Zx81plus38 rev1.10 video issues
Re: Zx81plus38 rev1.10 video issues
I replaced the 541 chip and noticed a change
When I press load “” the screen appears as 2 large vertical thick lines and several horizontal lines.
When I turn on the Maxduino the video screen turns black/off
When the maxduino finishes the screen comes back on and then returns to the way it appears when load command is entered
I can press the break key and ket a k screen. Press list and get a 0/0. So it appears at this point the program is not loading into memory?
Best thoughts anyone?
When I press load “” the screen appears as 2 large vertical thick lines and several horizontal lines.
When I turn on the Maxduino the video screen turns black/off
When the maxduino finishes the screen comes back on and then returns to the way it appears when load command is entered
I can press the break key and ket a k screen. Press list and get a 0/0. So it appears at this point the program is not loading into memory?
Best thoughts anyone?
Re: Zx81plus38 rev1.10 video issues
I went about and changed all the ic’s and there was no change.
I’m going with the theory of a bad pcb track issue and decided to solder up the next board in my pile so 2 down and eight more to go…
Take a few days
Best and thanks
I’m going with the theory of a bad pcb track issue and decided to solder up the next board in my pile so 2 down and eight more to go…
Take a few days
Best and thanks
- 1024MAK
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Re: Zx81plus38 rev1.10 video issues
The LOAD command on ZX80/ZX81 and clones is rather less sophisticated than the ZX Spectrum and clones. These are the possible outcomes (IIRC, I don’t load from tape very often) after you have tried loading from tape or equivalent:
So, you really do need to see what waveform you are getting at the input pin of the 74HC541 chip or on the collector lead of Q9.
Mark
- The program loads correctly and you either end up returned to BASIC at the inverted K or the program auto starts. If you get the inverted K, then RUN it works. Or for a BASIC program that is not protected, LIST works.
- The machine never finishes loading, hence it stays in loading mode (black screen on modern TVs and monitors, see #1) even after the tape or equivalent stops feeding in audio.
- The data that is loaded is not correct and hence as the RAM is filled up, it is now composed of garbage, hence either the computer crashes or returns to BASIC and reports an error or returns to BASIC (inverted K) but it has disregarded the corrupt data.
So, you really do need to see what waveform you are getting at the input pin of the 74HC541 chip or on the collector lead of Q9.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Amp
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ZX81 Chip Pin-outs
ZX81 Video Transistor Amp
Standby alert
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Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Autumn is here. Bye bye summer 2024...
Re: Zx81plus38 rev1.10 video issues
1024mak: And the ZX80, ZX81 and clones do not produce ANY valid sync pluses during tape operations.
This is not correct.
If a valid signal (strong enough) is beeing sent during the inv.K or a listing is shown, the screen show the horizontal stripes and flickering after play.
Do the following:
- Enter a dummy program like - |1 REM xxxxxxxxxxxxxxx|
- Enter |save "TEST"| and record
- After finishing press play without doing anything on ZX clone.
If nothing appear on the screen, either the hardware is not working (cable connection, no amp used, UNO does not work etc.), or the signal which is recorded is too weak and if not, the output from player is too weak.
Sure it can be also the clone, but I made more than 5 clones of plus38 but V202 and all are working with SAVE/LOAD together with AMP and Microchip Audio Development board.
This is not correct.
If a valid signal (strong enough) is beeing sent during the inv.K or a listing is shown, the screen show the horizontal stripes and flickering after play.
Do the following:
- Enter a dummy program like - |1 REM xxxxxxxxxxxxxxx|
- Enter |save "TEST"| and record
- After finishing press play without doing anything on ZX clone.
If nothing appear on the screen, either the hardware is not working (cable connection, no amp used, UNO does not work etc.), or the signal which is recorded is too weak and if not, the output from player is too weak.
Sure it can be also the clone, but I made more than 5 clones of plus38 but V202 and all are working with SAVE/LOAD together with AMP and Microchip Audio Development board.
- 1024MAK
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Re: Zx81plus38 rev1.10 video issues
The majority of modern TVs (LCD type and some of the later CRT type) require sync signals that comply with the relevant TV/Video standard. In FAST mode, which is used for tape operations (LOAD or SAVE), the correct sync signals are not generated by a ZX80, ZX81 or most clones.
Indeed, the ZX81 ULA doesn’t have a separate tape out pin, it uses the video out pin.
Older (but not the all earlier valve/tube) CRT TVs don’t need a compliant sync signal, as they will produce an image regardless, as they have “flywheel” oscillator circuitry that always generates the horizontal (line) and vertical (field) drive signals for the scan coils that deflect the electron beam. In these designs, the sync signal actually synchronises the “flywheel” circuitry with the sync in the incoming signal.
LCD TVs and monitors sample the incoming signal and store it in memory. They work out where the sync is in order to extract the picture information. As the method of display generation is completely different. If the processor in it can’t detect a valid video signal that it recognises (including correct sync signals), then typically either it blanks the display (blue or black being typical colours) or displays a message.
Mark
Indeed, the ZX81 ULA doesn’t have a separate tape out pin, it uses the video out pin.
Older (but not the all earlier valve/tube) CRT TVs don’t need a compliant sync signal, as they will produce an image regardless, as they have “flywheel” oscillator circuitry that always generates the horizontal (line) and vertical (field) drive signals for the scan coils that deflect the electron beam. In these designs, the sync signal actually synchronises the “flywheel” circuitry with the sync in the incoming signal.
LCD TVs and monitors sample the incoming signal and store it in memory. They work out where the sync is in order to extract the picture information. As the method of display generation is completely different. If the processor in it can’t detect a valid video signal that it recognises (including correct sync signals), then typically either it blanks the display (blue or black being typical colours) or displays a message.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Amp
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Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
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ZX81 Chip Pin-outs
ZX81 Video Transistor Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Autumn is here. Bye bye summer 2024...
Re: Zx81plus38 rev1.10 video issues
This is very good description, thanks.
Please refer to the attached picture what happen if a signal is send to the ZX clone.
Please refer to the attached picture what happen if a signal is send to the ZX clone.
- 1024MAK
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Re: Zx81plus38 rev1.10 video issues
Apart from the socket, the tape input circuit is the same as Mahjongg‘s design, so they both should perform the same for LOADing.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Autumn is here. Bye bye summer 2024...
ZX81 Chip Pin-outs
ZX81 Video Transistor Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Autumn is here. Bye bye summer 2024...
Re: Zx81plus38 rev1.10 video issues
Correct.
PS: The image is shown by a new 10" LCD from China with S-Video input (yellow).
PS: The image is shown by a new 10" LCD from China with S-Video input (yellow).
Re: Zx81plus38 rev1.10 video issues
When I have used the TZXduino with a regurlar ZX81, I have voltages 0V and 5V on the output of the TZXduino. When this is the case, the loading works with a real ZX81. However if you have a ZX81plus38 that has a built-in amplifier, this signals might be too strong for the ZX81plus38. I don't know that ZX81plus38 expects.
- 1024MAK
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Re: Zx81plus38 rev1.10 video issues
Granted, the signal generator in the following simulation is not at all representative of an actual tape input signal, but it gives an idea of what the input circuitry does:
Link to simulation
Mark
Link to simulation
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Autumn is here. Bye bye summer 2024...
ZX81 Chip Pin-outs
ZX81 Video Transistor Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Autumn is here. Bye bye summer 2024...