Tektronix 2455B A5 PCB Cleaning - Page 1
Forum section: electronics / testgear

author: 11mrjones
author_rank: Contributor
timestamp: April 12, 2024, 06:09:13 pm
content: Helloooo - I had replaced the battery on my A5 board (Tek 2455B) awhile ago and saw, I guess, is old flux from previous re-working. Left it as is for awhile as I operated the scope to verify function, and all is well. Now this is coming back to mind. Should I try to clean it up or let it be as scope works fine.A gentle push with sharp pin flakes off the residue quite easily, so I think cleaning should not be too difficult and I would like to clean it up if I can safely get it done. The issue I'm thinking about, if I clean, is that I have IPA and MGchem flux remover at hand to use, but I'm not sure about the electrical conductivity of these fluids and if I clean the board these fluids may short out the on board sram backup battery and thus losing the cal data.So the questions are: Leave it, or, clean this up and how so ,ie, soak with ipa or flux remover then scrub with say a toothbrush, or gently mechanically scrap most off with sharp pin or xacto knife (as it readily flakes off) then scrub with ipa or flux remover and toothbrush, I think this 2nd option would work well. My big concern is of course losing cal data somehow if the cleaning fluid shorts the battery out.Or just leave it be as unit is working fine?Suggestions appreciated.I hope the attached pics can show the issue appropriately as I had to reduce the image size to fit the 800k total pic limit.Thanks,Victor

author: calibrationfixture
author_rank: Regular Contributor
timestamp: April 13, 2024, 07:10:01 am
content: Hi 11mrjones,Use Cotton Swabs with some Acetone (not soaked). Faster then other solvents. Solder Mask's of PCB's have no problem with it. Doing this for ages.https://www.traskinstrumentation.com/pdf/app_notes/Conductivity_Chart_of_Liquids.pdfSuccess,Calibrationfixture

author: tggzzz
author_rank: Super Contributor
timestamp: April 13, 2024, 08:23:07 am
content: Personally I normally use IPA since that "attacks" fewer types of plastic than acetone. Yes, it takes longer to remove flux residues. Washing time is not important to meOf course if you know the manufacturer used acetone (or another solvent) during production, or have assessed all materials in the vicinity, then use that solvent.

author: coppercone2
author_rank: Super Contributor
timestamp: April 13, 2024, 08:37:25 am
content: if the crap dissolves in solvent it becomes conductive

author: jonpaul
author_rank: Super Contributor
timestamp: April 13, 2024, 09:16:41 am
content: NEVER Acxetone! No petro distillates!USE ONLY 91 or 99% Isopropyl Alchol (NOT 70% duugstore junk!)Un aware 2455B but 2465B A5 may have leaking SMD tants which leak corrosive liquid and damage componets and PCB traces, inner layers, vias.See 79 page thread,2465B TeardownBon ChanceJon

author: calibrationfixture
author_rank: Regular Contributor
timestamp: April 13, 2024, 09:31:40 am
content: Hi jonpaul," Use Cotton Swabs with SOME Acetone (not soaked)"I suggested it as solution for his "problem". Not for using it as a way to wash complete Boards etc. etc.Calibrationfixture

author: tggzzz
author_rank: Super Contributor
timestamp: April 13, 2024, 09:39:10 am
content: Quote from: coppercone2 on April 13, 2024, 08:37:25 amIf components dissolve in solvent they stop working.Choose your solvent wisely

author: 11mrjones
author_rank: Contributor
timestamp: April 13, 2024, 07:52:58 pm
content: First tried a swap damped with 91% IPA, the flux residue removes quite readily, so I think that would be aggressive enough to do the job.My concern now is do I need to worry about shorting out my cal data stored in the sram somehow if the IPA is conductive enough to do that?Thanks Calibrationfixture for your conductance chart link, from that I see (not sure what the *, ** , refers to)--------------------------------------Conductivity Chart of LiquidsName, µS/cmWater, NYC 72Water, distilled .04*Acetone .02*ISO-propyl Alcohol 3.5**M-Propyl Alcohol .05** conductivity too low for mag** Low conductivity appl.-------------------------------------------------Question for all, I'm thinking IPA is equivalent to getting water on the board which is actively powered on by the battery, so the possibility of shorting out the sram and losing cal data?In the attachments I outlined the chips that have the residue on their pins on the underside of the A5 board, and also where the battery is of course, which has no issues.What do you guys think, maybe I should just leave it alone? Or no worries about conductivity/shorting things out with cleaning with IPA?ThanksVictorP.S. board has new nichicon caps and no smd tants on this version.

author: MarkL
author_rank: Unknown
timestamp: April 13, 2024, 10:24:55 pm
content: I would just leave it alone.You can make a backup of your cal data via the GPIB port if you have that option, or by taking a video while scrolling through the cal data in the EXER 02 service menu.If you decide to clean it... You are right to stay away from the battery circuit area, but also stay away from U2460, which is the RAM being powered by the battery, plus the Q2070 / Q2170 / Q2270 area which controls the chip enable (CE2) to the RAM.MG Chemicals has a #4140 flux remover for PCBs which is specifically non-conductive.

author: jonpaul
author_rank: Super Contributor
timestamp: April 14, 2024, 12:27:15 am
content: ANY use of Acetone can damage cap seals, plastic NEVER USE NEAR ANY ELECTRONICS.Weus only 99% Iso Alc.The RAM data is not affected by a few uA lk during cleaning if battery is OKj

author: 11mrjones
author_rank: Contributor
timestamp: April 14, 2024, 06:28:18 pm
content: Yes I have made a backup of cal data (via video). I have some MGchem 4140 flux remover, but as you suggest, I think now I'll just leave it be. I don't want to press my luck , I was nervous as hell when I changed the battery.Thanks everyone for your help.Victor

author: coppercone2
author_rank: Super Contributor
timestamp: April 15, 2024, 01:52:33 am
content: yeah I see that my function generator flashed memory outage when I changed the battery even though I did it exactly as the manual said, and soldered in a backup battery (tab welded) to make sure there is no funny buisness wit the contacts while I was actually replacing in the battery on the PCB. so solder on battery soldered to wires through resistor, solder off old battery, then solder on PCB mount battery, then remove the wire connected battery. as far as I know the voltage on the IC should have been good the whole time. but no it flashes power loss WTFI started to think its my iron and that I should use butane pencil or something. its super lamekirchov laws only suggestion for old circuit