PCs

Cracking Open the Radio Shack TRS-80 Model 4P

While the Osborne 1 claims to be the word's first self-contained portable personal computer, the Radio Shack TRS-80 Model 4P can lay claim to being one of the next generation of portable computers. Eerily similar to the Osborne 1, the Model 4P made major strides in construction and usability. This TechRepublic Cracking Open Photo Gallery reveals how the TRS-80 Model 4P improved upon the initial luggable design to takes its place in the history of portable personal computers.

About

Mark Kaelin is a CBS Interactive Senior Editor for TechRepublic. He is the host for the Microsoft Windows and Office blog, the Google in the Enterprise blog, the Five Apps blog and the Big Data Analytics blog.

56 comments
ralgas1
ralgas1

Hey! I still have one and every so often I still use it. (on old basic progs)

rjonese
rjonese

i have one but my powersupply is dead

jimmcfall
jimmcfall

I owned one. Made a lot of money with it. Started programming in 1979, used all trs-80's. had model 1's, 3's, and a 4p.

santiago
santiago

Remember the Operating System?... way more powerful than old DOS, I wonder why this PC was doomed to extinction. I started programming with one of these (an older model,grey, TRS80-II I believe), after my first experience in Fortran with mainframes in the early 80s...

mikesmccurdy
mikesmccurdy

I've got a Kaypro....Still boots types a doc and prints it before my Vista gives me a logon...

pdelbauve
pdelbauve

Great job, how bout cracking open a IBM PPC and TRS80 model 1 computer one of these days

franmill
franmill

Thanks for doing this and the pictures. It brings back such fun memories, both my late father in law and I each had a Model 4 and loved to compare notes about them. That thing was a beast, a Sherman tank and incredibly reliable. Wish I had kept both of them...

ka5s
ka5s

I scrapped mine a couple of years ago. It had given good service during the green screen text only internet days. The floppies were single sided, but could be upgraded to 360K as I did. You could also add tracks for a little more capacity, if the drive had enough mechanical play. TRS-DOs and LDOS loaded quickly, then one loaded (say) Super Scripsit for word processing. On occasion I forgot the Scripsit disks and had to write a line editor in Basic to do small editing jobs. Lots of EMI filtering on this computer. However, adding a modem downgraded it to Class A. Later, Tandy had FCC problems, one reason they hired me in the late 1980's. By then they were moving to IBM compatibility. There WAS a HDD avaialble. $900 for 5 meg. That was 3 months of CompuServe! Cortland

hlhr
hlhr

I would LOVE to see an intellivision II xracked open, PLEASE!

gsbarton
gsbarton

I still have one in pristene condition.

techbyte
techbyte

Wow! Brings back a lot of good memories. Using basic and just learning how computers operate. I used to work for Radio Shack and sell these computers until the Tandy 1000 came around (IBM compatible? Hmmm) I remember ruining the RS-232 port because I didn't get the hang of connecting the ribbon connector the first time. As a matter of fact, Rosendo Parra who is now with Dell used to be my regional manager when I was with Tandy. Gee! Those were the days !!!

dgritten
dgritten

Brings Back Memories... Wrote my first inventory management program on this one... Hammer

jkstill
jkstill

This brings back bad memories. I managed a repair shop for Radio Shack when these first came out, and I hated working on those things. Very cramped. Try running one of those with the boards out so test points can be reached. It required and extender cable IIRC.

chuck.tomasi
chuck.tomasi

I love the cracking open series. This is definitely Technorama podcast material. Let me know if you want me to crack open my Kaypro II (another Z80 luggable) from 1982.

trygstad
trygstad

I'll bet with all that metal that Tempest certification would have been a breeze...

petrasys
petrasys

Brings a tear to my eye.

greghartman
greghartman

does anyone want one ??? i have one of the originals. gghartman@yahoo.com

OldGeezer
OldGeezer

Picture 36/37 is not for power but the electronics of the CRT

williamjamesw
williamjamesw

The insides look a lot more modern than I would have expected for a machine of this vintage. Also considering that CRTs usually need voltages over 50 KV (if I remember right) those warning labels are a very good idea.

regolf
regolf

anyone wanting a 'virgin' 4P (never opened) let me know. I have been trying to figure out what to do with it.

jan80trs
jan80trs

The cover is the wrong way round. If you turn it 180 degrees, the machine will stand straight up, instead of tilted. At least, that's the way I do it with the 3 4Ps I have standing here. :-) One of wich with a 40 MB external IDE HD and 512 KB RAM, 640x240 Hi-Res and external 3.5"drives. Neat machine.

BALTHOR
BALTHOR

Sounds like the wave of the future to me.

Mark W. Kaelin
Mark W. Kaelin moderator

I purposely did not out-right identify many of the chips found in the TRS-80 Model 4P this time because I wanted to give the adventurous an opportunity to strut their stuff. Help us out and show what you know by identifying some of the more interesting chips you see in the images. I also linked to the technical specification sheet where the real low down can be found for this personal computer.

deepsand
deepsand

Had what appeared to be a dead power supply on mine; but, when I opened it up, discovered that, with the wiring in certain positions, it worked. Found a good position, fixed the wiring in place with a rubber band, and was back up & running. Over time, of course, the rubber band deteriorates from the heat, and needs to be replaced.

glenn.lockwood
glenn.lockwood

This was my second computer which I upgraded to load ldos into upper memory and had 4 floppy drives! I used it for quite a while after PC revolution as a dedicated ascii terminal. The first was a model I bought on 12/30/1983. That machine had a glitchy NEC floppy controller and I learned Z80 assembly in order to reconstruct the CRC/DAM between data sectors. The first paragraph in the user manual was prophetic. "Kiss your wife and kids goodby for the next 6 months as you explore the world of TRS-80 computing". I often quote David Lien's book on BASIC that I bought in the RS bargain bin. "There are 2 ways to write a program. One is to write your ideas down in outline form and then proceed to progam from this design. The other is to go to the trashcan and pick up any listing and modify it until it works." Some things never change.

Mark W. Kaelin
Mark W. Kaelin moderator

I had an Intellivision myself, and would be happy to crack one open if it comes my way.

Mark W. Kaelin
Mark W. Kaelin moderator

I would love to see a cracked open Kayrpo II to compare innards.

propaint
propaint

The main problem was using TRSDOS.

jason.short
jason.short

Not true OldGeezer as that section is deflection and EHT. The EHT (Extra High Tension) is the major power supply rail for the CRT. A monochrome CRT of that size and vintage probably had an EHT supply in the order of 16~18KV, hence many warning labels. And the horizontal deflection coils with approx' 2KV across them. I would consider 16KV from a B+ probably around 90VDC to be a good power supply. The large black component with the EHT lead coming out of it appears to be the flyback transformer and tripler housed in a single unit, as it is done today. Known as an EHT transformer it not only supplies the CRT with it's EHT but also the filament voltage for elctron gun assembly heaters and often other sub-rails. It should be noted that the author took care around the 250V capacitor in the primary section of the switch mode power supply however did not indicate such care around the CRT and EHT section. The CRT is quite a good capacitor and can turn the EHT section extremely lethal under the right conditions. cheers!

deepsand
deepsand

However, as they've rotated the guts from the normal orientation, and have the cover of the power supply cage, with it's attached PC board dangling off in an odd direction, it's difficult to picture what it really looks like.

dupuy
dupuy

A monochrome display rarely used over 16,000 volts, and this is a smaller one, so it's likely it was closer to 10-12k. Still, nothing to sneeze at!

wbutler559
wbutler559

The first Hard drives I saw were on the Model II, customer lost a stepper trans and slowly lost all his Company accounting data after 2 weeks from the smoke smell, no backups

deepsand
deepsand

Base configuration was dual SSDD 5.25 180K FDs, although some late production models used DSDD TEAC drives.

manfred
manfred

I had 3 4P's running LDOS, networked to 1 20 meg hard drive using a multiplexer. Data collisions were prevented by yelling "Saving!" before pressing the Enter key. Great lille machine - sold them all 3 yrs later when we graduated to a 6 mHz 286 running multi-user ConcurrentDos with 4 Wyse terminals hanging off it. Wow...

rick
rick

Yes, the 17XX is/was a (3rd-generation, I think) SMC second-source of the Western Digital 1771 etc. line, unless I'm hallucinating. In the era, system builders would demand each chip be second-sourced, then beat up both IC vendors on price.

TheSwabbie
TheSwabbie

Backups? LOL... You had to buy the Handy Dandy Cassette Player, Cassette Tape and special cord to plug into it....Wa La...you had your backup.

wbutler559
wbutler559

I was top field Engineer for Tandy (N/S Calif, mid 80's) and made many TRS-80's, Had a clone TRS-80 Mod 1 and built my own Super Color Computer, but the Mod 4 was my favorite, I cracked the Bios Chips and put client security information (Company and Address) on the Boot Screen, Ah to be young and smart again, now we're just old and still do not know how to program VCR's, the other post is correct on 64Kx1 ram, U82 is ROM, had many upgrades to systems, the Gold memory chips were very bad for coming out of socket, the heat/cool would walk the chip out of the socket and most of the time if I just reseated the chip and it worked I would not charge the client, made more money for Tandy that way, they went and bought a Model II and a CC for the kids, I loved my job.... bb

Gnuggs
Gnuggs

You've just got too much free time on your hands!

kheard1
kheard1

That chip is a 64Kx1 memory chip.

DaemonSlayer
DaemonSlayer

we all know Mr. Gates chose the second option when it came to his BASIC. (then started to cry foul on pirates that took his borrowed/stolen IP. That was before He decided piracy actually help his sales, an now... we're all treated as if we pirated the OS, and have to jump through hoops every so often to prove we didn't.)

sweber
sweber

On one of the large business machines. I loved it. I don't remember anything especially weird about it. Transitioned to various _nix machines afterwards and remember missing TRSDOS occasionally.

barakaat
barakaat

This was the first PC I owned. It ran two operating systems that included TRSDOS. The other operating system was a predecessor of MSDOS. I was able to learn most of what I learned about command line processing, word processing, and spreadsheet processing on the TRS80, Model 4P. Radio Shack is credited with showing that PCs would sell to the home market. Because IBM had 90% of the mainframe market, they introduced the PC to their customers and dominated the PC market for awhile. This was because number crunching could be done from a desktop instead of having to share time on a mainframe. VisiCalc was the spreadsheet program that made this possible. Then came Lotus 123 and Excel. It was the spreadsheet capability of the PC that initially caused its popularity to increase. Then came the Graphical Users Interface (GUI) and the mouse which was created by Xerox although many think it was McIntosh. The GUI quickly became popular and responsible the the tremendous growth of the PC. What is fascinating to me is that computers are used to create more powerful computers and I can't think of any other industry where this is happening except in teaching as one of my students reminded me.

Mark W. Kaelin
Mark W. Kaelin moderator

It was suggested that I remove the CRT from its housing to get a closer look, but I didn't think it was worth the risk. I did indeed take the warnings to heart. The only warning you nowadays when you crack open a computer is that you are going to void the warranty.

rball
rball

At that voltage the current will be so small that it won't do much more than make you go "OW!" real loud. At least, in my experience! :-) A 9-volt could kill you if there were enough amperes.

mauriceb
mauriceb

That was the first computer for which I bought a HDD (and it was a much nicer computer than my Osborne that preceded it). The HDDs were very, very, very expensive (as in the price range of a reasonably good second-hand car). If I recall correctly, there were two versions of the HDD - one of 10 MB, the other 20. That, in those days, was *a lot* of storage space! I had mine divided into 4 virtual drives: #2 (0 and 1 were the floppies) for *all* my software (WP, DB, SS, etc), 3 for *all* my data, 4 for a b/u of 2 and 5 for a b/u of 3... and there was plenty of space left over! I also had a couple of external floppy disc drives that were chained into the series as well. The beauty of the OS was that you didn't have to nominate the drive to find a file, it went through the drives automatically to find the correct one (it took me a while to remember to nominate the drive when I switched to PC/MS-DOS computers)

JimboInChi
JimboInChi

As I recall, there was a nice 'fix' to the cassette backup published in one of the electronics magazines of the time. It somehow evened out all the audio waves streaming either to or from the tape unit, and eliminated a lot of the figgiting one had to do to get the volume control "just right". I built several, used one and gave 2 to my other two friends with Mod 1's as Christmas presents, all encased in a nice project box. They were simple, and their new owners were very grateful!

GVernon
GVernon

Yes having to buy high quality tapes and hope that your backup would load after you created it. Having to play with the volume control sometimes to get it to load. But it was a fun machine

DaemonSlayer
DaemonSlayer

You mean the CoCo that was supposed to come after the CoCo 2, and never made it because of the late-to-the-market CoCo 3 became the goal? Too bad Tandy didn't release that super coco and the coco3 sooner. and too bad they never really treated it as a serious computer that, had they designed more, could have been higher up in the ranks in comparison to Commodore and Atari.

nrmullins
nrmullins

is this like an archeologist who studies pieces of pottery from the Ming dynasty?

Terabyte Computer
Terabyte Computer

Does it really still work with that chip falling out of it's socket? Cool post. Brings back memories of my childhood when I disassembled my older brothers electronics projects....only to find out that they worked before I dissected them. Oh well, if he wanted them he would have taken them with him when he moved out. lol.

deepsand
deepsand

I don't recall whether of not it came with the Mod 12, but the Mod 16 included XENIX as well.

deepsand
deepsand

Which, had Digital Research's Gary Kidall not blown off IBM, might have become the basis for PC-DOS, rather that Bill Gate's cobbled together derivative of the QDOS (Quick and Dirty OS) that he bought from Seattle Computer Products, which was later rename MS-DOS.

deepsand
deepsand

In that case, perhaps you'd loan me the Wayback Machine. I'll have it back to you in no time at all.

jan80trs
jan80trs

The model 4P had the possibility of using 2 banks of 64 KB, It's possible that the 'unseated' chip belongs to the upper memory bank. That way, It wouldn't interfere with the normal operation of the machine or the OS, wich is completely in the lower 64 KB. It would only show up when using MEMDISK.DCT, the driver to use the upper 64 KB memory as a diskdrive, or in some SYSTEM commands, adressing the upper memory banks (as bank 1 & 2, 2x 32 KB) You could put 80% of your OS in those upper memory banks, either in a diskdrive or as SYSTEM copy (command SYSRES) making the model 4 and 4P amzingly fast, without disk-access for DOS-tasks. TRSDOS 6.1 is the DOS you show, was made by Logical Systems, and the last DOS for the models 4 and 4P was LS-DOS 6.3.1.

Mark W. Kaelin
Mark W. Kaelin moderator

It does indeed look unseated to me, but it still works and I was afraid to mess with it and break a pin or something.