Resolved iMac G3 DV 400Mhz from 1999 FIREWIRE doesn't work

[philgxxd]

Hi there.

I recently repaired my little iMac changing the Flyback transformer and a little Potentiometer which is for adjusting the B+ voltage for it.
I'm by no means an expert, just an amateur electronics guy.

I got the hint from a german technician and would recommend everyone to try just replacing this potentiometer for some more robust CERMET type.

Here is the Post for anyone interested: https://www.macuser.de/threads/imac-dv400-crt-problem.110173/

So the mac works again but now it's missing working Firewire ports!

First i thought that maybe it only needs a PRAM reset...a NVRAM reset...PMU reset...Cable?...Nothing!

I can't find a schematic for my iMac G3 but i found the Datasheet for the Firewire chip. I will attach it also here for references.

Maybe someone could guide me through what i could check for or provide a schematic for the motherboard.

Thanks a lot!

 

[MacTech68]

First things, first. Check in System Profiler that you can see a Firewire port. What does it say?

Secondly, how are you 'testing' the Firewire port?

And thirdly, if you've accidentally plugged the firewire cable in upside-down, then the port on the Mac and/or the external device may be fried. It happens, and one of the tell-tale signs is the "narrow" end of the connector's outer metal shell is slightly separated.

Thus:

Pics may also help.

LATE EDIT:

If you DO have a 1999 version of the iMac DV, you may have the original version of the logic board that requires a daughter board for FireWire. This daughterboard contains the Firewire controller TSB12LV23, but still requires the PHY on the main Logic Board.

 

[philgxxd]

Hi @MacTech68 !
Thanks for your attention and detailed response.

Thats a great hint to look for (that bented outer metall shell) and while of low probability that i did this...you never know...as i only work on these things during the night while the kids are sleeping but i will look for.

In the system profiler (i have OS9 installed by the way) it's showing the Firewire BUS but it never gets anything recognized when i plug something in.
So far i tried an external Harddrive enclosure with Firewire (which is working on my Powermac) and a IDE-Firewire bridge from Granite Digital which also works on the other mac.
Furthermore an external LG Dvd burner which is in a firewire enclosure also.

Now it gets quite interesting because i totally overlooked and wasn't aware of the pickyback firewire-board you are mentioning which i'm sure it's actually on my motherboard!
I will have to look this night.
Do you think it could eventually only be a loose connection?
Should i lift off the daughterboard and do an visual inspection ?

 

[MacTech68]

Definitely unplug the board, have a look and re-seat it (plug it back in). You may need to squeeze a nylon peg or two to release it.

It's just possible it's worked loose. (do check for any gouge marks too - just in case).

These daughter boards are not present on later motherboards.

 

[philgxxd]

Wow...reseating did the trick!

Thanks a lot again for your help @MacTech68!

 

[MacTech68]

Glad I could help!

I should also give out a reminder/WARNING that early Slot Loading iMacs should have their firmware upgraded BEFORE you even so much as BOOT from a MacOS X installation. Specifically 10.2 or later.

This occurs even by booting 10.2 Install Disc 1 CD !!

As Apple points out in a now deleted Tech Article:

https://web.archive.org/web/20150723181340/https://support.apple.com/de-de/HT2377

This must be done to avoid severe corruption of the video settings, which can cause the machine to power on but shut-off a few seconds later when it attempts to power on the video/analog circuitry.

This can be extremely difficult to rectify especially if you then decide to zap the PRAM - usually a normal procedure, but a much worse disaster if you do so in this situation.

The firmware update can only be applied when booted from MacOS 9.1 up to 9.2.2 ONLY.

It's still on Apple's downloads site:

https://support.apple.com/kb/DL1283?locale=en_US&viewlocale=en_US

There is only one potential issue with this firmware - it's more strict on RAM module compliance.