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Post by Radiotech on Feb 15, 2022 20:49:29 GMT 12
I was recently given this and while it delivers an output, the frequency display isn't doing its thing. Has anyone got one of these that's working properly?
I would love to borrow it for a few days so I can compare waveforms and timing info between the various ICs. There's something weird going on.
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Steve
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vintageradio.co.nz
Posts: 734
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Post by Steve on Feb 19, 2022 10:49:44 GMT 12
It was a project from the Electronics Australia, April 1982 edition. I was in a similar situation - I was given one of these years ago (its still sitting in pieces somewhere in a box... don't ask where). But I was also given an A3 photocopy of part of the article, which I'll attach here as it might be useful. Mine had exactly the same problem - I never got to the bottom of it as I was given a different one that worked so I just used that. Its not the whole article - but hopefully its enough to help... the frequency counter section is described on page 38... Someone out there might even have the magazine in their pile...   |
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Post by Radiotech on Feb 23, 2022 16:00:35 GMT 12
It was a project from the Electronics Australia, April 1982 edition. I was in a similar situation - I was given one of these years ago (its still sitting in pieces somewhere in a box... don't ask where). But I was also given an A3 photocopy of part of the article, which I'll attach here as it might be useful. Mine had exactly the same problem - I never got to the bottom of it as I was given a different one that worked so I just used that. Its not the whole article - but hopefully its enough to help... the frequency counter section is described on page 38... Someone out there might even have the magazine in their pile... <button disabled="" class="c-attachment-insert--linked o-btn--sm">Attachment Deleted</button> <button disabled="" class="c-attachment-insert--linked o-btn--sm">Attachment Deleted</button> Thanks for that Steve.
I solved the issue(s).
Whoever built this kit or worked on it before it came into my hands didn't have particularly good soldering skills. They had done the various modifications that EA had recommended and are mentioned in the construction sheet, but their soldering left a lot to be desired. I went around and tidied up a lot of what had been done - and substituted better quality components for the mods than what had been used. Looking at the various timing waveforms I noted that the signal going in to one of the Scmitt triggers was a nice square wave, but when it came out the other side it was still a square wave but bouncing up and down. Following the track from that pin to the next IC I spotted a tiny little blob of solder shorting the track to the next one. Not visible to the naked eye, but under the microscope I found it. That resolved the counter issue and everything is working as it should now.
The next mission is to change out the frequency control pots and re-jig the way they're connected, because the adjustment is not very linear and is cramped up one end of the rotation. The pots are the original ones supplied with the kit so I don't think they have been swapped out at any point.
I'll dig out the original Exar product sheet which I have a copy of and see what is suggested.
If you ever find your one, I can now help with timing and waveform info to assist you getting your one working.
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