Dueling RCA restoration part 6: Repairing the focus coil

Opening and repairing the focus coils plus some electrochemical experiments
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[@PaulinesPastimes]

Having thought about my comment, I should add that the battery experiment was a brilliant piece of troubleshooting.

[@PaulinesPastimes]

You made a battery! You could market that idea for sure, people might find a use for batteries one day. 😄👍

[@billharris6886]

Thanks Bob for demonstrating the problem by using the Evapo-Rust paper towel blotter and showing the focus coil internals. Since cloth tape was used to hold the windings in place, I suspect most of the leakage current took place between the steel coil housing and where the leads were soldered to the coil windings. Hopefully your repair attempt will suffice over time. It seems we are never too old to learn something.

[@mikefinn2101]

Bob one of the best educational video really great for me love my channel. Bob you are the of best

[@user-tu6xc7cx2z]

I had this exact problem with my Avo 8 meter when Duraleak problems struck. It leaked into the battery compartment and got onto the Bakelite front panel range switches and was giving erroneous readings, and when testing the internals with my digital meter I got the same phantom DC voltages. Several attempts at cleaning it with vinegar and citrus acid to neutralise the alkali fluids haven't worked, very annoying as beforehand it was extremely accurate, and was a Ministry of Defence panclimatic model I had been happily using for almost 20 years.Learnt a lesson the hard way there...

[@rlgrlg-oh6cc]

That rubber band will not last. Even just sitting in a drawer, they rot after some years, and immediately break if stretched.

[@eDoc2020]

I've heard rubber bands are rated for 2 years. I have older unused ones which seem fine, however ones stored stretched around an object always seem to crack when touched. For testing a rubber band is obviously fine but I agree it's not good enough for a restoration. Probably 5 years max. An o-ring is generally a better choice.

[@ElectroRestore]

I often find dust bunnies in sets I work on. However, I never found any energizer bunnies! Definitely not a fun result from deep cleaning! 😂

[@randomsteve4288]

7:05 The explanation is simpler. Unless it is 100% potted the coil will act like a wick and your evaporust will soak into the coil. Now with this old enameled wire you always have microscopic cracks in the coating due to deterioration of the flexibility of the enamel coating not withstanding the repeated thermal expansion and contraction of the underlying copper conduit. Under normal operation that is not immediately an issue since for a short between adjacent turns to occur the cracks are too tiny and would have to overlap at exactly the right position and mechanical pressure on the coil would need to force the minuscule exposed surfaces together. But the moment any liquid wicks in mayhem starts. The coil is at 200+V with respect to its metal enclosure, and immediately electrolysis will start, resulting not only in forced erosion/dissolving of the copper (producing conductive ions enhancing the conductivity of the solution) but also the nascent oxygen created on the copper will crack, lift and break up more enamel coating, thus increasing the contact area. Maybe take the old coil, put the coil at say 200V with respect to the metal enclosure, measure the current and watch how it self destructs. And no, there is probably no saving this coil. You would have to rinse and maybe cook it in destilled water to dilute any electrolite soaked into the windings and dissolve any hygroscopic residue, then rinse in alcohol and cook in WD40 to expel all water and finally pot/cook in wax or a heavy transformer oil. And still the enamel coating may have been widespread destroyed to where you have shorted turns now.

[@randomsteve4288]

14:24 the corona dope will not last. Plus you tested with the coil laying on the bench. So the metal enclosure of the coil had no connection to chassis. You should have taken a microamp meter and checked for leakage current between the metal chassis and the metal enclosure of the coil. Any reading would indicate that there is still some moisture in that coil finding a way to bridge the copper coil to the steel housing. And just by heating in ur oven u will not drive out any liquid that wicked into that coil. Sorry to say so, this fix may come back to bite the owner after some hours of run time.

[@bandersentv]

I've reassembled and it's working fine after a few hours of use

[@Runco990]

I didn't quite see, but did you also attach the metal case to the chassis? I think that's where your problem arose.

[@RetroPC-vy3kt]

Thinking this could be rinsed, soaked in demineralized water, then tie a strong string around the center and spin it around like a centrifuge, maybe that would help remove most of the water?

[@eDoc2020]

I don't think centrifugal action will do much of anything for embedded moisture. Baking in the oven is going to work much better. A vacuum chamber will probably also help.

[@user-yn8mz5bf9y]

Radio Shack had a awesome book on A/C and what it does to a inductor under varies situations, which can be calculated You needed a higher level of algebra to do all the calculation Shango proves no restoration needed just plug it in LOL

[@cool69rr]

Would it have been useful to have a hipot tester to find that focus coil problem?

[@bandersentv]

Possibly, but even with my basic DMM I was able to detect a problem. It took me longer than it should have because I hadn't encountered this problem before.

[@shango066]

Over the years, I have made a lot of money off people who Pressure wash their Vehicles engine.

[@chetpomeroy1399]

Pressure washing a vehicle's engine that's loaded down with lots of emissions junk is not advisable. At the very least, the water jet could dislodge a hidden vacuum hose, and water could get into vacuum ports and cause damage, as well as getting into the distributor housing.

[@quetzal4042]

Sp: "dueling", not "dualing".