leeds and northrup decade divider box top restoration? - Page 1
Forum section: electronics / repair

author: coppercone2
author_rank: Super Contributor
timestamp: March 05, 2021, 08:52:37 pm
content: I have an old leeds & northrup box that has a wooden base and some kinda plastic top, perhaps bakelite. The bottom of the box is stained mohogony. I am ok with the wood top but the top part is rather dirty/worn and I am not sure how to restore it.I thought to clean up as much as possible with alcohol and gentle scrubbing and then run over the top using automotive polishing compounds after the switch shaft holes are plugged with earplugs or something. Is this a good plan? I don't want to distrub the divider (you need to desolder hard silver plated wire). The switches I have used deoxit, tarn-x and alcohol to clean OK. The contact plate that rotate on top I dip in a ultrasonic with tarn-x in it to bring back to fresh copper and then wash, dry and coat with deoxit.The shafts I used brasso with a small buffing wheel in a drill press, they come out great. I can do the galvanized screw tops using noxxon with a buffing wheel in the drill press (usually comes out good if its not too far gone).And how about the plastic knobs? I was thinking ultrasonic with soap and maybe some vinegar plus manual scrubbing.

author: coppercone2
author_rank: Super Contributor
timestamp: March 05, 2021, 10:42:30 pm
content: well,the knobs are clean but the white paint on the letters wore off, so I will need to repaint it. I have a micro paint applicator pen so I should be ok.Simple green, H2O2 and Vinegar did a great job cleaning the brass and copper bits, but the problem is after I thought I could use tarn-x on the pure copper parts to reduce polishing time, but the small amount of brass used to joint the copper together had some kind of reaction and started tin plating everything like weird metallic cows. Brasso on a polishing wheel cleans it up though. I think the effect is only on the exposed surface, when i look into the area between the plates it looks copper, so its only a minor setback that will have me wash a few more buffs, I should be finished with the metal cleaning by tommorow.However the plastic top is still a mystery, and there is a few rotten ball bearings stuck in it. I will try WD40 to remove them I suppose? I can also try to drill a small hole under neath and punch them out, I am not sure if WD40 will harm this stuff.

author: coppercone2
author_rank: Super Contributor
timestamp: March 06, 2021, 12:20:30 am
content: Got most of the metal clean, I will try different grade compounds (my usual MO is to go from the ultra cut down to a #2). I see online brasso is used but I am not sure, I think that might be a misapplication, since car compound works fine on epoxy, polyurethane, paint, clear coat, etc. I don't think this can be that different that it requires a different hardness and friability but we will see.

author: Stray Electron
author_rank: Super Contributor
timestamp: March 06, 2021, 01:33:15 am
content: FWIW I have a Gen Rad 1658 Digibridge. One of the ones with the LED display behind a red plastic bezel with white markings on it. The first time that I cleaned it I used water with a small amount of Windex in it and it took most of the lettering off of the bezel! Lesson: be very careful about what you use to clean GR equipment with and test it first! I don't know what they used to use for the white lettering but it comes off VERY easily!IIRC Conrad Hoffman has some kind of L&N device on one of his web pages that he has cleaned up to where it looks likenew!

author: coppercone2
author_rank: Super Contributor
timestamp: March 06, 2021, 03:14:33 am
content: ehh I found some bad junctions, but going at it with xtra coarse mequries followed my light cut followed by polish made it look alright, but it had alot of dents and divets and stuff so I did not go crazy like on my car.Otherwise it works good, the resistance dropped from 0.450 ohm with it zeroed on the multimeter to like 0.08withoutzeroing the leads. I used probobly 60 q tips, 3 3 inch polishing sponges, 8 dremel buffs, 3 microfiber towels. I hope I can recover the polishing sponges with the washing machine, some seriously greasy shit came off (maybe tobbaco). I will apply deoxit grease on top (just used red spray for now after cleaning with q tip alcohol, tarnx then wiping with a microfiber towel) later, when its ready to be put back together.I need to restore a handful of rusty screw heads that attach the knob to the shaft, restore the front contacts (still did not clean those, only the knob that goes on top was polished, so the resistance might yet drop a little, maybe that deoxit will work a little magic over the next day too).I repaired one bad solder joint (the low range resistance wire popped off the joint), hopefully the other failures are also bad solder joints and not fried components). The brass shafts I polished and coated with automotive ceramic wax.Wow, I must have bought this in 2015.that resistance drop is wonderful though, 1/2 an ohm is terrible, now its like 30 miliohms. Maybe when its done I will put in some lugs and kelvin connect it to measure it.All that late night youtube playlist restoration watching sure paid off.

author: Stray Electron
author_rank: Super Contributor
timestamp: March 06, 2021, 04:22:37 am
content: Pictures or it didn't happen!FWIW a few weeks ago I picked up an L&N five decade Wheatstone Bridge just like the one that Conrad Hoffman has on his website, except that I got the cover with mine :-) and the finish on mine appears to be nickel over brass instead of just brass. I hope to clean it up in the near future so I'm looking forward to hearing what's involved.Here's Conrad'shttp://conradhoffman.com/L&N_Bridge.htmGR and L&N sure made someprettyequipment back in the day!PS has anyone got a manual or a schematic for this old beast? I can't figure out how they manage to multiply the decades.

author: coppercone2
author_rank: Super Contributor
timestamp: March 06, 2021, 04:59:33 am
content: when its done maybe, the problem is still the wood, I want to wait till the weather is nice to do the wood. The plastic is kinda what it is at this point.I wanted to sand it down and give it a good coat of lacquer in a month.. I have more inside activities to do right now so I don't want to fight mother natureI attempted to restore a antennas paint job in this weather (old standards measuring one) and I likely should have left it alone with how the paint behavedMine is a much older unit that is not KV, it just a divider (big ass), 13 knobs, 7 and 6 on the other side, the biggest setting is 3 step (10k or 1k) and the lowest is 6 step (20% of smallest decade).

author: coppercone2
author_rank: Super Contributor
timestamp: March 06, 2021, 07:08:52 am
content: I did a kelvin measurement because I am suprizingly interested in this, the resistance across 13 switches reads ~0.030 and 0.032 ohms on slow, 6.5 digit connected 3Hz filter 34401A @ 10Gohm input impedance (2 meters). I must have did a good jobacross half the device its 0.015.Is this considered good or bad? I just know its a huge improvement from the 0.45 I was getting before cleaning. I found the other fault and it was again a broken low resistance wire shunt, easy fix in 5 seconds. 1 to goOn the broken dial it looks like the external wire is broken on the resistors, I managed to patch 4 of them up with a solder bridge (hard to do) but the third one is giving me a problem, I will try to solder some kynar in there to bridge it.one of them i put a jewlery bead on the wire, filled it with solder after crimping and then soldered it to the other wire. quite useful i think it will hold ok, its not going to survive a 450 foot roll though lol