ZX80 WILCO2009 VIDEO PROBLEM

[Gino]

Hi guys (It doesn't matter if we're almost all around 60 ... ),
In 1983, if my memory does not betray me, I build my first ZX80, using an original Sinclair PCB. I had requested it from Clive (for free), writing him a letter as a "poor" student... After about a month the PCB arrived and I started assembling "my first PC", which worked great. I was 20 years old.
After a few years I lost sight of it but I always had the desire to start over. A few months ago, by chance, I found Wilco's blog and immediately got to work. In a few weeks I made his "clone" and I must say that it worked immediately without problems, except for the video output. I have seen that there are other enthusiasts (for example JoJo and abaffa viewtopic.php?t=4067) who have had similar problems, but no one has really described how to solve them. Can any of you help me?

On the video (either using the native mode of the ZX80 or the one with the LM1881) the letters are not fully formed. In the photos that I place you see the numbers from 1 to 9 repeated twice per row, the result is what you see. It does not depend on the LM1881 settings nor on the "abaffa modification" proposed on Wilco's blog (in my example I made it but it does not solve the problem) http://wilco2009.blogspot.com/2017/07/p ... ading.html.

I think it is due to some IC having some problems. In particular I use for IC5 (74373) the LS version instead of S, for U2 (7411) the LS version instead of AC and finally (perhaps the most important) for U5 (7408) I use a HC version instead of LS (unfortunately it is not easy to find all the right TTL, and in this case it is even a CMOS version ...).
The Eprom is M27C512-45XF1.... 45 ns access time
The RAM is CY62256NLL-70PXC.... 70 ns access time
The CPU is Z80ACPU...
Do you have any suggestions?
Thank you.

Gino

ZX80 original:

ZX80 with bachporch

Wilco ZX80

[Gino]

Damn, very active huh, huh? do not answer all together that I can not follow ....

[mrtinb]

This problem requires deep technical knowledge and also knowledge about the Wilco.

Very few people on the forum have this knowledge. So don't hold your breath for a quick answer.

[Gino]

OK, I am agree with you....We have waited forty years from the original version, now wait a few weeks or months it doesn't matter.

[1024MAK]

The problem appears to be a timing issue caused by a design or implementation fault.

That’s rather hard to solve by remote/distance fault finding techniques. Unless one of the people with the exact same board has an oscilloscope or logic analyser and can post some waveforms.

I would try to help, but I have very little hobby time at the moment, and this situation will continue for many weeks…

Mark

[Gino]

The problem appears to be a timing issue caused by a design or implementation fault.

That’s rather hard to solve by remote/distance fault finding techniques. Unless one of the people with the exact same board has an oscilloscope or logic analyser and can post some waveforms.

I would try to help, but I have very little hobby time at the moment, and this situation will continue for many weeks…

Mark

Thank you of your help. I can post the signals by using a scope...the logic analyser is not in my lab.
I think that the problem is an implementation fault, because the Wilco project was replied by many users.
Alejandro (Wilco) said me that:
"... it is the 74LS00 incompatibility that I have mentioned in my blog.
Try: Try Changing IC11 with another 74LS00 (try another chip brand for example). Try using a 47pF capacitor between pin 1 and pin 7 of IC11 and a 2k7 resistor between pin 1 and pin 14 of IC11"
I used all his suggestions, but the result is the same.

Please Mark, help me!
Best
Gino

[jojo]

there must be forum members who suffer the same problems , AND there must be members who have working wilco's .

let's hope they read your qusetion .

And come up with the components used .


- mine is all LS and suffers from non-inverting inverted characters .

[Gino]

Hi guys,
the problem was solved!!! now the board that I soldered (using Wilco's project) operate! I have only a marginal problem with the keyboard: I used keys of Keystone Electronics (5134TR) but I think that are small for this use.
However the problem was in the filter on the pin 2 of IC11 (Baffa's improvment): the correct value is a capacitor of 100pF and two resistor, one of 330 ohm versus GND and one of 1k ohm versus +5V. The central point of the two resistors connected in series is connected with the capacitor, while the other pin of the 100pF is connected to pin 9 of IC18, as reported in Baffa's design. Another improvment that help to solve the problem is to mount the D11 diode (NTSC only): in this case, I use a PAL TV, but the signal is better. Wilco said me to mount a trimmer in R25 position (5K ohm): in this case is possible to regulate the frequency of the filter (to pin 9 IC16) at the best value.
Thanks to Wilco, Baffa, and all guys of this forum.