Atari 1040STFM failed on moving from 2 chip Rom into 6 chips.

[radzio222]

Hi,
I'm New to the forum. I got. ATARI 1040STFM. It is a German version. So I decided to chenge TOS into English version.
I soldered 4 28pin brackets, resolder 1MB pins and sokder 256kB pins. Downloaded 1.04 TOS then I splot it with a CARTridge MANager into 6 images (3 Low and 3 High), burnt them on M27C256B EPROMS.
And after chip installation I Just got only White screen. Did I missed something?

Reverse proces to 1MB chips worked.

[atarifreakz]

So are you saying you went from 2 TOS roms to 6 TOS roms?

if so then you need to move the 3 solder pads from 1mb to 256K and remove the 16pin LS11 chip

[rubber_jonnie]

OK, so it would help if you could add some pictures showing how you have the jumpers soldered and showing the soldering of the sockets and bypass capacitors.

I would add that you can get away without the bypass caps, however my personal preference is to ensure they are installed.

A fully white screen generally means a ROM issue.

@atarifreakz may be correct in that the LS11 might need removal, however having done a few like this, that hasn't been my experience. If all the jumper pads are correctly soldered to 256K then the LS11 is actually bypassed and shouldn't need removal.

The schematic does show 3 pads that need to be changed:

Screenshot 2025-07-07 at 11.12.28.png (379.81 KiB) Viewed 2086 times

With the pad near U68, the LS11, needing to be changed as well to 256K. I've missed that one in the past and my upgrade didn't work.

So remove the solder from all 3 1M pads and check for continuity between them to be sure they are clear of any solder whiskers, then go on to solder all 3 256K pads together and try again.

[radzio222]

So it means that i forgot third jumper as in the picture right?

PXL_20250705_121905231.MP.jpg (312.69 KiB) Viewed 2065 times

[exxos]

So it means that i forgot third jumper as in the picture right?

Yes.

[rubber_jonnie]

Yes, immediately above U56 and marked CE

[radzio222]

Hi, I resoldered third jumper and still same effect. What about those bypass capacitors? Do I need to desolder some of them?

PXL_20250713_123953613.jpg (361.45 KiB) Viewed 2013 times

[stephen_usher]

The caps make no difference. They're just there to suppress spikes in the power rail caused by the chips switching logic internally.

Check that you've fully cleaned the 1M pads. The second one on the left looks as if it may still have a connection. Check with a multimeter.

[rubber_jonnie]

As I mentioned previously, you need to use a multimeter in continuity mode to see if there is any remaining connection on the 1M pads, it only takes a fine whisker of solder to make an unwanted connection.

I'd suggest cleaning the pads with some solder wick and a bit of flux to help things along.

As @stephen_usher said, the caps aren't something to worry about, the design calls for them to be there, but it doesn't really cause any issues if they aren't. If they are there, and it looks like they are in your photo, then just leave them in place.

[radzio222]

I checked them with multimeter and there wasn't any connection.

I'm thinking if there are some problems with a ROM itself. Are there any limitations if you have a German version of ST, or maybe different ROMS between ST, STF and STFM?