NeXT Computers

NeXT Computer, Inc. => Black Hardware => Topic started by: m18e on April 27, 2019, 04:16:33 am

Title: NeXTStation raising exception on boot
Post by: m18e on April 27, 2019, 04:16:33 am
Starting just a couple days ago my NeXTStation started throwing an exception at boot:

Exception #3 (0xc) at pc 0x1000646 sp 0x4000600

Has anyone seen this before? It was working just last week :(

It's a Turbo Color, 128MB ram, and a CF AztecMonster compact flash -> SCSI 2 adapter.
Title: Re: NeXTStation raising exception on boot
Post by: barcher174 on April 27, 2019, 06:45:35 am
Try disabling memory parity in the ROM setup.
Title: Re: NeXTStation raising exception on boot
Post by: m18e on April 28, 2019, 04:58:43 am
Tried that, no joy :(

It seems to happen after the NeXT logo disappears, during the OS boot.
Title: Re: NeXTStation raising exception on boot
Post by: barcher174 on April 28, 2019, 05:28:15 am
I'm not sure there is a formal explanation of that exception, but it's either RAM or SCSI related in my experience. Try removing SIMMs and a different HDD. Have the caps been replaced? Those are then the next likely suspect.
Title: Re: NeXTStation raising exception on boot
Post by: m18e on May 18, 2019, 04:31:43 am
I've tried all combinations of memory sticks that I have. It seems to require two at a minimum; if I only use one it doesn't even begin the POST. Anyways, all the combinations I tried didn't make a difference.

I tried drives in, drives out, booting from the network (or, at least setting en/tp as the boot devices, not actually getting it to boot from the network).

Nothing's worked :(

Capacitors appear fine, nothing's leaking, bulging, or looking off... I wish I had a clue to what was going on.

The first time this happened I had tried using an LCD flat panel with a 13w3->VGA connector. The monitor supported sync-on-green but it said it was running at 1024x768, not 1120x832... could anything bad have happened from that? (It showed the POST boot splash fine, but it went to the exception prompt)
Title: Re: NeXTStation raising exception on boot
Post by: barcher174 on May 18, 2019, 05:45:34 am
Have you tried pulling the battery? Let it sit for a while with the battery out.
Title: Re: NeXTStation raising exception on boot
Post by: m18e on May 26, 2019, 04:21:47 am
I pulled the battery for a few minutes but no change. Does it need to be out for longer?
Title: Re: NeXTStation raising exception on boot
Post by: barcher174 on May 26, 2019, 07:09:51 am
Given the sudden change and that you've eliminated the RAM and HDD as a concern I suspect the caps need to be replaced. You wont necessarily see any visual problems with them.
Title: Re: NeXTStation raising exception on boot
Post by: m18e on May 28, 2019, 03:32:34 am
Okay, that's fine. Do you happen to know if there's a capacitor parts list kicking around?

I see 3 220uf 25V electrolytic capacitors on the motherboard; are those the only ones?


disregard! I found this topic: http://www.nextcomputers.org/forums/index.php?topic=3941
Title: Re: NeXTStation raising exception on boot
Post by: m18e on June 02, 2019, 02:43:15 am
I recapped the motherboard (all radial and surface mount capacitors swapped). One of the old surface mount caps looked like it was leaking after all. However, even after doing so, the same issue is happening. Same exception, same program counter, same stack pointer.

Any tips on where to look next?

Title: Re: NeXTStation raising exception on boot
Post by: m18e on June 17, 2019, 03:55:16 am
One thing I noticed as I was stepping through the disassembly via the ROM monitor is that the return-to address from the exception handler is the RTE instruction it's trying to execute (ie: it's returning to itself).

Do the EPROMS ever flake out? I noticed the sticker over the crystal on the EPROM was no longer there. I was wondering if it's worth checking if the ROM's been corrupted or anything...

I'm kind of losing hope here :(
Title: Re: NeXTStation raising exception on boot
Post by: barcher174 on June 17, 2019, 04:15:25 am
A bit flip in the ROM could cause any number of weird behaviors. Certainly worth checking out.
Title: Re: NeXTStation raising exception on boot
Post by: t-rexky on June 20, 2019, 09:44:17 pm
Wouldn't a bit flip cause a checksum failure though?
Title: Re: NeXTStation raising exception on boot
Post by: barcher174 on June 20, 2019, 10:22:57 pm
Quote from: t-rexky on June 20, 2019, 09:44:17 pmWouldn't a bit flip cause a checksum failure though?

Yeah, good point.
Title: Re: NeXTStation raising exception on boot
Post by: Andreas on July 04, 2019, 08:27:41 am
Quote from: barcher174 on April 27, 2019, 06:45:35 amTry disabling memory parity in the ROM setup.

If we are talking about the 30 PIN RAM: On my expierience its always parity RAM no matter if parity check is on or off in the BIOS. Remove all the RAM and start the NeXT. You get an error that there is no memory, but i assume no exception anymore. (at least on a cube that works)
Avoid 3 chips and 9 chips RAM sticks - they may run on NeXTs but mostly not. Take only 8 chips RAM. Use the latest boot ROM in your slab.
Title: Re: NeXTStation raising exception on boot
Post by: m18e on July 11, 2019, 03:05:50 am
Hi Andreas!

When all the RAM is out it doesn't boot; there's a diagnostic LED on the motherboard that flashes. Nothing comes up on screen.

The slab has 72-pin SIMMs; each SIMM is a 16-chip 32MB piece. I've tried a number of combinations of them, both in two and four SIMM configurations and nothing seems to work.

Appreciate the input, every little hint helps.
Title: Re: NeXTStation raising exception on boot
Post by: Andreas on July 11, 2019, 05:36:23 am
Quote from: m18e on July 11, 2019, 03:05:50 amThe slab has 72-pin SIMMs; each SIMM is a 16-chip 32MB piece.

to be clear - you have a turbo slab with 4 slots for RAM instead 8 slots?
Title: Re: NeXTStation raising exception on boot
Post by: krazycat on July 11, 2019, 06:12:35 pm
Quote from: Andreas on July 11, 2019, 05:36:23 amto be clear - you have a turbo slab with 4 slots for RAM instead 8 slots?
as far as I can tell, the turbo mobos only have 4 x 72-pin ram slots...






Title: Re: NeXTStation raising exception on boot
Post by: m18e on July 14, 2019, 04:46:31 am
Quote from: Andreas on July 11, 2019, 05:36:23 amto be clear - you have a turbo slab with 4 slots for RAM instead 8 slots?

Correct.
Title: Re: NeXTStation raising exception on boot
Post by: barcher174 on July 15, 2019, 06:04:48 am
It seems I have a mono turbo station with the same problem. Recapped, drive swaps, RAM swaps, and cable swaps with no success. I'm convinced there's a board level fault. I'll let you know what I find. The SCSI portion is identical between the color and mono systems.
Title: Re: NeXTStation raising exception on boot
Post by: m18e on July 16, 2019, 03:49:18 am
Good to hear! (Well, not really :) ) Hopefully we can get these problems licked; I'm really missing playing around on my slab!
Title: Re: NeXTStation raising exception on boot
Post by: barcher174 on July 16, 2019, 04:17:50 am
Mine is working. I think in the end it's a different error though. I had an exception #4 which I confused with your error #3. For me the issue was a shorted pin on the ASIC controlling the SCSI controller which was only visible under a scope. I bent it back and reflowed with success. Here's what I would try in your case:

There's an exceptions section of the 68040 user guide:
https://www.nxp.com/docs/en/reference-manual/MC68040UM.pdf
You want Table 8-1. Exception Vector Assignments

From this we see that the vector number and code match to the table. So it looks like NeXT used this table directly which is good news going forward. The description says:

8.2.2 Address Error Exception
An address error exception occurs when the processor attempts to prefetch an instruction
from an odd address. This includes the case of a conditional branch instruction with an
odd branch offset that is not taken. A prefetch bus cycle is not executed, and the
processor begins exception processing after the currently executing instructions have
completed. If the completion of these instructions generates another exception, the
address error exception is deferred, and the new exception is serviced. After exception
processing for the address error exception commences, the sequence is the same as an
access fault exception, except that the vector number is 3 and the vector offset in the
stack frame refers to the address error vector. The stack frame is generated containing
the address of the instruction that caused the address error and the address itself (A0 is
cleared). If an address error occurs during the exception processing for a bus error,
address error, or reset, a double bus fault occurs.

Looking at the schematic here:
http://www.nextcomputers.org/NeXTfiles/Docs/Hardware/Schematics/Turbo_slab/CSlab33-04.pdf

The 7F543s look like a good place to start. Check for any really hot ones.

Title: Re: NeXTStation raising exception on boot
Post by: m18e on July 17, 2019, 05:17:22 am
Two of the 74F543's (U14, U23) do seem to be running hotter than the others. Not hot enough to scald but definitely uncomfortable to touch.

Hardware's not my forte; what else should I be looking at as a consequence of the hotter than normal latches? Broken solder joints?

One thing I did notice when I had the motherboard out tonight is that there's something (capacitor?) soldered across a couple CPU pins on the backside of the motherboard... here's a picture: https://i.imgur.com/Z7MUgzb.jpg

Is that normal?

(I straightened out the pins in the top left so they wouldn't come close to touching)
Title: Re: NeXTStation raising exception on boot
Post by: barcher174 on July 17, 2019, 06:25:57 am
The resistor is normal. That blob of solder next to it is not. You should clean that up. Is your Cpu soldered down or socketed?  Those possibly shorted pins are concerning.
Title: Re: NeXTStation raising exception on boot
Post by: m18e on July 18, 2019, 04:26:21 am
I don't think that blob between the pins was solder, it seemed to be a bit of flux or something. It cleaned up well, but doesn't seem to have helped.

The CPU is socketed. I've never removed it; though once this ordeal is over I might pop the heatsink off to re-apply thermal paste :)
Title: Re: NeXTStation raising exception on boot
Post by: barcher174 on July 18, 2019, 05:39:29 am
If you have an extra you may want to try swapping out the cpu.
Title: Re: NeXTStation raising exception on boot
Post by: m18e on July 27, 2019, 04:30:47 am
I received another 68040 and dropped it in; no luck.

(Well, at least I have a processor upgrade for my LC575 now...)
Title: Re: NeXTStation raising exception on boot
Post by: m18e on September 07, 2019, 09:36:14 pm
I received a fresh v74 ROM from Rob @ Black Hole and, again, no dice; still the same errors on bootup. ¯\_(ツ)_/¯

I guess the next thing I can do is get some new RAM; maybe all my SIMMs are shot?
Title: Re: NeXTStation raising exception on boot
Post by: barcher174 on September 07, 2019, 09:44:03 pm
That seems very unlikely. Probably a board level problem here.
Title: Re: NeXTStation raising exception on boot
Post by: Rob Blessin Black Hole on September 08, 2019, 03:10:17 am
I agree with Brian... it has to be a board level problem.