512K Disappointment

[superjer2000]

I picked up a 512k today - I already have two other 512s but I wanted to get this one as I spotted a SCSI port at the battery location.

I removed the SCSI plate and was happy to see only minor corrosion from the battery, and all confined to the battery holder.

The unit does have a MacSnap SCSI but unfortunately that's it.  No CPU upgrade or even a RAM upgrade.  I'm not sure how useful a SCSI port will be with 512k RAM.

I haven't booted the machine yet as the seller said it wouldn't start (it just clicked).  The model was a M0001WP (and indicated 220V on the back) so I figured he was trying to run a 220V board here on 110V, but when I opened up the unit, it seems to have a 110V analog board so it must have been retrofitted at some point.   I'll install my usual new caps, rectifiers and other upgrades and I'm sure that will get it going again.

 

[Juror22]

I just picked up a 512k with one of these as well, but it also came with the 2MB board.  Mine starts with a normal startup bong, then shows this exact screen pattern 

https://68kmla.org/forums/uploads/monthly_2018_12/IMG_0152.JPG.ce426fee7e7481d7f9dbf7771c053972.JPG

(the link is from another post about SE/30 Micron card issues, but shows the issue perfectly)

I thought that it was an issue with the SN74L538 chip [as mentioned in the Dead Mac Scrolls], so I swapped in another of those and the issue is still there.

Pressing on the analog board, about midway down, using appropriate care, will show the desktop, arrow cursor and flashing disk icon, so I think there is a reasonably easy fix, I'm just not sure where to go next.

I guess that we both have work to do to get these working correctly.  Good luck with yours.

 

[Crutch]

@superjer2000 I just noticed this 2MB MacSnap board on eBay for what seems a reasonable price — including the 512KE logic board it’s attached to.  https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F254263385588

 

[superjer2000]

Thanks @Crutch, that's more than I'm keen to spend. I'll just restore the analog board and live with my 512k of ram...

 

[superjer2000]

I just picked up a 512k with one of these as well, but it also came with the 2MB board.  Mine starts with a normal startup bong, then shows this exact screen pattern 

https://68kmla.org/forums/uploads/monthly_2018_12/IMG_0152.JPG.ce426fee7e7481d7f9dbf7771c053972.JPG

(the link is from another post about SE/30 Micron card issues, but shows the issue perfectly)

I thought that it was an issue with the SN74L538 chip [as mentioned in the Dead Mac Scrolls], so I swapped in another of those and the issue is still there.

Pressing on the analog board, about midway down, using appropriate care, will show the desktop, arrow cursor and flashing disk icon, so I think there is a reasonably easy fix, I'm just not sure where to go next.

I guess that we both have work to do to get these working correctly.  Good luck with yours.

It might be good to try to resolder the plug for the cable that goes to the logic board as it carries the video signal. 

 

[Juror22]

It might be good to try to resolder the plug for the cable that goes to the logic board as it carries the video signal. 

Yep, that did it.  It still amazes me that a perfectly solid appearing solder joint can be bad.

Thanks for the assist and sorry that your MacSnap didn't turn out the way you wanted.

 

[superjer2000]

Got it all working - 

I fully disassembled and cleaned the machine, mouse, keyboard and retrobrited those parts.

I recapped the analog board and changed out the components I normally do on Pre-SE analog boards (CR1, CR5, CR20, CR21, U3, Q1, Q2 and Q3), resoldered flyback, logic board connector and replaced J1 and corresponding plug.  I fired it up expecting it to work on the first try and just got the repeating flup noise which I think is what the prior owner indicated was the issue.  Looked at Dead Mac Scrolls and tested the 5V line on the cable between the analog board and the logic board and sure enough, no continuity.  There is a 2.5A inline fuse in the wire harness that tested open.  I ended up just replacing that wire (i.e. removing the fuse) and presto the machine fired up.  

When I was testing the machine I noticed that all keys on the keyboard worked except for the delete key.  I pulled the key switch and disassembled and noted a fair bit of corrosion.  I soaked it in vinegar for a couple of days (with a piece of wire separating the two plates in the switch), soaked it in distilled water with baking soda, dried it, applied some contact cleaner/lubricant and that fixed that key switch.

I just tested the SCSI port and that works great as well.  Only downside is not a lot of software runs within 512k but a fun project nonetheless.

Note, although it is an M0001WP, it had the 110V analog board installed.  It must have been swapped out at some point.

 

[Jinnai]

Awesome job! The SCSI port is awesome, I have one, just need to figure out how to get power over it so I can use an SCSI2SD .

 

[Juror22]

When I was testing the machine I noticed that all keys on the keyboard worked except for the delete key.  I pulled the key switch and disassembled and noted a fair bit of corrosion.  I soaked it in vinegar for a couple of days (with a piece of wire separating the two plates in the switch), soaked it in distilled water with baking soda, dried it, applied some contact cleaner/lubricant and that fixed that key switch.

This post was rather timely, as I've noted before, I was working on a 512 of my own and today I was working on the keyboard (the 'u' key did not work) and I used some of this post as a guide.  I pulled the key, desoldered and disassembled the switch and finding corrosion, removed some by scraping with a pin and then put it into a small bowl of vinegar, followed by a water/baking soda mix, then water, then contact cleaner.  Testing the reassembled switch confirmed it was working, so I reattached it and have a fully functional keyboard.

Congrats on getting your 512k with SCSI up and running as well.