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[ried]

I acquired a Sun Remarketing SCSI card a while back and installed it in a Lisa 2/5. After installing MacWorks 3.0 and attaching a SCSI2SD v5 to the card, I tried booting into Macintosh System 6. After pressing the soft switch to power on, the Lisa quickly died, making unpleasant sounds... and smells. Something shorted inside. I quickly pulled the power plug.

Opening up the Lisa, there was no visually obvious damage anywhere. All of the boards looked fine. Using my nose, I isolated the burnt component to the CPU board - somewhere near the video state ROM. That is where the smell is coming from, at least.

I pulled the SCSI card out of the expansion bay, swapped the CPU board for a known good one, and the machine subsequently booted as normal. Somehow, this Sun Remarketing SCSI card killed a perfectly good CPU board, or one of its key components.

I asked sigma7 about this offline and he correctly guessed that the yellow cams on the Lisa's ZIF connectors were broken. Apparently, this contributes to possible misalignment of the card's fingers with the Lisa's connector, which seems to have been what happened in this case. I'm sure me pressing the SCSI2SD onto the card's DB25 connector didn't help, either.

In any case, I hope this report is somehow useful as a cautionary tale for those who have a Sun Remarketing SCSI card. Alignment in the slot is critical. I learned the hard way this time.

[sigma7]

... a cautionary tale for those who have a Sun Remarketing SCSI card.

The early version of the SCSI card looks very different (parts spread out over the whole board. lots of vias. Lots of orthogonal traces and corners). It did not have a card stop, but instead relied on the card hitting the chassis (requiring that it was being inserted with the cage fully in the chassis). It was easy to misalign it and damage to the card or computer would sometimes result.

guessed that the yellow cams on the Lisa's ZIF connectors were broken.
...
Alignment in the slot is critical.

The broken yellow cam will potentially affect alignment of all expansion cards (not just the SCSI card).

I recently ordered some prototype 3D Printed replacement cams. The first was SLS Stainless Steel made by JLCPCB - it arrived and after some 30 minutes of detailed cleanup and fitting, is in use and I think successful.

Since the metal SLS cleanup was not easy, I've also ordered SLS PA12 Nylon with glass fibre from PCBWay, but they haven't entered production.

Once the Nylon prototypes are evaluated, I'll post more info so others can try them out.

edit: added pic of early SCSI card

[ried]

My suspicion is that after attaching the SCSI2SD and plugging in its USB power cable, the card was pulled in the direction of the broken yellow cam. The SCSI card lacks any kind of slot cover, which presumably would have secured it against the Lisa's rear cover for a more precise fitment.

I have since tried the card in multiple Lisas and it prevents each from booting. Odd snow-like artifacts instantly appear on the screen when powered up, and no POST. Seems I killed the card, too. The Lisas subsequently boot fine when the SCSI card is removed.

In any case, my bad 

[sigma7]

ZIF Cams... intact, broken, and prototype metal 3D print...

[sigma7]

SLS PA12 Nylon with glass fibre from PCBWay

Nylon cams arrived and (the first one at least) required very little cleanup.

The original cam design has a bump (see pink oval) that seems designed to provide a detent when the ZIF is fully closed.

The metal cam is so stiff that the bump inhibited comfortable rotation from the closed position, so I removed it on the first metal prototype.

On the nylon cams, this bump causes the plastic to bend when the ZIF is opened, applying extra stress to the thin fin engaged in the slot at the end of the black housing. After removing the bump on the first sample, the cam is noticeably less distorted when opened.

The spring force from the ZIF contacts seems more than adequate to give a good feel for when the ZIF is closed, so I think the bump is actually counter-productive.

[sigma7]

The ZIF design is such that if the circuit board is not fully inserted, the cam jams hard against the board. The spring force as well as the force turning the actuator puts a lot of stress on the cam which sometimes breaks it (possibly aggravated by deterioration over time and repeated jamming and bending due to the detent bump described above).

In an attempt to reduce the chance of damage, I've taken to putting a slight bevel on the end of the card edge (green oval), as well as a chamfer on the cam (blue line). Although the improvement is small, these seem to work to nudge a slightly protruding expansion card into the correct position instead of just jamming the cam.

[sigma7]

Update on 3D printing a cam replacement: Replacing a broken yellow cam on a Lisa expansion card ZIF socket with 3D print