Advice for diagnosing scsi failure on Quadra 800?

lobust

Tinkerer
Nov 14, 2021
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Any hints or pointers gratefully received!

Symptoms:

Machine was working fine, I have been using it probably a few hours every other night over the last few weeks, booting from a SCSI2SD v6 attached to the internal scsi. Couple of days ago it started cold booting to the flashing ? disk, but would then boot normally after a restart. After doing that a couple of times it changed to booting to blank gray screen with cursor, then a long (~20 seconds) delay, and then the flashing ? disk, and no amount of coercion will persuade it to find the boot drive. I have a few other drives including a micropolis HD and the 800's cd300i caddy loader, all verified working in my 700, but all fail in the 800. I don't currently have any other means of booting it, I doubt the floppy drive is working and I don't have any boot floppies for it anyway. I also don't have any external scsi drives I can plug in to see if it's just the internal port that's dead, but I am working on acquiring something to test that. It does still chime normally, so I'm guessing it's something with the scsi controller directly...

I also mounted the 800 board in my 700 to rule out PSU issues, to no avail.

One notable data point is that the cd300i did not even try to eject when starting up with the mouse button held down...

Background, for context.

I got the Quadra 800 in bad shape a couple of years ago, I bought it mainly because the plastics were intact and in good order. It had been stored in someone's shed and had had paint thinners or something like that leaked all over it, completely destroying all the metal parts of the case and the PSU. In spite of all that the logic board was in really pretty good shape. There are a small number of IC legs that are slightly dull I guess from vapour from whatever was spilled on it as there is no evidence of liquid contact with the board. Nothing too bad at all, and the pcb itself is immaculate. I rebuilt it with a replacement PSU and some case parts donated by a dead 8500 that someone was parting out on ebay, and have been using it that way since.

@trag , I noticed in another thread you had acquired a large quantity of 53C96's, might you be persuaded to part with a couple of them? Assuming they are the 100 pin QFP variant... They seem to be pretty difficult to acquire except in bulk quantities... I assume the 53CF96, while pin compatible, is not a drop in replacement?
 

trag

Tinkerer
Oct 25, 2021
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@trag , I noticed in another thread you had acquired a large quantity of 53C96's, might you be persuaded to part with a couple of them? Assuming they are the 100 pin QFP variant... They seem to be pretty difficult to acquire except in bulk quantities... I assume the 53CF96, while pin compatible, is not a drop in replacement?

My understanding is that the 53CF96 is not a drop in replacement. Someone posted that the internal registers are fairly different. I haven't dug into the datasheets enough to have first hand knowledge.

You are welcome to a few 53C96. I just need to remember to look for them while I'm at home. I have an inventory that tells me which box they're in. With luck they're in one of the boxes I got out of the attic in the last couple of months. The attic ladder is broken at the moment, so if they're in the attic, that's a problem.
 
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lobust

Tinkerer
Nov 14, 2021
50
34
18
My understanding is that the 53CF96 is not a drop in replacement. Someone posted that the internal registers are fairly different. I haven't dug into the datasheets enough to have first hand knowledge.

You are welcome to a few 53C96. I just need to remember to look for them while I'm at home. I have an inventory that tells me which box their in. With luck their in one of the boxes I got out of the attic in the last couple of months. The attic ladder is broken at the moment, so if they're in the attic, that's a problem.

Grateful to you - I did since find this listing on ebay for a more reasonable quantity, if it's a nuisance for you I'm happy enough to buy a lot of those. Let me know...
 

trag

Tinkerer
Oct 25, 2021
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@lobust I have the chips in hand. Two bricks of 330 parts... I pulled four of them out of one of the bricks. Nice to finally find a use, if only for a few of them. Interestingly, while the chips are marked NCR53C96, the label on the brick has an Apple 337S5396 part number on it. Guessing these were originally sold for manufacturing Quadras and then never used.

PM me with your shipping information.
 
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lobust

Tinkerer
Nov 14, 2021
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@lobust I have the chips in hand. Two bricks of 330 parts... I pulled four of them out of one of the bricks. Nice to finally find a use, if only for a few of them. Interestingly, while the chips are marked NCR53C96, the label on the brick has an Apple 337S5396 part number on it. Guessing these were originally sold for manufacturing Quadras and then never used.

PM me with your shipping information.
PM sent, much obliged!
 

lobust

Tinkerer
Nov 14, 2021
50
34
18
An update:

Thanks to member @trag I now have some brand new scsi IC's.

Out of curiosity I was probing around the 53C96 with my scope and in the process it started booting from the internal scsi. I tried it a number of times without touching anything on the board and it booted normally every time.

Then, I pulled the scsi cable and reseated it, and after that it wouldn't see the internal scsi again. So I assumed a dry solder joint on the scsi header and reflowed it. No change.

Then I replaced the 53C96 with one of the new ones provided by trag, and again no change.

I'm still thinking that there is a broken connection somewhere, dry via or something. Going to have to spend a little more time on this...

I bought a cheap lcd screen magnifier (Adonstar AD206) and it works pretty well for this but the distance from the stand to the lens is only about 2-3" so I need to make a new stand for it in order to be able to study the whole board under it.
 

lobust

Tinkerer
Nov 14, 2021
50
34
18
After a whole lot of messing around, including repairing two floppy drives and a not-booting G3 Minitower, and acquiring some actual floppy disks, I have an alternate boot method and an update.

SCSI Probe says that the bus is not terminated.

The Wombat board has active termination circuitry that turns on if nothing is plugged in to the external port. As best as I can tell, it seems to be working properly. It uses a Motorola 142235 active terminator, and it is getting enabled, and it does measure the correct 110 ohms at each of it's outputs when nothing is plugged in anywhere on the bus.

However, when something is plugged in to the internal bus, the outputs of the 142235 seem unstable.

SCSI Probe reports that the bus is not terminated in any case.

I have bought and am waiting on the arrival of an external drive and terminator to test.
 

lobust

Tinkerer
Nov 14, 2021
50
34
18
An update,

External drive was no different, seems the entire subsystem is not working.

I bought an active terminator with leds for term power, sel, ack, and req. It shows termpower, but zero activity otherwise.

53C96 seems to be getting correct voltage where it needs it and an active 20MHz clock signal going into it, but no life...

I feel like I am going to have to get a logic analyser (and learn how to use it). It's a nuisance that I only have a Q700 to compare against which is not quite the same architecture.

I am wondering if some fault lies with the IOSB chip... I tried a different CPU (known good out of my Q700) with no different results, so not that...

Really need another wombat board to compare (or ultimately replace), but having a hard time finding one.
 

hageir

New Tinkerer
Mar 6, 2024
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Reykjavík, Iceland
Hello from Iceland.
Sorry for the necro bump..
Any updates on this?

I have a Quadra 660AV that I want to use as a MIDI Sequencer and I'm having this problem. I repair synthesizers for a living, I've recapped the board, cleaned and inspected a few times.

Mine doesn't see anything on the internal Bus. I can boot off an External SCSI CD Drive, the Apple Legacy Restore disc works (it has the correct System Enablers). Anyways, on there the Quadra doesn't see any SCSI HDDs nor Floppy disks; it says "Initialize" and finally fails and ejects any floppies/CD inserted into the internal drives (I make the floppies on a Performa and they work fine on a Power Macintosh I have).

I suspect that Automatic Terminator...


-Geir
 

Kai Robinson

TinkerDifferent Board President 2023
Staff member
Founder
Sep 2, 2021
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@lobust I have the chips in hand. Two bricks of 330 parts... I pulled four of them out of one of the bricks. Nice to finally find a use, if only for a few of them. Interestingly, while the chips are marked NCR53C96, the label on the brick has an Apple 337S5396 part number on it. Guessing these were originally sold for manufacturing Quadras and then never used.

PM me with your shipping information.
I have a brick of PowerPC 601's from IBM with apple part numbers on the label, probably the same issue - never used!