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Model 1 Lower case problem

B

Biff

Member
Joined
Jul 13, 2017
Messages
43
Location
NE Ohio
Hi,
I bought a Model 1 system on eBay recently, and it has a lower case mod.
I assume it is an Electric Pencil equivalent - but not sure.

In the auction pictures, it showed it running LDOS just fine with lower case - and considering how well the system was packed, I have no doubt the pictures are accurate.
After I received it, instead of immediately plugging it in and verifying everything, I instead decided to perform a power supply re-cap on it.
And since I had it open and it had the original interconnect cable, I just couldn't resist replacing the cable with a spare 40 pin one I had laying around.
(removed the cable and installed 20 pin RT angle headers - which the 40 pin cable plugs into)

When I was finished with the mods, I powered it up - and was greeted with a screen where all of the space characters are " ' " and other random gibberish.
It reminds me of how my original model 1 would behave in Level II BASIC when I had lower case enabled via the usual SPDT toggle switch.
This install doesn't have a toggle switch, so I was assuming it would be fine under LDOS - just like in the auction pictures.
I booted LDOS and well - no difference.
I also tried booting NewDOS 80/V2 and issued the command to enable lower case, but that made no difference either.

I tried a simply FOR-NEXT loop under BASIC to poke 0-255 into video memory and it looked reasonable, but I can't recall if the character set is supposed to repeat like I saw.
(Unfortunately it's all powered down and opened up so I can't re-do that test tonight and take a picture)

I'm pretty sure the fault is mine - but I'm not sure where to look.

If I'm doing it correctly - there should be a couple pictures attached to this post...

One showing a shot of the screen, and another showing the LC mod.

IMG_6820.jpgIMG_6822.jpg
 
Biff,
Will you post a better picture of the Lower Case Mod, and also include a good photo of the Character Generator Z29 along with
the Part numbers that are on it.

The good thing is it is all working, it's just the character for SPACE 0x20 (32 Decimal) is displayed as 0x60 (96 Decimal) and that
is the incorrect character. Do you also know what Version ROM you have?

There is a posting on Lowercase at:
http://www.vcfed.org/forum/showthre...case-to-a-Model-1-in-2016&highlight=Lowercase

Notice Posting #17 with the best way to do the modification now days, with the correct Character Generator.

Thanks.

Larry
 
Last edited:
That looks like the LC Mod from "The Custom TRS-80". Make sure the wires didn't get knocked off a pin somewhere, or the piggy backed RAM is still on good and a leg isn't intermittent, however that really looks like LDOS was expecting the LC Mod and its not activating. Also make sure a pin isn't shorting on the chip with three wires going to it, or the one with two and no jumper, as those are the ones that toggle it on and off. It looks like its stuck off but LDOS is still a disk that was made with it on.

I had that happen to me once and had to make a new floppy, but that was on a computer that didn't have the LC Mod installed. Looked exactly like that, but the space was ok. The space being off makes me think you might have a VRAM issue (very common part that fails if you look at the computer wrong).

Also, triple check the work around the keyboard cable, all the lines go through there and a bridge or bad line could still cause you all kinds of weird stuff.

Something else to check for, solder flakes. Thats a lot of solder to remove from the keyboard cable and unless you've got a vacuum sucker going, you're bound to have a flake pop out somewhere.
 
Last edited:
ldkraemer said:
Biff,
Will you post a better picture of the Lower Case Mod, and also include a good photo of the Character Generator Z29 along with
the Part numbers that are on it.

The good thing is it is all working, it's just the character for SPACE 0x20 (32 Decimal) is displayed as 0x60 (96 Decimal) and that
is the incorrect character. Do you also know what Version ROM you have?

There is a posting on Lowercase at:
http://www.vcfed.org/forum/showthre...case-to-a-Model-1-in-2016&highlight=Lowercase

Notice Posting #17 with the best way to do the modification now days, with the correct Character Generator.

Thanks.

Larry
Click to expand...

Ack, looked closer. Yeah look at the numbers and ? and the LC Mod is activating right. I would check the RAM chip stacked on top of Z45 and make sure all the legs are good (two should NOT be connected to the chip below, and bend out, 11 and 12). Need to do a VRAM test, level II basic without the EI connected is fine.

Code: 
VIDEO RAM TEST PROGRAM
5 DATA 1, 2, 4,8,16,32,128
10 Y = 6: X = 15360: POKE X,64
20 IF (PEEK (X) AN 0 64) = 64 THEN 30 ELSE 150
30 POKE X,160
40 IF (PEEK (X) AND 64) = 0 THEN 50 ELSE 150
50 FOR X = 15360 TO 16383
60 FOR Y=O TO 6
70 READ Z: POKE X,Z
80 IF (PEEK (X) AND Z)=ZTHEN 90 ELSE 140
90 POKE X,O
100 IF (PEEK (X) AND Z)=O THEN 110 ELSE 140
110 NEXT Y
120 RESTORE: NEXT X
130 PRINT "MEMORY GOOD" : END
140 IF Y = 6 TH EN Y = 7
150 PRINT "BIT"; Y; "OF MEMORY LOCATION"; X;"CHECKS BAD"
160 IF Y = 6 THEN 50 ELSE 110
 
OK
Tonight I went over the piggybacked 2102 with my lit magnifying glass and a dental pick.

Pins 1, 3, 4 were merely touching the pins below. They had solder on their shoulders near the chip, but none where it counted.

I pressed them firmly while touching them with the soldering iron, and verified they made contact this time.

Hooked it up the monitor and power supply - and no difference...

Looked at the jumpers attached to pin 11 and 12 of the 2102, and the one on pin 12 was merely resting on it.
The wires were not wound around the pins, but just tacked onto them, and the wire on pin 12 had broken loose.

I removed the jumper from pin 12 completely - it was only tacked at the other end - z60 pin 4.
I added a freshly stripped jumper from 12 to z60 pin 4, and powered it up again.

This time, the video display was perfect - but now I have a keyboard issue.
Dunno how this happened, since I wasn't mucking with anything keyboard related.

Since the keyboard and motherboard have headers on them now, I easily removed my 40pin interconnect cable.
Even w/out the keyboard present, I'm getting the "auto-enter" syndrome for "Memory Size". I can see a "(" character being entered before it displays ?SN ERROR

I have verified that there are no shorts between any two pins on my keyboard header.
I'll investigate it further tomorrow.


Jim
 
This post should appear after my previous post - I hope.
(new member moderation blues)


Turns out, the issue with the auto-entering MEMORY SIZE? was simply plugging one of the RT angle headers into the wrong row of pins in my 2x20 cable.
I wish I could find a nice 1x20 cable with female connectors at both ends - would make this braindead simple...

That fixed the keyboard issue - I knew it was something silly since the keyboard was working fine earlier.

Earlier, I had done some searching on this forum for some info on a replacement character gen with descenders, and I found these two posts
(both top of their respective pages)

http://www.vcfed.org/forum/showthread.php?43675-Rescued-a-TRS-80-Model-I/page2

http://www.vcfed.org/forum/showthre...g-for-updated-character-generator-for-Model-I

Based on these posts, I ordered a MCM6674P from littlediode.com.

I installed it after fixing my keyboard cable issue, and was immediately disappointed. I was hoping for true descenders, but this ROM is just as bad as my original 8046670, and it swapped
[] etc for the arrows - ala Model III.

My quest for true descenders continues...
 
Yep, I found out the hard way. Pretty sure I bought the last 6673 from little diode and have been asking them for updates once in a while.

On the ribbon cable. I found that digikey will make you a new cable (much better quality) like the original. This doesnt quick detach, but it really is good. I've been brutal on the one I've swapped for six months now and it shows not signs up letting up.

Here it is:

https://www.digikey.com/product-det...-connectors/A9AAT-2002F/A9AAT-2002F-ND/161544

Don't worry, they make them same day usually ( I ordered some for my Model III to replace the old ones for the RS232 and FDC (longer versions).
 
Jim,
The Photo you sent me has a repeating pattern. I've tried to mark it out on my Laptop to get the correct spacing so I can look for the
repeating pattern. Here is what I have so far:

RADAO SHACK LM-MD AA BASIC (((( ((((
READY (((( (((( ((((
6W (((( (((( ((((
1234567 000000000111 ((((
123456789111



M MO
EEEGRY SIZE?(((( (((( ((((

I EVEL II
RADAO SHACK LM-MD AA BASIC (((( ((((
READY (((( (((( ((((


So the following Characters are incorrect:
"M" ox4D is "E" 0x45
0100 1101
0100 0101
D3 is WRONG

"O" 0x4F is "G" 0x47
0100 1111
0100 0111
D3 is WRONG

"I" 0x49 is "A" 0x41
0100 1001
0100 0001
D3 is WRONG

"E" 0x45 is "M" 0x4D
0100 0101
0100 1101
D3 is WRONG

"V" 0x56 is "-" 0x2D
0101 0110
0010 1101
CRAZY

"L" 0x4C is "D" 0x44
0100 1100
0100 0100
D3 is WRONG

" " 0x20 is "(" 0x28
0010 0000
0010 1000
D3 is WRONG

Well, the spacing doesn't show up correctly on this posting.

Plus, there is a repeating pattern meaning that one of your Address Lines is stuck. You can test that easily by creating a NOP tester
from a spare Z80 CPU. I sent you a PM.


Larry
 
Jim,
You should be able to locate the Cursor Character

..............0x00
..............0x00
..............0x00
..............0x00
1 1 1 1 1 0x1F
1 1 1 1 1 0x1F
1 1 1 1 1 0x1F
1 1 1 1 1 0x1F

and change it to

..............0x00
..............0x00
..............0x00
..............0x00
..............0x00
..............0x00
..............0x00
1 1 1 1 1 0x1F


Larry
 
Larry,

If you enclose your text in (CODE) and (/CODE), using square brackets in stead of parentheses, your spacing will be preserved.

Matt
 
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