PDA

View Full Version : IBM PCjr won't boot



alexkerhead
June 28th, 2006, 01:30 PM
I have an original IBM PCjr with the 4863 color display and chicklet keyboard. It was never used, but not in plastic wrap.
I plugged the monitor into the computer, plugged the power into the monitor, and plugged the power into the computer, then installed 4x AA batteries into the keyboard.
I turned the monitor power on and then turned the computer on.
It beeped twice and nothing is happening, I have tried turning on with the stock boot disk in the drive, nothing happens, just beeps twice when I turn on the power.
Any ideas?

atari2600a
June 28th, 2006, 03:23 PM
Nothing on the display or anything?

alexkerhead
June 28th, 2006, 03:53 PM
Nothing on the display or anything?
Nothing at all.
It does go black when the power of the computer is switched on, and is light grey when the PC power is off.

modem7
June 28th, 2006, 04:11 PM
According to Scott Mueller's 'Upgrading and Repairing PCs' book (5th edition), on IBM's, two beeps is a video related problem.

But going through the listing of the XT's BIOS, two short beeps occurs on failure of the enabling of the timer/keyboard interrupts. By then, video has been initialised, and one also sees an "ERROR (RESUME=F1 KEY)" message.

I dont know why there's a discrepancy there.
I know the XT is not a PCjr, but I would have expected some similarity.

I would suggest a video problem, but Mbbrutman knows a lot about PCjr's. Hopefully he'll comment.

mbbrutman
June 28th, 2006, 04:49 PM
Just to be absolutely certain, you said 'two beeps' and no other activity? Can you confirm that he diskette drive didn't seek and that nothing showed up on the monitor?

According to the Guide To Operations, two beeps is bad news. When things are find you get a splash screen and one beep.

According to the Hardware Maintenance and Service manual two beeps and no image on the screen is a Power problem. Here is the diagnostic procedure:

Remove all external devices from the ports on the back of the machine. This includes the monitor. The only cable going to the machine should be the power cable. Power on and try again. If you get one beep then power off, connect the monitor, and try again.

If that does not clear it up, remove the 64KB memory card and try again.

If removing the memory card does not clear it up, remove the diskette controller. Disconnect the diskette drive power connector from the power card, but do not attempt to remove the diskette drive. There is a separate set of wires for the fan - remove those as well. Removing the diskette drive is a pain in the arse and it results in broken plastic if it is forced.

At this point it is a stripped machine - 64K and no diskette drive connected. If it doesn't work then we will need to whip out the multimeter.

mbbrutman
June 28th, 2006, 04:53 PM
I would suggest a video problem, but Mbbrutman knows a lot about PCjr's. Hopefully he'll comment.

Besides being the local PCjr Technical God and Moderator Deluxe, I have claimed the title of Holder of Useless Knowledge.

Terry Yager
June 28th, 2006, 07:30 PM
Nope...Wrong! I claim that title! Do you know anyone else who can do board-level repairs on a TRS-80? (Even though I've forgot everything I ever knew)...

--T

alexkerhead
June 28th, 2006, 08:58 PM
No drive seek or anything on screen.
Thanks for the tips Mr. Brutman, I will go do them now.

alexkerhead
June 28th, 2006, 09:13 PM
Darned PCjr.
Tried everything in all configurations.
Still two beeps, nothing else.
Could the cap on the psu be bad because it sat up for 23 years?

mbbrutman
June 29th, 2006, 06:04 AM
Could be. The other possibility is that memory in the first 128K is bad. You removed the 64K card, so that limits it to the memory on the motherboard, or a power supply problem.

I have the wrap plugs necessary to run advanced diagnostics on it and get a better answer. If it is a bad memory chip soldered on that's a pain, but not deadly. I've never had a memory problem with the 64Kx1 bit chips or the 256Kx1 chips from that era, but the way your machine is behaving it probably is memory.

(Two beeps is a sign of intelligence. It's getting at least the 5V that it needs to run the CPU.)

alexkerhead
June 29th, 2006, 08:17 AM
Interesting. I can't see any discoloration or burning, so it would have had to be bad from factory?. I did have everything out, I even cleaned the prongs where the power card plugs in with rubbing alchohol, still two beeps.

mbbrutman
June 29th, 2006, 08:54 AM
I doubt it is power. Usually if the power brick or card fails, it's just plain dead. The way to check it is to measure the outputs from the power card. The tech ref has the exact voltages and tolerances in it. There is a bug in the tech ref, and one of the outputs is listed incorrectly. (I have to look it up.)

atari2600a
June 29th, 2006, 03:02 PM
Can't you plug an old generic PSU into an XT mobo? That would surely destroy all remaining suspision of the PSU being the problem...

alexkerhead
June 29th, 2006, 04:39 PM
PCjr is 100% proprietary.
No XT. Uses proprietary power card with three prong power brick.

atari2600a
June 29th, 2006, 04:53 PM
Crap, did I say XT? Sorry, simple typo!:p

mbbrutman
June 29th, 2006, 05:00 PM
Atari,

Seach google for PCjr. Look at what the power supply looks like. Then you'll understand why you can't use a generic power supply.

atari2600a
June 29th, 2006, 05:06 PM
Ah, I see!:p

alexkerhead
June 29th, 2006, 05:45 PM
Atari, IBM making it fully proprietary was one of the things that made is not sell so well. Even serial and parallel ports were proprietary, along with monitor connections, although you can use a composite out.

mbbrutman
June 29th, 2006, 06:14 PM
Let's have a terminology discussions.

Proprietary means that it was a design that nobody else could use because it was not licensed.

I think the better term for the PCjr connectors is non-standard. The serial port was a standard RS232 port - it just had a non-standard connector. The parallel port is the same as on a PC. The video connector had to be different because the PCjr supports audio through the monitor, which the other IBM monitors did not.

In retrospect, the serial port and the joystick ports are the only two connectors that were designed wrong. Those should have been standard parts. The other ports wouldn't have been compatible with a PC anyway because of signal differences. Those included the keyboard and display ports.

alexkerhead
June 29th, 2006, 06:47 PM
ah, I see. Difference noted.
I do like the audio in the monitor feature, the two beeps are really loud that way..lol

carlsson
June 30th, 2006, 03:05 PM
When it comes to joysticks, didn't Atari have some kind of patent on their design? I know a lot of home computer manufacturers probably ignored that and implemented digital joysticks in the same way, but supposedly IBM was a too big target to do something stupid that could end up in a lawsuit, and whether Atari were willing to license the concept or not, I dunno. After all, IBM PC (and PCjr) were potential competitors to their 400/800 and later 600XL/800XL series.

Anyway, did anyone else other than IBM at that time use a motherboard power connector in the same style as on the original PC and later XT? If not, you could say that design itself was proprietary, non-standard or whatever. If the interface was patented, why couldn't IBM use it on the PCjr as well? Ah, they wanted to separate the professional IBM PC sales from the more home-oriented PCjr sales by making as many components as possible different?

mbbrutman
June 30th, 2006, 04:03 PM
It would be hard to believe that Atari had a patent on a digital joystick. There would have been a lot of prior art. Digital (on/off) is good for taking abuse, but doesn't provide anywhere near the information or feedback that an analog joystick provides. Then again, the analog joysticks are a pain because they constantly need to be recalibrated.

The power connectors on the motherboard were probably not a new design either. A lot of what was in the IBM PC was off the shelf parts that you could buy from AMP and similar vendors.

The PCjr had an entirely different design point. Using an external power brick cut down on the heat generated inside of the machine, and thus reduced the cooling requirement. It also cut down on the weight of the machine, which was important considering the plastic case. The brick steps the voltage down to 17VAC, and then an internal card produces the DC outputs.

A PCjr doesn't need a fan unless the floppy drive is installed. In the base configuration, it is a fanless machine.

Also the power supply in the machine is much smaller because it doesn't have space for a hard disk or second floppy drive. Integrated circuitry and lack of expandability meant that the power supply could be tailored exactly to the machine. The original power supply provided just 33 watts, which is very small. An improved power supply put that up to 45. The power supply design with the external brick takes up much less room than the PC or XT power supply, which is built for much bigger loads.

Of course all of this fell apart when people started to expand their machines. With more than 2 sidecars you need to consider adding additional power, via a sidecar of course. And all of the expansion deck products provided their own power supplies too. There was one option (the Cluster Adapter) that was so power hungry that you couldn't even have it on a machine with a floppy drive unless you had a power sidecar added.

Integrated designs are great on paper, but sometimes they fail the reality check. The PCjr failed because people wanted more expansion than the machine was designed for.

Terry Yager
June 30th, 2006, 04:30 PM
I wonder if the 'proprietary' part refers to the design of the switches themself? I don't recall seeing those little metal bubble thingies anywhere else.

--T

carlsson
July 1st, 2006, 08:30 AM
Re joysticks: Possibly Fairchild Channel-F predated Atari VCS. As far as I know, both systems use the same joystick pinout. It was not that the joystick was digital per se they would have some patent on, but more like the chosen pinout and functionality.