Repairing turns counter dial?

[Dekatron]

I just bought an old Oltronix 2500V power supply that has a problem with the turns counting dial, it is stiff and it seems like the second gear is not fastened correctly on the shaft.

I have the manual and schematics for the power supply but there is no mention of the turns counting dial manufacturer or any other detail on it, the only part that is mentioned is the 10 kOhm 10 turn 2W potentiometer used.

Can anyone point me to who manufactured this turns counting dial so I can try to find any more information on how to properly fix it?

[mark_in_manc]

That looks a lot like the mile (sorry, km!) counter in a vehicle speedo. I've had these apart before - the ones I have seen are pretty self-evident, with a trip on the side of the less-significant-figure which hits the small white gear between it and the more-significant-figure, making it advance one as the former goes over the zero. So long as it is not riveted together, I should think it would come apart and back together fairly easily, in good light and on a tray to catch all the bits!

[factory]

Originally Posted by mark_in_manc

That looks a lot like the mile (sorry, km!) counter in a vehicle speedo.

Also used in lots of other things such as tape counters, clocks, etc. You can even get counting dials of that type to directly attach to control pots.

But this one looks to have extra gearing before the counter to match the ten turns of the pot to indicate up to 2500 on the counter. Is the problem in the gearing or the counting dial part?

David

[Dekatron]

I believe the problem is that someone has used the wrong kind of grease, in the gearbox, in an attempt to soften it. All of the gears are made from brass and the top grease has become green over the years, it also looks like there is remains from another type of grease underneath the green looking grease that looks grey, at least it comes apart as two colors when I removed some. It feels like it has seized up due to too much grease and possibly the wrong type of grease.

There is also a mechanical brake that is engaged by the chromed wheel on the front and that has also seized up a bit.

I can give it a try just as it is but if someone can recognize the make/model it might be possible to get hold of some datasheet or other information that might point out how to dismantle it properly and also what grease to use.

[TonyDuell]

I've come across a green grease (or a grease that has turned green) in the focusing threads of camera lenses. It sets rock-hard and generally has to be scraped out of the threads with a sharp pointed tool -- once you get them apart.

I don't believe it has been replaced or the wrong grease used. Rather the original grease has decayed in some way.

[Dekatron]

Originally Posted by TonyDuell

I don't believe it has been replaced or the wrong grease used. Rather the original grease has decayed in some way.

Yes, I didn't think about that but that might be what happened, it might even have separated into the green and the grey looking hardened grease.

I'll definitely have to use a sharp tool, tested with a small screwdriver and the grease came off in small hard lumps that cracked like if it was thread locking glue.

I'll probably have a go at it this weekend. I'll let you know how it goes and I'll also try to contact Bourns and see if they know anything, this as the 10 turn potentiometer was manufactured by them.

[TonyDuell]

That sounds like the same stuff. I seem to remember some solvents will soften it (try actone, white spirit and isopropyl alcohol, for example) but only use those if they won't harm other parts of the unit. On a metal focusing thread you can try most things, on a plastic mechanism take more care.

[Radio Wrangler]

Some of those solvents might remove the white numbers from the barrels even if they don't damage the plastic used in the mechanism.

I'd try a mild penetrating oil first then an alcohol. Acetone would be for if I was getting desperate. If you can find something which dissolves the grease, even slowly, but doesn't damage the plastic or the printing, then time can help. As there is grease on the mechanism then it's a good bet that the plastic isn't susceptible to oils.

HP used a similar mechanical counter on a tuning pot in the 3580A spectrum analyser. I think it's a custom metal frame with a two-speed gearbox and a purchased shaft-input counter. One of those pull out the knob for low gear fine adjustments arrangements.

David

[Dekatron]

I did have a go at it and it works very nice now.

It was quite straightforward to dismantle it (except for two small things that I missed first which I mention below). There were a few spacers with different thickness between the four shafts that keeps the two flanges mounted to each other, you can see two of them to the left on the round and square shafts in one of the pictures.

I only lost one of the white numbers but I saw a few that were cracked before I started so I'll see if I can find some clear glue to apply on top of those so they might stay in place. I'll try to find some white paint to fill in the lost number as it looks quite poor and irritates me.

It turns out that it is a gearbox that makes it count up to 300, it has 300 stamped on its side which confirms this.

It looked like someone had used some kind of solvent to try to unseize it but that hadn't done almost anything to the hardened grease - I couldn't find any solvent myself that made it softer so I had to go the mechanical route and remove it with a pair of very thin tweezers and a scalpel. I didn't wait for more than 20 minutes with the few solvents I had so waiting longer might have disolved it properly. I tried IPA, white spirits, methanol, acetone and chemically pure gasoline.

I also had to clean the shaft with the black wheels as there was some kind of very sticky oily substance on there. I used a lithium based grease there especially made for plastic like cogwheels and stuff that I got when I repaired sticky keys in my daughters Yamaha Clavinova digital piano.

There were two small copper spacers that I didn't see when they fell out, I only found them an hour after I removed the counter, missing those resulted in a problem in mounting the shaft brake. I didn't realise that they belonged to the counter as they had fallen into the power supply and I found them at the back of the unit. They were supposed to be placed in two small indentations in the brake unit just behind the flange of the counter and I didn't see those indentations until I disassembled the whole unit with the shaft and potentiometer one more time, see the photo where I am holding the shaft brake with them in their correct place.

One more thing that I found was that due to that it had seized up someone had tugged quite hard at it making the second of the two angled cogwheels come lose from its shaft on the input of the gearbox. It uses a grubscrew with a very small size, possibly below 1 mm in outer diameter with a very thin Allen(?) hole. I have never seen that small Allen-tool so I had to use a plier on the outside to fasten it, fortunately it worked and it works very well now that the counter is smooth. Since it was loose I had to adjust it to the right position so that the counter stops at zero when the potentiometer is at its zero position. I also had to position this cogwheel at the correct depth so that it wouldn't snag on the ptfe-isolator on the shaft to the potentiometer.

So now I'll have to check the rest of the components in the power supply, there are a few dried electrolytics to replace and possibly a diode and some resistors that have gotten hot. The previous owner had tested the power supply recently and it worked he told me, but he didn't know capacitors sometimes go bad over the years so he was lucky that nothing did go bang when he switched it on. I'll also have to find proper high voltage contacts and cables as the ones in the unit are not the original ones but some specially made for some kind of prototype medical equipment.

[Kentode]

Martin, I'm glad that you sorted out the problem.

I worked at ENM (English Numbering Machines) for 9 years and all assemblies were dry, with no grease.

The logic was "no grease, no dirt".

PS. The hand tally in the picture is 25 years old and works faultlessly, often held behind their back by airline stewards counting people onto the plane.

[emeritus]

Hydrocarbon greases usually consist of a mixture of an oil (to provide lubrication) and a soap (to keep the oil in place). Hardened grease consists of the soap that is left behind after the lubricating oil has evaporated. This is probably why hydrocarbon solvents that are good for removing non-hardened grease, are often ineffective with hardened grease. Although I have had success cleaning gears with petrol lighter fluid, mechanical removal with a sharp needle is usually necessary.