAC G5 PSU (again.. sigh)!

Have to fix the mainboard. That's the problem. All those Nichi's have to go. TC sells a kit, I think.

Reduce the reports down to the basics. Every wire is not necessary.

Look at the board and see what goes where.

Essentially, you have 5vsb, 24vsb, ground(blacks), +3.3, +5, +12.

If 5vsb is up, then you have 1/2 the battle solved.

Topswitch is a -VERY RARE- failure. (how's that for a subtle hint)

If 5vsb is there, the TOP is fine.

Check Q1 and ZD6. What is the SB voltage @ Q1 collector?

Have you recapped the unit, especially the 4 next to the mains caps?

Search the forums for these either by 4PC46 or API4PC46.


T

[JEWilson]

Re: iMAC G5 PSU (again.. sigh)!

Y - recapped the PSU
All of them except the main large can lytics for the primary and PFC
Someone had been there before me - did part of the job

Funny, post recap
Got the unit to start (with 15-16 jumpered)
Now it won't - very odd....
So will check Q1 and ZD6 - thx

Does the earth tag in the PSU need attachment to the PSU case?
It was not with this PSU

Will get the PSU right before the logic board recap

Will check the posts as recommended

[Toasty]

Re: iMAC G5 PSU (again.. sigh)!

>> Does the earth tag in the PSU need attachment to the PSU case? <<

Not sure what you mean by that question.
If you mean the ground wire coming from the socket, then yes. Once the board is installed back in the case, that wire goes to the PSU case on the nearby tab.

Your voltages all look(ed) good.

Need that collector voltage on Q1 at standby. ~16v

Make sure you're measuring from the HOT side (-)

T

[JEWilson]

Re: iMAC G5 PSU (again.. sigh)!

Update

This unit had a bad Q1
I replaced D2 and ZD6 anyway
Replaced Q1 with a 350mW part

Seems to be ok again

Now... load testing
Any thoughts on using an ATX go/no go PSU tester
with the cables mapped to the Apple PSU?

Ok... before people start saying no; this is just for
future use with these PSU, before, that is,
I get my hands dirty

How would you handle 24V on an ATX tester

[Toasty]

Re: iMAC G5 PSU (again.. sigh)!

Parts used? Numbers? Supplier?

You could rewire the connector I'm sure. Or make up a "patch" one to use it on either. Grab the male connector from an old mobo and the female from a trash PSU and wire it for the Apples.

The 24v would be a matter of a resistor or Zener with a LED or 2. Remember that on some of these, the 24v line doesn't come up full until the unit is running. It sits around 19-20v in standby.

T

[JEWilson]

Re: iMAC G5 PSU (again.. sigh)!

Ok

Zener ZD6 - NXP BZV55-B16,115, Mouser P/N - 771-BZV55-B16115
Diode D2 - Fairchild FDLL4148_D87Z, Mouser P/N - 512-FDLL4148D87Z
Transistor Q1 - Fairchild MMBT2222A, Mouser P/N - 512-MMBT2222A

Thx

[Toasty]

Re: iMAC G5 PSU (again.. sigh)!

Have you been using that Zener with success?

T

[JEWilson]

Re: iMAC G5 PSU (again.. sigh)!

Well....

This is the first time I have used this part
So.. we will see if it does the trick
Will do load testing and see how this plays out

Have another of the same PSU model (and got a working delta)
What would you typically use for ZD6?

[Toasty]

Re: iMAC G5 PSU (again.. sigh)!

I was curious as to how you arrived at a 16v zener. Did you test a good part or go by the color coding?

T

[JEWilson]

Re: iMAC G5 PSU (again.. sigh)!

No code

No Test

Took your word for it (found it in the forum)

Thx