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iMac G5 wont start

JoyBed

macrumors regular
Original poster
Jun 14, 2019
183
154
Hi folks! I finally got something with a G5(I know i wanted a PMG5 Quad, I am still searching for one). Its a iMac G5 this one https://everymac.com/systems/apple/imac/specs/imac_g5_1.8_20.html with 2 gigs of ram installed. The thing is it was for sale as "for parts/repair". When I try to turn it on the light in the down right corner lights up and just the diagnostic LED 1 and 2 are lit up. No backlight, no fans, no sound, no nothing... First thing I noticed are the caps on the boards. Any other idea?

image2.jpeg
image3.jpeg
image1.jpeg
 

sparty411

macrumors 6502a
Nov 13, 2018
508
433
I can see bulging caps in your pictures, like you said. Replace them, then go from there. In my experience, replacing bulging caps solves no boot problems roughly 90% of the time.
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Hi folks! I finally got something with a G5(I know i wanted a PMG5 Quad, I am still searching for one). Its a iMac G5 this one https://everymac.com/systems/apple/imac/specs/imac_g5_1.8_20.html with 2 gigs of ram installed. The thing is it was for sale as "for parts/repair". When I try to turn it on the light in the down right corner lights up and just the diagnostic LED 1 and 2 are lit up. No backlight, no fans, no sound, no nothing... First thing I noticed are the caps on the boards. Any other idea?

View attachment 849646 View attachment 849647 View attachment 849648
 

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JoyBed

macrumors regular
Original poster
Jun 14, 2019
183
154
So far I replaced all the caps in the power supply and these six on the mobo. The error persists. I cant source the other caps in my local shop or in my work. Sorry I forgot to take a picture of the PSU.

988A4FD3-0380-4938-8E2C-3037B69D64A8.jpeg
 
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Eriamjh1138@DAN

macrumors 6502a
Sep 16, 2007
649
487
BFE, MI
You still have some bad caps to the left of the G5 Heat sink in the first pic. Replace all of the caps of any type if a single one of them is bulging.
You can buy caps from mouser.com, digikey.com.
 
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sparty411

macrumors 6502a
Nov 13, 2018
508
433
So far I replaced all the caps in the power supply and these six on the mobo. The error persists. I cant source the other caps in my local shop or in my work. Sorry I forgot to take a picture of the PSU.

View attachment 849719
I counted 13 bulging caps on the main board. I highlighted them in your pic I edited.
 
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JoyBed

macrumors regular
Original poster
Jun 14, 2019
183
154
I counted 13 bulging caps on the main board. I highlighted them in your pic I edited.
Dont worry I see them, but as an electrical engineer I dont trust even the good looking ones that are parallel to the bad ones. So its 18 to replace without the 6 I already replaced.
 
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tigerintank

macrumors regular
Jun 16, 2013
231
25
You can swap the iMac PSU for a standard PC PSU with some pin swaps in the connector. Iirc there's a post on this sub forum somewhere
 
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Eriamjh1138@DAN

macrumors 6502a
Sep 16, 2007
649
487
BFE, MI
JoyBed asked for a pics of my mobo questioning missing caps. It is not uncommon for some components to not be populated in final production.

Here's my 1.8GHz G5 non-iSight mobo. It's never been recapped. Either it hasn't been used much or I got lucky.

G5momo.jpg
 
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JoyBed

macrumors regular
Original poster
Jun 14, 2019
183
154
JoyBed asked for a pics of my mobo questioning missing caps. It is not uncommon for some components to not be populated in final production.

Here's my 1.8GHz G5 non-iSight mobo. It's never been recapped. Either it hasn't been used much or I got lucky.

View attachment 850232
Thanks for this photo! I am missing some resistors and two transistors... Now just to kill myself. I can ask for you to measure the the resistors for me but you cant just slap any transistor there. I want to cry.
 
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rslanna

macrumors newbie
Mar 23, 2020
2
0
it is a little bit dumb question but... have u tried to test the RAM modules? i had a G5 17'' here with same problem as you and even after recapping it won't work at all.
i solved replacing the ram modules
 
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Alexis Trinquet

macrumors member
Mar 1, 2020
64
62
Gouvieux, France
IIRC the diagnostic LED 1 lights up whenever there is a trickle voltage from the PSU has been detected, the 2nd LED lights up normally when the computer is turned on and that the PSU is powering the board.

Now if LED2 is on but the compter does not fire up... Seems like the fault is in the logic board somewhere.
 
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JoyBed

macrumors regular
Original poster
Jun 14, 2019
183
154
IIRC the diagnostic LED 1 lights up whenever there is a trickle voltage from the PSU has been detected, the 2nd LED lights up normally when the computer is turned on and that the PSU is powering the board.

Now if LED2 is on but the compter does not fire up... Seems like the fault is in the logic board somewhere.
Then it’s the missing resistors and transistors. The pads look like someone took them off. IDK why...
 
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JoyBed

macrumors regular
Original poster
Jun 14, 2019
183
154
JoyBed asked for a pics of my mobo questioning missing caps. It is not uncommon for some components to not be populated in final production.

Here's my 1.8GHz G5 non-iSight mobo. It's never been recapped. Either it hasn't been used much or I got lucky.

View attachment 850232
Thank for the photos. it helped me a lot in searching what components are missing. There was like 20 resistors,2 caps, 2 coils, 1 transistor and 1 diode missing. Can you please make a picture of the whole board from both sides? In good resolution so I can compare it to my board. But still it doesnt boot. Power light is on, diag led 1 and 2 are on. but no fans turning, no backlight, no chime. After a while powered like this led 4 light up so it starts to overheat without the fans. Either there are some more missing components or the GPU is dead and I need to replace it. Did someone tried just swapping the PPC970 for 970FX ? Also I noticed the unpopulated sata connector that is marked as DEV. In schematics of the board between the DEV sata connector and the chip that controlling the sata there are just 4 ac decoupling caps. I am curious to see what happens if i solder on the caps and the connector and plug a drive in there.
 
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