View Full Version : old computer electronics question

02-01-2008, 08:44 AM
Good morning!

My TRS 102 laptop (ca. 1988) has finally shown signs of aging. I'll spare you the juicy details. Suffice it to say it won't go beyond "lighting" the LCD screen; doesn't "initialize".

With some expert guidance, I've found that with power on, pin 36 (the "reset" switch) on my 102's cpu (80C85) reads 0v regardless of the position of the reset button.

It's in "permanent reset".

Is this something that can be kick-started back into operation? Quick shorting across two points to get it back in business?

Or is this a fried cpu?

Any ancient computer enthusiasts here? Knowledge of the M102 motherboard?


02-01-2008, 12:50 PM
Only "old" processor I have any real pin-out data for is Zilog's Z80 DMA. For that I have ZIlog's "User's Manual" and "Product Specifications Databook". No real help.

I would think there'd be SOME Web resource for 8085 Intel info. oldcomputers.com?

This was kinda neat:


02-01-2008, 02:18 PM
boy oh boy.... did you ask the right question in the right place.

OK... for starters.

Have you been here? https://www.club100.org/

this is the last bastion of TRS80 laptops. If they can't help you nobody can. Post a question on the list and see what comes up.

Rick Hansen (the guy that runs the website) has a garage full of parts and does refurbs. He probably has another cpu if it comes to that.

Actually... I just remembered... if it comes to needing a new chip they are still readily available at major electronic supply places. Z80's were used all over the place... I bought one for a Noritsu photo processing machine for about 10 bucks back in '99 and revived a $1800 motherboard. I've heard rumors that the original Nintendo Gameboy was running on a Z80

{edit} oops - 8085... that's right. Doc was the one that said Z80. But I do have a 8085 assembly programming book and I think it has pin-outs in the back too. {/edit}


I have the factory service manual for the Model 100. I am not familiar enough with the differences between that and the 102. But I'll dig it out and see if I can figure out anything from the schematae...

won't have an answer for you til monday probably. But at least I know exactly where it is located.

02-01-2008, 02:25 PM
Hey! I have the Zilog books in-hand, bub. Knew right where they were, too: In th' Elan's glovebox. /bcforum/images/%%GRAEMLIN_URL%%/devilgrin.gif

*neener-neener* /bcforum/images/%%GRAEMLIN_URL%%/jester.gif

02-01-2008, 02:35 PM
aha! victory is (maybe?) at hand!

I'm trying to trace pin 36 to the R86/T10 junction. Getting totally lost in trying to follow that thin (insulated) copper trail on the PCB. I've got a break somewhere along the line.


02-01-2008, 05:13 PM
Hey! I have the Zilog books in-hand, bub. Knew right where they were, too: In th' Elan's glovebox. /bcforum/images/%%GRAEMLIN_URL%%/devilgrin.gif

*neener-neener* /bcforum/images/%%GRAEMLIN_URL%%/jester.gif

Some people would say "why are your Zilog books in the Elan's glovebox?"

I on the other hand say what a Ko-ink-a-dink....

All my TRS80 paraphernalia is in a laptop bag in the boot of the TR3. That's the only reason I know where it is right now.



i'll dig-em out and let you know - can't imagine that the basic board changed much... I seem to recall that the 102 just had some more memory but I doubt that the board design changed much - the slots were always there.

I love those keyboards - heard say that they copied it directly from the IBM Selectric typewriter keys to help with the journalist sales.

02-01-2008, 05:47 PM
I don't mean this as an insult or to be disrespectful, but why on earth does a club exist for TRS users? I can see collecting old electronics, and I can understand restoring them to working condition. But what is the point of actually using the thing? What would you use it for and why?

02-01-2008, 06:48 PM
Wow, you've got some vintage electronics there, especially with an 8085 micro. As someone who works on digital hardware and software, I'd say most likely that reset line is attached to what's called a microprocessor supervisor. That's to make sure the power supplies are stable before letting the microprocessor come out of reset to make sure strange things don't happen. It could be that either the power supplies are malfunctioning, or if there is a reset button on the unit it could be having problems. The simplest alternative to having an actual microprocessor supervisor chip is just a resistor and capacitor combination that puts a delay on the reset line once the +5 volt supply comes alive. First, check that the +5 volt supply looks good, but you might look for either a shorted capacitor or open resistor connection to the reset pin. Sorry I don't have a schematic handy to offer more than that, but if it is just a resistor/capacitor circuit then it shouldn't be too awful to troubleshoot. Good luck!

02-01-2008, 07:13 PM
Thanks for all the suggestions gang. I found a schematic and did some troubleshooting. There's several problems in the reset system; many of the resistors don't show the proper voltage. I can *sometimes* get the 102 to initialize by running a line directly from cpu pin 36 to R86 - but not always. Mostly likely a break/crack in the PCB somewhere, affecting that reset. Reset button itself tests fine - but things go downhill as you go back from there.

Why do I like the 102? To me it has the best keyboard for a laptop ever used. Feels really good - like the Selectric typewriter. And ... if you've ever tried to work in tight quarters (catalog data entry in library stacks) with a laptop and folding screen, you may have discovered they can tip easily, and the flip up screen takes up vertical space. The 102 is flat "box". To me, for simple text entry it can't be beat. And running 14 hours straight on four AA cells is pretty nifty.


02-02-2008, 12:11 PM
If you like it that much, you could (should) pick up an extra one or two on e-bay. they seem to be rather cheap.

02-04-2008, 02:01 PM
I don't mean this as an insult or to be disrespectful, but why on earth does a club exist for TRS users? I can see collecting old electronics, and I can understand restoring them to working condition. But what is the point of actually using the thing? What would you use it for and why?

nutmeg basically nailed it above but I'll add my $.02.

The keyboard IS a dream. My Dell keyboard is too [censored] small and is too mushy. I have an old IBM 5250 terminal keyboard that I use at my desk here at work for the same reason. I get grief all day every day because it is so dang loud and "clicky".....

But what to do with an old computer like this? Text input. Plain and simple. You turn it on immediately (on AA's no less) and you can be typing text in less than 2 seconds.

OK so what? then what do you do?

It has a RS232 interface. There is a DOS program that still works in XP/Vista - you just plug it into your PC serial port (if you still have one) - type a command, and 20 seconds later all of this text is in a folder on your PC.

That's it - beautiful keyboard for banging out text on the fly - no muss no fuss. If I could attach that keyboard on an old PALM and I'd be golden. I type at the speed of thought. Anything I write by hand that fast is unintelligible by the time I get back to it. I edited an internal newsletter for technicians at an old job and I'd just slip in little tech nuggets whenever someone would call with them with this thing on my lap in the car or a phonebooth (remember those?)... At the time I was on the road at least 2 weeks a month and my $12 goodwill-store model 100 was all I needed to keep track of all this information until I could compile it at home.

02-04-2008, 02:08 PM
Fair enough, Jim! That seems like a pretty valid reason to use such a machine even though a modern computer would do it just as well. If it's quicker and easier then one needs no further reason.

I know what you mean about the old IBM keyboards. They weigh a ton and keep the neighbors up at night, but they really are rock solid. I finally weened myself off of them and onto modern keyboards. I do miss the weight but I no longer miss the big keys.

I went a step further recently and bought an Enermax keyboard. It uses laptop-style keys in a full-sized aluminum frame. It does take a while to get used to the "flat" keys and I made a lot of typos for a couple months. But now I type far faster than I ever have and I love the weight of it. This thing must weight as much as three standard keyboards. It does get cold on the wrists in the winter though! /bcforum/images/%%GRAEMLIN_URL%%/smile.gif

02-04-2008, 03:40 PM
The only problem I had with the model 100 was going through airport security.

All these high-powered exec-types would pull out their fancy laptops and turn them on and look at me like I was a leper when I'd pull out my crap-tastic Tandy.


I even rigged up a phone cord with some shrink tubing and rounded off paper clips and I could dial into CompuServe as late as 1999 and check my email from the hotel.... ah the beauty of a 1200baud built-in modem....

02-04-2008, 03:52 PM
Pine, yes?

02-04-2008, 04:42 PM
Nope. Compuserve mail. All delivered via 8 line high screens and menus with numbers to select. The last remnants of a BBS on a nationwide network.

02-04-2008, 04:58 PM
Non-102 users can see a bit of what we're talking about by downloading the Model 100/102 emulator at:


Runs on Linux, Mac, Windows.

Hmmm - anyone have an old working 100 or 102 they want to sell?


02-04-2008, 06:31 PM
never will sell mine... sorry

but.... there's always the Ebay...

and Rick Hansen still has some for sale:

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]A word about the three grades of computers I offer:
There is a big difference between a "Pristine" a "Like-New" and a "Shop-Grade" computer. These are my terms. A "Pristine" unit has, for the most part, never been used or used so little that there are no signs of ware. A "Like-New" unit has been used but looks like it has not unless you look closely. For the most part, a "Like-New" unit appears to be unused. A "Shop-Grade" is obviously used. It shows ware, and although the unit is cleaned, it does not look great. My "Shop-Grade" units are intended to be out of sight, in use in a shop or in a machine room.

Model 102s
Pristine 32K (a few in stock): never used - $350
Like-New 32K (several in stock): excellent condition - $250
Shop Grade 24K (some in stock): excellent on the inside - outside worn but clean - $150

Model 100s
Pristine 32K (none available at this time): never used - $200
Like-New 32K (a few in stock): excellent condition - $150
Shop-Grade 24K (a few available): excellent on the inside - outside worn but clean - $75

Model 200s
Normal Condition (none available at this time): $??rare??

Portable disk drives (replacements ... cable and system extra)
TPDD: $75
TPDD2: $85
TPDD Cable: $25
TPDD2 Cable: $35
TPDD System Disk: $2
TPDD2 System Disk: $2 [/QUOTE]


that being said... when I bought mine i had 4 dead keys - cracked traces on the PCB - the beauty of this thing is that the board is so lo-tech that you can replace a lot of the traces with some creative soldering and jumper wires....

02-04-2008, 07:14 PM

I've brought some old Toshi Satellite laptops back from th' dead with the same solder-n-jumper techniques.

02-04-2008, 08:59 PM
I feel the PAIN and the PRIDE here. I recently took my Atari IBM compatible Palmtop off its battery charger, and removed its batteries. It was still in perfect operating condition, so it was a very emotional choice for me.

Wow, those were heady days when our little machines were (expensive) cutting edge!

02-04-2008, 09:00 PM
All I have is an old complete Commodore 64 setup... and an ancient Heath/Zenith Z80.