Oil contaminated switches. - UK Vintage Radio Repair and Restoration Discussion Forum

jim_beacon · 21st Aug 2004, 8:06 am

I have recently been working on a Tektronix 535A oscilloscope, and found problems with the triggering circuits. The fault was eventually traced to leakage across a switch wafer.

On closer examination, the switch appeared to have been "cleaned" with something similar to WD40, which had left a large amount of oil on the paxolin wafer. Over time, this had attracted dust, and lead to a low resistance path across the paxolin.

As these are special to type switches, I decided to try cleaning. The wafers were removed from the shaft, washed with "Ultraclense" de-greaser, and scrubbed with a small tooth brush (the brush head from electric toothbrushes are ideal), then left to dry.

A quick test with the Megger showed the insulation restored, and the the paxolin restored from a dark gloss brown to its normal pale matt colour.

The contacts were lubricated with a little "Electrolube" from a pen type dispenser before re-assembly.

I don't know if this will always work, but you may want to try it as a last resort.

Jim.

Norm_Leal · 21st Aug 2004, 3:28 pm

Hi Jim

I have a similar problem with a digital volt meter. Batteries leaked and got acid on the circuitry. Tried cleaning and drying but didn't get all conductive material out. Next I plan to use an ultrasonic cleaner.

Norm

Great Poohbah · 11th Feb 2006, 7:47 am

Norm:
An ultrasonic cleaner may destroy any solid state devices you have.

Zulu95 · 24th Mar 2006, 10:46 pm

I remember the GPO Telephones putting out a tech bulletin advising the removal of silicone swith lubs/grease from issue because it was tracking into switch units and coating the contacts. It could creep a good distance! Once on the switch it would form insulating crystals if subjected to arcing. This was back in the days of Strowger exchanges.

21st Aug 2004, 8:06 am	#1
jim_beacon Retired Dormant Member Join Date: Mar 2003 Location: Bishop's Waltham, Hants, UK. Posts: 939	Oil contaminated switches. I have recently been working on a Tektronix 535A oscilloscope, and found problems with the triggering circuits. The fault was eventually traced to leakage across a switch wafer. On closer examination, the switch appeared to have been "cleaned" with something similar to WD40, which had left a large amount of oil on the paxolin wafer. Over time, this had attracted dust, and lead to a low resistance path across the paxolin. As these are special to type switches, I decided to try cleaning. The wafers were removed from the shaft, washed with "Ultraclense" de-greaser, and scrubbed with a small tooth brush (the brush head from electric toothbrushes are ideal), then left to dry. A quick test with the Megger showed the insulation restored, and the the paxolin restored from a dark gloss brown to its normal pale matt colour. The contacts were lubricated with a little "Electrolube" from a pen type dispenser before re-assembly. I don't know if this will always work, but you may want to try it as a last resort. Jim. Last edited by Paul Stenning; 26th Dec 2004 at 10:58 pm. Reason: Fix link or code for vBulletin

21st Aug 2004, 3:28 pm	#2
Norm_Leal Retired Dormant Member Join Date: Jan 2003 Location: Livermore, California, USA. Posts: 139	Re: Oil contaminated switches. Hi Jim I have a similar problem with a digital volt meter. Batteries leaked and got acid on the circuitry. Tried cleaning and drying but didn't get all conductive material out. Next I plan to use an ultrasonic cleaner. Norm

11th Feb 2006, 7:47 am	#3
Great Poohbah Retired Dormant Member Join Date: Feb 2006 Location: Port Orchard Wa Posts: 1	Re: Oil contaminated switches. Norm: An ultrasonic cleaner may destroy any solid state devices you have.

24th Mar 2006, 10:46 pm	#4
Zulu95 Retired Dormant Member Join Date: Mar 2006 Location: Savannah, Georgia, USA. Posts: 31	Re: Oil contaminated switches. I remember the GPO Telephones putting out a tech bulletin advising the removal of silicone swith lubs/grease from issue because it was tracking into switch units and coating the contacts. It could creep a good distance! Once on the switch it would form insulating crystals if subjected to arcing. This was back in the days of Strowger exchanges.