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).