have 2 ql's
question 1 first ql issue 5 m/b
has jm rom can it be replace with js rom with no mods ?
Yep, with no problems at all. Just plug in the new ROM set.
Note in case you use EPROMs instead of original ROMs, you need to change some jumper settings on the board. But original Sinclair JS ROMs can just plug in.
question 2 2nd ql issue 5 m/b
has jm roms but one rom is piggy backed with two roms in one socket with one pin sticking out connected to the m/b
can be removed and replaced with normal jm rom ?
That is an earlier board version, I think. Very probably the stacked chips are not ROMs, but rather EPROMs.
Does the board have an IC17 equipped?
Basically, there are two ways to upgrade this board to a new OS:
- Leave the piggy-pack thing as is, burn a set of EPROMs with the lower 16k in the left one, the upper 16k half and half into the 2 stacked chips (lower addresses in the bottom chip, obviously needs some soldering, keep JU1-4 as-is)
- Upgrade board revision to newer version:
- remove IC17
- remove the flying lead (the one conected from the pin of IC33)
- set JU2, JU3 and JU4
install new ROM set (2x16k)
An explanation what the issue 5 board supports in terms of ROM/EPROM combinations and required jumper settings can be found in the bottom-right text box of the issue 5 schematics
Easiest thing is: Find yourself a Tetroid ROM switcher
. This also allows you to change ROM versions on the fly.