Harlequin 128 2D RGB video output problem
Harlequin 128 2D RGB video output problem
There is an assembled Harlequin 128k 2d, please tell me how to correct the image distortion, replacing the chips does not work, the computer itself works fine, thanks to the creator-inventor for this clone. Where to start solving the problem??? Thank you for any help!
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1024MAK
- Posts: 5118
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Harlequin 128 2D RGB video output problem
Did you buy this board already made with all the components already fitted? Or was this a kit built? Or a build using a board that you bought, and then you obtained and fitted the components yourself?
If you have a link to where you bought it from, better yet, a link to the circuit schematic diagram, that would help. I ask this, because there are now various slightly different Harlequin versions.
Mark
If you have a link to where you bought it from, better yet, a link to the circuit schematic diagram, that would help. I ask this, because there are now various slightly different Harlequin versions.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
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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.
Re: Harlequin 128 2D RGB video output problem
OK, I didn't participate in the assembly, since I bought the board already assembled, I wanted to use the chips to build version 3H or higher.
But I decided not to disassemble and restore it to a working state.
Here is a photo of the board, the scheme I think is standard for the 2D version, the board is the previous owner from the free repository.
But I decided not to disassemble and restore it to a working state.
Here is a photo of the board, the scheme I think is standard for the 2D version, the board is the previous owner from the free repository.
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- HARLEQUIN_128_Issue_2D.pdf
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Re: Harlequin 128 2D RGB video output problem
Is there the same distortion with video out (CVBS)? Your TL712 looks a little bit strange - maybe that's the fault.
- A Harlequin I've assembled ...
Re: Harlequin 128 2D RGB video output problem
Since the production of chips is experiencing some difficulties, and stocks are slowly being exhausted, some chips are difficult to buy, so TL712 is replaced with a transistor, it is needed to download programs from cassettes, it does not participate in the process of forming a video signal.
I also replaced the U31, U32 74HC253 chips with 74HC153, did someone make such a replacement? and what can it lead to?
Maybe someone has information on the frequencies and waveform at the outputs of the chips U14 - U16, U30 pin 6, U29 pin 3, Hsync, Hblank, Vout signals...
I also replaced the U31, U32 74HC253 chips with 74HC153, did someone make such a replacement? and what can it lead to?
Maybe someone has information on the frequencies and waveform at the outputs of the chips U14 - U16, U30 pin 6, U29 pin 3, Hsync, Hblank, Vout signals...
Re: Harlequin 128 2D RGB video output problem
- TL 712 near RGB socket
- One in action..
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- the above in action
Re: Harlequin 128 2D RGB video output problem
It is right, that the TL712 isn't for video out signal - but it is only the first remarkable part which differs from the original. It is therefore possible that other deviations from the original assembly can lead to this error. Again, the question: Does the error also occur via the normal video output?
It seems, there is something with the CSync-Signal, but in this case the signal at J7 ("normal video") will have the same distortion. If not, there is something with the signal-way Q1, U30. Also possible is a "hum-loop", case is a missing or bad connection somewhere on the pcb or IC-sockets or RGB cable ... Have you tried an other TV or monitor?
At one (of meanwhile four 2D's I assembled) Harlequin I had a faulty TL712: it produced a inverse signal at pin 6 and so it wasn't possible to start in ZX Spectrum +2A or +2e mode. I got an DiagROM ULA error message "Port 254 (bit6) - EAR input stays high". I was able to fix this error by simply using the signal from pin 7 instead of pin 6. I would like to say that such a small part can also cause collateral damage, because there were no problems with the EAR and MIC signal...
Possible that the 74HC153 are the reason, because they produce a low output signal with STROBE high - the signal at 74HC253 has high impedance in this case (look at the TRUTH Table in the datasheet) - but this would also happen at normal video, not only at RGB ...
It seems, there is something with the CSync-Signal, but in this case the signal at J7 ("normal video") will have the same distortion. If not, there is something with the signal-way Q1, U30. Also possible is a "hum-loop", case is a missing or bad connection somewhere on the pcb or IC-sockets or RGB cable ... Have you tried an other TV or monitor?
At one (of meanwhile four 2D's I assembled) Harlequin I had a faulty TL712: it produced a inverse signal at pin 6 and so it wasn't possible to start in ZX Spectrum +2A or +2e mode. I got an DiagROM ULA error message "Port 254 (bit6) - EAR input stays high". I was able to fix this error by simply using the signal from pin 7 instead of pin 6. I would like to say that such a small part can also cause collateral damage, because there were no problems with the EAR and MIC signal...
Possible that the 74HC153 are the reason, because they produce a low output signal with STROBE high - the signal at 74HC253 has high impedance in this case (look at the TRUTH Table in the datasheet) - but this would also happen at normal video, not only at RGB ...
Re: Harlequin 128 2D RGB video output problem
There is also a problem on the composite video output.
Yes, you need to try using HC253, but it seems to me that the trouble is with the timing of the horizontal and vertical synchronization formation scheme.
There may be some kind of interference with the signals, the assembly of the board is not very high quality. probably have to disassemble everything, replace all the panels for the chips, wash and reassemble everything, but it will take some time))).
Yes, you need to try using HC253, but it seems to me that the trouble is with the timing of the horizontal and vertical synchronization formation scheme.
There may be some kind of interference with the signals, the assembly of the board is not very high quality. probably have to disassemble everything, replace all the panels for the chips, wash and reassemble everything, but it will take some time))).
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Re: Harlequin 128 2D RGB video output problem
Yes - to reassemble is a good idea. Are the values for C2,C4 (27pF) and Y1 (28.375MHz) correct? I'm asking because it is very difficult to find "blue" 27pF and also the 28.375MHz crystal types. With the latest pictures it seems there is a interference which produces this signal. So the areas around the crystals and caps near them should be checked.
By the way, I've left some 28.375MHz crystals...
At your pictures it seems like a "static" corrupt line on the screen - is it really so? If it is a horizontal scrolling line it will be a 50Hz "hum-loop", so it could repaired very easy by finding the bad pin connection (but the harlequin has very much solder pins...).
By the way, I've left some 28.375MHz crystals...
At your pictures it seems like a "static" corrupt line on the screen - is it really so? If it is a horizontal scrolling line it will be a 50Hz "hum-loop", so it could repaired very easy by finding the bad pin connection (but the harlequin has very much solder pins...).