It's going to be one of a few similar simple no-real-mystery stories.
1 - Pin was bent during initial factory install, but still touching so
that cursory testing suceeded.
Maybe MSPLAN worked fine for years before the chip moved enough to lose
connection.
Maybe MSPLAN never worked, but GTE didn't care because they didn't use it.
2 - I think less likely but not impossible: MSPLAN was installed
correctly and worked fine from the factory, but GTE replaced it with
their own chip, then replaced the original when decomissioning, and it
got bent at that time but no one cared or even tested it.
It's not unheard of for custom roms to be installed, even internally,
but I don't believe anyone bothered to preserve the original roms and
reinstall them years later before they threw the machines away. Even if
they had a good strict data wiping policy for decommissioned hardware.
#1 seems perfectly likely and common.
A random bent DIP pin in a socket does happen because the kinds of
machines inserting the chip back then can't detect when that happens,
they just punch like a stapler. And having the chip actually still work
is common too, at least for some time, and/or some percent of the time,
because the bent corner touches the top of the socket and is held there
by the other pins. Then over time both the bent pin and the top of the
socket lose their spring tension in the metal, and the other pins creep
out from temperature cycles and vibrations etc.
https://youtu.be/IPryUBnbM_I?t=1087
--
bkw
On 8/7/24 15:22, B 9 wrote:
Somebody who knows more can correct me, but I don't see any reason Pin
10 would be intentionally bent under. According to the datasheet, it is
address line zero, *A₀*, so the ROM would still be putting data on the
bus, it just would be choosing an even or odd address arbitrarily. On
the other hand, when I see pins bent through carelessness, it is usually
at the corners, not in the middle. Also, you said it looked like nobody
had mucked about inside before. Perhaps it was a fault at the factory
and this machine has never been able to run MSPLAN before?
image.png
---b9
On Wed, Aug 7, 2024 at 12:02 PM B 9 <[email protected]
<mailto:[email protected]>> wrote:
Great job fixing MSPLAN! I have never heard of a reason for the pin
to be bent under. All I can think is that perhaps this machine used
to be attached to something over the System Bus connector and the
ROM had to be disabled to not interfere.
For the missing RAM, you may already know this, but one of the
interesting things about the Tandy 200 is that it doesn’t
differentiate between storage and memory. So, if you save a file
that is 1,466 bytes, your working RAM will be reduced by the same
amount. Try hitting |F1| from the MENU to switch to a different bank
of 24K and see if that changes things.
… wait a minute!
Actually, now that I’m writing it, I am realizing that you said
HIMEM was reduced, so forget what I said about files. HIMEM marks
the start of the portion of memory which is off-limits to BASIC and
it can be changed with the |CLEAR| command. This is useful to stash
machine language programs, such as AsciiPixels
<http://club100.org/memfiles/index.php?direction=0&order=&directory=Ken%20Pettit/AsciiPixels>.
To reset BASIC back to using the maximum amount of RAM you can do this:
|CLEAR 256, MAXRAM |
—b9
On Wed, Aug 7, 2024 at 9:37 AM Tom Blum <[email protected]
<mailto:[email protected]>> wrote:
I'm having fun now. And success getting MSPlan running. Plus a
new mystery.
A close inspection of the T200 insides found the following:
1. Light corrosion on the negative terminal of the backup
battery; will replace that as soon as the new NiMH battery arrives
2. a bit of the coating on thermistor TH2 chipped away,
component still functioning (see below)
3. no signs of leaking capacitors or fluid/liquid intrusion
4. no signs of degradation or consequential damage to traces
5. on the bottom of the main PCB, some surface mounted
components with discoloration around the mounting pads and on
parts of the components: R185, M30, M32, T17-T19 in particular
(see below). All of my vintage computer experience has been
with Ohio Scientific boards manufactured before 1980 and not
involving components at these small scales. I can't tell if the
discoloration is due to excess flux or some sort of discharge.
Whatever the cause, the system is functioning. I'm certain I
don't have the skill/steady hands to work with components on
this scale.
6. No sign that anyone previously mucked around inside the system
7. The MSPlan ROM (M14) was installed with pin 10 bent all the
way under the IC. Before reseating the ROM, I bent the pin back
out.
Once the M14 ROM was reseated and the unit reassembled, MSPlan
launched just as it should. And all other ROM-based
applications launch as they should. BUT....
*New mystery*: the system now reports in BASIC 17,868 bytes
free -- that is 1,466 bytes fewer than should be the case.
HIMEM is also reduced by 1,466 bytes.
Now I am wondering if pin 10 was supposed to be left bent under
and the ROM just needed to be reseated. Exactly how that would
relate to the availability or non-availability of 1,466 bytes I
don't know.
Tom
On Tue, Aug 6, 2024 at 9:40 PM B 9 <[email protected]
<mailto:[email protected]>> wrote:
Brian is right that whatever happened to make tge builtin
ROM disappear is pretty serious. Birt has some good videos
<https://www.youtube.com/watch?v=1adlQo3UI90> on fixing up
such problems on his YouTube channel
<https://www.youtube.com/@HeyBirt>. Even if you don't have
the time right now to completely fix it, it would be good to
open it and clean up any corrosion.
One last thing to try, although I'm pretty sure it will be
exactly like running it from the menu: On my Tandy 200 you
can launch MSPLAN from BASIC by using `CALL 61167, 1`. What
does it do on yours?
—b9
On Tue, Aug 6, 2024 at 8:00 AM Brian K. White
<[email protected] <mailto:[email protected]>> wrote:
I can only confirm that MSPLAN works with no option rom
installed.
Could be either bad ram or bad rom. There are two rom
chips inside
besides the option rom socket outside. Or anything else
like a corroded
trace making a stuck address line. These units all have
leaking caps and
batteries by now, even if they are still working.
Don't be loath to open it, run to open it to arrest the
development from
getting worse as soon as possible.
--
bkw
On 8/5/24 09:51, B 9 wrote:
> That's actually pretty cool and I'm curious what
GTE's firmware does.
> What software version are you seeing?
>
> I'm not sure why they would overwrite MSPLAN yet
leave it in the menu,
> but if they added an "option ROM", I believe you can
run it with `CALL
> 61167, 2`.
>
> —b9
>
>
> On Sun, Aug 4, 2024 at 6:10 PM Tom Blum
<[email protected] <mailto:[email protected]>
> <mailto:[email protected]
<mailto:[email protected]>>> wrote:
>
> Hello,
>
> New to the community and apologies if I'm raising
a question/issue
> already addressed. Just purchased a working
T200. Power cycles
> nominally and shows classic menu options.
Selecting Multiplan from
> the menu places the T200 into a frozen state.
LCD screen appears to
> fill (shaded) completely but program does not
start, no visible
> text/graphics. Resetting and power-cycle
necessary to get back to
> the main T200 menu. Noted that this T200 has a
property label on
> the bottom indicating that GTE, Inc. (the telecom
company) was a
> previous owner and appears to show a unique GTE
software version #.
> Is it possible that the original/built-in
Multiplan ROM was (or
> could be) removed from the T200. As a newbie to
the T, am loathe to
> open up a working unit to see if a ROM is
missing. Is there a past
> or present ROM option module for the T200 that
would have Multiplan
> installed (or installable)? Tom
>
--
bkw
--
bkw
