4Mb MMU Socket Upgrade questions

[polbit]

Well, after I disabled on-board memory with the resistors and attempted boot, the machine would show nothing, wouldn’t even seek floppy. I wanted to go back to known good state, so I removed the upgrade, and connected the resistors back. Now everything works, but I get thin, black, vertical lines every 1/3 inch or so (mono screen) They don’t move, are completely steady... Any ideas?

[rubber_jonnie]

Well, after I disabled on-board memory with the resistors and attempted boot, the machine would show nothing, wouldn’t even seek floppy. I wanted to go back to known good state, so I removed the upgrade, and connected the resistors back. Now everything works, but I get thin, black, vertical lines every 1/3 inch or so (mono screen) They don’t move, are completely steady... Any ideas?

Which resistors did you pull up to 5v? Do you have a picture? Also, if you connect 5v to the the wrong side of the resistors, it won't work.

EDIT:

You need to pull up R59, R60 & R61 at the end furthest from the RAM and connect all 3 to 5v. If you currently have 1MB installed you need to do the same for R71, R72 & R73 as per the guide here: https://www.exxosforum.co.uk/atari/last/4MBMMU/index.htm

[exxos]

You should probably run YAART You might have bad RAM or just video interference.

[rubber_jonnie]

You should probably run YAART You might have bad RAM or just video interference.

My bet is interference.

[polbit]

You should probably run YAART You might have bad RAM or just video interference.

Ran two passes, RAM is OK.

Tried two shifters, reflowed all legs of the socket I had to install for it.

The only other change I’ve done is install a blitter socket (no blitter yet) but I did not open up the vias, so I don’t think that would impact it. The computer worked perfectly fine yesterday...

[exxos]

Is your power supply recapped at least ? ... But I think you are drifting onto another topic here relating to video interference not RAM issues.

[polbit]

Is your power supply recapped at least ? ... But I think you are drifting onto another topic here relating to video interference not RAM issues.

I am using a Mean Well RD-50A for PSU right now, and it works fine in my main 1040STF with 4Mb RAM.

[exxos]

Well video issues you should open up a new topic and concentrate on the ram issue in this thread. But noise on the video is a inherent issue on most machines anyway, so its unlikely fixable.

Also as mentioned, please post a image of how you disabled the onboard ram.

[polbit]

I just fixed a 520STF motherboard (replaced CPU), and want to attempt upgrading with the 4Mb kit again. With that said, can someone tell me exactly which 68R resistors do I need to lift and tie to 5V? This MB seems to have few extras...

20200912_081413.jpg

[exxos]

It will be the 68R ones..