Mac SE/30 After recap get an unreadable disk error loop

[se30]

Looking for some guidance. I have acquired a SE/30 that was sitting in a closet for nearly 25 years. When I first got it, it would simasimac, but cleaning the board of the build up of dust largely resolved boot issues. I was able to boot into the original 40MB SCSI drive. I was also able to boot off of an external disk drive, the internal disk drive needed to be lubricated and cleaned so I never attempted to boot off it before the recap.

After recapping C1, C3, C4, C5, C6, C7, C8, C9, C10, C12 and C13 with Tantalum capacitors the system would boot to a floppy icon with an X. If I connect a disk drive to either the external floppy port or the internal ribbon, the drive head will move and spin even when no disk is inserted. I have tried this with two different drives, one of which worked fine before the recap.

If I boot into the installed OS on the SCSI drive I just get into a loop of seeing "Disk is unreadable" which goes from pointing to the internal drive to an external drive and back again (see video) blocking the system from fully booting up.

Anyone seen anything like this before?

I've read "The Dead Mac Scrolls" and it talks about checking the bourns filter. I checked it and get 50ohms across all pins but ground. No unexpected shorts.
I have noticed a 77ohm short to ground when the system is off on pin 11, 22, 30 and 44 of the SWIM chip but when powered up it gets 5v on those pins. I have also traced all pins from the internal ribbon cable to the pins on the SWIM chip and haven't found any broken traces.

I am a bit stumped, is there any other way to determine of the bourns filter is ok? Is there anything else short of replacing the SWIM chip that I should be looking for?
Thanks!

 

[se30]

Just as an update, I pulled the bourns filter as an attempt to see if it would make any difference and pulled my capacitors. The 5v line is now showing 90ohms to ground. The bourns filter definitely seems fine based on this video. With the bourns filter in I was getting not so good looking ohms readings to ground after all, but with it pulled out it works as described. That leaves the SWIM chip. I order new chips and will attempt a replace next. I think the SWIM chip is ultimately where my problem is going to lie as it just continually toggles between ENABLE 1 and ENABLE 2 and HDSEL never goes high.

All Phase lines are chatty and based on some internet sleuthing and this doc. I don't think it is behaving normally. Will know more once I get the SWIM chips in tomorrow.

 

[se30]

I just thought I would provide a quick update for anyone who happens upon this post in the future. It turned out to be that the SWIM and the resistor network were both bad. The 77 ohm changed to ~95 ohms after removing the resistor network. I could then at least boot into the SCSI drive and use the computer at this point but both internal and external drives were not operable. I replaced the SWIM chip and resistor network at the same time using a couple of different sources that sold the SWIM chip as new old stock and the resistor network set I got was used. I was aware of the homemade solution to the resistor network but decided I wanted my board to look original.

Once I finished replacing both chips the resistance on the 5V rail shot up to ~450 ohms and I can now use both internal and external floppy drives. So yea, my hunch was correct. If you see low resistance on a power rail, you probably have a bad chip or trace somewhere.