I ordered MicroAce‘s 8K ROM and Flicker-Free Video Upgrade board. When they arrived I easily changed ROMs and the 8K worked fine. The instructions for the upgrade kit were minimal, to say the least, but they did contain John Strain‘s mod (Sep.81).
When I soldered the capacitors, I left enough leads so they could be bent down close to the board (knowing that space would be tight). Then I attached John’s mod right on the edge of the FF board, using the resistor and transistor leads for support. I clipped off all the IC and socket prongs from both the ZX80 and the FF board on the solder side. This allowed the 2 boards to get close together, saving space.
I put a piece of 5 mil acetate plastic on the ZX80 board to insulate it from the FF board bottom and taped them together. Finally, I put another piece of acetate on the ZX80 case where the FF board might touch. The case went together fine, not even a bulge. The FF upgrade works fine. It even works the FAST and SLOW BASIC commands, like the ZX81, with no problems whatsoever.
A Silver Springs, MD, Reader
My new ZX81 is inconsistent with regard to “glitches.” Sometimes I get 1 per minute, othertimes none for an hour. The AC adapter measures 13.75 Vdc, not 9.75 Vdc. Should I return it to the factory?
Bill Hulett, Jackson, MS
Skip Hammel of Sinclair says your glitch problems probably result from your home wiring. Appliances can cause power drops, as when a refrigerator kicks on. Try a line filter (available cheap from Radio Shack) to prevent these problems. The voltage you measured is OK for an unloaded line. When in use, the voltage drops to around 9 V.–AZ
I had a problem with my 16K RAM pack dumping programs on my ZX80. The slightest movement of the RAM pack caused it to dump. I took the eraser from a pencil and gently rolled it down between the computer and the RAM pack about 1/4″, just enough so the RAM pack fits snugly on the computer. The RAM doesn’t lift up when pushed. I’ve had no problems with dumping.
Jim O’Toole, Ridge, NY
Vol.2 No.11 mentions upgrading a ZX81 to 2K RAM by replacing one chip. One article says to use a #6116 (Hitachi); the other says to use a #4816 and one jumper. How do I obtain info on which is which and how to do it? Also, can I use a larger keyboard? What kind?
Howard Kaplan, Van Nuys, CA
To get chip information, contact the manufacturer’s local rep or the company itself. See classified ads this issue for a 6116 source. People we’ve talked to do better with the 6116 chip. To install either, remove the RAM chip(s) on the right of the ZX81 board. (If you got an assembled one, pry the feet off and remove the screws underneath to open the case.) If you have only one RAM chip, it’s in a socket with 4 spare pins. Remove this chip and plug in the 6116 or 4816. Remove the jumper marked L1 on the right of the socket and make the connection marked L2 (printed on the board, or see a schematic). If you have two RAM chips, remove them both and install a 28-pin socket where the rightmost chip was, then make the new connection and plug in the new chip.
You can attach a larger keyboard to your ZX81. Commercial keyboards, kits and plans are available from LJH Enterprises and A.P. Electronics, both in California (see ads this issue.) You can also build one yourself using surplus materials. Check our how-to articles in Dec.80 and Mar.81.–AZ
My SABRE 4K memory board came with clear assembly instructions and drawings showing where to put the diodes and jumpers. My only trouble was not telling them I intended to use the board with a 2K MicroAce. When I wrote them about my problem, Mr. Sisco called to tell me that their board bats heads with the 2K MicroAce. They sent me a modification kit, but I just pulled the RAM out of the MicroAce and got 4K with the board. You’ll come out money ahead by buying the complete kit from SABRE at $45. You don’t save much looking for the parts. The cheapest I found the 6116 was $15.95.
LaVerne Hoffman, Canby, OR