Recent content by David Cook

Thank you!

It looks like the jumpers follow a predictable binary pattern EO=+1MB E1=+2MB E2=+4MB E3=+8MB E4=unknown So, to get +8MB (9 in total with motherboard 1MB), pull jumper E3. To get +7MB (8 in total), keep E3 but pull E2+E1+E0. This explains why the board with 2 megabytes already soldered to it...

That's wonderful news! Congratulations. Your persistence paid off.

Yes. For 8 MB, I moved E3 to E1. So, all jumpers populated except E3. I will play with it further to figure out how to make it 7 MB for use in the 5126. I believe the RAM slot is limited to 4 MB (recent recreations use an extra wire to provide more). Additionally, the system provides the...

As a workaround, adding a >=1MB RAM disk in the Portable control panel seems to prevent crashing. The error is a memory manager error. That's suggests a bug or limit in System 6 beyond 8 MB. I tried using System 6.0.8L without success. I wonder whether a Macintosh LC with > 8MB will crash. I'm...

I have soldered on all the RAM. It works great in System 7.1 on a 5120 Portable. It shows 9MB total and passes all the memory test applications. However, in System 6.0.8, it crashes when doing something as simple as displaying the About box in the Finder. I recall reading about a solution for...

I just bought a Dynamic Engineering Macintosh Portable RAM card with 2 MB of RAM installed. I also purchased new old-stock Toshiba TC 518512FL-80 PSRAM chips to bring the card up to 8 megabytes. My plan is to use this on a 5120 (non-backlight) Portable. The jumpers on the 2MB card are all...

From your expression of concern at the start of this thread, I related to how you felt about being the possible cause of damage. We've all been there. The logical side of us knows that these old things are going to break once in a while, and that we fix more than we harm, and that it is better...

Holy moly! Check out that second picture from @Oelmuvun. I did not expect so much grime/tarnish.

Thank you for your perseverance -- even in sickness. When you're up to it, bump the speed back to 33 MHz. I'm almost positive that the root cause was residue on the connector rather than the speed. I think other people will run into the same situation as they swap and store boards.

I have reached the end of my Macintosh Portable pile. The final Portable did not power on and did not change current usage (as displayed on the bench power supply) when a key was pressed on the keyboard. That suggested a bad Power Manager chip. I originally believed that was a death sentence, so...

Hope you feel better soon! I don't think the clock speed has anything to do with it. Thanks for cleaning the fingers. It will be interesting either way.

Paul Tavenier (left Apple end of 1984) has one. He's responding to forum posts if you have any questions. https://68kmla.org/bb/threads/128k-analog-recap-photos-and-wtb-128k-motherboard.48622/post-583537

I know exactly your concern about DeOxit. I think you should play it safe and just use IPA on the motherboard for the first attempt. Don't be disappointed if it doesn't work -- this is just a theory I have. I am going to look through some of my Macs from that era and see if I can find one...

Attached is Apple's Color Classic schematic. See page 12 for the connector pinouts. We assume the LC 520 pinouts are the same, even if the part numbers are renumbered.