Macintosh IIfx repair

[HomeLate]

Hi all,

Looking for help narrowing down an issue on a recapped Mac IIfx. Long story short, I think IOP A may be dead, but I'd like a sanity check from people with more knowledge before I go further.

Background:

• Board was fully recapped (electrolytic → presumably new electrolytics, not tantalum)
• After the recap, it booted successfully into Mac OS and was usable
• Sound did not work after the recap (never confirmed working post-recap) but sound worked through the headphone jack
• Next boot: hung partway through startup
• Boot after that: degraded to a uniform static screen
• All recap joints have since been reflowed — no change

Current symptoms (bare-bones config — SCSI and floppy removed, NuBus video card only):

• Single chime on power-on (confirmed via headphone jack), no second chime, nothing further
• Steady black/white raster pattern
• ADB completely dead: caps-lock LED does not respond to keypress
• PRAM reset (Cmd+Opt+P+R) has no effect
• This exact video card has previously booted fully to Finder in this exact machine

Questions:

1. Is "chime fires, ADB completely dead, PRAM reset dead, hangs before video" a known/recognized IOP A failure signature on the IIfx?
2. For anyone with the schematics (or @TheRealBolle's recreation) open — which net/rail feeds IOP A's local supply, clock, or reset line, so I can probe it directly?
3. Is IOP A failure something that's been seen as repairable/socketed, or is this generally a "find a working donor board" situation?

Happy to provide more diagnostic data (voltage readings, etc.) if someone can point me to what to check.


Thanks!

 

[Phipli]

Long story short, I think IOP A may be dead, but I'd like a sanity check from people with more knowledge before I go further.

So, generally, 99.9% of the time, it is a bad or marginal trace or dry joint somewhere, or PSU issues.

Chips actually fail very infrequently. Often when people repair something by replacing a chip it is really that they have cleaned and resolder as part of putting it in. There are a few exceptions like if there has been a serious issue (lightning) and some components that are known to be unreliable.

 

[David Cook]

The IIfx's memory sockets are very fussy. Pull bank B. Then reseat bank A. If that doesn't work, try it a few more times and swap memory SIMMs. I swear if RAM in bank A does not pass you do not get the chimes of death. It simply does what you experience (power on chime and then nothing).

 

[Durosity]

Chips actually fail very infrequently. Often when people repair something by replacing a chip it is really that they have cleaned and resolder as part of putting it in.

This is why I like swapping chips between boards, with one being a known working one.. then you can test if the original problem suddenly plagues the previously working system.. it is more work of course.

 

[David Cook]

Chips actually fail very infrequently.

I agree. For all the Macs I've repaired, I have only experienced two types of chip failure:
1. Chips immersed in capacitor goo. There are sections on the SE/30 and IIci that routinely damage the nearby jelly bean chips.
2. Anything on the Macintosh Portable -- due to a bad power design.

Board was fully recapped

@HomeLate There are two types of IIfx boards: Those with only two surface-mount electrolytics (C9 and C24), and those with many surface mount electrolytics. Not counting the large axial electolytics, how many does your board have? That will help us determine where the damage is.

Also, seriously, check the RAM sockets for corrosion.

See my post here:

New tool to remove capacitor and rust corrosion - the dental scaler!

I purchased a IIfx that appeared to be in great shape. No battery leaks. Light capacitor leakage (no damaged traces). I recapped it and cleaned it with an ultrasonic cleaner. With the original memory in Bank A and Bank B, I would get sad mac chimes. In Bank A only, it would chime but not...

tinkerdifferent.com

"it would chime but not activate the NuBus video card or continue to boot"

 

[HomeLate]

@David Cook It's the one with many elektrolytisch unfortunately. I already found some corroded traces near the simm sockets, near C24. My plan is to remove the corrosion and repair if necessary. If that isn't sufficient, I'll remove the simm sockets and check for corrosion. I already removed the simms in bank B and swapped the simms in bank A but the issue remained.
I'll be also checking the area near the ADB ports as the keyboard does not work. Caps-lock does nothing and the PRAM reset procedure also doesn't work.

 

[adespoton]

I agree. For all the Macs I've repaired, I have only experienced two types of chip failure:
1. Chips immersed in capacitor goo. There are sections on the SE/30 and IIci that routinely damage the nearby jelly bean chips.
2. Anything on the Macintosh Portable -- due to a bad power design.

I've got another:
3. Chips that are physically cracked or have damaged pins by rough handling during re-pasting.

I've seen a few of these over the years.