Mike's PCjr Page

I pulled my 2nd jr out of the closet to play around with.

I have found at least 3 problems and I have solutions/workarounds for them, I think. Then I have another problem for which I could use some advice.

1) Problem 1: Wouldn't read from disks reliably. Cleaned drive heads and lubricated rail. Now reads reliably from disks created on my other PCjr.

2) Problem 2: Keyboard malfunctioning (kept spitting out "0-+" randomly, Backspace dead). Replaced keyboard, all good on the machine side. Will troubleshoot keyboard later. Maybe.

3) Problem 3 (unfixed but worked around): When I run a program off of floppy, it may not start properly, or it may start and then malfunction. For example if I run the "64K RAM Ought to be Enough" demo, the machine reboots before the 3rd scene change. If I run Hargle's cartridges-dumped-to-floppy, then each game appears to load, but then malfunctions and/or reboots.

If I run the diagnostics (CTRL-ALT-INS) everything works as expected including memory count up to 128K.

Workaround: If I attach a jrIDE, all of the above programs work. What is jrIDE replacing on the main board that would bypass this problem? RAM?

4) Problem 4: I put a 2GB Transcend 40-pin DOM on the jrIDE. I bought it used off eBay. The jrIDE recognizes it as "TRANSCEND." When I try to boot from it (because why not), I get a few lines of "GRUB" and stuff that resembles a mangled partition list. Ok, so there's stuff on it that I don't need, no big deal. HOWEVER, if I try to boot from a DOS 5 floppy, it loads a few tracks, then the jrIDE drive activity light comes on, and it freezes, which is repeatable. If I pull the DOM off the jrIDE (with power off of course), then I can boot into DOS 5. I haven't yet tried booting from another version of DOS with the DOM attached.

Any tips to boot into DOS 5 with the DOM attached so I can repartition the drive? Or will I need to plug the DOM into some other computer and repartition it?

Are you using a keyboard cord or is this infra-red? Is this the real PCjr keyboard or something more modern with a scan-code converter?

Problem 3: You might want to clean the heads again. The jrIDE is not replacing anything in the lower memory and it's memory is not being used unless you boot DOS and use a device driver like jrConfig. (Are you doing this?)

It's possible you have bad RAM on the motherboard. There is no parity checking so it's not as obvious as it would be on a 5150 PC. Running the diagnostics is not enough to test the memory; you need a memory testing program. And even then, you won't be able to test all of it as DOS and the video buffer will be in the way.


Problem 4: If you are booting from a floppy then the DOM should not be read or touched. Is there something on your boot disk that refers to drive C?

I would boot something like DOS 2.1. There is a debug script you can use to wipe out the first sector of the DOM so that you don't have to move it to another machine first:
That tells debug to create 512 bytes of zeros at 9000:0000, then write it to the first hard drive.

Thank you for your response.

Keyboard: I'm using the factory cord. Started with the second revision keyboard. Replaced it with a NOS Chiclet keyboard (same cable).

Regarding jrIDE attached/detached: Whatever is happening, I can reproduce it; attached = the programs I tested work; detached = failures. These are booters so jrConfig is not in use and I agree that the jrIDE RAM should not be in use. I can't explain why this phenomenon happens.

On the final problem, I have nothing in autoexec.bat or config.sys. I'm not sure why the DOM is being touched, or even that it's being intentionally touched, but again it's empirically observable--DOM installed = lock-up, DOM not installed = complete boot to prompt. Forgot to mention, I can boot the same DOS 5 disk on my primary PCjr with jrIDE and a known-good DOM and it completes the boot and allows HD access.

I should and will try another version of DOS when I get back to it at the end of the week. I didn't have time to do that before I had to step away.

You say you have nothing in config.sys or autoexec.bat. For DOS 5 it is my understanding that you NEED "stacks 0,0" as first line of your config.sys. That won't help with the booter disks of course. Also each bootable disk, including your DOM needs to have its boot sector patched for DOS 5 and above. There are instructions on how to do so elsewhere on this site.

Here is the procedure and an attached copy..
(credits to Mike B.)

PATCH DOS 5 BOOT SECTOR TO WORK WITH PCJR

• BEGIN:
• BOOT PCJR FROM DOS 3,4 VERSIONS
• START DEBUG.COM ( this must be the running DOS version )

• (For this step you will need a ready to go bootable DOS 5 disk )
• PLACE BOOTABLE DOS 5 DISK IN DRIVE A: / B: TO MODIFY
• TYPE: L 0 <x> 0 1
<0> A:
<1> B:
<2> C:
(hit return key to end)

• CHECK FIRST 3 BYTES.
• TYPE: U 0 L3
(hit return key to end)
• RESULTS: JMP 003E NOP (Something like this)

• CHANGE JUMP TO BYTES
• TYPE: A 0
• RESULTS: JMP 01C0
(hit return key to end)

• CHECK TARGET AREA.
• TYPE: D 1BF L27
(hit return key to end)
• RESULTS: 'Replace and press any key when ready'
• NOTE: (quit now if this is not the results)

• CHANGE FIRST BYTE.
• TYPE: E 01BF 0
(hit return key to end)

• PATCH CODE NOW.
• TYPE: A 01C0
PUSH DS
MOV DS,AX
MOV AX,[415]
MOV [413],AX
POP DS
JMP 003E
(hit return key to end)

• SAVE YOUR WORK.
• TYPE: W 0 <x> 0 1
<0> A:
<1> B:
<2> C:
Q (quit debug)

• NOTE YOU MUST INCLUDE ON YOUR WORKING DISK:
CONFIG.SYS
STACKS=0,0 (on the first line ! )

• ADD JRCONFIG AS NEEDED.

Update:

PCjr seems to be error-free. I could not find diagnostics/ram test that would run in 128K (other than the built-in). Google searches show me others looking for the same thing and finding nothing as well. However, I've been putting it through its paces including the floppy drive and now it seems fine. One program that would not run does run now; I suspect that was a dirty drive issue. Two other programs that would not run without the jrIDE attached still won't run without the jrIDE attached, but that's because they need > 128K, which I did not know. One of them was Hargle's Cartridges on Floppy, which from this thread it's clear it won't run in 128k: viewtopic.php?f=3&t=364

So... root cause analysis points to my stupidity, as with many other issues I've faced in my life.

DOM: I wiped the first sector using Mike's instructions above and then I could boot DOS 5 from floppy without hanging up polling the DOM. You can see the activity light flash during successful DOS startup--I believe it does poll the fixed disks, and failed either because it didn't like what it saw on my used DOM, or because of the next oopsie. At this point, the DOM was still acting flaky--intermittently, writes would not actually work. Turns out I forgot to enable the "5v on pin 20" jumper on the jrIDE. Doing so fixed that problem. Same root cause as above.

DOS 5: I did get DOS 5 installed on the DOM on the jrIDE. After booting from a patched floppy and format C: /s, I tried to use PATCHDOS and it didn't work. I rebooted, retraced my steps, etc., but it still reported an error and aborted. So I followed the DEBUG-based instructions and those did work. My experiences are similar to those in this thread: viewtopic.php?f=1&t=582&start=20

Keyboard: no attempts made to address it; I'm getting by with the Chiclet keyboard. I never used one so it's a new experience. Lack of printed keycaps sucks, otherwise, it's OK and feels slightly better than the reissued keyboard.

Now that I'm sufficiently convinced the jr, jrIDE, and DOM are OK (not so sure about myself...) I'll move on to installing the PC Sprint and Tandy mod.

Don't feel so bad; it's complicated. People with new machines and modern operating systems have no idea about how difficult home computing used to be. And the PCjr just adds an extra level of complexity.

And writing your experiences here helps remind people of what they might be screwing up when they come looking for help.

True. Back in the day I did no more to my jr than add memory and speech sidecars. Then I moved on to the Atari ST and Amiga. Later I gave in and got back on the PC route, building my own machines from XT-class through P4--lots of fun with IRQ hell and DLL hell, but not the same as the idiosyncrasies of the jr.

Some success today -- I installed the PCjr Sprint and Tandy mods from Chuckphd53. Luckily no damage to the case upon disassembly. Now I need to find switches and cables to run enable/disable outside the case.

Hey great job, glad to see them installed and working.
What ver is your Chess ?
I may have an earlier version, and may like a copy...