I'm trying to repair an oscilloscope in which two of the front panel (pot) controls are situated right at the back of the instrument and drive spindles connect them to the front panel knobs by long aluminim shafts!
The pots have broken becuase of misalignment of those long shafts. I could fix this if I could get hold of some miniature universal joints (sometimes used on older radio sets in which they took up the slack of misaligned shafts.)
Trouble is I can't find any - maybe becuase I don't know the tiny versions are called :-) Does someone know of a model shop etc that sells such things? Thanks
Model shops that carry parts for model boat building often have some,they are used to align motors to propellor shafts. In some low stress situations though a length of flexible tube like the stuff used for fish tank air or car windscreen washers will work. G.harman
Their prices are always bad, but at least you can find what you want, but sometimes it's worth the extra cost to save the time and hassle. You can often use the manufacturer's information that you find there to find it elsewhere too.
I've seen them done with fibreglass shafts before, presumably because they allow for a little flexibility... until the fibreglass splinters and breaks :-)
Are we talking huge bends here (because you want to mount replacement pots 'somewhere else' within the chassis, so it's far more severe than in the original design)?
Yes, a 'real' UJ would be nice - but if the angles are shallow then I wonder if a small break in the shafts bridged by a bit of heatshrink tubing would be sufficient? It's not like these are hooked to a motor spinning at high RPM for long periods. I really don't know if it'd have too much 'twist' to it though (so the front dials wouldn't give an accurate enough indication of pot position), but it was just a stray thought.
(of course if these shafts are driving switches rather than pots, I suspect you'll need a proper 'solid' UJ)
It's often done with insulating shafts for the brightness & focus controls as these are often at a very high negative voltage with respect to earth. By using insulating shafts and mounting the pots on insulating material any reasonable voltage is possible. I'm not sure why any 'scope would have metal shafts for these. It doesn't really make sense. 1/4" nylon rod would be better & would give a degree of flexibility too. It could be joined onto shortened pot shafts with straight couplers, which are easier to find (but still not very easy!).
We used to have heated arguments (friendly) with the RS rep (Dave Plumer) about prices. He knew he was pissing in the wind, and had been for may years. Whatever he came up with, we'd shoot him down in flames from almost anywhere 'cept R(eal) S(hit) Components. Great bloke though who enjoyed a cup of tea :)
Too much whiplash. Fix the misalignment and use a rigid coupling or else you'll never get repeatable settings.
If you really want UJs and the misalignment is small then cut the shaft in two. Sleeve one piece so the other is a loose fit in the sleeve. Cut a slot down the sleeve across the diameter and make a T piece on the end of the other section of rod to engage in the slot. Adjust the slop by widening the slot until it works.
Ta again for these helpful ideas. Yes - the two controls in question are indeed focus and brilliance so cal points are not a problem. I thought it strange to use metal shafts too. Another (better) 'scope I have (Tektronix), uses nylon/plastic for the same purpose.
I try to avoid them, but sometimes there is little option. The most pricey single item I've had from RS was a timer relay. IIRC it was about fifty quid .... plus ninety odd pounds delivery!!! At the time I was on site at a bakery just outside birmingham, supervising the fitting of a new control panel for a prover and was asked to look at another problem while the production line was down. I worked out that to cure the problem they needed to add in a timer relay and they wanted to try my solution, but they didn't want to hold up restart of the production line. RS managed to deliver from the depot at Corby, sixty-odd miles away, in just over an hour and a half. That was well worth the cost.
My memories go back to the days when they were known as Radiosopares, when their main market was radio & TV repairers. Our rep was Derek Underhay.
Main competition, in our neck of the woods, was from RTS (Pye group) and Norman Rose - whose limited range offered much better value.
Radiospares always went to great lengths to hide their sources. When Dubilier produced their brightly coloured polyester replacement for the waxed paper capacitor, Radiospares launched their own in its house colour - grey. The only difference in marking was the obvious indentation where the moulds had been adapted to replace the Dubilier name with Radiospares ...
As time went on, the product range widened as electronics became an increasingly wide market, and Radiospares became RS Components ...
Derek still came round every month with his usual greeting, then set off to the far end of the workshop to put the kettle on for tea - we had our reps well trained!
His box of new additions became a game for us, to see if we could guess the original manufacturer of each item but Derek would always tell us the answer if we were stumped ...
1969, a new life - and a new RS rep ...
"Who makes that?" "RS Components!"
"And who makes that?" "RS Components!"
We were a mixture from various backgrounds - and nobody liked him!
I'd been away for a couple of days when he came round on one occasion ...
"Who makes that?" "RS Components!"
"Who makes your potentiometers?" "RS Components!"
"Strange. I was in the AB Electronics factory in Abercynon yesterday and they showed me the machine that was doing life tests on the potentiometers that they manufacture for you ..."
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