Ongoing IIfx Saga

[nathall]

Spent some more time trying to troubleshoot the elusive IIfx death chime issue.

I found a broken trace next to R4 that disappears underneath it and then disappears under whatever that black cubicle component is. Anyone know what this connects to, and how? Both the aforementioned components have multiple connection points and if it connects them, it is not at all clear how.

 

[nyef]

Looking at the bomarc IIfx schematic, R4 is on sheet 1 of 8, right next to connection point C (to sheet 2), this is part of the power-switch and ADB functionality. UB16, which I think is that black box with the wire segments poking out the top, is a dual inductor that's one of the last stages of the headphone output path... and in proximity to the reset handling for some reason (why reset handling routed through the audio subsystem, or why there are two reset signals escapes me at the moment).

Still, either that trace connects to one side or the other of R4, or there's a via underneath R4. The latter should be simple to check for (it would likely be visible on the other side of the board)... but it looks like the trace from the other side of R4 heading to the left may also have rotted away.

As for R4 itself, one side connects to R23, C27, and pin 2 of UJ18, and the other side connects to the power switch, and pin 5 of UB15 (a quad inductor), and through that to C61 and pin 2 on both ADB ports. I don't know if having the power signal "stuck" or "floating" in some way can cause the symptoms that you're seeing or not.

Editing to add: Just found your images from last year. This looks like trace rot from C9 having let go (and it looks like at least one trace from R2, next to the power switch, may also be affected). But if C9 has let go then C24 probably also let go, and that's right next to the RAM slots. I'd suggest continuity-testing the traces for the RAM slot pins. They may be fine, but if they aren't then you have something that would almost certainly cause a startup failure.

 

[Bolle]

 

[nyef]

Okay, so that's the ADB power-switch (as opposed to +5v source) connection. That would prevent using ADB power buttons to turn the computer on, but I doubt that it would cause chimes of death. The iffy-looking R2 trace that I called out looks like it goes to the negative side of C7, which is one side of the headphone audio path, specifically the signal that is also routed to the speaker, but tapped just after the speaker connection, so also not likely to cause chimes of death.

At this point, I'd suggest checking for more trace rot around UC17 (the 8530 serial port chip) because it's a digital part in proximity to C9 and, as mentioned earlier, the RAM SIMM slots because they're in proximity to C24.

 

[nathall]

Thanks to both of you guys. This would explain why I can’t power the computer on from the keyboard, at the very least.

I replaced both C9 and C24 in the past year, but I agree there may be some damage I’ve missed. I’ll check out the area of C24 and post some more photos in the coming days.

 

[nathall]

Found a few bad traces around C24. Ran a wire and patch or two but didn’t change anything.

I think there is at least one more, but I need to review the schematics before doing anything further.

UC17 passed all the continuity checks I performed.

 

[amedeo_68k]

Do you see anything on screen ? I have a IIfx too that just does death chime

 

[nathall]

Depends on the video card. A Radius card just shows the initial raster with the Radius logo, an Apple video card and the display stays black.

I haven’t gone back to the IIfx since the last post. It’s been ongoing for around 3 years now and I’ll work on it in spurts but get burned out after a while and making almost absolutely zero progress so I take a break for a while and work on other things.