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TRS-80 Model 3 Extremely low end model (?)

T

the731272

Experienced Member
Joined
Sep 16, 2015
Messages
59
Location
Bath NY
Hi!
So, I got this little beauty from the dump a long time ago and its sat on a shelf basically unused. I've just now started to investigate into it.
It has a grand total of 0 floppy drives and 0 hard drives. Literally just the built in basic.
Its dirty and grungy and has a key missing, I'm sure the insides are no cleaner. The reset button is stuck and some of the keys feel like they had Jelly poured into them.
If anyone has any suggestions on how to clean this thing it'd be well appreciated! Plus, at least a floppy drive for the thing would be a welcome addition.
http://puu.sh/kxc3L/20ccc12635.JPG
http://puu.sh/kxc7J/64db2f5524.JPG
http://puu.sh/kxcsp/6c27701a91.JPG
http://puu.sh/kxd01/900f7902eb.JPG
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Does it say 16K RAM on the badge? Lowest end Model III was 4K with Level I BASIC - not many of those around.

If nothing else, you should replace the RIFA caps in the power supply before turning it on. Chances are pretty good they'll go up in a disturbing amount of smoke. http://akhara.com/trs-80/psrepair/index.html

16K Model III cassette was my first computer. *sniff*, get's me all choked up thinking about it :)

Seeing the left shift missing reminds me of a hardware quirk that has affected my touch typing ever since. The Model I wired both shift keys together so the Z-80 only had a single bit to check if either were pressed. On the Model III there is a bit for each shift key. The Model III Editor/Assembler on cassette (EDTASM, to friends) didn't change the keyboard scanning code so only the left shift key worked. As a result I started to only use left shift in every program and typewriter. At least it prepared me for the days when there was only left side CTL and ALT keys.
 
48K of RAM on the badge.
Funny you should mention that though! I already turned it on once to see if it worked! I certainly dodged a bullet with that...
Yeah, I wont turn it on until I get those caps replaced. Thanks for the tip!
 
48k and no floppies is an unusual configuration. Could you show us pictures of the back and bottom?

I'm guessing it's a school unit that used floppy or hard drives that were shared through a Network 3 network. If so, then it should have an RSC-232 board with a DB-25 connector visible through a hole in the bottom of the case. It's possible that inside you have the rare Network 3 boot ROM with checksum 2764, which was mentioned in the 1983 "MODEL III/4/4P DIAGNOSTICS MANUAL", but has never been dumped and posted to the internet for posterity.
 
Thanks for the pics. Yes, that's a DB-25 serial port connector you have there.

When you get it working, you can check which ROMs you have -- and exercise the keyboard -- by typing in and running this BASIC version of MEMTEST:

10 FOR R=0 TO 2:?"Model III ROM ";CHR$(R+65);" Checksum is: ";
20 FOR M%=M% TO M%-1+8192/2[R:S=S+PEEK(M%):NEXT M%
30 FOR D=0 TO 3:T=FIX(S/16):A=S-T*16
40 H$=CHR$(A+48-(A>9)*7)+H$:S=T:NEXT D
50 ?H$:H$="":S=-2*R*PEEK(14312):NEXT R

(The left bracket in line 20 is the exponentiation operator, which is entered with the up arrow but displays as a left bracket.)
 
I might as well just try this when I get home, if the caps blow the caps blow, lol.
Shouldn't take more than a few minutes to check this anyways.
 
Petrofsky said:
48k and no floppies is an unusual configuration. ...
I'm guessing it's a school unit that used floppy or hard drives that were shared through a Network 3 network. ...
Click to expand...

It is quite possible that the diskless 48K Model III's (and later the diskless 64K Model 4's) sold for Network III use were sold in the largest quantity of any of the Model III/4 line. The two local high schools in our county had largish labs full of these; many more diskless RS-232-connected stations than ones with any kind of disks. They were mostly used for typing/keyboarding classes.

I do have a couple of slightly corrupted images of the Network III OS disks, but none of the stations.
 
the731272 said:
Ah so that kinda ruins the rarity. Oh well! Still a beautiful machine!
Click to expand...

I think it's pretty cool that you can look at that machine in that condition and call it a beautiful machine! You are one of us! BTW, I have a Network 3 controller and the accompnaying OS that I have yet to play with. I was thinking about setting up a retro computer lab if I ever find a good bulk deal on some ex-school Model IIIs.
 
About 15 years ago I had a Model I whose left shift key was also broken off by a pervious user. I guess there must've been some TRS-80 users with unusually strong left pinkie fingers!

Single-drive Model IIIs and 4s seem to be the most rare; most are either diskless cassette-only models, or dual-drive models. In fact, in the later years of the Model III and for the Model 4's entire run, I don't think you could even order a single-drive model; so such a configuration would only happen if someone had a cassette-only model and then upgraded it with a single drive.
 
the731272 said:
Hi!
If anyone has any suggestions on how to clean this thing it'd be well appreciated! Plus, at least a floppy drive for the thing would be a welcome addition.
Click to expand...

It's great that you've got an RS232 board in that! That's something I'd love to get my hands on for my Model III. Software transfer would cease being a pain :)

Your model likely doesn't have a floppy controller inside, and finding one to stick into it is like finding a needle in a haystack. Your best bet with that one is to use the cassette port. The TRS-80 cassette drives came with the proper connecting cable. The only goofy thing about the Model III is that you can transfer cassette software at different baud rates depending on the computer used to write the cassettes. If memory serves me correctly, you need to specify the baud rate when loading software.

As for cleaning, you're probably going to have trouble typing on that thing. Fixing the keyboard takes a bit of work. You need to pop all the key caps off, unsolder them from the board, disassemble every key, and clean the contacts and the pads with isopropyl alcohol. I did that with mine, and the keyboard now works 100%

trskey1.jpgtrskey2.jpg
 
I didn't think of the controller problem. I'm too young to remember there was a time before the controller wasn't integrated I guess, lol. That disassembly process for the keyboard is a bit intensive, especially considering my soldering ability isn't great. Is there A lazy-mans way of cleaning it? Lol
 
It's great that you've got an RS232 board in that! That's something I'd love to get my hands on for my Model III. Software transfer would cease being a pain

Your model likely doesn't have a floppy controller inside, and finding one to stick into it is like finding a needle in a haystack.
Click to expand...

Bungo I sell both items on my web site and have done so for TRS-80 collectors for the past couple of decades. Neither are hard to find or expensive. Certainly I charge much less for them than Radio Shack did in 1983.

A 48K diskless system is a good candidate for the FreHD kit I sell for diskless TRS-80 Model IIIs and 4s. Alternately one can install a FDC and run a long cable from the top connector of the FDC downwards and out of the case and connect an external disk drive. There are many options, including the cassette port you mention, it's all about how heavily the OP wants to delve into usage of the system.

On the subject of 48K diskless systems they were quite popular here in Australia in the early 80s during the BBS craze when adding an RS232 to a Model III and 48K was inexpensive, so was a 300 baud modem, and the comms software loaded quickly and easily from tape, I know a few guys used such a set up for 5 years or more.

Cheers,

Ian.
 
I have the MIII Diskless FreHD autoboot setup on a cassette only MIII and it is all you really need these days for many purposes. In addition to the hard drive emulation, you can mount any of the 1000s of DSK floppy images available using the FreHD as well. It brings new life to the cassette bound MIII without messing with floppies or hard drives.
 
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