Thread: Zx81
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Old 24th Mar 2020, 7:17 am   #160
John Earland
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
Default Re: Zx81

Originally Posted by SiriusHardware View Post
I think all that happened was that you shifted the output frequency when you put the lid on - as mentioned earlier, the 'transmitter' in the modulator is just a simple free-running oscillator and putting the metallic lid on it probably just made the transmitter frequency detune to one side a bit.

All you likely needed to do after putting the lid on (at which point the signal disappeared) was to retune the TV a little.

You can test this theory if you like: Tune it in as best you can with the lid on, and then flip the lid off - does the signal disappear? If so, tune around and find it again. Then, put the lid back on - does the signal disappear again? If so, tune around again until you find it again.

If everything in the previous paragraph is true, then all that's happening is that the modulator output frequency is changing slightly when the lid is present / is not present.
Yes, that makes sense. I will try the PCB today. I feel more confident about the soldering now. By the way, I bought a new soldering kit with temperature control so I hope my skills improve further. It also came with a desoldering unit.
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