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lyonadmiral
March 12th, 2012, 04:50 AM
So I just stumbled across a cache of 7 revision two cards that don't have the jumper block on them, but I was wondering, couldn't you short the connect using a graphite pencil? If not, what would be another inexpensive way to replicate the functionality of the dip block without actually finding one and soldering it on.

8189

Picture: minuszerodegrees.net

Stone
March 12th, 2012, 05:04 AM
You know those wires inside the paper or plastic twist-ties in the produce department... just strip down the ends after you cut them to size.

lyonadmiral
March 12th, 2012, 10:40 AM
Couldn't I just take a graphite pencil and draw between the two contacts?

Chuck(G)
March 12th, 2012, 12:09 PM
Couldn't I just take a graphite pencil and draw between the two contacts?


Maybe, but you'd have to get the resistance down to about 600 ohms or less--assuming that the pullups are 2K or so. i.e.

5* (600/2600) = 1.15V, which should be a pretty good "low".

Personally, I'd just stick a 4-position DIP switch there permanently.

lyonadmiral
March 12th, 2012, 06:31 PM
I know the switch would be the best option but I have zero soldering experience.

Chuck(G)
March 12th, 2012, 08:31 PM
If you have one of those conductive ink pens or rear window defogger repair kits, that would work as well.

Are you trying to determine drive types supported? That's pretty well documented. The first (all jumpers open) is for a 10MB ST412 (and clones) drive, the fourth is for a 5MB (ST506) drive (both jumpers closed). The first two bytes in each 16-bit entry are the number of cylinders; the third byte is the number of heads.

Two jumpers for each drive. The four drive types are cyls/heads (all are 17 sector) in order of oo ox xo xx for jumpers:

306/4
306/6
375/8
306/2

The drive table's somewhere around offset 3E7 in the BIOS ROM on these things. You can patch whatever you want into there, so long as you recalculate the checksum for the ROM. Some boards used 4KB ROMS; some used 8KB (you'll note that there are extra pads for a 28-pin ROM), but the BIOS image fits into a 4KB ROM/EPROM nicely.

modem7
March 12th, 2012, 11:13 PM
The first (all jumpers open) is for a 10MB ST412 (and clones) drive, the fourth is for a 5MB (ST506) drive (both jumpers closed).
ST-506 = 153/4, not 306/2
I fell for that trap about 2 years ago, and Per brought it to my attention.

Chuck(G)
March 13th, 2012, 08:45 AM
Oops, you're right--that should be "ST406". Half of an ST412 (buffered seek).