exxos's Atari, Amiga & retro forum

Hi guys,

I'm working on an STFM C070523-001 and it has a couple of jumper wires from the +5v of the 4700uf cap to R91 & R90. I haven't seen this before. It has a marpet memory upgrade so I wondered if this was required as part of that.

Let me know cheers

Hi. They are part of the Marpet to disable the original ram chips.

Ah Cheers Tony :)

I saw the pic and instantly recognised it. :lol:

Looks like it's for RAM disable, but you'd need to double check where the other ends are connected to to confirm, as they don't look like the usual resistors you'd tie to 5v to disable the RAM.

Also you usually need to tie 3 resistors to 5v, R59, R60 and R61 and also R71, R72 and R73 if present, and I only see two wires, though to be fair it may be either the angle of the photo, and it could be a mainboard variance.

Here's the thingy for it.

Marpet only disable RAM on 2 resistor per bank in manual if I remember correctly. So the board only have 512Kb RAM on board (disabled now).

DoG wrote: 13 Aug 2020 15:32 Marpet only disable RAM on 2 resistor per bank in manual if I remember correctly. So the board only have 512Kb RAM on board (disabled now).

Yep, just checked the manual, looks like it's definitely the connections to disable RAM in bank1 as per Marpet instructions. R90 & R91 for bank 1 R93 & R94 for bank 2. Page 21 of the guide.

Guys just checking - if I remove the 512k of ram (all chips) from the board, I'm guessing it is probably a good idea to remove the wires going from 4700uf 5v to R90 & 91? Just to be clean

Been wondering this meself, after seeing people having to remove it due to issues with their machines.