Mac IIx - Boots to White Screen; Weird Chimes of Death

[warmech]

Howdy everyone!

I'm looking at a Mac IIx that I've cleaned, recapped, and replaced the batteries on; there appeared to be damage to one trace between a couple of pins on UB2 that I bodged, and that looks like all the visible problems I could find. When powered on, the screen comes up white (like it's about to load the cursor) and the initial boot chime occurs but, a few seconds later, a *da-DA* chime is produced, followed by a fast chime of death. I've never run into this kind of double-chime before, and am a bit thrown by what that means. I've been unable to find anything in my research that indicates a set of chimes like that, so I'm scratching my head at the moment. I don't have a lot of experience with Mac II's, so I'm hoping someone here might have some insight. Attached is an audio recording of the chimes in action.

Also, I'm a bit confused by something else; performing a continuity test at the PSU connector shows the +5v rail tied to GND, but the machine powers on. What the heck is up with that? Wouldn't that just cause a short and keep the machine from powering on to begin with?

View attachment chimes.m4a

 

[warmech]

Too late to edit, but, after flipping through the Dead Mac Scrolls, I came across this: 

"On startup, you get the normal startup chime, then you get a high note, followed by an even higher note, followed by a do-do-da-da sound. Then the raster blacks out." My raster doesn't black out, but, that is the issue I'm experiencing. The issue is described as having an onset after upgrading RAM and to check/replace the SIMMs in slot B. Well, there's nothing in any of the B sockets, unfortunately. Earlier in the Mac II section, however, there's this:

"On startup, the normal startup chime is quickly followed by an error chord, then a do-do-da-da sound. The internal hard drive doesn't make its usual noises. The disk drive doesn't pulse. Raster never comes up on the monitor(s)." That issue is described as having an onset "out of the blue." While I get raster, the stated cause is a "dust short" on the logic board. I'm curious if this is related to the apparent short described in my first post.

Edit: Upon closer inspection, the IC at UG8 (a 74F240D-type address buffer) is bad. The legs looked a little too grody and, upon removing the chip, pin 4 fell right off. Pin 10 is also very loose, but didn't just fall of like 4 did. Going to see if I can pull one from another dead board I have or, barring that, order one from Mouser. I suspect that would definitely have an impact in system function, lol. Besides this, is there anything else I should be looking for?

 

[warmech]

Replaced with a working 74F240 to no avail; back to the drawing board.

 

[Rony Okal]

Replaced with a working 74F240 to no avail; back to the drawing board.

have you drawing board for iivx?

 

[davidg5678]

If I understand correctly, I think the sounds the computer is making mean that it is crashing shortly after starting up. My best guess is that there is still a broken trace somewhere on your board. It sounds like there was some considerable capacitor leakage, so it is very possible that something is corroded.

Can you provide some photographs of the motherboard? Many of the common faults with these computers occur near the power button circuitry, so a close-up photo of this section could be useful too. It sounds like there was some damage to this area already (in the vicinity of UB2), so it is possible that something is not working there. I think you might find this webpage helpful: https://www.downtowndougbrown.com/2015/03/explanation-of-the-macintosh-iiiix-power-onoff-circuit/

If you have some alternative RAM SIMMS, it probably wouldn't hurt to try swapping them into the computer as well, just in case. For troubleshooting purposes, I would also reccomend removing every expansion card from the computer aside from the video card.

 

[warmech]

If I understand correctly, I think the sounds the computer is making mean that it is crashing shortly after starting up. My best guess is that there is still a broken trace somewhere on your board. It sounds like there was some considerable capacitor leakage, so it is very possible that something is corroded.

Can you provide some photographs of the motherboard? Many of the common faults with these computers occur near the power button circuitry, so a close-up photo of this section could be useful too. It sounds like there was some damage to this area already (in the vicinity of UB2), so it is possible that something is not working there. I think you might find this webpage helpful: https://www.downtowndougbrown.com/2015/03/explanation-of-the-macintosh-iiiix-power-onoff-circuit/

If you have some alternative RAM SIMMS, it probably wouldn't hurt to try swapping them into the computer as well, just in case. For troubleshooting purposes, I would also reccomend removing every expansion card from the computer aside from the video card.

I can take some high res images in a little bit and post them here; a broken trace is my worry, as well. All of the RAM I've tried aside from the SIMMs that came with this thing give me no boot chime or error tones, just slow chimes (as opposed to the boot chime/error tones/fast chimes with the present config). I'm... not really certain why that's the case either. The IIx seems to accept 256K/1M/4M SIMMs, so I may dig around and see if I can pull RAM from another machine and try that.

At lunch, I plan on trying out the diagnostic mode outlined here: https://mac68k.info/wiki/display/mac68k/Diagnostic+Mode

I have to say that, in all the years I've been collecting Macs, I've never heard of this before. I have the means to get it working, so I figure I can at least see if it's aware of what its own problem is.

 

[davidg5678]

At lunch, I plan on trying out the diagnostic mode outlined here: https://mac68k.info/wiki/display/mac68k/Diagnostic+Mode

I've never really seen much about this before, either (certainly never any written instructions). It sounds fascinating -please keep us updated with how the diagnostic mode works out for you. Maybe I'll have to start using it with my Macs too!

 

[warmech]

AARGH - RAM!

After testing in my Classic, two of the four 1MB SIMMs are bad. The Mac IIx can boot off of 1MB of RAM, so long as it's in the form of four 256K SIMMs in the four seats in bank A. Now that I'm down to two 1MB SIMMs, I need to take something apart to test with other SIMMs.

EDIT: Huzzah - I now have a working Mac IIx! Grabbed the RAM out of my SE, dropped it in, and it fired right up! I'm thinking this is case closed.