Thick Black Bars
Dear Editor:
Thick black bars on the display screen may be caused by 60 Hz. A.C. hum resulting from a failing capacitor in the power supply. Cure is replacement. On my MicroAce this involved breaking open the external power supply case at the glue lines, and replacing the large 1000 M.F.D. capacitor with a new one. Be sure to observe the polarity if you make this replacement.
Cecil Bridges
[address omitted]
Help Wanted
Dear Editor:
Do you think that a receive only teletype program could be written into the 1K of RAM or would it take more?. . .
Thanks for producing a fine magazine for a pretty neat little computer.
James S. Johnson
Dear Editor:
I have had my ZX80 micro computer for a few months now and I must say I am very pleased with it. The only drawback to the system is its limited RAM. I know that a 16K RAM pack is available, but I feel I do not need that much. I would be satisfied with 2K or even 4K.
I am very familiar with electronics and have done extensive breadboarding of digital projects so I would like to see an article showing a do-it-yourself memory expansion with schematic diagram and all the details.
Eric Bergstrom
[address omitted]
Dear Editor:
I have a Sinclair ZX80 with 8K ROM and 16K RAM. Can you suggest where I can get information on how to:
1) Use the ZX80 as a terminal with coupler.
2) Decode and display Morse Code and RTTY from shortwave (see QST magazine, July 1981, p. 30).
3) Connect external inputs such as switches or analog inputs to connector or ear-jack.
4) Connect a printer (Is the ZX81 printer available?).
5) Implement “slow” display mode.
Ronald Silver
[address omitted]
Ed.—Readers who have suggestions for meeting the above requests are invited to send their ideas to SYNC letters. The ZX printer will not be available yet in the US market although it is available in the UK.
Scrolling REM Statements (4K ROM)
Dear Editor:
When entering a machine language program into a REM statement, you want to scroll the REM off the screen. After entering the Basic program, use the immediate instruction POKE 16403,A. A should be the next Basic statement number after the REM statement. Poking this puts statement A at the top of the screen. I have found this much easier than using dummy statements, and I have not found this technique suggested elsewhere.
Richard Van Workum
[address omitted]
Cecil Bridges’ LED Load Monitor
Dear Editor:
Cecil Bridges’ article entitled “Adding an LED Load Monitor to the ZX80” (SYNC 1:1) actually describes this useful hardware modification for a MicroAce and not a ZX80. If a schematic were available for this modification to a ZX80, it would be greatly appreciated since the MicroAce diagram is useless to me.
Also, no part numbers are listed for the Radio Shack LEDs that have been used or at least their low current requirements.
Hopefully you can provide me with the necessary information.
Cal Butler
[address omitted]
Ed.—David Ornstein points out that Cecil Bridges’ LED Load Monitor can be adapted to work with the ZX80. Although the title implied that the circuit was for use with a ZX80, the connection diagram given was for the MicroAce, as Reader Butler correctly notes. To use the circuit with the ZX80, connect the X wire as shown in the article. The Y wire should be connected to ground. A good place to tap ground is just below IC17, on the large silver pad on the printed circuit board.