lecroy spare parts? (potentiometers... well, endless turns potentiometers)

[JPortici]

in the quest for repairing (now actually restoring) a lecroy 7200A, there are some potentiometers that are really scratchy.



^ THIS.

These are no ordinary pots, of course 
Endless rotation.
No, these are not encoders.

Service manual calls them conductive plastic pot 5k and in the schematic they are indeed marked as potentiometers.. and of course they are.

Basically, shaft rotates 360 degrees, the two gangs are opposite, so while one is at the middle, the other is not conducting
using an encoder was too damn difficult in 1989  ?

I have checked some catalogs, emailed manufacturers and hopefully waiting for responces

Does anybody have a pointer? or a spare? i'm inclined to think that these were used in other scopes of the era too

it seems to be very hard to find lecroy spare parts.

[Jwalling]

Might be worthwhile to post to the Lecroy group on Yahoo.

[alm]

Maybe adding cleaning them and adding some appropriate lubrication (e.g. DeoxIT Fader) would restore their performance to a usable level? If disassembly is an issue, you can sometimes drill a small hole through which you can spray lubrication.

[JPortici]

well these are sealed and double gang so i think i'd need to trill two holes?

I'm wary of disassembling the pots, they are held together by four rivets. Even if i drill thourgh them to remove them i have no clue where to get new ones to close the pot


Unfortunately the lecroy user group is slow these days, only a handful of replies each month
Lecroy doesn't get as much attention/love as tektronix i'm afraid

[alm]

Then drilling might be the way to go. Obviously YMMV, but outside of parts donors these do not look like parts that are easy to source (I have not checked). And the costs would be minimal assuming you have the appropriate tools.

[JPortici]

yeah, i'm still wary of blindly drilling. also, is conductive plastic affected by the chemicals in the deox?

i can't find donors at the moment i'm afraid, whot i may do is swap one of the pots (the really scratchy one, used in data entry) with another (megazoom or multizoom or whatever is called vertical placement)

later i'll add a keyboard to the scope, i see that they still make those with a 5 pin din plug for like 20 euro w/ amazon prime, who would have tough of that?

[alm]

DeoxIT Fader is specified for both carbon-based and conductive plastics pots/faders. My tiny tube of DeoxIT Fader F100L says "Lube for Conductive Plastics" under the product name, so I am pretty sure it will not negatively affect conductive plastics.

[neo]

well these are sealed and double gang so i think i'd need to trill two holes?

I'm wary of disassembling the pots, they are held together by four rivets. Even if i drill thourgh them to remove them i have no clue where to get new ones to close the pot


Unfortunately the lecroy user group is slow these days, only a handful of replies each month
Lecroy doesn't get as much attention/love as tektronix i'm afraid

For what it's worth i love the looks of that monster of a scope.

[David Hess]

Tektronix liked to use these as encoders also and they actually work pretty well.

It looks like it is constructed like a MOD-POT.  Drill out the rivets and it should come apart for easy cleaning.  My guess is that material worn off from the carbon brushes has caked with the lubricant preventing good contact.  Clean and then lubricate with a silicon or polyphenyl ether oil.  Replace the rivets with small screw hardware.

[lowimpedance]

  My guess is that material worn off from the carbon brushes has caked with the lubricant preventing good contact.  Clean and then lubricate with a silicon or polyphenyl ether oil.  Replace the rivets with small screw hardware.

This is the best way, there must be a hobby store you could look up (RC models etc use fine screws). Just drill only the head of the rivet enough that it falls of then drift the pin part out.

[JPortici]

It looks like it is constructed like a MOD-POT.

LOL the datasheet

BENEFITS

• Versatility
• Wide Resistance Range
• Versatility
• Versatility
• Versatility
• Versatility
• Versatility
• Moderate Size
• Versatility
• Non-Magnetic
• International Acceptance

seems pretty much versatile. incidentally, i did already contact them but they replied that they usually don't do metric sizes (3mm shaft, 45mm lenght etc) so i am scared to ask for a quote. There shouuld be at least one RC toy shop in the area... but i shouldn't get in. it's a hobby i wanted to try for some time

i was already planning to make a small board to convert a regular encoder to generate two out of phase ramps (like this is doing) but of course i had to find one fith the correct shaft 
thanks david, i'll also have another look at the tektronix parts databases even thought i didn't find them at first

[carl_lab]

...they replied that they usually don't do metric sizes (3mm shaft, 45mm lenght etc) so i am scared to ask for a quote.

The original shaft may be a modified 1/8" (3,17mm) shaft, and 45mm is very close to 1,75" (44,45mm):

[JPortici]

thanks for noticing that!

a thing i noticed, on the front plate it says "claro usa"
guess, what? now they're part of honeywell. but of course they haven't replied to my emails (contacted them a week ago)

In the meantime, i asked my boss and the guy who makes our enclosures, we disassembled one of the potentiometers, cleaned and sprayed lots of contact cleaner and reassembled, to keep everything in place i used a bit of solder at the end of the rivets, until we find a better solution. checked the travel with a scope it doesn't seem to scratch anymore. tonight i'll mount it back and check if it actually works.

I'll post photos later tonight, there are quite simple to reassemble and since it appears it was an US part adapted for metric.. maybe i can get the parts i need and not the actual pots for state potentiometers (potentiometers.com) which have been really kind for now, actually answering my questions. they make custom assemplies and have one series that looks quite simillar to these pots, minus the fact that they don't do metric.

[carl_lab]

...minus the fact that they don't do metric.

What' the problem with 1/8 inch shaft?
If the hole in your knob is too narrow, why not bore up to 3.2mm?
And excessive shaft lenght can be cutted by hack saw or dremel.