SE/30: Yet another scsi issue

[jmacz]

Well the thing is, the two capacitors aren't making a difference for me. Whether the 2.2uF or 0.1uF or both are connected doesn't change the outcome. What does change the outcome is that 470 ohm resistor across REQ and TERMPWR. Without that resistor, it almost rarely works. With that resistor it seems to currently always work. Right now I have just the resistor connected and the capacitors removed and everything is still good. If I disconnect that resistor, stops working again.

The PSU is a recapped Sony. No other PDS cards currently installed. Vanilla board with the one ZuluSCSI and that's it. It's ranging between 4.9V to 4.95V so I think that's close enough? I can check later if there's a pot to bring up the voltage but I think that's probably close enough?

 

[jmacz]

Finally got time to spend time on this again, and determined that the issue is due to a bad SCSI chip.

I swapped SCSI chips (same part number) between this SE/30 and my workbench IIci. The issue followed the chip and is now occurring on my IIci. I then put the same 470ohm resistor between the REQ pin on the SCSI chip and the term power fuse on my IIci board and it starts working just like previously on the SE/30.

Looks like this particular SCSI chip is having issues thinking REQ is getting pulled down.

I'm going to leave this SCSI chip with the resistor on my IIci board for now to observe if it's fully working with the resistor modification. I did pickup two more battery bombed IIci boards from a recycler a couple weeks back so I can harvest their SCSI chips if I need to.