Atari found out, that DRAMs from particular series "remember" bits for a long time after the power is off. And if you switch power off and on to force cold start, the computer boots with garbage on screen, then hangs up. So they developed a fix: mix each set of DRAMs with a single chip from another batch, the "fast forgetting" one, and the assembled computer passes tests OK! It was easy and cheap, so they did it.
Can't see anything unbelievable in such a story. It is recommended to add one or two different chips when replacing defective RAM in XL/XE's, it's common practice actually. And I didn't make it up, it came from guys good at electronics.
About this single different chip, think I know the explanation. It might be factory fix for some known bug.
RAM chips are able to keep data stored up to 15sec. without refreshing. And there is no procedure for cleaning up/zeroing memory that Atari performs on booting. So - if you power off the computer, then turn it on immediately - it is likely that Atari just hangs up due to some residues of data still existing in RAM.
A working solution is to replace single memory chip with another with different access time. For instance - one chip 200ns vs all the rest with 150ns. Or just put in one chip made by another manufacturer - the one replaced will be almost identical as the rest, but almost is enough to do the trick.
This guy retrobrites without exposing plastics to sunlight, uses warmth instead. Just covers plastics with 12% peroxide cream, wraps carefully in black foil, then keeps it in dark warm place for one week. This treatment seems to be quite "safe", I mean, looks like prolonged procedure and avoiding UV-light prevent plastics from partial discoloring etc. imperfections.
I think the best way is to retrobrite something cheap and easy to replace first. Such as an old XC12 recorder, or STM-1 mouse. When you fine with the outcome, use the same treatment to your precious ST case.
There is a Tom2 reviev already on YT, submitted by larek (youtube.com/watch?v=b5yR4HXQjYw)
It's in Polish language, so here is my brief summary:
1. The device as it is won't fit Atari joystick port; the dongle is a bit too large. So you have to buy (cheap) joystick port extension cable with it. 2. Once you have Tom2 plugged in, it works with 8-bit Atari with flying colors. Larek had it tested with: XE computer (modified), XEGM with expanded memory, and stock 800XL 3. Logitech gamepad for PC - performed excellent on Atari as joystick controller 4. Microsoft wireless PC mouse - worked excellent on Atari as ST/amiga mouse.
You may find this webpage useful. It is hosted by jer, a qualified technician worked at Atari authorized repair center for years.
In Printers section, there is a diagram of 1027 printing head with all the dimensions. And an idea, how to refurbish a worn out one:
"Durability of [rubber] band with fonts is limited, so after more than 30 years (actual age of this equipment) it hardens, becomes brittle and breaks making the printer unusable. To get a replacement font band, you may try to order a custom flexographic plate, or just ask at inking stamp shop. Several attempts may be required to match the appropriate dimensions of the band to the printing head. But, you may elaborate a few new bands with different font styles and charsets."