Atari STF 4mb RAM Issue

[BlameCanada]

Hi!

I am in dire need of help, I've been troubleshooting my RAM work for a few days now and can't make it work:

My machine is an American 1040STF with a C070523-001 "Silly-style" Rev.D motherboard and TOS 1.00 in ROM (I usually load TOS 2.06 from floppy, then boot from UltraSatan). I have also installed the Exxos PSU which works great and helped a lot with the video quality!

With the onboard RAM disabled and the 4MB board installed, I have no video (my display can't handle 15.7khz; I guess it would show the "no-ram-banks" black screen with white borders if it did handle it; I only have a monochrome adapter to VGA). The power LED is lit and the floppy LED lights up for a split-second then nothing; no floppy seeking, though the drive is known to work.

The Atari still works as it should with its onboard RAM re-enabled, the shifter in the adapter, and even with the MMU adapter in the MMU socket (as long as the ribbon cable is not connected; otherwise the machine goes haywire, which I assume is normal behaviour with the redundancy).

The usual Nintendo cartridge stuff didn't work (pushing hard, holding the board in, praying to any given deity, resetting the computer a thousand times, etc.), Deoxit didn't help, continuity checks all seemed fine (I checked from the header pins of the MMU board to the video shifter pins and all the shifter adapter pins and from the MMU board to the MMU socket pins on the underside of the motherboard), changing the MMU board to 1MB didn't help, looking up every single thread on this forum about issues didn't help.
As long as the onboard RAM was disabled, the results were always the same; no video and no floppy seek.

The only thing I haven't tried is removing the onboard RAM (which I would wish not to do at very least before it works), and plugging the RAM in another ST (because I don't have one around).

I will have to buy another MMU board (among other things) no matter what since I messed up its 4MB pad while troubleshooting, but like I said earlier the MMU won't cooperate in any jumper configuration (1MB or 4MB), and never did. I did not cut the pins for clearance (yet; I wanted it to work first, then see if it cleared without the RF shield, and then cut them if needed), I just ran it with the keyboard on a plastic container atop the floppy drive.

I will provide pictures if needed, thank you all for your help, and have a nice day!

[exxos]

Yeah it will probably help to post some images of how you have it all set up..

[BlameCanada]

No problem, here are some. Unfortunately, I won't be able to take other pictures or try things until tomorrow afternoon (around 21 hours from now).

shifter1.jpg (118.04 KiB) Viewed 4249 times

mobo1.jpg (121.68 KiB) Viewed 4249 times

mmu3.jpg (92.92 KiB) Viewed 4249 times

mmu3.jpg (92.92 KiB) Viewed 4249 times

mmu2.jpg (81.03 KiB) Viewed 4249 times

mmu1.jpg (89.37 KiB) Viewed 4249 times

mobo_hirez.png (3.31 MiB) Viewed 4249 times

[exxos]

With the onboard RAM disabled and the 4MB board installed, I have no video (my display can't handle 15.7khz; I guess it would show the "no-ram-banks" black screen with white borders if it did handle it; I only have a monochrome adapter to VGA). The power LED is lit and the floppy LED lights up for a split-second then nothing; no floppy seeking, though the drive is known to work.

I would assume the video is outputting low resolution which your monitor cannot display..You really need a monitor which can display the image as it will give you clues on what is not working with the RAM.. Alternatively you can get a diagnostic cartridge and serial link it to a PC for it to diagnose hopefully what the problem is.

[frank.lukas]

There are only four resistors. There must be six because of old ram CAS_0H, CAS_0L, RAS_0 and CAS_1H, CAS_1L, RAS_1. Think ...

[BlameCanada]

There are only four resistors. There must be six because of old ram CAS_0H, CAS_0L, RAS_0 and CAS_1H, CAS_1L, RAS_1. Think ...

I figured there was something weird with this mobo revision (two resistors are missing; I saw on the Marpet install guide it would be enough to tie those four resistors to 5v to isolate the RAM - but I should've completely isolated it to begin with).

Anyways, I poked around and found out that the four resistors already there were the CAS signals and that the RAS signals of the DRAM chips went to the two unpopulated pads next to the resistors, so I took two 68r resistors I had lying around and wired them from the pads to 5v, but the results are the same, still no video or floppy activity.

I would assume the video is outputting low resolution which your monitor cannot display..You really need a monitor which can display the image as it will give you clues on what is not working with the RAM.. Alternatively you can get a diagnostic cartridge and serial link it to a PC for it to diagnose hopefully what the problem is.

That's what I would assume too. I'll have to go with the diagnostic cart as RGB monitors are hard to come by (can't SCART my way out of this in NTSC-land; and I really was mostly going to use the Atari in hi-resolution mode).

It'll probably take around a month for it to get here, though, with Canada Post being stupendously overwhelmed and all; I'll come back with the results when I can!

Thank you both for your help!

[BlameCanada]

I received the diagnostic cart today and gave it a spin;

" I1 RAM/data line error 0000000000000000 1111111111111111 000008 "

With both 4Mb kits (any shifter board and RAM board combination).

(It doesn't output anything to serial when the board is run without the video shifter in, but I would assume this is normal behaviour)

The only thing I can think of is to completely remove the onboard RAM, but I'm not sure enough to do it without hearing your two cents; and I would like to keep the RAM in if possible, just in case.

[exxos]

Oddly this seems to be exactly the same issue as posted in this thread with another upgrade https://www.exxosforum.co.uk/forum/viewt ... =23&t=3119

I think removing the old ram may well help ( the simplest way is just to use some side cutters and cut all the RAM pins off first).

Maybe the power supply just is not capable ?

[BlameCanada]

I found out what was wrong - while I was trying to pull down the outputs of the ram chips with resistors (which doesn't work) and praying to random gods (which may or may not work), I ended up making it boot by removing the +v link to the RAS and CAS resistors (removing the long brown wire in the pictures), BUT untying the resistors from each other made the computer too unstable to boot properly (I1 random crashes at boot).

It then booted the diag cart enough so that I could test the ram, and it came back with many errors,
so I went all in and removed the original RAM;

and it now works without errors.

The only thing remaining is to make SELTOS.PRG work again with the 4Mb of RAM or find a way to make a TOS 2.06 ROM fit in there, but I'll make a new thread if I end up stuck.

Thank you very much for all the help!