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Weird TRS-80 Model 100 fault with paste button

P

Primitive Person

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Mar 21, 2022
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I got a really nice TRS-80 Model 100 from eBay a few days ago. I got it all set up and running, and all appeared to be well - a 24K machine that seemed in good order. I soon found my way around the machine and successfully got data flowing in both directions via the RS-232 port.

So far, so good. But...something very odd happened when I cut some text and tried pasting it. On pressing the "paste" button, I didn't get the text I'd selected, I got a string of letters and symbols (A^B^C^...and so on).

This has happened every time I've tried. It's also immediately eaten about 3k of memory each time, and once the file is deleted, this memory stays unavailable, only returning after resetting the machine.

All very weird. I'm hoping it's just a loose connection or something. Other than that weird issue, the machine seems to be fine.

In case it's relevant, it's a European model (no modem, socket blanked off). The date format when setting it is dd/mm/yy rather than the US mm/dd/yy format.

Any ideas?

Lee
 
Thanks for the welcome! I hope someone can help, I'm a sucker for the battery-powered-portable form factor, and the Model 100 is the grandaddy of them all. I have a Cambridge Z88 and an Amstrad NC-100 as well. I got the NC-100 and the Model 100 talking to each other within minutes!
 
Did you ever cold restart the laptop?
You dont say if you purged it or not.
It sounds like file system corruption.
 
Twospruces said:
Did you ever cold restart the laptop?
You dont say if you purged it or not.
It sounds like file system corruption.
Click to expand...
I've cold restarted it several times, as it's the only way to get the memory back to 24K, but the fault happens again every time.

I don't know the machine's history, but I'm guessing it was hidden away in an attic for years before I bought it, so I don't know if that offers any clues.
 
Ok that is good to know.
Are you using Paste correctly? You probably are, but anyways
Ex. go into text, and select some text.
turn on labels
select text using F7
copy with F5 (this puts characters into the "paste buffer"
Paste it

the paste buffer is a special file in the file system. if it has garbage in it then you can paste garbage.

Your M100 should have a socketed main ROM, but all the 3 RAM modules should be soldered? Reseat the main ROM?

You could run a memory test to test your ram modules?

Club 100

Continued Support for Tandy/Radio Shack Model 100, 102, 200, WP2 -&- NEC PC8201A Computer Owners Since 1983
www.club100.org

not unheard of that the old M100 memory modules can develop defects.
 
Twospruces said:
Ok that is good to know.
Are you using Paste correctly? You probably are, but anyways
Ex. go into text, and select some text.
turn on labels
select text using F7
copy with F5 (this puts characters into the "paste buffer"
Paste it
Click to expand...
Yeah, I'm following those instructions properly. Example of what happens below. Pasted text should read "test4":

20220321_173441.jpg
Twospruces said:
the paste buffer is a special file in the file system. if it has garbage in it then you can paste garbage.

Your M100 should have a socketed main ROM, but all the 3 RAM modules should be soldered? Reseat the main ROM?

You could run a memory test to test your ram modules?

Club 100

Continued Support for Tandy/Radio Shack Model 100, 102, 200, WP2 -&- NEC PC8201A Computer Owners Since 1983
www.club100.org

not unheard of that the old M100 memory modules can develop defects.
Click to expand...
If the RAM is defective, is getting it repaired or replaced an easy thing to do?

I haven't opened the machine yet as I've not had time, but I will do, and update when I can.
 
very odd.
things to do and watch for strange effects in the file system
1. load up a few .BA and .DO files. Or make them. See if the file system keeps track of them or if the files become corrupt.
2. do a ram test from club100.

If the ram modules are soldered in, it is a more involved repair than if they are socketed.
First thing is to find a way to prove the ram has a problem.

that sequence of bytes in the paste buffer are really strange!

What should it have pasted? What did you expect?
I guess you are saying the entire sequence from ^A to ^Y is what was pasted.

thx
 
Primitive Person said:
I've cold restarted it several times, as it's the only way to get the memory back to 24K, but the fault happens again every time.

I don't know the machine's history, but I'm guessing it was hidden away in an attic for years before I bought it, so I don't know if that offers any clues.
Click to expand...

Are you just using the reset button or doing a proper reset using the cntrl-shift-break sequence?
 
what is printing is a sequence from 1 to 26, with 26 = EOF. very strange. hard to imagine that sequence is in RAM
 
Last edited:
Twospruces said:
what is printing is a sequence from 1 to 26, with 26 = EOF. very strange. hard to imaging that sequence is in RAM
Click to expand...
I've just opened the machine up. Besides it having 40 years of fluff inside it, everything seemed OK on first inspection.

The RAM expansion chips were socketed so I levered them both out and swapped positions. Same fault again.

I did notice a bit of gunge on the PCB to the right of the ROM chip which looks like a bit of capacitor leakage. I wonder if it's shorting pins on the ROM, so I'm going to lever it out and give everything a good clean. Everything else seems clean and sound, including the memory battery.
 
So you have a 26-3801 (8k) and it had 2 upgrade ram modules? (the UK model with no Modem?)
did you try to reseat the main ROM?
The RAM module that is used first, would be the 2nd expansion module. What I mean by first is that your system RAM is 3 groups of 8k, starting at 40k address. A000h - BFFFh.
If you remove the 2nd upgrade RAM, you would have 16k available starting from C000h - DFFFh

The ram file system starts at the lowest RAM address.
The point is by swapping and/or removing modules you will be changing what ram module is used for the start of the file system.
Sounds like you did the right thing.

The "soldered in" ram module should always occupy E000h - FFFFh.

I am assuming that your machine is really stock and there is a single soldered in ram module.

If the RAM is good, have to assume the ROM, or another strange hardware problem.

(try a ram test - my modified Paul Globman ram test is attached. Load as a .DO ASCII file and run, then run MEMCHK.DO)
 

Attachments

  • memchk.zip
    603 bytes · Views: 6
A little bit of fact checking on my side.
The paste buffer is actually in the upper RAM segment E000-FFFF.
This means it is the "soldered in" ram module that is suspect.

I think running that ram test should be revealing. It should complain.
 
Twospruces said:
A little bit of fact checking on my side.
The paste buffer is actually in the upper RAM segment E000-FFFF.
This means it is the "soldered in" ram module that is suspect.
Click to expand...
Yeah, that would have to be the case. :( It's the only memory common to all machines, so I guess all the important system variables and data live there.
Twospruces said:
I think running that ram test should be revealing. It should complain.
Click to expand...
I've run the program and created the machine code - how do I load and run it? I'm a complete n00b here. :) What will it tell me if there's a problem?

There genuinely seem to be no other problems in operation. I've typed in quite a lengthy text document (without using Paste!) and all seems well.
 
Just move the cursor on top of memchk.co and press enter. Should run and beep once for good and 5 beeps for bad
 
can you try running it a different way? I just realized that you will also get 1 beep if it does not load and run. IE an error.

go into BASIC
type
LOADM"MEMCHK.CO"
you should see some start, end, exec addresses and no error message

then
CALL (to the EXEC address 64704?)
 
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