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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 11th Mar 2020, 9:07 pm   #1
John Earland
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Default ZX Spectrum Tuning Issue

Hi folks, I have a ZX81 and a ZX Spectrum. To cut a long story short I can tune an old CRT TV into the ZX81 (picture is poor but I'm working on it), however I have modified the Spectrum to work on modern TVs - which it does. Now here's the thing. I can't now get the Spectrum to run on this old TV - however, I have a Commodore 64 which will via its RF output! I use channel 36 and both the ZX81 and C64 both work on the TV. Is the fact that the Spectrum won't work now on this TV due to the modification to composite output? Any help would be gratefully received!
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Old 11th Mar 2020, 9:16 pm   #2
SiriusHardware
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Default Re: ZX Spectrum Tuning Issue

If the composite modification was done in the usual way, yes, that's the reason.

Normally it's done in the modulator housing and in its simplest form the modulator's input and output are disconnected inside the modulator housing and the video-in signal is then taken straight to the centre terminal of what was originally the UHF-out socket.

If so, your Spectrum is no longer outputting a UHF signal, only a composite video signal, so a normal TV will no longer be able to receive it through the aerial input. If the TV in question has a yellow 'AV IN' phono-type socket (same as the one on the modulator), that would be the place to connect the Spectrum to now.
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Old 11th Mar 2020, 9:20 pm   #3
John Earland
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Default Re: ZX Spectrum Tuning Issue

I see-thought so. That’s very clear. I think I shall attempt the ZX81 modification to produce a composite signal too. Many thanks!
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Old 11th Mar 2020, 11:31 pm   #4
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Default Re: ZX Spectrum Tuning Issue

Tried connecting it to 2 tv via the yellow AV function-nothing. I can here that the Spectrum is running and the keyboard ‘clicks’ but no picture. Any tips folks?
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Old 11th Mar 2020, 11:32 pm   #5
John Earland
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Default Re: ZX Spectrum Tuning Issue

I know it did work-we run games in it but now nothing!
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Old 11th Mar 2020, 11:46 pm   #6
SiriusHardware
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Default Re: ZX Spectrum Tuning Issue

Sorry to have to ask, but do you have the correct 'AV' input selected on the TV?

What sort of / how many different inputs does the TV have?

What sort of lead are you using to make the connection between the Spectrum and the AV-input on the TV? It should either be a single lead with one Phono / RCA plug (of any colour) on each end, or if you have a three-wire 'AV' lead with Yellow, White and Red plugs on each end, use the section which has a yellow plug on each end to make the connection between the Spectrum and the TV.

I've just looked at the Daewoo you linked to and I can only see a SCART socket on that, I don't see RCA 'AV' connections on it, unless they are hidden under a flap somewhere? Or are we talking about a different TV now?

Last edited by SiriusHardware; 11th Mar 2020 at 11:52 pm.
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Old 12th Mar 2020, 8:08 am   #7
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Default Re: ZX Spectrum Tuning Issue

Hi, yes the Daewoo only has SCART and I tried linking the phono type of lead to the yellow socket on a SCART adapter-nothing. Could get the tv to tune into it-but then I’m not entirely sure how to shift it onto the SCART setting! Then I tried it on my Sony Bravia via SCART and by the RGB - still nothing. I have a Xenius too. An obscure TV but I am sure that is the one we used before, nothing this time. I plugged the spectrum into the yellow socket via a phono lead and via the SCART - still nothing!
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Old 12th Mar 2020, 12:09 pm   #8
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Default Re: ZX Spectrum Tuning Issue

You seem to be tying yourself in knots a little bit. Let's go right back to basics.

Disregarding any instructions regarding leads and connections earlier in the thread, connect the Spectrum to a TV you know it worked with, using a lead you know it worked with, connected the way you used to connect it when it worked.

Does it still work that way?

If not, could you please show us some images of the conversion which was applied to the Spectrum to make it output composite video?
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Old 12th Mar 2020, 5:17 pm   #9
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Default Re: ZX Spectrum Tuning Issue

I once converted a small analogue TV into a monitor. The remote was missing.
I looked up the pin-out for the SCART connector and added a 1K resistor from an internal 12 volt rail to one of the pins.
It killed the tuner and made it come on on composite video mode when power was applied.
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Old 12th Mar 2020, 6:08 pm   #10
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Default Re: ZX Spectrum Tuning Issue

I think John has the relevant remotes in each case but may not be sure how to select 'AV' mode or, if the TV has more than one video input, a specific AV input.
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Old 12th Mar 2020, 6:56 pm   #11
John Earland
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Default Re: ZX Spectrum Tuning Issue

Yes-correct. I do have the remotes. I will open to the Spectrum and send photos.
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Old 12th Mar 2020, 7:06 pm   #12
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Default Re: ZX Spectrum Tuning Issue

Here are the photos! Forgive the soldering!! Be kind.
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Old 12th Mar 2020, 7:36 pm   #13
SiriusHardware
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Default Re: ZX Spectrum Tuning Issue

We are always kind here.

To me it looks as though that is a 'straight through' conversion with the connection carrying the ULA's video-out signal to the centre terminal of the phono (UHF) socket. It's not absolutely clear because the picture is a bit dark but the second image appears to show that the 'new' wire is soldered to the leftmost white-circled pad in your second picture. Is that correct?

I've never tried that but in principle it should work. You've wisely insulated the wire where it passes over the edge of the modulator box and I hope we can assume that you don't put the lid of the modulator on over the top of that.

Recheck your connections at both ends of that link wire, just in case you have a 'C2' situation there - joint not as good as you hoped it was. Also make sure that the wire has not melted a hole through the insulation when you heated it up to solder it, otherwise it may be shorting to the metalwork after all despite the measures you took to prevent that.

There's a slightly neater way to carry out your mod, by passing the wire through the left hand hole in the plastic insulator - illustrated in this article.

http://www.retrogamescollector.com/s...composite-mod/

If you do it that way you can put the lid of the modulator back on. However, for now, just try to get this working.

Next, focus on whichever TV it is which has a yellow 'AV' input instead of or as well as a SCART connector - which one is that, what make and model is it and if possible can you show us an image of the remote for that TV - we need to be able to read what it says on the buttons so maybe several images, top, middle, bottom.

One afterthought - the phono-to-SCART adaptor which you were using in some of your earlier tests, does it by any chance have an 'IN/OUT' switch on it?
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Old 12th Mar 2020, 8:00 pm   #14
John Earland
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Default Re: ZX Spectrum Tuning Issue

Quote:
Originally Posted by SiriusHardware View Post
We are always kind here.

To me it looks as though that is a 'straight through' conversion with the connection carrying the ULA's video-out signal to the centre terminal of the phono (UHF) socket. It's not absolutely clear because the picture is a bit dark but the second image appears to show that the 'new' wire is soldered to the leftmost white-circled pad in your second picture. Is that correct?

I've never tried that but in principle it should work. You've wisely insulated the wire where it passes over the edge of the modulator box and I hope we can assume that you don't put the lid of the modulator on over the top of that.

Recheck your connections at both ends of that link wire, just in case you have a 'C2' situation there - joint not as good as you hoped it was. Also make sure that the wire has not melted a hole through the insulation when you heated it up to solder it, otherwise it may be shorting to the metalwork after all despite the measures you took to prevent that.

There's a slightly neater way to carry out your mod, by passing the wire through the left hand hole in the plastic insulator - illustrated in this article.

http://www.retrogamescollector.com/s...composite-mod/

If you do it that way you can put the lid of the modulator back on. However, for now, just try to get this working.

Next, focus on whichever TV it is which has a yellow 'AV' input instead of or as well as a SCART connector - which one is that, what make and model is it and if possible can you show us an image of the remote for that TV - we need to be able to read what it says on the buttons so maybe several images, top, middle, bottom.
Thank you for being kind. Yes, I do insulate the connection before putting the lid back on the modulator and I will pass the wire through the hole provided.
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Old 12th Mar 2020, 8:08 pm   #15
John Earland
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Default Re: ZX Spectrum Tuning Issue

Iíve resoldered it-pics attached.
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Old 12th Mar 2020, 8:45 pm   #16
John Earland
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Default Re: ZX Spectrum Tuning Issue

Quote:
Originally Posted by SiriusHardware View Post
We are always kind here.

To me it looks as though that is a 'straight through' conversion with the connection carrying the ULA's video-out signal to the centre terminal of the phono (UHF) socket. It's not absolutely clear because the picture is a bit dark but the second image appears to show that the 'new' wire is soldered to the leftmost white-circled pad in your second picture. Is that correct?

I've never tried that but in principle it should work. You've wisely insulated the wire where it passes over the edge of the modulator box and I hope we can assume that you don't put the lid of the modulator on over the top of that.

Recheck your connections at both ends of that link wire, just in case you have a 'C2' situation there - joint not as good as you hoped it was. Also make sure that the wire has not melted a hole through the insulation when you heated it up to solder it, otherwise it may be shorting to the metalwork after all despite the measures you took to prevent that.

There's a slightly neater way to carry out your mod, by passing the wire through the left hand hole in the plastic insulator - illustrated in this article.

http://www.retrogamescollector.com/s...composite-mod/

If you do it that way you can put the lid of the modulator back on. However, for now, just try to get this working.

Next, focus on whichever TV it is which has a yellow 'AV' input instead of or as well as a SCART connector - which one is that, what make and model is it and if possible can you show us an image of the remote for that TV - we need to be able to read what it says on the buttons so maybe several images, top, middle, bottom.

One afterthought - the phono-to-SCART adaptor which you were using in some of your earlier tests, does it by any chance have an 'IN/OUT' switch on it?
Yes the SCART adapter does have an IN/OUT switch and I put it into IN mode. The TV with the definite yellow socket is the XENIUS-an obscure TV but it was working on this one. I have attached pictures of the TV model number and the remote-though I know the remote is not original.
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Old 12th Mar 2020, 8:46 pm   #17
John Earland
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Default Re: ZX Spectrum Tuning Issue

Here are the images
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Old 12th Mar 2020, 8:48 pm   #18
John Earland
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Default Re: ZX Spectrum Tuning Issue

I checked both ends of the wire and there is no resistance. I checked the outside of the aerial socket and the middle section (where the wire is connected inside the modulator) and it read 0.40 on 20k ohms.
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Old 12th Mar 2020, 8:55 pm   #19
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Default Re: ZX Spectrum Tuning Issue

Yes, that's better. The resistance seems OK and shows that there is not a short between the phono socket outer and inner. Even if you were putting more insulation on top before putting the lid on before, the lid would be such a snug fit that the metalwork could easily bite through the insulation. The way you have it now is a lot better.

Edit in light of your own edits and additions: Yes, IN is obviously the correct position for the switch.

It's quite awkward that the remote for your X... TV is not the original one as this is just the sort of function which might not work on a replacement remote.

OK, so try your Daewoo, for which you presumably have the real remote. Plug your SCART adaptor into that, connect the Spectrun composite-out to the yellow input connector on the SCART adaptor with an appropriate lead.

Do you have anything like the following on the Daewoo remote?

'AV'?

or, a symbol of an arrow pointing from the left into a slighly distorted rectangle?

Last edited by SiriusHardware; 12th Mar 2020 at 9:04 pm.
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Old 12th Mar 2020, 9:04 pm   #20
John Earland
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Default Re: ZX Spectrum Tuning Issue

Yes - I have two SCART adapters - one with IN/OUT and one without. I've tried them both. When I have used the one with the IN/OUT I have set it to IN. On the Xenius TV's remote I can select AV etc. On the left hand side there is a button labelled 'AV' and you can move through the different options e.g. YRGB, Ext 1, Ext 2, HDMI. I presume (because there are two) that the SCART is either of the Ext 1 or Ext 2 options.
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