New ZX80 boards

[Paul]

Hi Lee,

I also misinterpreted the photo. Luckily I could see #4 in live.
The yellow wire connects the additional diode directly from R37 to D13, no connection to R31.

I hope that makes it clear.

Why my modification from 1K to 500 Ohm did not increase the video level I cannot tell. I checked the value of 500 ohm with my multimeter, maybe there is a cold soldering in my modification.
I am able to load files with loadsave (via the serial port of a pc), but I still cannot save files to loadsave or cassette.
This weekend I had my first keyboard problem. The top right keyboard row sometimes gave the top left key row (0=1,9=2 ...)
this was only temporary and I will check my soldering side very closely because there are no "feet" under the mainbord yet.

[Lee Hart]

Hello Jens (and all),

Thank you for the clarification. So the yellow wire and diode connect *above* the pad for R31, and not to the pad itself, correct? If so, then this patch should do the same thing that the parts already on the board should do.

I re-read my previous post, and see I described it wrong! I think there is an error on the schematic, which is copied to the PC board. /SYNC (U18 pin 8) resets U21B, but not U21A. I'll check this out.

> Why my modification from 1K to 500 Ohm did not increase the video level I cannot tell.

This mod raises the DC voltage on the video output. Pot R32 then has twice the range. However, the video on some monitors automatically corrects for level, so more voltage may not give you more brightness or contrast. What happens to brightness as you adjust R32?

On the keyboard: Yes, I wish I understood what is happening here. I seem to recall similar keyboard problems with my old ZX81, but I thought it was the keyboard going bad. There may be something "funny" in the ZX80/81 design that causes marginal keyboard reading.

Oh yes... the battery does nothing with the stock Sinclair software, but is there for a future feature. The battery maintains RAM contents when power is off. With a software "patch" to the ROM (Wilf Rigter describes this on his website), programs in RAM will be retained with power off, and can even be executed automatically on power-up or reset.

[zx81jens]

Hi again!

I never had any problems with the keyboard - erverything works fine here.

Exept:

Some days ago I saved a little program to tape - and could load it in again without problems.

that doesn´t work now - if I load in a original-ZX80-tape (I have some - you can found them here: http://forum.tlienhard.com/phpBB3/viewt ... 2007#p2007 ) eyerything is fine. When I save this program on a new and blank tape, everything is fine. When I´m trying to load it in again, the ZX80-Legacy crashes !!!

If the first signal comes in, it look´s like a RAM-Crash... after that only a reset helps...

I use the same DATA-Recorder and the same cable... and reducing the LOAD-IN-Level doesn´t help.

Anyway - I am so happy to have this fine computer!!

Jens

[Paul]

Yes, correct no connection to the pad of R30.

Thanks for the description, this explains why nothing happened to the signal level: R32 is exactly in the middle position,
I forgot to try to change its setting , or even to compare their settings, because there is absolutely no problem with my monitor, and the Output on my TV-set via AV input gives a very clear picture. I never saw a ZX80 on a 16:9 Screen before. Marvelous!
My kids will not be able to watch TV or play their PS3 anymore

[Lee Hart]

Jens, the tape loading problem is really weird! How can it tell the difference between the two tapes? Here are a couple things to try:

1. If you listen to the two tapes by ear, do they sound any different?

2. Could your tape recorder be inverting the signal? On some recorders, a positive-going signal on the MIC input plays back as a negative-going signal on the EAR output. Maybe the ZX80 software isn't smart enough to deal with this?

3. Can you patch the TEST input (the red/green logic probe) to the EAR input, and watch the LEDs to see if you can see any difference between the two tapes? You may to put a capacitor in series due to the voltage offset). For example, are they dimmer on one (lower amplitude), or is one LED brighter than the other?

[zx81jens]

well, it was the tape - it was damaged! now everything works fine.

greetings
jens

[Paul]

After his last visit, Jens found out that every line is shifted by one "Subrow" upwards with Jumper 5-6 set. You can see this quite good using the shift-S Character as all lines are used there
It is the same with my board, with ZX80 and ZX81 rom.
Is this the same on the other boards?
@Lee, has this to do with the VSync issue?
Thanks in advance
Paul

[Lee Hart]

Hello Paul (and all),

Sorry for not posting much on this project. It's summer in Minnesota, and we have to take advantage of the good weather when we can. So I've been on vacation, and not spending much time in my basement lab working on the ZX80 board. I'll try to post more on my progress, and not leave people waiting.

I have mine most of the way assembled, but not complete and working yet. I am eager to check out the keyboard, VSYNC, and this new problem with the line counter being off by one. I think you're right, that the VSYNC and line counter problems are related. The line counter is probably not being reset as it should.

[sirmorris]

I've added the diode and I can report that it solves the vsync issues that I had!

Charlie

[ollie]

Hi Lee

I've just come across your ZX80 board, are you planning to produce another batch?
if not, where can I get hold of the PCB file so I can make my own