On Sun, 22 Mar 1998, Doug Spence wrote:
>
> Note: I've changed the subject line to the appropriate chip labels. My
> error when posting originally.
>
> On Sat, 21 Mar 1998, Don Maslin wrote:
>
> > > The Kaypro II has a chip with a sticker marked "81-146A", with the "A"
> > > stamped on in read ink. The Kaypro 2 has a chip with "81-232" on it, in
> > > the same location.
> >
> > If the layout of the two boards seem identical, the chip in the II marked
> > "81-146A", which is the character generator ROM, is in the wrong location
> > (U47). It should be in U43. The one in U47 should be either "81-149" or
> > "81-232". They may have gotten swapped.
>
> Sorry about that, the chip in location U47 was "81-149C", not what I
> wrote above. I guess I made the error because of the orientation of the
> machines - they were connected to each others' drives and thus reversed
> front-to-back, and I ran out to the other room to read the labels while in
> the middle of the post. I must've read the chip location off one board,
> then scanned directly across to the chip on the other board, without
> taking into account the reversed orientation. :(
>
> > > The chips at position U87 on both motherboards are marked DM74LS390N, but
> > > the one in the Kaypro II has been messed with. It's a 16-pin chip, and
> > > pin 1 has been bent upward and a wire soldered onto it, which leads to pin
> > > 6. Pin 9 is missing. Pins 12 and 15 are attached with a wire.
> > >
> > > Is this normal for a Kaypro II, or has someone made a modification?
> >
> > It is a modification.
>
> Do you (or anyone else) know if it's a known modification? What I mean
> is, does anyone know why this chip might be wired up this way? Does it
> solve some known problem with the Kaypro II, or make an enhancement?
There were a couple of common mods that were made to K-IIs - the first
more frequently than the second. The first bumped up the processor speed
from 2.5mHz to 4. The second was rather more involved and upgraded the
machine to double sided drives. I have not been involved with either, so
I cannot do much more than relate that information. You might want to
check the TCJ website and see if they have any information there.
> > > Anyway, I managed to make a copy of the WordStar disk that came in the
> > > drive of the II today, using my Amiga 1000, A1060 SideCar, A1020 5.25"
> > > floppy drive, and TeleDisk. So now I have a disk that boots reliably
> > > instead of 1 out of every 5-10 times. That meant that I now know there's
> > > something wrong with the Kaypro 2, because it won't boot at all with the
> > > new disk. Before, it may have just been a borderline disk that was
> > > causing the problem.
> >
> > Not necessarily. Unless both machines used the 81-232 boot ROM, there is
> > every chance that they both will not boot from the same bootable disk.
> > The boot ROM determines the revision of the operating system required.
>
> Humm... so I've been working from bad assumptions all along. They don't
> use the same boot ROM. However, as I mentioned, the Kaypro 2 did boot
> from this disk when attached to the II's drives instead of its own.
>
> Is it possible the drives themselves have different specs that might
> interfere as well?
Not to my knowledge.
> > > So (tell me if this was a bad/dangerous thing to do) I opened both
> > > machines up and attached them to each others' disk drives. They were
> > > plugged into a power bar, so I powered them up simultaneously with that.
> > >
> > > The Kaypro 2 boot up with no problems, using the II's drives, and the II
> > > was incapable of booting using the 2's drives, so I've got the problem
> > > located to drive A of the Kaypro 2 now.
> >
> > Maybe not. See above.
>
> <sigh>
>
> > > And BTW, both the II and the 2 have full-height drives.
> > >
> > > Both keyboards have missing keys (including broken plungers). Will this
> > > be easy to fix?
> >
> > The usual failure mode is for the cruciform projection on the switch
> > plunger to get broken off.
>
> Yup. I do have a couple of missing keycaps with good plungers, but
> generally I'm looking at what you describe.
>
> I really wish people would treat old hardware better in the Salvation Army
> stores. That's where I got both of these machines (at different times),
> and from previous observations, that's where I'd guess the damage
> occurred.
>
> > You will need to unsolder the switch and
> > replace it with a good one. With the benefit of a solder sucker, it is
> > not necessary to remove the circuit board from the keyboard metal work.
>
> OK. I've had the keyboards open and it doesn't look like an easy job,
> though. :/ Looks like time to review Tony's (un)soldering techniques. :)
>
> > > I'm thinking of fixing the 2, and using the II for parts, simply because I
> > > like the colour of the 2's green phosphor monitor better (and some other
> > > minor things). :) Is one model more rare than the other? IOW, does one
> > > warrant saving more than the other? If not, I'll go with my feeling and
> > > fix the 2 with parts from the II.
> >
> > The 2 is probably less common.
>
> OK. Considering the differing boot ROMs, though, it's possible that the
> only repairs that will need doing will be to the keyboards. I'd rather
> save BOTH machines than cannibalize one of them.
>
> I'm hoping the plungers are still made and easily available. Or
> salvagable off of something of lesser value, like old PC keyboards.
When you can determine the keycaps and switches that you need, send me
private e-mail. We can probably arrive at some arrangement so that I can
supply them to you.
- don
> Thanks for the info, Don!
>
>
> Doug Spence
> ds_spenc_at_alcor.concordia.ca
>
>
donm_at_cts.com
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Don Maslin - Keeper of the Dina-SIG CP/M System Disk Archives
Chairman, Dina-SIG of the San Diego Computer Society
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Received on Sun Mar 22 1998 - 17:46:54 GMT