Video problems when running games and... I am new

Discussions about Sinclair ZX80 and ZX81 Hardware
bola_dor
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Joined: Wed Oct 02, 2019 5:32 am

Re: Video problems when running games and... I am new

Post by bola_dor »

1024MAK wrote: Sat Oct 19, 2019 2:18 pm Where are you picking up the composite video signal from on the PCB?

Mark
I have to thank you for your buffer circuit.. It ended up working very well!!!.. thanks!!
About were to pick the signal.. there is something I still don't have clear.. mine is a TS1000 with a ch2-ch3 selector working at 60mhz at 1st I picked up signal from the original 1st wire coming from ULA pin 16 (blue arrow).. when checking to solder the new circuit I found I didn't have continuity with ULA anymore (!?) But had continuity with the hole and track in the board next to the right.. (red arrow ) .. so I soldered a wire were three were nothing before... It is working now but I wonder what happened??? May be one comes at 60hz and the other at 50hz for different markets?? And I blew off the first without knowing?? May that be the problem at first??
Thanks again
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20191029_195343.jpg
Ernesto
ZX80 USA, ZX81UK, ZX Spectrum, ZX Spectrum+, ZX Spectrum 128+ UK, ZX Spectrum +2/A, Sinclair QL, CZ1000, CZ1500, CZ2000, CZ1000Plus, CZ1500Plus, CZ Spectrum, CZ Spectrum Plus, TK83, TK85, TK90X, TK95. TS2068. And more to come :D
bola_dor
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Re: Video problems when running games and... I am new

Post by bola_dor »

One last question about this ..
After a while I see vertical thin bars as interference..
Were does it comes from? ULA getting hot?
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2019_10_29 18_54 Office Lens.jpg
Ernesto
ZX80 USA, ZX81UK, ZX Spectrum, ZX Spectrum+, ZX Spectrum 128+ UK, ZX Spectrum +2/A, Sinclair QL, CZ1000, CZ1500, CZ2000, CZ1000Plus, CZ1500Plus, CZ Spectrum, CZ Spectrum Plus, TK83, TK85, TK90X, TK95. TS2068. And more to come :D
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1024MAK
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Re: Video problems when running games and... I am new

Post by 1024MAK »

bola_dor wrote: Tue Oct 29, 2019 11:54 pm About were to pick the signal.. there is something I still don't have clear.. mine is a TS1000 with a ch2-ch3 selector working at 60mhz at 1st I picked up signal from the original 1st wire coming from ULA pin 16 (blue arrow).. when checking to solder the new circuit I found I didn't have continuity with ULA anymore (!?) But had continuity with the hole and track in the board next to the right.. (red arrow ) .. so I soldered a wire were three were nothing before... It is working now but I wonder what happened??? May be one comes at 60hz and the other at 50hz for different markets?? And I blew off the first without knowing?? May that be the problem at first??
There are various variations for the video circuitry for ZX81/TS1000 boards, depending on which country they were sold to/in.

The reliable connection points to pick up the signal from the ULA (apart from IC1 pin 16) are:
  • Left hand lead of resistor R29 (1MΩ) (as viewed looking at the board with the modulator top left).
  • PCB pad used for the U.K. modulator, labelled ‘UK’ above the pad and labelled ‘2’ below it (as you have found, the connection shown with the red arrow in your photo :mrgreen: )
  • Anode lead / pad for D9
The original connection (the connection shown by the blue arrow in your photo) for the type of modulator used in a USA TS1000 model goes via a diode and resistor. While the modulator used for UK modulator is fed directly with a feed from pin 16 of the ULA.
bola_dor wrote: Wed Oct 30, 2019 12:01 am One last question about this ..
After a while I see vertical thin bars as interference..
Were does it comes from? ULA getting hot?
It’s thought to be digital switching noise. I’m not certain where it is coming from, but as components like the ULA warm up, the noise level will increase slightly. So yes, the ULA is the prime suspect.

It may be possible to gain an improvement by improving the supply decoupling. You could try adding a 100nF to 470nF ceramic capacitor wired directly across the ULA power pins (pin 34 and pin 40). Note that I have not tried this myself. So if it works, please do report back.

I’m glad that you found my video buffer useful.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

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dessony
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Re: Video problems when running games and... I am new

Post by dessony »

Bola_dor,

I am also very glad that you used 1024MAK's buffer circuit with the Veroboard/stripboard. However, out of my curiosity, what kind of transistor are you using? BC548? NTE123AP? Or whatever? The way you set the transistor on the board triggered my curiosity, not criticism. But, I am happy to know about your successful result with the board on the ZX81/ TS1000 board! :-)

Thanks,
Dessony
bola_dor
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Re: Video problems when running games and... I am new

Post by bola_dor »

1024MAK wrote: Wed Oct 30, 2019 11:42 am
bola_dor wrote: Tue Oct 29, 2019 11:54 pm About were to pick the signal.. there is something I still don't have clear.. mine is a TS1000 with a ch2-ch3 selector working at 60mhz at 1st I picked up signal from the original 1st wire coming from ULA pin 16 (blue arrow).. when checking to solder the new circuit I found I didn't have continuity with ULA anymore (!?) But had continuity with the hole and track in the board next to the right.. (red arrow ) .. so I soldered a wire were three were nothing before... It is working now but I wonder what happened??? May be one comes at 60hz and the other at 50hz for different markets?? And I blew off the first without knowing?? May that be the problem at first??
There are various variations for the video circuitry for ZX81/TS1000 boards, depending on which country they were sold to/in.

The reliable connection points to pick up the signal from the ULA (apart from IC1 pin 16) are:
  • Left hand lead of resistor R29 (1MΩ) (as viewed looking at the board with the modulator top left).
  • PCB pad used for the U.K. modulator, labelled ‘UK’ above the pad and labelled ‘2’ below it (as you have found, the connection shown with the red arrow in your photo :mrgreen: )
  • Anode lead / pad for D9
The original connection (the connection shown by the blue arrow in your photo) for the type of modulator used in a USA TS1000 model goes via a diode and resistor. While the modulator used for UK modulator is fed directly with a feed from pin 16 of the ULA.
bola_dor wrote: Wed Oct 30, 2019 12:01 am One last question about this ..
After a while I see vertical thin bars as interference..
Were does it comes from? ULA getting hot?
It’s thought to be digital switching noise. I’m not certain where it is coming from, but as components like the ULA warm up, the noise level will increase slightly. So yes, the ULA is the prime suspect.

It may be possible to gain an improvement by improving the supply decoupling. You could try adding a 100nF to 470nF ceramic capacitor wired directly across the ULA power pins (pin 34 and pin 40). Note that I have not tried this myself. So if it works, please do report back.

I’m glad that you found my video buffer useful.

Mark
I'll try to that !! I know nothing about electronics, I am doing some copy solder here.. so If don't get it wrong you suggest to link pin 34 to pin 40 with a ceramic cap.. Can it be done directly over the ULA socket? Perhaps without soldiering? Do you suggest me to try different nF values? In that case which ones?
Thanks again!!!
Ernesto
ZX80 USA, ZX81UK, ZX Spectrum, ZX Spectrum+, ZX Spectrum 128+ UK, ZX Spectrum +2/A, Sinclair QL, CZ1000, CZ1500, CZ2000, CZ1000Plus, CZ1500Plus, CZ Spectrum, CZ Spectrum Plus, TK83, TK85, TK90X, TK95. TS2068. And more to come :D
bola_dor
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Re: Video problems when running games and... I am new

Post by bola_dor »

dessony wrote: Wed Oct 30, 2019 3:50 pm Bola_dor,

I am also very glad that you used 1024MAK's buffer circuit with the Veroboard/stripboard. However, out of my curiosity, what kind of transistor are you using? BC548? NTE123AP? Or whatever? The way you set the transistor on the board triggered my curiosity, not criticism. But, I am happy to know about your successful result with the board on the ZX81/ TS1000 board! :-)

Thanks,
Dessony
I used a BC548.. I downloaded the datasheet and discovered that as an NPN the shape is back wise of that of the drawing.. as know very little about electronics I am surprised it worked at all.. I just followed your drawing.. stripes are horizontally.. the board has no stripes so I soldered some of the component legs likewise ..
Thank you again
Ernesto
ZX80 USA, ZX81UK, ZX Spectrum, ZX Spectrum+, ZX Spectrum 128+ UK, ZX Spectrum +2/A, Sinclair QL, CZ1000, CZ1500, CZ2000, CZ1000Plus, CZ1500Plus, CZ Spectrum, CZ Spectrum Plus, TK83, TK85, TK90X, TK95. TS2068. And more to come :D
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1024MAK
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Re: Video problems when running games and... I am new

Post by 1024MAK »

bola_dor wrote: Wed Oct 30, 2019 11:58 pmCan it be done directly over the ULA socket? Perhaps without soldiering? Do you suggest me to try different nF values? In that case which ones?
The value is non-critical, hence me suggesting a range of values, as I don’t know what is available to you. Ideally a larger value is better than a smaller value. If you have / can get a range of different values, by all means try each value to see what, if any difference it makes.

You could try holding it onto the pins to see if there is any difference (being careful not to accidentally short anything out), but for permanent fitting, I suggest putting it on the bottom of the board and solder it to the pins of the socket. You may need some insulated sleeving to guard against the leads of the capacitor any other pins or connections.

Please keep in mind, we are in the experimental game here. There are no certainties...

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

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1024MAK
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Re: Video problems when running games and... I am new

Post by 1024MAK »

Traditionally, the lead out details of transistors assume that you are viewing the device from below. NOT from the top.

Some basic details are given on this web page.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
bola_dor
Posts: 398
Joined: Wed Oct 02, 2019 5:32 am

Re: Video problems when running games and... I am new

Post by bola_dor »

1024MAK wrote: Thu Oct 31, 2019 12:28 am Traditionally, the lead out details of transistors assume that you are viewing the device from below. NOT from the top.

Some basic details are given on this web page.

Mark
Well this keeps me learning!!!
I thought wrong drawing reference was on the other transistor.. any way I soldered it as were the letters description e b c in the 3D drawing and triple checked it.

About ULA bridge with the capacitor is there any risk involved? Beyond me making any sort of short circuit and ending up in fire :? ?
Ernesto
ZX80 USA, ZX81UK, ZX Spectrum, ZX Spectrum+, ZX Spectrum 128+ UK, ZX Spectrum +2/A, Sinclair QL, CZ1000, CZ1500, CZ2000, CZ1000Plus, CZ1500Plus, CZ Spectrum, CZ Spectrum Plus, TK83, TK85, TK90X, TK95. TS2068. And more to come :D
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1024MAK
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Re: Video problems when running games and... I am new

Post by 1024MAK »

bola_dor wrote: Thu Oct 31, 2019 12:49 am About ULA bridge with the capacitor is there any risk involved? Beyond me making any sort of short circuit and ending up in fire :? ?
The only significant risk is an accidental short circuit caused by shorting out one of the other pins to pin 34 (0V/GND) or to pin 40 (+5V). A short circuit may damage the ULA. If you have steady hands, pressing the two leads on to the part of the chip pins where they enter the socket should be no problem. If your don’t think you can do this, or prefer not to try this, then just solder the capacitor on the bottom as I described earlier.

If you accidentally connect one lead of the capacitor to the wrong pin, there is a risk that you may crash the program and you will need to reset (power cycle) to get back to normal. It is unlikely that doing this will cause any permanent damage, but it’s best to try to avoid doing this.

When you first connect the capacitor, or if you don’t make good contact, you may see interference on the video picture. But no damage will result. This is just the capacitor charging up quickly.

It is also possible that adding this capacitor may make no significant difference, that is, it may not solve the problem.

Are you okay with knowing the numbering of DIL chip pins?

Also, just to be clear, when temporarily pressing the capacitor onto the chip/socket, the idea is that this is done with the computer powered up and with it displaying the vertical lines, the objective being to see if adding it makes any difference.

If soldering it on the bottom, this should be done with the computer switched off or disconnected.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
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