Random pixels on the screen with programs taking up more than half a mega of RAM.

[Roberto]

As its random, have you checked the pull up resistors on the data and address lines?

I once had a SIL resistor on a Mega ST that had a crack in it, gave me weird issues. Might be worth doing the mandatory fixes, at least the pull ups.

I tried to physically see where the pull up resistors are. They should be close to the shifter or RAM, but I'm not sure, I wouldn't want to change them all! Are they the ones in the blue, red or yellow box?

IMG_4019.jpeg (972.34 KiB) Viewed 437 times

[HigashiJun]

@Roberto

Just check here:

viewtopic.php?f=17&t=2235#p27504

[exxos]

I'd suggest disabling the upper ram bank for starters.

Also, it's hard to tell, but if the ram problems get worse over time, generally several seconds, it tends to be a ras / cas fault.

I've seen it where when the machine is turned on (after been turned off for a while) the screen looks fine. Then after turn on, it's like random pixels start appearing and get worse until the screen is totally corrupted.

[Badwolf]

From your screenshots it does look like mostly the bad pixels come in columns, which suggests individual bits.

I wonder if you're better off just doing a 4MB RAM upgrade that eliminates all that old RAM.

Or, like Exxos says, reducing the system to one bank of RAM (I guess that would involve removing one of the RAS/CAS resistors?) and stealing good RAM from the second bank to repair the first until you can source replacement chips.

BW

[Roberto]

Hi guys, unfortunately my friend decided not to continue with the work, since he bought another Atari 1040 ST at a very cheap price and it is fully functional.

There is something strange, however, that I wanted to tell you: in these days of vacation I found an old Atari 1040 STF in the attic that, when turned on, gave more or less the same problems as my friend's, indeed, even stranger. This Atari showed a black screen, or it reached the Desktop, or it still displayed bombs, or at a certain point it did a reset by itself.

Treasured what you advised me to do with my friend's Atari, I went over all the welds a bit and magically now it works.
Here, I wanted to tell you that at least all this led me to revive and bring to life another Atari that, I remember by now, I gave it up.

Thank you and happy new year!