Cleaning old muddy PCBs of high performance scope? - Page 1
Forum section: electronics / repair

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: February 18, 2024, 08:18:59 am
content: Hi, I am planning to go get a TEK 7904 in the next couple of days, and I just wanted to know the methods of cleaning the PCBs of such high-performance scopes.I cracked this guy open at the recycling center and there was mud everywhere inside. I mean dirt from the earth; lots of dust too. It was very likely rained on and maybe under an evergreen tree from the number of sticks and thin leaves inside. I hope to restore this scope.I know that some people use soapy water to clean PCBs of lower-end devices, but this scope is specified at 500MHz, and I just wanted to know other "proper" methods.IPA baths? Use only air and toothbrush? Use copper(II)chloride to dissolve all aluminum to clean the vias? (joke)Thanks

author: Vgkid
author_rank: Super Contributor
timestamp: February 18, 2024, 08:59:36 am
content: First thing is to get the dirt out , so use soapy water than that. Nothing wrong with it either . Tektronix even recommended it.https://www.byan-roper.org/steve/manuals/Tektronix/Tek%20Scope%20Cleaning%20by%20C%20Phillips.pdf

author: srb1954
author_rank: Super Contributor
timestamp: February 18, 2024, 12:05:52 pm
content: Don't use any solvents around the front end circuitry. Tek sometimes used special PCB material, which had superior electrical properties to the normal FR4 material, for the front end attenuators and amplifiers but this material was extra sensitive to damage from solvents and heat.It might pay to check through the old issues of Tekscope; these often include articles for the procedures for servicing and cleaning scopes of that era. The July 1972 issue specifically covers the procedure for washing a 7000 series scope.

author: Gyro
author_rank: Super Contributor
timestamp: February 18, 2024, 12:21:07 pm
content: Don't forget the last stage after soapy water washing etc. should be a really good flush with distilled/deionised water (buy a few big bottles) followed by a looong air dry. You would normally use IPA to remove the water, but it's not really practical with something as big as a scope (and heed srb1954's warning) even front panel button labels are sensitive to IPA. Things like the transformer and EHT supply components will take a long time to dry out.

author: CaptDon
author_rank: Super Contributor
timestamp: February 18, 2024, 06:49:30 pm
content: We were very lucky to have a chamber at the hospital where I worked. We would pull it down to 1/2 atmosphere and run the temperature up to about 150F and leave items in there for 24 hours. I revived dozens of pagers that either fell in a toilet or a janitors bucket. Flushed the out with clear warm water and sometimes brushed with a camel hair brush and then into the chamber. BE AWARE....any battery powered circuit, even 1.5vdc will quickly eat and destroy PCB traces when powered and exposed to wet contaminants!! Some pagers with internal batteries simply looked like green slime inside with traces completely gone if they weren't flushed quickly with clear warm water. One of the places I worked at put about $100,000 worth of test gear in the dumpster and insisted it be crushed and destroyed before leaving the property!!! Think of how many Vo-Tech schools or even high school shop classes could have benefited!! I dearly hate corporate dis-positioning rules for equipment!! I used to auction off lab gear to the employees when the declared value on the books became zero. The rule to the employees was to give the equipment a good home like a local ham radio club or maybe a model railroad club etc.

author: David Hess
author_rank: Super Contributor
timestamp: February 19, 2024, 12:44:53 am
content: Distilled water with a little bit of dish soap works very well. The boards can be scrubbed with bristle brush or toothbrush.If necessary boards can be removed and cleaned with soapy water and a brush, however this is difficult with the vertical CRT amplifier board because of the lead dressing connecting the output to the CRT. Luckily this board is on the side of the oscilloscope so tends not to pick up very much dirt, unlike the horizontal CRT amplifier board above it.

author: coppercone2
author_rank: Super Contributor
timestamp: February 19, 2024, 01:11:12 am
content: soapy water is the least aggressive thing you can use on basically anything

author: Jwillis
author_rank: Super Contributor
timestamp: February 19, 2024, 05:25:05 am
content: I got an Hitachi V650F that looked like it was pulled out of a swamp. Took out all the boards and soaked them in warm soapy water and blew all the crud out with an air compressor set to a moderate pressure. Final clean up with IPA. Shoved the case and frame into the dish washer, then after put the whole thing back together. Got it working again but haven't got around to doing a calibration. Surprising how tough some of the old stuff is.