oolidjr@hubcap.UUCP (Joe Moll) (08/17/88)
First a responce to this one...
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From: jnp@calmasd.GE.COM (John Pantone)
I have been using my Mod 4 for 5 years now - without so much as a
glitch - one of the most useful and reliable machines I've ever used;
until yesterday! :-(
Symptoms: Put boot disk in drive - Power up - Drive light comes on,
drive spins - garbage on screen and no boot. Cannot boot in Mod I
mode (reset switch while pressing break key) either. I have tried
several LSDOS boot disks, and several CP/M+ boot disks - same results.
Fried ROM? Anybody have such a problem? Any guesses about price for
repair?
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First of all, you prob. don't have any ROM problems. The ROMs used in
the old Mod 3's and Mod 4's are tanks. You prob. have a dead disk
controller chip. I had the same trouble with my old Mod 3 and the new
chip did the job.
Since it will not boot in cassette mode (when you hold break and reset),
check to 8-pin jumper that is near the CPU on the mother board (can't
miss it, just a piece of flat piece of plastic with wires inside) and
make sure that it is plugged in good. That jumper connects the
CPU/MEMORY address busses to the video generation chips. Also, if that
doen't work, swap out the 74LS245 chips that are SOCKETED (yes I do mean
SOCKETED) near the Z-80 and the Character Generator chip (looks like a
28 pin ROM, actually that's what it is).
Also, try reseating the floppy drive cables. Sometimes that will fix
those problems.
Oh, yes almost forgot. The Controller chip is a WD1793 or equil. Goes
for about $10.
Now, to the next one.
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From: tech@auvax.UUCP (Richard Loken)
I need to play some intimate games with my model II disc controller but I
know nothing about it and taking the machine apart and peering at the board
didn't help.
Does the controller use a Western Digital chip like most of the world or is
this something the guys at Radio Shack devised? I need such info to make the
Dysan DDD11.ASM disc analysis program work.
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That controller chip is a WD1792. Good luck finding the specs on it.
Happy Hunting!!
Joe
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