ZX48K bad video
I have 48K with bad RF video output: photo
It seems to work otherwise, because you can hardly see letters 'copyright sinclair..' etc on power on.
I had no original power adapter so I used generic +3,+6,+9,+12V stabilised DC power that can do max 1000mA on +12V.
I read that speccy needs 1400mA on +9V.
Could that be the problem?
If not, what else?
It seems to work otherwise, because you can hardly see letters 'copyright sinclair..' etc on power on.
I had no original power adapter so I used generic +3,+6,+9,+12V stabilised DC power that can do max 1000mA on +12V.
I read that speccy needs 1400mA on +9V.
Could that be the problem?
If not, what else?
Post edited by orange on
Comments
Try and see what the composite video output is like - you'll be able to get a usable signal off the input to the modulator - that way you can tell if it's a bad modulator or something else.
er.. where do I get composite out from?
The one of two lines going in modulator? I remember trying that with +3 but it didn't work.
I mesured the voltages on those two inputs to modulator: one is 4,76V and other is about 2,4V I think
edit: nevermind, I found it: link
However, I would not trust on that 1000mA for your PS.
What is voltage at output of PS? 9 V should be enough if is clean.
Is it filtered well ?
I just did the composite out hack, and it provided clear white picture with "sinclair ..." in bottom.
thank you very much..
The speccy alone will draw a lot less than the 1.4Amp max rating on the PSU, the only reason for this overhead is that the spectrum has to power all the peripherals you plug into it. Sinclair got burnt with the ZX81 when they released the ZX Printer, which drew a fair amount of current. They had to ship the ZX Printer with another power supply to replace the one that came with the ZX81 to ensure that the ZX81 and printer got enough juice, this was expensive.
When they made the 48K they included a PSU with enough headroom that it could power pretty much anything you could throw at it, Int1, Int2, ZX Printer and 8 Microdrives. All that had to be powered from the main PSU, so it had to be able to power a lot more than a bare speccy.
Sinclair stuffed up again tho, the ZXPrinter pack was the same if you were buying for a ZX81 or a 48K, except if you were buying for a 48K they took out the new PSU. The documentation however was identical and the 1st page had the warning that you HAD to use the PSU that came with the printer to avoid potential damage to the computer. This freaked out 48K buyers as there was space in the box for a new power supply, and it looked as if it was missing. Cue many calls to Sinclair from people warned off plugging it in by Sinclairs own doco.
I got the black picture (same as now on 48K, when I forgot to disconnect modulator). If I only knew then..
(I figured that the reason was the sound must come in modulator with that same wire and composite carries only picture so it couldn't be it)
My TV has had only RF and composite. RF was always very very bad (esp. with coloured border) because here we use PAL/BG and +3 was bought in London where there is probably different PAL. I think there is a potentiometer for fine tuning sound on motherboard, but IIRC it made no difference.
Anyway, is it safe to assume this hack would work with +3 too?
(just curious, I plan to finally buy a new TV with RGB scart)
http://secarica.ro/html/plus3_hardware.html#compositevideo
Now you only need to add picture "qualityfix" :wink:......
I've done a video to show the difference.....
http://user.tninet.se/~vjz762w/
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