Don't really know, but looking at a few character sets, it looks as if bit 7bit 6 of [7..0] is stuck high. It loops 40h-7Fh twice, then C0h-FFh twice. That might mean hardware failure of some sort.

[oh, further evidence, ascii 20h is space and 60h is `. So it looks like it's printing loads of ` when it should be space.]

snufkin wrote on 2021-12-04, 17:11:

Don't really know, but looking at a few character sets, it looks as if bit 7bit 6 of [7..0] is stuck high. It loops 40h-7Fh twice, then C0h-FFh twice. That might mean hardware failure of some sort.

[oh, further evidence, ascii 20h is space and 60h is `. So it looks like it's printing loads of ` when it should be space.]

So which piece of hardware takes care of the characters?

Hezus wrote on 2021-12-04, 18:16:

So which piece of hardware takes care of the characters?

'fraid I don't know and can't find a service manual. How do the other character mode tests look?

snufkin wrote on 2021-12-04, 18:42:

Hezus wrote on 2021-12-04, 18:16:

So which piece of hardware takes care of the characters?

'fraid I don't know and can't find a service manual. How do the other character mode tests look?

Same problem as far as I can tell.

Still can't really help, but a quick read around says that IBM CGA graphics card had a 8kB ROM chip that stored font symbols. Maybe the LT has something similar (separate character ROM) and one of the address lines has latched high. Given the computer boots and can run programs then the problem seems to be isolated to how it displays stuff.

Check your code page with chcp and make sure it's not getting set weird .
It should be 437. If it's not, you can change it to 437 with "chcp 437" if it's prepared in config.sys.

If it is a hardware issue, I probably have an extra main board I would be willing to give you if you intend on keeping that machine running.

kvg21 wrote on 2021-12-05, 06:03:

Check your code page with chcp and make sure it's not getting set weird .
It should be 437. If it's not, you can change it to 437 with "chcp 437" if it's prepared in config.sys.

If it is a hardware issue, I probably have an extra main board I would be willing to give you if you intend on keeping that machine running.

I thought about using the codepage command, but the numbers are already messed up when it's counting up memory, way before DOS loads. I guess that pretty much means it comes down to a hardware problem.

If you have a spare mobo for this model that would be greatly appreciated! Can you send me a private message so we can work out the details?

EDIT: Just verified that the codepage is set to 437 as it should for IBM XT compatibles. Or rather 'tsw' as my screen displays it now, 🤣.

I'm certain I have an extra. I have 8 of these laptops that I purchased for various parts. Someone scavenged the hinges for who knows what out of one of them, so I will verify that the board is still working properly and let you have it. I don't see a direct message link yet, so I may need to post a few messages before I can PM you. If you can send me a message first, maybe I can reply to it. 😀

I verified the board works. What I'll do is send you the base. It has a bad fdd in it, but you may be able to fix it if you really want to. It might be easier for you to just transfer the top of yours to this one, with the fdd(s) and/or hdd than to try to swap the board. There's just 1 ribbon cable connecting the base to the top for the monitor, and a few screws for the keyboard if you want to swap the keyboard. When you remove the top, the ribbon cable is on the right side in the middle. Just lay it over to the right and it'll come off easily. Remove the 5 screws from the bottom and the top 3 screws from the back to remove the top from the base. The monitor can be taken off by popping out the two clips on the arms and then simply sliding the monitor off, but the springs were removed from the hinges on this one for some reason, so you'll need to swap the whole top if you go that route.

kvg21 wrote on 2021-12-05, 14:46:

I'm certain I have an extra. I have 8 of these laptops that I purchased for various parts. Someone scavenged the hinges for who knows what out of one of them, so I will verify that the board is still working properly and let you have it. I don't see a direct message link yet, so I may need to post a few messages before I can PM you. If you can send me a message first, maybe I can reply to it. 😀

I'll send you a PM!

I can see your PM, but I can't respond to it.
Searching through other threads, it appears there's a minimum number of regular posts that must be made before access to submit PMs is allowed, but that number isn't listed in the thread... and I'm not going to just spam posts until I can send a PM, because that just defeats the purpose of the rule. I'll see if I can find something useful to respond to and up my count.

kvg21 wrote on 2021-12-05, 16:59:

I can see your PM, but I can't respond to it.
Searching through other threads, it appears there's a minimum number of regular posts that must be made before access to submit PMs is allowed, but that number isn't listed in the thread... and I'm not going to just spam posts until I can send a PM, because that just defeats the purpose of the rule. I'll see if I can find something useful to respond to and up my count.

That's quite redicilous. I'll PM you my email adress and then we'll talk there.

Pictures of the board when you dismantle things would be nice. There's a very small chance (not actually zero, but not far off) that it might be possible to identify the part. Maybe the problem is just a failed solder joint and a simple resoldering will fix it, at which point there's another working board.

I like the screen colours, very C64 ish.

snufkin wrote on 2021-12-05, 21:22:

Pictures of the board when you dismantle things would be nice. There's a very small chance (not actually zero, but not far off) that it might be possible to identify the part. Maybe the problem is just a failed solder joint and a simple resoldering will fix it, at which point there's another working board.

I like the screen colours, very C64 ish.

Sure thing! Here are shots of the entire board and close ups of the video portion:

As you can see, stuff is already highly integrated and I cannot spot a seperate character ROM like the IBM CGA card used to have.

I can't immediately see anything particular, but you may want to have a good close look around the MN1288. I can't find a datasheet for it, but there's an MN1287 from Panasonic that handles some sort of character generation. Datasheet for that is available; it only handles 7-bit characters and the character set is different, but maybe the 1288 is an updated version. The datasheet is mostly in Japanese, which I can't read to find out how it's supposed to work.

Look to see if there are any solder bridges between pins, broken tracks, or bad solder joints. Also, if you have a meter, check resistances (with board disconnected from everything), to find which pins connect to Ground and which to the supply voltage (+5V I assume). Be suspicious of any traces that look like signals (thin tracks) but connect directly to Ground or +5. You can probably use the board mounting hole as a Ground, and the vias on the fat trace next to the mounting hole (I'm assuming that's +5V) as handy probe points.

Of course, even if it is something to do with that chip then the fault could be inside the chip, at which point kvg21's offer of swapping in a whole replacement board is probably the way to go, rather than trying to swap chips over.

Hezus wrote on 2021-12-05, 17:39:

kvg21 wrote on 2021-12-05, 16:59:

I can see your PM, but I can't respond to it.
Searching through other threads, it appears there's a minimum number of regular posts that must be made before access to submit PMs is allowed, but that number isn't listed in the thread... and I'm not going to just spam posts until I can send a PM, because that just defeats the purpose of the rule. I'll see if I can find something useful to respond to and up my count.

That's quite redicilous. I'll PM you my email adress and then we'll talk there.

If you sent another PM, I didn't see it.

kvg21 wrote on 2021-12-06, 14:29:

Hezus wrote on 2021-12-05, 17:39:

kvg21 wrote on 2021-12-05, 16:59:

I can see your PM, but I can't respond to it.
Searching through other threads, it appears there's a minimum number of regular posts that must be made before access to submit PMs is allowed, but that number isn't listed in the thread... and I'm not going to just spam posts until I can send a PM, because that just defeats the purpose of the rule. I'll see if I can find something useful to respond to and up my count.

That's quite redicilous. I'll PM you my email adress and then we'll talk there.

If you sent another PM, I didn't see it.

I did, but let me try it again.

@snufkin:
Thanks for the info! I'll poke around those chips and check the traces.

Hezus wrote on 2021-12-06, 14:32:

I did, but let me try it again. […]
Show full quote

kvg21 wrote on 2021-12-06, 14:29:

Hezus wrote on 2021-12-05, 17:39:

That's quite redicilous. I'll PM you my email adress and then we'll talk there.

If you sent another PM, I didn't see it.

I did, but let me try it again.

@snufkin:
Thanks for the info! I'll poke around those chips and check the traces.

Got it that time.