snarkdluG

On AtariMania you can check how much memory each demo needs. If you need ST/STe/Falcon and so on.

Yup, it is the correct memory modules but... ...I didn't look that closely at the pictures and how the board was attached apparently. What you got is not a Marpet or a Frontier Solution board but a John Russel Innovations board and it's called the JRI-RAM+. It also got two video shifter attached so you got 4096 in the colour pallette to choose from. Normal ST have 512. Not that useful really. You can still only display 16 colours on the screen at once. So I don't think it's that easy to make this board to use 4MB as I thought. But I know it can be done, but I don't think it is soldered in for that at the moment. Manual for that board is nowhere to be found. I think most people bought it from B&C Computer. Some more info here about it. Just guessing here if you are interested: (Seems that the board got R, L and H solder point for RAS1, CAS1L and CAS1H on the left side for bank 1 (upper part, back part of board where the solder points are). H, L and R on the top right side of the RAM-board is probably unsoldered (since you don't use bank 2) on your board and is used for CAS2H, CAS2L and RAS2. In the middle there are W for WE and 9 A. Probably the nine address lines (MAD0-8). and the first solder point on the left is O for OE. So should be possible. Most of the signal is transfered through the flat cable attached on the DRAM chip so some solder points is not needed on top of the board. Bank 1 and 2 could be the other way around I suppose).

You could easily upgrade the 2,5MB machine to 4MB. Fit 2 more 1MB modules, 30pin, non-parity. You have to desolder the on board ram though. It's just a matter of desoldering one side of 2 resistors and connect it to +5V. Manual. It's the two bottom ones. Marpet bought Frontier but it is the same manual for the board. Regarding PSU I fitted a meanwell RT-65B in my Mega 1. A snug fit. Should fit a regular ST bracket as well. There are other meanwell that maybe have a better fit. Centurion Tech or exxos have ready replacement PSU boards. But they are on the other side of the pond from you so could be a bit pricey. So just cap change maybe be the best choice as you already stated. Maybe get a new rectifier bridge on the PSU as well.

For info: converting from 6 to 2 chips you will also need a 74LS11 on the board. Sometimes that is missing and sometimes it may also not be a place for it depending on board layout and revisions.

You can create blank/formatted ST files under floppy menu in Hatari. Otherwise just format with F-Copy or something similar if you already have stuff on it.

Glad to hear it worked out.

If you remove the Shifter chip (large chip in the middle) what does it say on the board? If its for a Mega 2 then all the wires should attach to another board which fit over the MMU. So the ram upgrade has been modified for a ST instead. Look here: https://docs.dev-docs.org/htm/search.php?find=Z-RAM

2 computers without modems needs a null modem cable to be able to talk to each other. It flips some wires in the cable, for example the send is connected to receive in the other end, handshaking, carrie detect and so on.

It' still a DS1307Z just marked on top as a DS1307:

Key caps sold in Germany by RTS I believe. Came with new rubber domes apparently. Called "RTS Tastenkappen / Tasturkappen".

TOS images can be found at http://www.avtandil.narod.ru/tose.html for example. You have to split them though. Use http://atari.8bitchip.info/ROMSPLIT.ZIP

Atari Mania got both the preview version you want and a full version.

Great work!

You can use on board memory with the Marpet if you want to. Usually you disable one or both banks on the board and just use simms in the Marpet simm holder. I'm not sure if it would help in this case since a whole bank is gone. The Marpet board just connect on top of the mmu and the shifter. So if either of those two chips is bad it would not solve it.

US is a hard disk drive replacement. ST and MSA are floppy disc drive images as you know. Use a Gotek or a HxC to replace a floppy disc drive for a more modern usage.