Anything anywhere on the bus could be holding an address line high since
they're all attached to essentially the same wire, so, pull the main
rom, see if it's still stuck. If so, pull the ram even though that does
mean desoldering which requires some care & technique to avoid damaging
the motherboard.
The execute basic might be normal because there is a feature in the main
rom to run a certain program at boot if it's been set up, kind of like
autoexec.bat. I don't remember the specifics but it's in the regular
user manual. But you're right that right now that doesn't matter because
all bets are off and no data matters no matter what it looks like until
that address line is unstuck.
--
bkw
On 1/1/24 18:27, Eric wrote:
Happy New Year Everyone!
After probing around, I found that M12 ROM Pin # 20 (A11) is stuck high
(5V). Does this suggest a faulty ROM or is there something else that
could cause this condition? The ROM chip is a SHARP LH535618. Computer
serial number starts with 307xxxxxx.
I also have data from the logic analyzer (big thanks to Jeff Birt and
his videos). Data was taken during a Cold Boot. It seems that the
computer is skipping the "Boot Routine" and attempting to run and
endless loop of 0804H "Execute BASIC program". There also appears to be
a lot of garbage data. This may not be entirely meaningful being that
ROM pin A11 is stuck high.
Eric
On Friday, December 29, 2023 at 06:18:35 AM PST, [email protected]
<[email protected]> wrote:
Eric,
Sent you a mail off list with a link to my capture files, etc.
Jeff
*From:* M100 <[email protected]> *On Behalf Of *Eric
*Sent:* Friday, December 29, 2023 2:00 AM
*To:* [email protected]
*Subject:* Re: [M100] Model 100 - LCD Shows Pixels Only
Hi Jeff,
Luckily my logic analyzer does have more than 8 channels.
Can you give me some feedback on these settings:
Chip M2 TC40H245P - Octal Bi-Directional Bus Buffer
Simple Parallel Decoder
Sample Rate: 6.25 MS/s or 10 MS/s?
Clock State: Rising Edge
Voltage: 1.2 Volts, 1.8 Volts, or 3.3 Volts?
Stop recording after 2 seconds
Eric
On Thursday, December 28, 2023 at 10:53:55 AM PST,
<[email protected] <mailto:[email protected]>> wrote:
You can check each address line at the ROM to see they are all being
twiddled and that those connections are good. This is not fool proof as
a bad bus latch or any chip on the address bus can much up one of more
lines.
The data lines are more complicated. If you test at the ROM you will see
them twiddling but you need to look at the ROM chip select at the same
time to make sure you are seeing data from the ROM. Then you need to
look for the same thing back at the processor to see if all the lines
are good back to there.
If you have more than 8 channels on your LA it will be much, much
easier. As I recall I used channel 0 for the /WR had the Saelee software
filter out all data there that bit was not low. Then I had to guess at
what bit 0 might have actually been by looking at the disassembly. A lot
of work but I learned a lot on the process.
Good luck,
Jeff Birt
*From:*M100 <[email protected]
<mailto:[email protected]>> *On Behalf Of *Eric
*Sent:* Thursday, December 28, 2023 12:00 PM
*To:* [email protected] <mailto:[email protected]>
*Subject:* Re: [M100] Model 100 - LCD Shows Pixels Only
Thank you everyone for the quick response!
When I power up the computer, all pixels are on and remain dark (LCD is
entirely "black").
Contrast potentiometer: Seems to work as intended. The display will
lighten or darken as the potentiometer is adjusted.
LCD PCB: No signs of corrosion and/or damaged traces.
ROM: I'll ohm out the traces to see if I can find any broken
connections. Otherwise, are there any other troubleshooting steps I can
take?
RAM: Jeff, great video! Thank you for sharing. The M100 Test Harness
sounds like an ideal tool.
I have limited experience with a logic analyzer however it looks like a
fun challenge.I'll try to duplicate your setup but I may need some tips
on how to configure the Saleae software...
Eric
On Thursday, December 28, 2023 at 08:17:02 AM PST, Josh Malone
<[email protected] <mailto:[email protected]>> wrote:
--
bkw
