We’ve been making banners with the IBM 5362 (System/36)! More midrange people at #TechXchange who recognized and knew how to work with the machine than I could have ever expected! Lots of folks very excited to play with some old IBM gear and get some printouts to take home!
I’m in Orlando this week for #TechXchange I packed this crate for CCL’s of the IBM Archives booth 290! Come see me there this week and what we will have setup!
March 22 marks the 60th anniversary of the introduction(*) of the Digital Equipment Corporation PDP-8, which more or less introduced the "minicomputer" as a new category of computer. It cost a mere $18,000 and fit on a desk, and while it was a small, simple computer, it became extremely popular.
Got it all working and reassembled. There was a cracked trace causing an address line to be connected to only two of the RAM chips, and nothing else. This was acting like an antenna and picking up noise.
Still missing a couple keytops (1, Z, and left Shift), but I found a couple I could substitute.
I used the ram viewer to look at that address space. It looks like the first 4KB of that ram has that one byte stuck… Which is odd because these are 32KB chips and there are two setup to make a 16-bit wide interface wired up as 32Kx16. I wonder if one of the ram chips is *still bad*?
And once I got a JAMMA harness rigged up… Well darn more diagnosing to do. At-least we know for sure now that it definitely has an issue in that battery backed ram. Which is where that ram chip was messed with. Good thing is my repair seems ok after some feeping around with the meter.
Well first side quest was to fix this arcade monitor. This is one of those cheap turn a TV picture tube into an arcade monitor chassis. It uses… very many no-name cap brands. So those needed changed. I left the three biggest ones alone hoping at-least those still worked and they seem to.
With the glue on the board now and the relatively thick wire. I had to get “creative” to make the chip sit right. Well it’s either going to work or I’ll find out something else is wrong with this board. I have to burn a rom then get out an arcade monitor and JAMMA harness and give it a go tomorrow!
It’s not fun or easy. I kinda had to put some glue down under the new “pads” cure that. Hope it holds and tack the wire to the trace. Then clean all that flux up. Rough up the board. And put some more glue down to be sure it all holds well. Multiple times the first glue down didn’t hold great…
Having a binocular microscope helps. Using 30awg wire and flattening it out with flat nose pliers close to the inside of the lever point to get a lot of leverage to flatten it. The one pad near a via is easy. That’ll hold without glue. The other pads/wires I gotta try and UV glue down.
Well I guess this is why I got this Neo Geo 4 slot board-set for free… Looks like someone diagnosed the bad ram then tried replacing it with a hot brick and lead free solder or something. We’ve certainly all been there at some point in our soldering journey… Let’s try and fix it!
The other models of Sound Canvas I have, SC-88 ST, SC-88 ST Pro, and SC-55 MK II all have through hole caps that look fine. Always good to take things apart to check it out.
Apparently the Roland SC-88, the original tall unit, has SMD capacitors on the logic board. That was fun to clean up and replace. Trying to clean up the leads of the one chip lead to me messing up some pads. Doh, had to whip out the scope for a fix. Works great now.
