PCs

Cracking Open the IBM PC Jr.

Parallel

The circuit board in the parallel port expansion module is fairly standard.

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.

77 comments
willwilco
willwilco

Can you set it up so that we can click on the full-size pictures and then to click next and previous while remaining in full-size?

JanaMarkowitz
JanaMarkowitz

While the copyright you show on the PCjr is 1983, the PCjr was announced in February, 1987. I know because I did the announcement for my IBM branch office and I was 7 months pregnant with my son, who was born in April 1987. At the announcement I told the audience we were "adding to the PC family" and "I wasn't sure why they picked me to do the announcement." I got a good laugh. The copyright was likely acquired while the machine was in early development.

Captain_Carrot
Captain_Carrot

I remember this little puppy and some of those other great failures from IBM for example PS2s with micro channel architecture and WARP..... What a ya do when WARP fails go to impulse power. They thought they were so big they could go it alone and change the market place... hahahaha

freedos
freedos

The person writing the comments to the pictures of this breakdown doesn't seem to have a clue about basic computer technologies almost 30 years back. Those solder "fixes" were quite common those days to fix initial design flaws or to make simple repairs. And a 8250 is not directly used for a modem but it is a gernal UART/serial port chip. And it looks like he hasn't seen some real dust in an old computer either...

tamasic1
tamasic1

The Racore almost doubled the size of the computer adding a 2nd drive and other add-ins.

adi.asyraaf
adi.asyraaf

Mod the casing and install modern Atom or H55 mini ITX board

KNPepper
KNPepper

I still have several of these stored away - one even has a Quadram expansion chassis (looks like another jr stacked on top). What I'd really like to have is one of the Legacy expansion units with all the flashing LEDs :)

wompai
wompai

A cooled floppy drive, sweeet...

alan
alan

Great, but wld be better if they were labelled - thumbnails as well (in case U dont want to browse thru every pic) :)

slow43
slow43

A pack of 8 by 4k7 resistors in white ceramic.

jeff
jeff

I worked for the company that published "Jr." magazine, devoted to the PC Jr. When our tech editor returned from the first pre-release demo of the computer, the first two words out of his mouth were "Chiclet keyboard." What a colossal disappointment! Of all the ways to avoid competing with the IBM PC, the toy keyboard was possibly the worst. At a time when a new computer still needed the support of hardcore techies to be taken seriously, the Chiclet keyboard guaranteed the Jr. would be ridiculed, even with Chaplin as its spokesperson. Jeff DeTray http://www.AstronomyBoy.com

parkinsonp
parkinsonp

I used to do a lot of dBase programming on it. Not the best machine but it replaced my Osborne which had become sadly useless due to MS-DOS replacing CPM. I still have my original ST506 and ST412 disks from that era. Hard to think now we have 3TB units at a fraction of the size.

andre.renaud
andre.renaud

The 8250 uart was used as serial ports, either for modems or serial printers. The beckman is a resistor network 4.7Kohm, now they are still used but measure only approx 1/8th of an inch. As for AMD they were making slice processors for mini computers much more powerfull than the 8088.

Roc Riz
Roc Riz

The 8088 Intel (or AMD) CPU could be extracted, and replaced with a NEC V20 chip, whose speed was a whopping 9 Mhz. Twice as fast as the Intel/AMD. I worked on quite a few of these vintage machines. Some had Intel CPUs in them, some had AMDs. Whatever was in it, it was an 8088 chip. So you see, AMD was a secondary vendor for CPUs for IBM I guess. Juinor was the PC that got me hooked. With jr, and a modem, I could get on all the local BBSes, and swap shareware with friends. I learned BASIC on the thing, not that I am a programmer. It kept me company many evenings, while I learned what makes PCs tick. Hard to believe it was almost 30 years ago... Perhaps it's time I retire from this.

Matchstalk Man
Matchstalk Man

I remember Qume when I worked in the Civil Service (UK). There was a lot of really old kit there. I think they made printers. As for the Beckman (white) chip, I think it's a resistor network. Maybe 8 resistors each 4.7k ohms.

cynic 53
cynic 53

Someone mentioned Vacuum Tubes, or what we Brits called (Thermionic) Valves .Ah the love of my life! I used to work with these in my teens in 1967 when I took up electronics as a hobby. The nomenclature was different in the USA and the UK, for example what would have been a 6V6G in the USA would have been a EL34 in the UK. It is an (Audio) Output Pentode. In the UK (Mullard) system the first letter was the heater voltage, the second the valve type, the first number the base type and the second number if it was straight = even or variable Mu = odd. Thus the EL34 had a 6.3 volt heater, was an Output Pentode, with an International Octal Base and was straight. As an another example a UABC80 would have been used in an FM Radio with a series heater chain , and was a triple diode triode with a nine pin B9A base. My eyes still go misty when I think of value (tube) circuitry but I simply can't find the same pleasure from modern solid-state electronics.

tmarshall
tmarshall

Qume use to make Daisy wheel printers and also make a line of computer terminals back in the late 70's-early 80's

WacoJohn
WacoJohn

Uhm .. BASIC is a programming language .. (interpreted). The PC Jr OS was IBM PC-DOS 2.10.

jel
jel

Can't comment specifically on the PC JR, but jumpers were used on the pre-PC, mini's (desk size 8K computers) of the 70's to enable additional features. The hardware for the lowest to the highest model was the same, but the jumpers enabled various features as the price went up.

nospam
nospam

Bloomin `ell talk about dragging up the past. Its dead folk let it die in peace :D

nospam
nospam

Bloomin `ell talk about dragging up the past. Its dead folk let it die in peace :D

gwinnrl
gwinnrl

Still have a "luggable" version of this machine. Get it out and fire it up once in a while just for grins. (remember booting off of a DOS single sided floppy anyone) The technology certainly has gone a long way..

awarren2002
awarren2002

It is fun to read all the comments. My husband worked for IBM for 30+ years and we got our PC jr for our son to use in college. We gave it away to a young techie a few years ago who was thrilled to get it. He may have taken it apart as you did, or experimented with using it. It still worked!

Mid-Hudson Tech
Mid-Hudson Tech

This was my first computer back in the day. My father worked for IBM for 35 years in upstate NY. He was able to purchase one as an employee for a discount. Even with that the PC, monitor and printer still cost upwards of $3K. We had 2 memory expansion cards on the side for a huge 512K RAM. Sure made playing King's Quest fun. Hard to beleve this was almost 30 years ago.

MacNewton
MacNewton

I Sold a few in 83-84, IBM just started to promote them along with the IBM AT That came out at the same time. The PC Jr's wireless IR keyboard was a way ahead of it time. But they did't sell, just to little to run on it and the cost was hight. Apple was out with the Macinosh 32K around that same time. It did better. and then there was the Apple IIc - yeck! more on that later... Yes the good old days

vanrossumj
vanrossumj

The chip is a tabbed delay, used for timing purposes

vmisic
vmisic

... two of the extra connections you mention are, in fact, resistors that have been omitted from PCB layout (remember, CAD software was kinda rare these days, so routing was most likely done by hand), and ... AMD was in the cloning business even then - those 8253 and 8255 chips were actually designed by Intel (which is why the labels begin with "8", just like 8088)

theo.vink
theo.vink

The Beckman chip is a bunch of resisters in a DIP-housing. The 89 is the type of the chip. The next 8 means a 16 pins DIP-housing. (the 9 was 14 pins). Then follows the resistor configuration. The 1 means that the resistor are in a bus-configuration with the common to pin 16. It seams to be a chip with 4.7K resistors in it. So, just an easy way to install resistors on a printed-circuit-board. ThQ.

alex6500
alex6500

I wll sell mine.Cash and carry.As-Is. Leave an offer over . $700.In the Hampton,Va USA 23605-1442 E-mail alex65001@cox.net

nealecat
nealecat

Here in New Zealand we got a Japanese version of the Jr called the JX. It used the same design concept but the hardware was quite different, we had a metal case and the first (if think) 3.5 inch disks in it. It could also take an expansion box that included a hard disk. There was also a full size keyboard available. Main weakness was the NEC colour screen, mine blew a power transistor that desoldered itself from the circuit board. KQ1 would only play on the Jr and JX, no other first generation PX could run it because of screen colour limitations.

wcg3ph
wcg3ph

What a great little machine, so way ahead in many ways, color, great sound, tiny chiclet wireless keyboard, and a fantastic platform for games, easy to take it in the car on trips away. I can remember paying $50 for 10 diskettes, and and exhorbitant amounts to add a printer port (nice the way the modules bolted on the side). Great times having a crowd of friends playing Kings Quest. Still got mine in its box stored away. Phil H

richard_volk
richard_volk

This was fun to see the pics, I never worked on a Jr. I did a crap load of XT/AT upgrades. thanks again !

ron_whittaker
ron_whittaker

Very well presented. May inspire me to 'crack open' a 1977 Processor Technology Sol20 built from a kit with socketed chips, 8080A processor, 64kb RAM and 8K S100 Buss Memory card. Weight 54 lbs with black and white monitor, external tape drive storage and cables. Also, a heavy dual Helios II disk drive (8 inch disks - 384kb).

wellcraft19
wellcraft19

Notable should be: wireless keyboard (although crappy IR link) and the fact that the fan sits on the floppy board and there is no heat sink needed on the CPU.

ibmtech
ibmtech

I used a modified version (640 KB memory) on my sailboat for several years for getting weather faxes over SSB as well as sending text over Ham radio with a PK-232. http://www.timewave.com/support/PK-232/PK232DSP.html Also doubled as a word processor etc. Never failed once even though it was in 100% humidity all the time. Great little machine - brings back a lot of memories!

brad.moon50
brad.moon50

I worked as an engineering tech at the Teledyne plant in Lewisburg Tennessee where the PC Jr. was built. The PC Jr. was built specifically for the then unknown home market. It was felt that the home market would not want a steal case. That is why the case was plastic. I think that the plastic case actually cost more than a metal one would have. To keep RF emissions down to pass FCC rules, the inside of the plastic case was sprayed with some sort of nickel coating. Even at that time nickel was not cheap! Of course a steal case would not have emission problems. Next let?s get the time line correct. The IBM XT had just become available shortly before the PC Jr. started shipping. The motherboard was far superior to that of the XT. For instance, for the XT to be able to have a color monitor, it required a full size expansion board (from the front of the case all the way to the back of the case). The PC Jr. did this with 1 gate-aray chip on the mother board. This expansion board also cost more than the entire PC Jr. The PC Jr. had less memory because the plan was to use ROM cartridges for all application. These were the slots located under the disk drives. The floppy controller was capable of running 2 floppy drives, but I don?t think the external drive ever became available to the public. On the down side the keyboard was bad and the power supply was inadequate. The power supply only had enough power to run the memory expansion card and the parallel printer card. There was an optional second power supply that connected to the explanation slot on the side of the case if more options were added. There was also an option for a disk drive controller that was capable of running 2 hard disk drives. I don?t think either option sold very well. If IBM had gone after the business market first, I think the PC Jr. would have been more advanced than the XT! They just could not justify increasing the price of the PC Jr. to get the same revenue enjoyed by the XT after pricing for the home market first. Thanks for the trip down memory lane and my first job out of school! The pictures were great!

dpresley_50201
dpresley_50201

Qume was an early PC drive manufacturer who was bought many years ago by I forget who (maybe Maxtor?). They did make quality, high capacity (for the time) hard drives as I recall. The wires on those boards usually indicate an engineering correction change. If an engineer puts out a design that requires too many of these and he's back to "flipping burgers." As I remember, the PCjr had many teething problems with its hardware requiring many engineering changes -- another factor contributing to its demise.

paajr
paajr

Notice that the Belfuse 8333 is mounted in between plug in sockets. Undoubtedly it is a power supply for the sockets, but it was probably meant to act as a fuse box to keep a bad board from destroying the mother board. You could also use low wattage resistors that would do the same thing. They would control the voltage and burn out if the current flow got to great. From a tube TV repair technician. Of course they developed very low current resistor-fuses. Belfuse is still making fuses. Take a look at www.belfuse.com

DNSB
DNSB

Near as I recall, the PC Jr. was not released in 1987, it was discontinued that year. My memory could be fading but as far as I recall, the company I worked for in 1984-86 purchased one and then promptly dumped it as being unusable. I left there in early 1986 but I still remember a couple of friends who still worked there getting an Xmas present in the shape of finding the doors locked and the offices cleaned out when they came to work on Friday, Dec. 19th. The staff's personal stuff was either taken or thrown in the dumpster.

Roc Riz
Roc Riz

It allowed you more memory with a sidecar, and an additional disk drive with an upper expansion chassis.

slow43
slow43

I remember seeming them on disk controllers in early non-pc boards, a kinda build your own processor where you wrote the microcode as well as the assembler.

pgit
pgit

I poke around tube type amplifiers and short wave radios for fun. Nothing beats the even-order distortion you get from a tube. Solid state is fundamentally unnatural, no matter how you try to process the signal it has agitation built in, and degradation of the signal piled on in order to mitigate the harshness. Give me tubes for audio any day. BTW 6V6 is my favorite for guitar amplification. The greatest tube type amp ever built in my esteem is the Ampeg SVT, six 6550 output tubes, 14 tubes overall. With one of those monsters you don't need to "go to eleven," "one" is about all you can take. You know what else is cool; a tube-type expander/limiter. The 60's wouldn't have been the 60's without it. Pop music on AM radio would have sounded flat. Plus you don't get the beautiful glow of Rayleigh refraction in a silicon chip! Nothing beats seeing a cloud of electrons waiting to rush out through the anode into a 20 pound iron output transformer!

Reg-nbs-seo
Reg-nbs-seo

I did the same thing in the early 90's The SSB speaker output went to a rs232 port adapter and was used to decode military weather faxes on the US east coast. Computer was used to reduce celestial readings, store tide tables, log, and storage lists. Boat was home for 20 years and cruised from 90 to 95. http://dotcom-productions.com/images/reg/seadove/sea-dove.htm 54' Sampson C-Breeze ferro cement full keeled ketch. Reg

ChessCanoe
ChessCanoe

I had 640k of memory installed on my PC Jr. as well, and used compiled BASIC and Assembler to write a program to do zoomed fractals. The first deep zoom took 4 hours less than 3 weeks of 24x7 runtime to produce a picture. I still have a photo of it.

p.a.ogden
p.a.ogden

The Belfuse 8333 is a tapped delay line used to generate clock phases for such as RAS and CAS signals for the memory.

t.rohner
t.rohner

Exactly right, except "8333" is probably the year and week of manufacture. The parts name is (was) 0447-0150-90... That was the time of the TTL-graveyards with 5 Volt lines as thick as welding cables and MathCo's at the price of a used car...

william.hacker
william.hacker

None of the components on that PC board were a mystery to me. I have been designing electronic circuitry since 1974. It struck me that that's 34 years ago. Where's my walker anyway? :-)