ZXmore - questions and answers (FAQ)

Any discussions related to the creation of new hardware or software for the ZX80 or ZX81
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PokeMon
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Re: ZXmore - questions and answers (FAQ)

Post by PokeMon » Thu Nov 23, 2017 1:35 pm

Can you please send a high resolution picture of your screen ?
One sharp pic of the start screen is enough. It looks strange and more like a different/changed charset.
What happens if you set A16 of ROM to GND to let the ZX81 instance directly start ?

dessony
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Location: Indiana, USA

Re: ZXmore - questions and answers (FAQ)

Post by dessony » Thu Nov 23, 2017 6:30 pm

Pokemon,
ZXmore result 11_23_2017.JPG
Latest result.
ZXmore result 11_23_2017.JPG (437.52 KiB) Viewed 240 times
Yes, I did the A16 grounding test, and get a black square with a half character of a white K plus too many thin "!" allover the screen and two thick black column bars on the right side of the screen. :(

Thanks,
Dessony

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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: ZXmore - questions and answers (FAQ)

Post by 1024MAK » Fri Nov 24, 2017 7:45 am

It looks like it is repeating the bit pattern, so you get half of a character, twice!

Check the pins on the parallel to serial chip (shift register).

Mark

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PokeMon
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Re: ZXmore - questions and answers (FAQ)

Post by PokeMon » Fri Nov 24, 2017 3:31 pm

I thought about it - really strange. Never seen before. ;)
The only thing that I imagine is maybe a problem with a double load of the shift register.
Could you check C7 (33pF) and R20 (680R) ?
And that there is no short of C7 ?

Shift register is loaded with signal LOAD (pin 11 of IC7, HCT32).
This is done when signal VIDEXON is low and a short pulse come from pin 8 of IC10, HCT00.

Do you have an oscilloscope to track this ?
The pulse must be at the beginning of a new clock cycle M1, every 1.2us.
I guess you will have two pulses, every 0.6us.

Bildschirmfoto 2017-11-24 um 16.27.02.png
Bildschirmfoto 2017-11-24 um 16.27.02.png (90.24 KiB) Viewed 217 times

dessony
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Location: Indiana, USA

Re: ZXmore - questions and answers (FAQ)

Post by dessony » Sat Nov 25, 2017 12:18 am

Pokemon,

C7 (33pF [331]) - no visual external short / potential internal short [ on the board, continuity position on my multimeter, a black probe to the C7's top leg, a red probe to the bottom leg: around 0.659/ the red probe to the C7's top leg, the black probe to the bottom leg: around 1.170]. I found the C7's via.

R20 (680R [blue/gray/black]) - 0.678 on an OHM area, 2K position on my multimeter.

I am using my own Logitech Webcam Pro 9000.
Here are results coming from my oscilloscope and its settings;
IC7 pin nbr 11 B.jpg
IC7 pin nbr 11 - AC/v2/TVH/int/us.2
IC7 pin nbr 11 B.jpg (28.64 KiB) Viewed 211 times
IC10 pin nbr 8.jpg
IC10 pin nbr 8 - AC/v2/TVH/int/us1/MagX10
IC10 pin nbr 8.jpg (28.36 KiB) Viewed 211 times
Between C7 & R20.jpg
Between C7 & R20 - AC/v2/norm/int/us.1
Between C7 & R20.jpg (27.97 KiB) Viewed 211 times
Bottom of R20.jpg
Bottom of R20 - AC/v1/norm/int/us.1
Bottom of R20.jpg (26.29 KiB) Viewed 211 times
C7's via.jpg
C7's via - AC/v2/norm/int/us.1
C7's via.jpg (26.62 KiB) Viewed 211 times
Thanks,
Dessony

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PokeMon
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Re: ZXmore - questions and answers (FAQ)

Post by PokeMon » Sat Nov 25, 2017 9:50 am

C7 should be 33pF.
If it is named as 331 this means it is 330pF.
It should be named 33 only or 330.
The last digit is the multiplier (0=1,1=10,2=100 and so on).

The first scope picture shows that the load pulse is too long (only a needle should be seen with 20-30ns) and two often (double) every 600ns instead of every 1.2us. So this could be caused if the capacitor is much to large, 330pF vs. 33pF. Please check or try to replace. Slightly higher may work, too (47pF). Or 27pF. Or you could use 2x15pF in parallel. But the bigger one must be removed then.

dessony
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Location: Indiana, USA

Re: ZXmore - questions and answers (FAQ)

Post by dessony » Mon Nov 27, 2017 1:39 am

Pokemon,

Out of my own curiosity, can you show your oscilloscope's screen to me. How did you figure out the load pulse on the oscilloscope to 20-30ns? I am still scratching my head. :? I just removed the C7 from the board. I found another capacitor, in a "junk" component box, equivalent to 330 but it was not soldered to the board yet. The capacitor's label showed, "+/- 10% ; "Black dot" 330 ; Z5P". It was somewhat improved in my screen little a bit, but officially not fixed yet. I have to wait until Monday morning to get more components at my local electronics retail store.

Thanks,
Dessony

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PokeMon
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Re: ZXmore - questions and answers (FAQ)

Post by PokeMon » Tue Nov 28, 2017 5:27 pm

Sorry for my late reply - forgot to take a few pictures of the signals.
Settings were 200us/div and 2V/div.

First pic shows the "needle" pulse created from C7 and R20.
The peaks are clipped a little bit (especially the negative from the internal clipping diodes of the ICs) but show the clock changes (up and down).
Important are the positive peaks which come every 300ns (every rising clock edge).

20171128_180311k.jpg
20171128_180311k.jpg (194.08 KiB) Viewed 145 times


The second pic shows the mixture with /MREQ signal (output pin 8 of IC10 or input pin 13 of IC7).
Here you see some ghost pulses as /MREQ and clock come together at different situations or M-cycles, too.
The middle pulses are not that strong than the first and the fourth fifth (1.25us difference).
This is mainly a trigger problem.

20171128_180317k.jpg
20171128_180317k.jpg (193.01 KiB) Viewed 145 times


And finally the LOAD pulse itself combined with VIDEXON, active only during video code execution phases (A15=1 and /M1 active).
This is the output of IC7 gate pin 11.

20171128_180402k.jpg
20171128_180402k.jpg (200.89 KiB) Viewed 145 times
Last edited by PokeMon on Tue Nov 28, 2017 10:11 pm, edited 3 times in total.

dessony
Posts: 150
Joined: Tue Oct 29, 2013 1:26 pm
Location: Indiana, USA

Re: ZXmore - questions and answers (FAQ)

Post by dessony » Tue Nov 28, 2017 7:24 pm

Pokemon,

I expect to receive a few capacitors (C316C330K5G5TA9750) plus a few components tomorrow. I will post a picture of my monitor screen as soon as I get the capacitor and soldered onto the C7's place within the board.

As for the oscilloscope of mine, it is Protek 40Mhz 6504.

Thanks,
Dessony

dessony
Posts: 150
Joined: Tue Oct 29, 2013 1:26 pm
Location: Indiana, USA

Re: ZXmore - questions and answers (FAQ)

Post by dessony » Wed Nov 29, 2017 7:24 pm

All of you, including Pokemon,

I received a package with my components inside from an UPS today around 11:30am. I found the capacitor (C316C330K5G5TA9750) and put it on the C7 area then soldered it onto my board. Behold the beautiful screen! :lol:
ZXmore welcome screen!.jpg
Behold the screen!
ZXmore welcome screen!.jpg (2.14 MiB) Viewed 106 times
:D :lol: :D
Thank you very much in advance.

Cheers,
Dessony

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