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Rescued a TRS-80 Model I...

A

Al Hartman

Veteran Member
Joined
Aug 13, 2013
Messages
912
Location
Keansburg, New Jersey, United States
Locally here on the M.A.R.C.H. list, a person had gotten a TRS-80 Model I in an estate sale. He thought it was non-working, didn't have the expertise to fix it, and was willing to give it away.

We went to pick up the TRS-80 Model I yesterday, we got the unit home and set it up. He was missing one of the power supplies, but I had one here from another unit.

It appears to have something wrong with the keyboard unit as it starts up with graphic characters all over the screen. Also, the "A" key does not appear to work. We popped the cap on the "A" key and tried manually closing the contacts, but that didn't work.

So, I have to figure out which I.C. on the logic board selects text characters vs. graphics characters and replace it (we tried reseating every socketed chip), and which I.C. on the keyboard is bad.

It's a unit with the DIN cable going from the keyboard to the expansion interface, so it won't work with my other keyboard unit which does not have the DIN.

So, that's for another day.

We opened the Expansion Interface, there was no doubler or RS-232 in it. I’m on the lookout now for one of each. In the meantime, I could rob them from my currently non-working E/I.
 
Good luck with this machine! I'm bidding on a Model I, and if I win it then it'll be my first experience with a Model I other than poking at one in a Radio Shack store before I had any clue about how a computer works around 35 years ago. The one I'm bidding on appears to still have an intact warranty sticker over the cover for the bus connector, so I think I might leave it as a cassette-only system with no expansion interface. I have a 128K Model 4 in which I've replaced the original drives with double-sided ones and added a FreHD and an autoboot ROM, so I already have the other end of the expansion spectrum covered!
 
Hi Al, here's a little help with your M1.

The keyboards on those early M1s suffer from busted solder joints under the key switches, I bet if you turn the keyboard over and look at the solder lugs under the A key with a magnifying glass, you will see they have come loose. Re-solder them and if the problem goes away, check every other lug on the keyboard, they will all be pretty close to coming loose. Re. all M1 keyboards, if one or two keys are not working, it will be the key switches, if a whole bunch of keys don't work then maybe a keyboard IC needs to be replaced. Check tech manual 26-2103 page 107... say keys A,I,Q,Y,1,9 and Clear all didn't work, then I would look at replacing Z3 on the keyboard PCB.

Re. the graphics/alpha problem, have a poke around Z10 and 11 (both are 74LS166) and video memory chip Z63 with a CRO and look for stuck bits ;-)

Cheers,

Ian.
 
There's a really useful article in the March 2014 edition of TRS8BIT magazine called 'How to diagnose and repair a TRS-80 Model 1' available here:

http://trs-80.org.uk/Tandy_Page_2x.html

Click to download PDF on the left hand side. Lots of good information, especially regarding the video RAM and general garbage on screen issues. Helped me track down a video RAM problem with my machine very quickly. Certainly worth a read.

Good luck with it.
 
Just FYI but a lot of times the flex cable running from the keyboard to the mainboard may have a few open traces. Take an ohm meter and check each trace to be sure you have continuity from end to end. If you find an open trace just run a wire to bridge the open run. I usually just pull the entire flex cable and run 24 gauge stranded wire from point to point. A little time consuming but in the end I think it's worth it. 20 wires in all.
 
I had replaced the flex cable in my first Model I. Someone stole it, broke it, and brought in to Tandy to fix it. They ripped out every single mod and even took away my ALPS keyboard with keypad and put another one in. I had to scream to get my keyboard back from them.
 
I ordered 4 74LS166 chips. About $6.00. Rather than futzing around, I'll desolder both chips, put in a pair of sockets and try the new chips and see if it changes anything. If it fixes the problem, I'll go on to fix the keyboard and then boot up Super Utility and test the RAM and the rest of the system.

Hopefully, the E/I I got with this system is in good shape.

Once I'm confident the system is good, I'll do the Electric Pencil mod on it for Lowercase, and add an external reset switch - which are my two "must have" mods to a stock Model I.
 
Anybody know what part number on the character generator is the later chip which has true lowercase in it?

I stupidly bid on an Aerocomp Doubler today, and won it. So, that will go into this E/I. Now, all I need is an RS-232 board for it.

I gotta sell some stuff to pay for all this stuff I'm putting on credit cards. *sigh!*
 
Back in the day (the day being 1981-82) I used to drool over the LNW-80 as seen in the many Mirco-80 mags I read. Given the irksome idiosyncrasies of the both the TRS-80 Model 1 and my M1 clone the Dick Smith System 80, the LNW-80 seemed such a rugged, well put together system with all the extras. Sure there was the Model III, but that wasn't completely compatible with all Model 1 software.

Tez
 
tezza said:
Back in the day (the day being 1981-82) I used to drool over the LNW-80 as seen in the many Mirco-80 mags I read. Given the irksome idiosyncrasies of the both the TRS-80 Model 1 and my M1 clone the Dick Smith System 80, the LNW-80 seemed such a rugged, well put together system with all the extras. Sure there was the Model III, but that wasn't completely compatible with all Model 1 software.
Click to expand...

The TRS-80 Model 4 ultimately offered many of the LNW80's advancements -- 80x24 text, 4 MHz CPU, and CP/M support.

And LNW's ROM was clearly a copy of Tandy's, just patched to say "L N W - 80," instead of "RADIO SHACK":

lnw80-display.jpg
 
I sold Model I computers in the early 1980's, both for Stoney Clove Computer Center, and Lawrence S. Epstein Associates (where we also sold Columbia PC's, Franklin Apple Clones, Cordata PC's, Televideo, and other computers.)

I love my Model I, but the LNW is one of my dream computers. Luckily, I own one.

0b58_1.JPG
 
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