4MB RAM Upgrade for Atari STFM 520 C103253 Rev 1 Board

[mcdoug]

Hi there,

Thanks again for recommending the kit, I ordered and installed as per instructions and noting that the MMU faces the other direction and got no video output. I am hoping someone may have some advice.This is my install, I lifter the resistors mentioned and hooked to +5v on the capacitor:

IMG_1364.JPG

I did continuity checks between the board connectors so knew the ribbon was seated correctly.

Fearing I had damaged something, I removed everything and put back to original state and everything worked ok again.

Next I cleaned the mmu contacts with IPA, let dry and then re-installed the board above the MMU only. I checked with a multimeter and have continuity from the top of the pins on the exxos board and the legs on the underside of the motherboard. I made no other changes and I didnt connect the ribbon cable and everything worked ok.

Then I added the shifter board (with chip in it) and I get no video output. So I removed the board above MMU and tried the shifter on its own, and still I get no output, when I put back to original state it all waorks again. So I was thinking there is something wrong with the shifter adapter board. I took it out and ran continuity on it between all pins to look for shorts and found pins 2 and 4 have a short. I measured the chip itself and the original connector socket and on these there is no connection between pin 2 and 4.

So I took my shifter board and examined repeatedly, cleaned with IPA and also reflowed the connections and I still get a short. I can see no physical connection between pin 2 and 4 in any of my soldering so am worried they are somehow connected in the board. Has anyone ever experienced something like this before with this kit?

IMG_1368.JPG

IMG_1369.JPG

IMG_1367.JPG

I think I may need to try and disassemble the shifter board and test for a short between 2 and 4 on the pcb itself but this will be a real pain to do so I was hoping someone may have some advice before I try this?

thanks,

Craig

[exxos]

Maybe this help ?

Capture.PNG

[mcdoug]

Excellent many thanks, I shall map my board to that and look for differences:)

Thanks for your help,

Craig

[mcdoug]

Hi thanks for the board file. I mapped the pins and they match this schematic, however there is a connection between the two pins indicated by the green arrows, is this normal? There is no such connection on the original socket or chip:

short.png

I am really confused, I cant see anything that connects these two pins and there is a whole other pin between them which is unaffected?

[exxos]

How odd.. Can you check if there is connection on those 2 pins to pin 20 ?

[mcdoug]

Hi thanks for your help again. I just checked and yes there is! a connection between all of these pins (2,4,20):

shifter.png

Does this help diagnose the issue? Is it an easy fix? I am really keen to get this all up and running :)

Thanks, Craig

[DoG]

Measured without shifter in place?

[exxos]

Sounds like there is a short from the IC pads to the copper fill which is connected to 0V (pin 20).. so I would suggest you remove the solder on those pins clean them up with IPA, and try and see if there is some damage from the solder resist somewhere shorting them out...


TOP & BOTTOM FILL

top.PNG

bottom.PNG

[mcdoug]

Thank you so much! That did the trick! It is crazy, I couldnt see any short even with a loupe but upon removing all solder, cleaning and reworking I had no short and the machine boots :D I was tearing my hair out so your help is greatly appreciated!

Quick question, do you know where I might find a .st copy of the xtra_ramtest.prg so I could load it using a gotek? I dont have a working floppy anymore :( Or alternatively, how I could do this myself?

[exxos]

Thank you so much! That did the trick! It is crazy, I couldnt see any short even with a loupe but upon removing all solder, cleaning and reworking I had no short and the machine boots :D I was tearing my hair out so your help is greatly appreciated!

Quick question, do you know where I might find a .st copy of the xtra_ramtest.prg so I could load it using a gotek? I dont have a working floppy anymore :( Or alternatively, how I could do this myself?

I would use this program...

https://www.exxosforum.co.uk/forum/viewt ... ?f=25&t=28

But not sure there is a .ST copy..