Another 1040 STFM and Exxos memory upgrade (1/4mb)

[ChaoticBiker]

Hey all,
didn't want to start another topic.

Here's my problem.
I also have just tried to install the Exxos 1/4mb memory upgrade, same as here- 2019 model.
My Atari is 520 STFM which had 512kb ram and was working all fine before.
It's C070789-001 REV.Di

What I done:
Removed the original memory chips (had to cut some pins)
Removed the wee blue capacitors that were next to them (cut them out)

Soldered the board, and checked connections.
Soldered in the resistors R71 R72 and R71, first 68 ohm then recently changed them to 33ohm as they are in now as read up here 68ohm can cause various issues and thought it might be it (it wasn't)
Changed location of C49 but it's soldered different to what's above - I got - soldered to where the pic above but + to where L51 connects as per original exxos instruction - see pic below
Please also note how I routed the provided wire for MMU pin - it's through one of empty TOS holes - any chance this could be the issue? Highly unlikely I think

2022-03-01 13.14.54.JPG

Atari was thoroughly cleaned before the install (including MMU and pins in socket), and it was working before and after the clean no problems.

I am getting the black screen with white border, regardless if board is in 1Mb or 4Mb position. For the diagnostics I unsoldered my switch so it should be permanently in 1Mb position now.

Any ideas where to look for a fault? Board has connection on all pins - checked with multimeter. Resoldered just to be sure.
Have I missed something? I am guessing it might be a broken trace somewhere but again checked all the now empty memory slots and found 2 and fixed them, but now all seems to be fine.

Any and all advice is appreciated!

2022-03-01 13.14.54.JPG

[PhilC]

@ChaoticBiker I've split your reply off into its own topic as it helps with clarity and will help others find the topic easier in the case they have similar problems :)

[rubber_jonnie]

Black screen and white border means no RAM generally speaking, I'd suggest a re-check of all of your work looking for shorts and bad joints.

Check all the socketed CPUs, in particular the PLCC types for bad connections.

[ChaoticBiker]

Thank you @PhilC for moving this into a new topc

Black screen and white border means no RAM generally speaking, I'd suggest a re-check of all of your work looking for shorts and bad joints.

Check all the socketed CPUs, in particular the PLCC types for bad connections.

Thank you for your suggestion.
I have re-seated the U56 and U65 chips and cleaned them, also checked each pin for continuity - it's there.

I am trying now to track all the memory traces to see if anything's been accidentally damaged outside where all the soldering took place but it's very time consuming - I'll have a look again after work.
I will definitely update once I solve the problem, so if there's no update it means I'n still fighting.. until then anyone looking at this please let me know if you have any other ideas, or questions for me.

I do have a feeling that as usual with my projects, it's something easy and stupid that I'm not seeing.

[rubber_jonnie]

Thank you @PhilC for moving this into a new topc

Black screen and white border means no RAM generally speaking, I'd suggest a re-check of all of your work looking for shorts and bad joints.

Check all the socketed CPUs, in particular the PLCC types for bad connections.

Thank you for your suggestion.
I have re-seated the U56 and U65 chips and cleaned them, also checked each pin for continuity - it's there.

I am trying now to track all the memory traces to see if anything's been accidentally damaged outside where all the soldering took place but it's very time consuming - I'll have a look again after work.
I will definitely update once I solve the problem, so if there's no update it means I'n still fighting.. until then anyone looking at this please let me know if you have any other ideas, or questions for me.

I do have a feeling that as usual with my projects, it's something easy and stupid that I'm not seeing.

BTW I presume that there is power to the expansion board?

[ChaoticBiker]

BTW I presume that there is power to the expansion board?

Which pin should I check this on? There was no instructions to route any external power to the board

[rubber_jonnie]

BTW I presume that there is power to the expansion board?

Which pin should I check this on? There was no instructions to route any external power to the board

Look at the pins that connect to the old holes in the mainboard and using a datasheet, figure out which pins from the RAM chips were 5v and chase it up to the expansion board.

[ChaoticBiker]

Which pin should I check this on? There was no instructions to route any external power to the board

Look at the pins that connect to the old holes in the mainboard and using a datasheet, figure out which pins from the RAM chips were 5v and chase it up to the expansion board.

OK I just tested a few pins, and I am getting +5v on the board, right here

2022-03-01 13.14.54.JPG

Generally tested a few other points and the board does appear to have power.

[rubber_jonnie]

Look at the pins that connect to the old holes in the mainboard and using a datasheet, figure out which pins from the RAM chips were 5v and chase it up to the expansion board.

OK I just tested a few pins, and I am getting +5v on the board, right here
Generally tested a few other points and the board does appear to have power.

And that power can also be found at the RAM on the expansion?

[Steve]

I know I may be a 'doomsayer' but my guess is broken traces on the top of the motherboard where the ram used to be. The expansion may need to be removed and traces checked. Note: you'll need to buzz them out, sometimes the trace can be a hairline crack not visable without a magnifying glass.