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View Full Version : Commodore PC 20-III (XT, PC compatible) hardware problems.



Jimbop
July 30th, 2012, 01:05 AM
I recently got this old computer which i used in the mid 90-s.
At the time it ran both dos 5.0 and win 3.0 perfectly, but now i have some problems with it that i'm going to explain here.

About the computer:
It has a 20mb harddrive and one 360kb 5.25" (B:)drive and one 720kb 3.5" (A:)drive. CGA and hercules graphics (changable though 4 switches on the back of the computer).

Problems

1: The 720kb unit has somehow become recognized to being a 320kb unit, and refuses to format DD(720kb) disks to other than 320kb even though i specify the format though the command (format a: /f:720). It then complains about how that disk can't be formatted that way.

2: Windows won't start, it gets to the startscreen of windows and after a short while after loading it just locks the whole computer and stops loading.

3: The mouse that i know has worked flawlessly won't work either. I've tried several different mouse drivers but nothing works. Is there some kind of diagnostic program that can check the mouse for errors that i could test it with? (This is the least problem, i guess i should try another unit).

4: When using my new 60" tv as a composite-port display. It (the TV) has a hard time to decide which one of two different NTSC formats to be used. It sometimes switches between NTSC 3.XX and NTSC 4.XX. Sometimes it lasts for a couple of minutes without a problem, then it's back to hesitating. Also when going into a graphical game (Leisure suit larry for example) the picture jumps smoothly up and down. For some reason you're able to steer/move the picture sideways by holding ctrl+alt and using the >< buttons to move the picture, and when having the picture not centered but in the sides it's completely still, but then it's cropped a couple of inches to that side. (this explanation was just so that you could get an idea of how the graphics behave).

5: I tried to clean up the whole motherboard from dust and battery leakage using a q-tip and some isopropanol, didn't seem to help.

6: The battery apparently should be replaced. Is it even possible to get hold of a new battery that fits?

7: Is it even possible to enter the bios and change settings?

8: I'd like if someone could give me some documentation over the jumper settings all over the motherboard.

:EDIT:

9: I wonder it it's possible at all to add a High Density Disk drive for both 3.5" and 5.25" to this computer?

10: Is there a softwareprogram for dos that i can use to change the bios settings in this computer?

modem7
July 30th, 2012, 03:55 AM
Is it even possible to enter the bios and change settings?
According to [here (http://www.vintage-computer.com/vcforum/showthread.php?29269)], it is possible, but the BIOS configuration doesn't hold much.


I'd like if someone could give me some documentation over the jumper settings all over the motherboard.
The final paragraph on the second page of the document [here (http://www.fragged.net.nz/PC10HDD.pdf)] may help.

modem7
July 30th, 2012, 04:04 AM
7: Is it even possible to enter the bios and change settings?

10: Is there a softwareprogram for dos that i can use to change the bios settings in this computer?
According to [here (http://www.commodore128.org/index.php?topic=3694.0)], Ctrl-Alt-Esc on the keyboard is what is required.

angel_grig
July 30th, 2012, 06:10 AM
1: The 720kb unit has somehow become recognized to being a 320kb unit, and refuses to format DD(720kb) disks to other than 320kb even though i specify the format though the command (format a: /f:720). It then complains about how that disk can't be formatted that way.



Have you tried to cover the high density hole (numbered 1 in the wikipedia photo) with tape ?
http://upload.wikimedia.org/wikipedia/commons/thumb/f/fa/Floppy_disk_internal_diagram.svg/170px-Floppy_disk_internal_diagram.svg.png

Jimbop
July 30th, 2012, 07:01 AM
yup. tried covering the hole with several materials. even used real dd disks without the hole. I also remember you could format HD disks to DD without parameters. I think the diskdrive is unaware there's something like HD disks so it normally doesn't care if there's a hole or not.

I also tried entering the setup with ctrl-alt-esc at several moments while booting the computer. Nothing happens.

SpidersWeb
July 30th, 2012, 12:34 PM
http://www.vintagecomputermanuals.com/Retro%20Vintage%20Computer%20Sytem%20Manuals/Commodore%20%20PC%2010%20PC%2020%20Users%20Manual/

I haven't read through the files above, but I wouldn't be suprised if the BIOS only registers disk numbers, and assumes they're all 320K, so you'd need to use the config.sys tool (DRVPARAM? something like that) in DOS to tell the machine it's actually a 720.

BIOS setup I beleive on these was just to set the clock and bootup speed. Which is a lot more advanced than you'd get on a normal XT (which had neither lol). Also has XTIDE standard, and a Low Level Format utility in ROM, and can be connected to almost any monitor known to man. Its unusual you can't get in to the BIOS with CTRL+ALT+ESC, rather than doing it at bootup, try it after the boot.

From memory every BIOS I've used that uses CTRL+ALT+something has been accessible anywhere rather than during POST.

Jimbop
July 30th, 2012, 12:45 PM
Thanks a lot. That might be useful!

SpidersWeb
July 30th, 2012, 01:03 PM
Unfortunately not, lol
I just read them. "User Manual" not "Technical Reference" - curses!

Reason I'm trying to find them is because I know I've read all about the PC-20 and it's switches and have owned them before, so I know the info is out there and it's annoying me that I can't find it.

Edit: still can't find it, but everything I'm reading indicates that even with the latest BIOS installed 720K was not supported natively, because there was no where to set the drive type.

If you are booting off the hard disc, and DOS is installed in C:\DOS then make sure this line is in your config.sys:

DEVICE=C:\DOS\driver.sys /d:1 /f:2

Tells DOS that drive 1 (A drive) is a 720Kb drive.

Edit2: no idea about the other issues though :/

Jimbop
July 30th, 2012, 04:10 PM
Thanks for your support.
About this line: DEVICE=C:\DOS\driver.sys /d:1 /f:2

I had to change it to /d:0 since 0 is the first drive and 1 is the second. I corrected that. Now after reboot i get a new unit. "D:" which seems to be some kind of emulation for A:. if i format a: it still fortmats in 320kb, but if i format d: it formats the disk in a: but in 720.
I'm 100% sure this wasn't how it worked before.
Is there some other parameters that we missed putting there?

Edit: I also tried more with the ctrl-alt-esc.. nothing happens. I even tried ctrl-alt and every other key there is, including del ;)

SpidersWeb
July 30th, 2012, 06:47 PM
lol damn it, I based that off someone elses example, they failed me.

At least you've got access to your floppy.

RWallmow
July 31st, 2012, 03:48 AM
...
4: When using my new 60" tv as a composite-port display. It (the TV) has a hard time to decide which one of two different NTSC formats to be used. It sometimes switches between NTSC 3.XX and NTSC 4.XX. Sometimes it lasts for a couple of minutes without a problem, then it's back to hesitating. Also when going into a graphical game (Leisure suit larry for example) the picture jumps smoothly up and down. For some reason you're able to steer/move the picture sideways by holding ctrl+alt and using the >< buttons to move the picture, and when having the picture not centered but in the sides it's completely still, but then it's cropped a couple of inches to that side. (this explanation was just so that you could get an idea of how the graphics behave).
Modern LCD/Plasma HDTVs are pretty terrible at NTSC, especially the just-barely-NTSC that most early computers/video games put out. For the best picture you really will want a CRT monitor of some kind OR some kind of scaler that was purpose built for displaying old computers/video games on modern LCD monitors. I would also look if you have something better than composite NTSC out on this computer, does it have an RGB port of some kind?


10: Is there a softwareprogram for dos that i can use to change the bios settings in this computer?
Yes, GSETUP (http://acrpc.net/utils/gsetup.zip), its a Generic Bios Setup software, made for AT era machines, not sure how well it will work on your setup though. I have used it on a few different BIOS's before, Compaq, AMI, and a Samsung (not sure if they licensed AMI/Phoenix, or if its their own creation), all with decent success, however it didn't set ALL the options I needed in the Compaq, but it did all the basics at least (always seems to do floppy & hard disk).

RWallmow
July 31st, 2012, 04:07 AM
6: The battery apparently should be replaced. Is it even possible to get hold of a new battery that fits?
Just figure out what voltage it is and solder on some leads to an off-board battery holder. If it needs 3volt, I go with a 2xAA or 2xAAA holder and plain off the shelf lithium AA/AAA's (lithiums last longer, and seem to be less leak-prone than alkaline, but if you pull them when you store it, alkaline is fine too). If its 6volt go with a 4xAA/AAA holder. It will usually be one of the two, 3v or 6v. Many AT era also used 4.5v packs, but it is almost always with a 6volt clock chip, so a 6 volt pack will work, and probably last longer (if you are really worried you could solder a resistor in line).

Other thing to consider is if the on-board battery was a rechargeable type you should solder in a diode in line with the + lead to prevent the motherboard from trying to charge your replacement (unless you replace with a rechargeable pack).