iMac G3 DV SE recapping

[didius]

After recapping my powerbook adapter and nearly finishing recapping a Powermac G4 PSU and a macintosh plus board I started a bigger project.

My iMac G3 died recently, when I pressed the powerbutton nothing happend. A bit of researched pointed me to the DCB and the PAV.

I've started performing the surgery. I really hate opening iMac G3's, and getting to the PAV board was quite complicated. But taking my time I got there. Since I didn't find much information about recapping these boards I intend to share the information here.

Here's PAV board, dusty!



And the much cleaner DCB board.



The DCB board looks allright, but that big cap on the PAV board (is it a cap?) looks bad...

What do you think?

 

[uniserver]

It's funny I took apart a IIcx power supply last night, the caps on the LV secondary side were gone, but hadn't expanded or leaked yet.

dust can cause issues. Dust + Moisture = good enough short.

 

[bibilit]

As far as i know DCB board is always OK (never seen one bad) unfortunately PAV board is the culprit usually.

I have collected 5 Imac G3's so far ... and 3 of them were gone.

You cant test the logic board (the service manual is really well done here)

When you wrote nothing... is nothing at all (no Led...) ?

The FBT is probably bad... but i don't know if a substitute is available.

 

[Byrd]

As bibilit notes, I'd be investigating the flyback transformer before the caps on a CRT iMac - the most common cause of failure.

 

[MacJunky]

Every slot loading iMac I can ever remember seeing has a massive capacitor that looks like it is bulging on the PAV. They are all slightly different bulges and sometimes different brands but every one of them certainly does not have a flat top. I never looked for these ones when the machines were new, but even a unit with very light use has a large bulging capacitor on the PAV.

 

[bibilit]

Unfortunately, all Imac G3's will suffer sooner or later of FBT failure (probably not the early tray loading ones... those have a fan to cool things down)

IIRC if the FBT is not working, you will not get any sign of life from the Imac.

Anybody has found new FBT somewhere ?

 

[didius]

Alright, repair is done!

I guess the flyback was still working. However, it wouldn't make any sense that if the flyback would be broken there wouldn't be any sign of life. Not even the power button led pulsing...

This block diagram can be found in the manual. The motheboard is getting its power through the Video neck board, the flyback doesn't seem involved.

Anyhow, here's more on the repair.

This is a list of the caps in the machine (and the ESR and capitance values I measured)

C936: 6,3V 330uF Samyoung KMG (105°C) 6x11 | measured: 303,7uF 1,40 Ohm
C939: 10V 1000uF Samyoung KMG (105°C) 10x12 | measured: 977,0uF 0,50 Ohm
C940: 10V 1000uF Samyoung KMG (105°C) 10x12 | measured: 926,8uF 0,50 Ohm
C722: 16V 47uF Samyoung SMS (85°C) 5x10 | measured: 41,8uF 1,42 Ohm
C947: 16V 47uF Samyoung SMS (85°C) 5x10 | measured: 38,5uF 1,26 Ohm
C713: 16V 100uF Samyoung SMS (85°C) 6x10 | measured: 91,3uF 0,82 Ohm
C948: 16V 100uF Samyoung SMS (85°C) 6x10 | measured: 94,8uF 0,62 Ohm
C938: 16V 470uF SAMWHA (105°C) 8x11 | measured: 454,5uF 0,20 Ohm
C951: 16V 470uF SAMWHA (105°C) 8x11 | measured: 430,2uF 0,20 Ohm
C602: 16V 1000uF Samyoung SHL (85°C) 10x16 | measured: 890,6uF 0,10 Ohm
C604: 16V 1000uF Samyoung SHL (85°C) 10x16 | measured: 939,2uF 0,10 Ohm
C941: 16V 1000uF Samyoung KMG (105°C) 10x16 | measured: 993,3uF 0,23 Ohm
C922: 25V 33uF Samyoung SMS (85°C) 5x10 | measured: 26,9uF 1,94 Ohm
C937: 25V 33uF Samyoung SMS (85°C) 5x10 | measured: 24,3uF 1,76 Ohm
C906: 25V 47uF Samyoung KMG (105°C) 5x10 | measured: 10,9uF 3,40 Ohm
C934: 25V 1000uF Samyoung KMG (105°C) 10x20 | measured: 948,4uF 0,17 Ohm
C935: 25V 1000uF Samyoung KMG (105°C) 10x20 | measured: 948,4uF 0,32 Ohm
C710: 50V 1uF Samyoung SMS (85°C) 5x10 | measured: 0,9uF 10,70 Ohm
C916: 50V 1uF Samyoung SMS (85°C) 5x10 | measured: 0,9uF 2,60 Ohm
C945: 50V 1uF Samyoung SMS (85°C) 5x10 | measured: 0,8uF 2,60 Ohm
C520: 50V 10uF Samyoung SMS (85°C) 5x10 | measured: 9,1uF 1,08 Ohm
C981: 50V 10uF Samyoung SMS (85°C) 5x10 | measured: 9,2uF 1,23 Ohm
C946: 50V 4,7uF SAMWHA (85°C) 5x10 | measured: 4,3uF 1,03 Ohm
C918: 63V 47uF Samyoung KMG (105°C) 6x12 | measured: 44,7uF 2,60 Ohm
C603: 63V 220uF Samyoung SMS (85°C) 10x20 | measured: 203,8uF 0,10 Ohm
C724: 100V 10uF Samyoung SMS (85°C) 6x10 | measured: 10,1uF 0,58 Ohm
C719: 100V 22uF SAMWHA (85°C) 12x25 | measured: 21,7uF 0,12 Ohm
C949: 100V 100uF Samyoung KMG (105°C) 10x20 | measured: 94,8uF 0,20 Ohm
C950: 100V 100uF Samyoung KMG (105°C) 10x20 | measured: 96,9uF 0,22 Ohm
C933: 200V 22uF Samyoung KMG (105°C) 10x15 | measured: 21,0uF 2,20 Ohm
C723: 200V 33uF Samyoung SHL (85°C) 10x20 | measured: 32,1uF 1,44 Ohm
C726: 200V 33uF Samyoung SHL (85°C) 10x20 | measured: 30,9uF 1,33 Ohm
C932: 200V 47uF Samyoung KMG (105°C) 12x20 | measured: 46,1uF 1,06 Ohm
C905: 400WV 470uF Chemi-Con (105°C) 30x60 | measured: 434,1uF 0,08 Ohm

Some caps, like the C710 seem to have strange readings. The big cap 905 was bulging. I decide to replace all of them, preventing the need to take the machine apart a second time.

I replaced all of the caps with 105°C ratings and low ESR if possible. I replaced some caps with higher values (because my local supplier didn't had them in stock)

C722 & C947: 16V 47uF replaced with 16V 100uF
C922 & C937: 25V 33uF replaced with 25V 47uF
C933: 200V 22uF replaced with 200V 27uF
C723 & C726: 200V 33uF replaced with 200V 47uF

Besides that I also replaced two resistors who looked burned and had lower readings than they should.

R957: should be 5,6kOhm but reading was only 3,3kOhm
R971: should be 100kOhm but reading was only 80kOhm

This is what the board looked like afterwards, loaded with nice and shiny new caps!



Before assembling the whole thing again, i decided to check voltage readings from the video neck board. Here are the results.

I didn't replace the caps on the Down Converter board because those caps still looked brand new. After connecting everything and cleaning all the dust trying it resulted in the happy mac sound and a smooth boot. I'm happy this one is saved!

 

[Macdrone]

Congrats great job. If you nee any parts let me know.

 

[bibilit]

great job

 

[CC_333]

I have an eMac I should have recapped this way.

It gets enough power to turn on, spin up any drives and the fan, and a partial chime before it goes dead and just sits there.

It will work perfectly fine if it gets put in a 110ºF room, or after sitting in it's 3/4 lifeless state for about 15-30 mins, which makes me think that perhaps some capacitors are bad (or almost bad).

Sorry for hijacking, and great job!

c

 

[techknight]

No wonder these CRT imac displays are crap. They are made by goldstar. lol. Well, LG.

 

[Hans]

Thanks Didius! You made my day. I had mine open today, with the very same board and problem.

I cleaned it and put it back together. No luck.

I gave up, then read your post. So I think about recapping it now.

My question: My trickle power is down to about 1.5 V instead of 5V. Can this big difference still be "just" a cap problem?

And:You wrote, that you checked the voltage at the video connector. Can one just plug the disassembled board in without any problem? (Well, respecting essential security rules. )

Thank you. Nice to know that there are more people out there, not giving up on their "old" electronics.

 

[Hans]

Sei'S drum.  Ich sitz gerade am Recapping des G3.

Kann mir jemand sagen, wie es zu diesem Größenunterschied der Caps kommt? Hab ich was Falsches geordert?

Kann ich den großen Brummer durch den kleinen ersetzen? :O

 

[Hans]

Hehe,

sorry for the german.

The question is. Can I replace the big with the small one? Did I order wrongly? Wonder wonder wonder

 

[Compgeke]

Yes you can, just make sure polarity is correct. Capacitors have progressed a lot over the years leading to smaller needed sizes for the same value.

 

[CC_333]

sorry for the german.

So that's what it is! German is your native language, I assume?

c

 

[philgood]

Hi there.

There are flyback transformers available still.

I'm in Spain and i found a company from Barcelona.

I already changed it and my iMac is working now again.

www.efiter.com and the model number for my Flyback was HR 46177

My iMac is the 1999 model called iMac G3 DV 400Mhz with Firewire and using the LG screen.

I think that matters as there were two different screen at least for my model.

Now to the reason i signed up here:

The mac is working again but i'm missing Firewire...

I don't know what happened but i tried hard to get any signs of life.

Did a PRAM reset, a NVRAM reset through OpenFirmware and a PMU reset (the little reset button on the motherboard) but the Firewire ports seems dead.

I found the Datasheet from the Firewire chip from the now defunct company called Lucent but i don't have much clue about what to check.

I think i should try to measure if the chip is getting power at least but i think without a schematic of the whole board it will be difficult to do a repair.

I'm only a electronics amateur and could need some guidance and/or schematics of the motherboard.

I attached the Datasheet of the Firewire chip!

View attachment DSAIH0008570.pdf