lecroy spare parts? (potentiometers... well, endless turns potentiometers) - Page 1
Forum section: electronics / repair

author: JPortici
author_rank: Super Contributor
timestamp: June 30, 2017, 11:30:56 am
content: 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 courseEndless 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 conductingusing an encoder was too damn difficult in 1989?I have checked some catalogs, emailed manufacturers and hopefully waiting for responcesDoes anybody have a pointer? or a spare? i'm inclined to think that these were used in other scopes of the era tooit seems to be very hard to find lecroy spare parts.

author: Jwalling
author_rank: Unknown
timestamp: June 30, 2017, 01:42:04 pm
content: Might be worthwhile to post to the Lecroy group on Yahoo.

author: alm
author_rank: Super Contributor
timestamp: June 30, 2017, 02:06:52 pm
content: 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.

author: JPortici
author_rank: Super Contributor
timestamp: June 30, 2017, 02:11:23 pm
content: 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 potUnfortunately the lecroy user group is slow these days, only a handful of replies each monthLecroy doesn't get as much attention/love as tektronix i'm afraid

author: alm
author_rank: Super Contributor
timestamp: June 30, 2017, 02:33:30 pm
content: 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.

author: JPortici
author_rank: Super Contributor
timestamp: June 30, 2017, 02:44:05 pm
content: 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?

author: alm
author_rank: Super Contributor
timestamp: June 30, 2017, 03:55:37 pm
content: 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.

author: neo
author_rank: Super Contributor
timestamp: July 02, 2017, 05:18:45 am
content: Quote from: JPortici on June 30, 2017, 02:11:23 pmFor what it's worth i love the looks of that monster of a scope.

author: David Hess
author_rank: Super Contributor
timestamp: July 02, 2017, 09:29:33 pm
content: 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.

author: lowimpedance
author_rank: Super Contributor
timestamp: July 03, 2017, 12:48:29 am
content: Quote from: David Hess on July 02, 2017, 09:29:33 pmThis 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.

author: JPortici
author_rank: Super Contributor
timestamp: July 03, 2017, 07:34:05 am
content: Quote from: David Hess on July 02, 2017, 09:29:33 pmLOL the datasheetQuote from:http://www.potentiometers.com/pdf/catalog70.pdfseems 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 timei 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 shaftthanks david, i'll also have another look at the tektronix parts databases even thought i didn't find them at first

author: carl_lab
author_rank: Frequent Contributor
timestamp: July 03, 2017, 03:06:16 pm
content: Quote from: JPortici on July 03, 2017, 07:34:05 amThe original shaft may be a modified 1/8" (3,17mm) shaft, and 45mm is very close to 1,75" (44,45mm):

author: JPortici
author_rank: Super Contributor
timestamp: July 05, 2017, 11:31:18 am
content: 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.

author: carl_lab
author_rank: Frequent Contributor
timestamp: July 05, 2017, 12:13:12 pm
content: Quote from: JPortici on July 05, 2017, 11:31:18 amWhat' 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.