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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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13th Mar 2020, 11:49 pm | #41 |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
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Re: ZX Spectrum Tuning Issue
Ah! No-these have three segments! I guess that’s the problem!! How embarrassing!!
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14th Mar 2020, 12:02 am | #42 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,482
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Re: ZX Spectrum Tuning Issue
It might be, depending on the 'geometry' of the sockets. I have a feeling those sockets on the ZX machines do not play well with typical stereo plugs due to the spacing between the socket contacts.
Do you maybe have a 3.5mm mono to 3.5mm mono jack plug lead, or do you have a couple of solderable mono plugs which you can use to make up your own lead? Ironically, I have a nicely made 3.5mm to 3.5mm mono lead sitting within arm's reach here. I could send you one, I know I have plenty, but you could probably order one yourself online just as quickly. |
14th Mar 2020, 12:18 am | #43 |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
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Re: ZX Spectrum Tuning Issue
Thank you so much for your kind offer-I’ve just ordered a couple from Amazon! Thank you though. When they arrive I shall let you know how I get on!!
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15th Mar 2020, 9:00 pm | #44 |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
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Re: ZX Spectrum Tuning Issue
Have now tuned the Spectrum into both a CRT TV and LCD TV both via the SCART socket and both give excellent results. The border is still a little fuzzy but totally acceptable. I am hopeful that using the correct audio cables will allow me to SAVE and LOAD programs as before!
Finally, I have discovered that this is a 48k Spectrum. I do remember it used to have this somewhere on the case but this one doesn’t. I found on the internet a PEEK command that would return a value of 255 if it was a 48k and that’s exactly what it did do - so doubly happy. |
27th Mar 2020, 12:10 am | #45 | |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,482
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Re: ZX Spectrum Tuning Issue
Brought over from the ZX81 thread:
Quote:
In an earlier post you seemed to find the image quality over composite on both of your displays acceptable - is there a particular reason why you think it needs a transistor buffer? If you can find a documented instance of a more complicated composite mod for the Spectrum by all means try it, but if it is working really well, it might be best to let sleeping dogs lie... Did you get those audio cables you were waiting for? |
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27th Mar 2020, 12:02 pm | #46 |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
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Re: ZX Spectrum Tuning Issue
Thanks for that-I completely agree with you. I shall leave it. No, I was just thinking it might enhance the picture but I’ll leave well alone.
The audio cables have arrived now and all working well. The cassette recorder is being picked up by both the spectrum and ZX81(when it works!) and I can read and write to it. Last edited by John Earland; 27th Mar 2020 at 12:17 pm. |
27th Mar 2020, 12:18 pm | #47 |
Dekatron
Join Date: Feb 2005
Location: West Cumbria (CA13), UK
Posts: 6,118
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Re: ZX Spectrum Tuning Issue
I thought the idea of the buffer was more one of protecting the internal circuitry rather than enhancing the quality.
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27th Mar 2020, 12:33 pm | #48 |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
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Re: ZX Spectrum Tuning Issue
Yes - it is - I am new to this world of electronics! I don't really know what I am doing - hence I greatly value people such as yourself to keep me on the right path!
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27th Mar 2020, 12:35 pm | #49 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,482
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Re: ZX Spectrum Tuning Issue
I think that on the ZX81 the ULA is not designed to drive the rather low impedance 75R load of a typical composite video input, it is designed to drive the input of an ASTEC modulator.
The Spectrum ULA seems more tolerant / more capable as shown by the fact that few people seem to bother with a buffer stage, although of course a unity gain buffer would give added protection as you say. I notice John's new CPLD based ZX81 ULA which he has on the way has a switchable setting to optimise the output for modulator input / for direct composite video out. |
27th Mar 2020, 1:21 pm | #50 |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
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Re: ZX Spectrum Tuning Issue
Yes - it's a really neat solution. I've seen images where this little vLA81 pcb fits inside the modulator. I'm not sure I like that though, not sure why because I would have no intention of putting it back to UHF output.
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27th Mar 2020, 1:24 pm | #51 | |
Nonode
Join Date: Oct 2008
Location: Warsaw, Poland and Cambridge, UK
Posts: 2,669
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Re: ZX Spectrum Tuning Issue
Quote:
Chris
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27th Mar 2020, 1:49 pm | #52 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,482
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Re: ZX Spectrum Tuning Issue
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27th Mar 2020, 1:51 pm | #53 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,482
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Re: ZX Spectrum Tuning Issue
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27th Mar 2020, 3:10 pm | #54 |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
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Re: ZX Spectrum Tuning Issue
Just an update: the new vLA81 has just arrived! I shall have a long think about whether I will try the swap myself. If I do I will do as you suggest and cut the old ULA out as close to the chip casing as possible. I've also been advised that as you melt the solder on each pin make sure you pull the pin out of the slot in a direction where you don't have the potential of tearing the printed circuits.
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27th Mar 2020, 3:23 pm | #55 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,482
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Re: ZX Spectrum Tuning Issue
The main thing is just to be sure that the solder on the pad is 'wet' (ie, melted) and then withdraw what is left of the cut-off pin straight upwards away from the top side of the PCB with something like a pair of fine pointed tweezers.
Don't worry about clearing the holes at that stage, you don't do that until you have removed all 40 of the original pins. |
27th Mar 2020, 5:02 pm | #56 | |
Hexode
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
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Re: ZX Spectrum Tuning Issue
Quote:
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