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UnderColor, Volume 1, Number 2, December 25, 1984

  • Title: Defuser
  • Author: Terry Kepner
  • Synopsis: Questions asked, questions answered.
  • Page Scans: Link


I have one of the early 4K Color Computers. lt has been modestly used, but was a store demonstrator before I bought it, so it may have had more use than I realize. The Enter key doesn't always make solid contact when pressed. Sometimes it doesn’t work, other times it seems to bounce and act as if l hit it twice. Can I remove the board and clean the contacts? Or could something be wrong with the chips or computer power supply?

Edwin McLean

Danville, CA

Yes, you can take apart and clean the keyboard, but you have to be very careful or you'Il end up with tiny parts all over the place and will face the monumental task of trying to put them all back where they belong.

I would suggest you invest the money in a new keyboard, of which several are now available (Radio Shack $39.95; Mark Data Products SuperPro Keyboard $69.96; and SuperPro with adapter $70.95; HJL’s Keyboard $79.95; and Keytronic's keyboard $89.95).

lf you decide to clean the computer, get "contact cleaner" from an electronics store to do the job right. Flubbing alcohol and cotton swabs will also do the trick, but not as well, or with as lasting effect.

I have a 64K Color Computer with Tandon 100-1 (drive zero) and Shugart 400L (drive one) disk drives. My problem is consistent failures when making two-drive back-ups (single drive back-ups work just fine). I also have unexplained crashes at wide intervals.

I have software for checking drive speed, and both drives are within a few rpm's of 300.

Now for my questions: must both drives have the same type head loading? Can you provide me with the proper program shunt settings for the Shugart and Tandon drives? Can you give me an address where I can get the service manuals for these drives? Would a disk drive analyzer enable me to adjust my drives?

C.C. Nichols

New Braunfels, TX

lf by head loading you mean whether or not both drives have to load the heads in the same manner, the answer is yes. lf they d0n’t, the operating system will think a drive is ready when it really isn’t. The

head should load as soon as the drive is selected (the LED comes on).

l can't help you with the Shunt settings since l don’t have the manuals myself, but you can order the Shugart Manual from Hamilton/Avnet, 800-527-3387 (Shugart has a $100 minimum order quantity, Hamilton/Avnet doesn’t). Ask for Shugart Part #39028. The repair manual should cost around $30. And the Tandon Manual is available from Tandon, P.O. Box 2107, Chatsworth, CA, 91311. Order part

#179022-001, $29.50.

Definitely a disk drive analyzer will help you adjust your drives; it's the next best thing to using an oscilloscope on your drives (the necessary documentation is supplied with the program).

I recently purchased a 64K Color Computer II, and have a question: is it possible to modify the Color Computer 2 so it will supply 12 volts to the cartridge slot so you don't have to buy the Multipak Interface for many hardware products?

Ian Mount

Phoenixville, PA

You could do that, but I wouldn't recommend it: you'll probably overload the power supply and burn it out. The conversion is difficult, because the Color Computer 2 doesn't have the 12 volt supply on board. You would have to tap into the power transformer and build your own 12 volt circuitry.

All in all, while it's more expensive to buy the Multipak Interface, in the long run it's a better choice.

Does anyone know how to copy ROMpaks to cassette, and do it successfully? Does anyone know of a program that will let me create my own characters?

Wayne Tracer

Chiloquin, OR

Copying a ROMpak to cassette is simple: cover the ROMpak initialization pin (pin one), plug it into your computer, set up your tape recorder, turn on your computer, and type: CSAVEM“filename”,&HC000,&HDFFF,&HC000. This will put a copy of the ROMpak on tape, but it won’t do you any good unless you have a 64K RAM computer. The ROMpaks use memory locations C000—DFFF, located above the ROMs.

If you have a 16K or 32K computer, the CLOADM routine tries to put the ROMpak program back where it was originally, starting at C000, where there’s nothing now. Hence, nothing happens because there’s no RAM in which to load the program.

There are only two solutions: relocate the program lower in memory where there is RAM (and take a chance that the program doesn’t just happen to need that lower RAM for graphics and other data), or reload the program into a 64K computer, switching to 64K mode via special programs.

I don't know of any programs that let you design your own character set; does anyone else?

In July's The Color Computer Magazine DEFUSR, you stated the Break disable wasn’t possible even though the routines are in ROM and can be intercepted. There have been several assembly language routines in all the Color Computer magazines, but most are elaborate and some just don’t work. The following program uses no memory and works on all Color Computers:

0 FOR X = 248 TO 254


2 POKE 470, 126;POKE 411,0: POKE 412,248

2 DATA 50,98,28,178,126,173,165


This must be placed at the beginning of a program. Line four is needed to start the program. If your program uses a For...Next command early on, line four can be omitted. The Break key can be turned back

on via: POKE 411,130, POKE 412,185. The routine also disables the Pause (Shift @) and trace (TRON) functions.

The only problem occurs when you PEEK at the keyboard addresses. Usually the values are not passed on. It appears as if no keys are being pressed.

Dave Satterfield

Carson City, NV

I didn’t say it was impossible, I said there wasn't a single POKE you could use to disable the Break key, as there is on the Model I and III computers. I said you need an assembly language routine to intercept the keyboard routine and filter out the Break key; which is what your short program does.

Your program does occupy memory; it is, however, below normal user RAM, down in page zero. You must be careful about using that area since it is reserved for future use by Radio Shack, and some commercial programmers are using that area for special tricks with their programs. It’s possible that a loaded·in program could erase your disable Break


I recently purchased a Radio Shack "Deluxe RS-232 Program Pak" (Cat. # 26-2226), and I have a few questions. First, can I use a Y adapter to plug in a disk drive with the RS-232 Pak? Do you know of any programs for this Pak? There are many faults in the program itself along with the manual. Finally, why does it give me an SN ERROR when I download a Basic program, and why can't I transmit many assembly language programs through the Pak? The assembly language programs will transmit, but won’t execute on either my machine or another after I have entered and exited the Pak.

I’m using a 64K Extended Basic computer with Modem I. Also note that there are problems using the Pak with the Radio Shack Multipak Interface; programs are lost when switching from Disk Basic to Basic.

Barton Fraize

Mount Pearl, Newfoundland, Canada

Are you planning to buy the Y connector to replace the Multipak Interface because of the lost programs when switching from Disk Basic to Extended Basic? If so, switching to the Y cable won’t really help: the RS-232 Program Pak and Disk Drive ROMpak use the same addresses, so conflicts will arise when you try to use either unit.

The problem in switching from Disk Basic to Extended Basic is due to interfacing Disk Basic with Extended Basic. Flipping the switch is a bit like performing a lobotomy on your computer, with anesthesia: the computer usually dies and everything in memory is lost. With most program paks you aren’t trying to save something in memory, so all you get is a quick reset.

If you’re trying to transfer a program from Disk Basic to Basic, the best way is to save the program to tape while in Disk Basic, turn off your computer, disconnect the Disk ROMpak, turn your computer back on, and reload the tape.

Have you examined your Basic program after downloading to make sure everything is OK before trying to run it? And are you sure the programs you’re downloading are Color Computer compatible?

After downloading a program, first check it out in the buffer for errors in transmission. The first line should start with a number. If it looks good, save the program to tape; turn off your computer; disconnect the RS-232 ROMpak; and reload the program. If you get a DS error, it means that Basic found a string of characters after a carriage return not starting with number. One way to fix this is to write a short Basic program that loads the program as a data file and stores it in an array, then find the error by scanning the array, fix it, write it back to tape, and try again.

The assembly language programs are more complex. You have to know their starting, ending, and execution addresses to use them. For details recheck your ROMpak manual.

I own a revision E board 32K Color Basic 1.1 version computer. One day l sat down at my computer desk, turned on the computer and display, and the keyboard failed to work; the computer ignored what I typed.

After resetting the computer several times the keyboard worked again, but it froze once more. Now the keyboard has been frozen for several days.

After examining the computer, I believe that one of my 6821’s (U8) is fried or worn. What’s wrong and what needs to be fixed?

Gary Mitchel

Mesquite, TX

You have three possible problems: the keyboard may be at fault, the keyboard/computer cable may be loose, or the PIA chip (U8) may be bad.

First, swap your two PIA chips. If U8 is bad, changing it will make the keyboard work properly. If that happens, you need to buy a new PIA chip to replace the bad one. Spectrum Projects (P.O. Box 21272, Woodhaven, NY, 11421, 212-441-2807) sells them for $9.95 each; the industrial grade PIA costs $14.95.

If changing the chips doesn't cure the problem, then either the cable or the keyboard is at fault. Unplug the keyboard (carefully) from your computer and put it back. If you still have a problem, try removing the cable from both the keyboard and the computer and putting it back on, reversed (the end that went to the computer now connects to the keyboard, and vice versa). lf that fails to cure the problem, you'll need to replace the keyboard. A new one ranges from $39.95 to $89.95, depending on what you want and from whom you purchase it (Radio Shack $39.95; Mark Data Products SuperPro Keyboard $69.95; and SuperPro with adapter $70.95; HJL’s Keyboard, $79.95; and Keytronic’s Keyboard $89.95).

Good luck.