Tube TV boards smell worse after cleaning off flux?  How to make smell go away? - Page 1
Forum section: electronics / general

author: CRTguy23
author_rank: Contributor
timestamp: December 20, 2024, 10:22:47 pm
content: I have an early 90s tube TV that had a bunch of bad solder joints so I re-flowed solder to all the joints on the boards using a no-clean flux. A lot of flux was left on the boards so I decided to clean the flux off with 91% isopropyl alcohol and a toothbrush. When I did this, I had the board oriented vertically on a table with paper towels underneath to catch the flux that flowed off the board from cleaning. Most of the flux was removed when I did this but when I connected the board back up (I did let it dry for a day) and operated it, the flux smell was 10x worse and gave me a headache. My TV boards have openings in them where some of the alcohol from cleaning seeped to the top the boards. The flux getting to the top of the boards may have worsened the smell. Next step, I cleaned the TV boards with some MG Chemicals 4140A flux remover with the same approach (toothbrush, board oriented vertically, paper towels underneath). I then cleaned the boards once more with a toothbrush and 91% isopropyl and let it dry. The flux smell was significantly reduced after this but after the TV has been running for about 30 minutes, the flux smell is very strong but doesn't give me a headache like before. Still, I almost don't even want to deal with using the TV because of this. This TV has a lot of sentimental value so I want to keep it. The bottom of the TV boards are perfectly clean and don't smell of flux. It's the top boards that smell but there isn't much visible flux at all on the top of the boards. I noticed that the MG Chemicals flux remover did fade the color of the top of the main board. As a last step, I used the 91% isopropyl again and cleaned the boards with alcohol soaked q-tips. The q-tips cleaned up quite a bit of flux but the smell hasn't gone away at all. It smells like the garden section at Home Depot where the garden hoses are.How can I get this flux smell to go away and why would the flux smell be worse after cleaning? Would the PCB itself have a smell and maybe I removed a protective coating on the top of the boards that sealed in a smell?Is this flux odor harmful to my health while the TV is operating?

author: coppercone2
author_rank: Super Contributor
timestamp: December 21, 2024, 06:52:03 am
content: this is why ultrasonic cleaning is used, flux is probobly trapped under the components and stuff. it can be very difficult to remove.Since it looks like you are having problems, I recommend a dip type flux remover, and ultrasonic cleaning if its reasonable.I don't know why it got more smelly, perhaps it was super baked and formed a kind of shell that was disturbed over it, exposing fresher flux.I would say electronics that smells like flux when it runs normally is not acceptable (your job is not done)https://www.chemtronics.com/flux-off-aqueousAlso, when you did your spray type cleaning,you might have gotten a thin film of flux on a power component, like the underside of a hot power resistor, that is evaporating itIt needs a bath.

author: CRTguy23
author_rank: Contributor
timestamp: December 21, 2024, 08:22:14 am
content: Thanks for the info. I don't have the money for an ultrasonic cleaning machine. Is there anyone on here that has an ultrasonic PCB cleaning machine, where, if I paid them, they would clean my boards for me? If I cleaned the board a few more times with a regular flux remover and toothbrush (maybe try something from a different brand), could it mostly eliminate the odor?

author: helius
author_rank: Super Contributor
timestamp: December 21, 2024, 08:24:42 am
content: Q. Would the PCB itself have a smell?A. YES.The circuit boards in this type of equipment are usually made of phenol-formaldehyde resin, which is cheaper (and more brittle) compared to the glass-epoxy laminate commonly used in electronics. It's possible that the resin became partially melted from heating or chemical cleaning and is now outgassing. It's also common for used equipment to have cigarette deposits and those have a strong smell (to a non-smoker).When you say the equipment smells offlux, what smell is that? The flux I use smells like wood smoke when heated with a soldering iron, and otherwise has little smell at all. The amount of flux I use is also tiny, so that little remains after rework and there is not much to clean up.

author: coppercone2
author_rank: Super Contributor
timestamp: December 21, 2024, 08:40:42 am
content: well I said IF possible. It would just work better.Dave Jones I think was making some threads about some great flux remover he found, and he had excellent results with just soaking it (non ultrasonic IIRC). Alot of people don't like ultrasonic because of concerns about damaging certain parts (i.e. crystal oscillator)For making a hot board generally smell less, if its smelling after you are sure its clean, there is a few hacks you can do, that usually is to find components that are getting hot and attempt to isolate them from the PCB. But I think phenolic has a very characteristic smell, and its not similar to flux..For instance,-a resistor that is at board level can be lifted with some standoffs to prevent it from heating the board (it gets better airflow and its farther from board).-sometimes it might be possible to add a small clip on heatsink to some transistorshttps://www.diyaudio.com/community/attachments/metal-spacers-jpg.309482/I have seen all sorts of what I call bad design decisions around CRT stuff. They seem to kind of have a problem of running pretty hot.I personally had to go through 2 big cans of flux remover to clean this one board last year, that shit would just not get clean. It does work, but not nearly as good as they claim IMO

author: CRTguy23
author_rank: Contributor
timestamp: December 21, 2024, 08:45:15 am
content: Quote from: helius on December 21, 2024, 08:24:42 amIf what you are saying is true and my TV boards are outgassing because the resin melted from chemical cleaning, will the outgassing end. When I say my boards smell like flux, I mean that they smell somewhat like the flux that I use for soldering. However, I've used this flux on a lot of tube TV boards and it's never smelled as strongly as the TV boards I'm referring to in this thread. My boards also smell like the garden section of a hardware store.Would this odor that my boards are emitting when they are running be harmful to my health?

author: coppercone2
author_rank: Super Contributor
timestamp: December 21, 2024, 08:48:23 am
content: You could also figure out which part is getting hot and really really clean the shit out of that area.For those big boards with the large power parts and stuff that get hot, you can also use bottle brushes to get around/under parts. You need agitation in places where its hard to reach. Tiny brushes, lots of work. I really suggest trying a soak and rinse with a aqueous removerDid you check the board to make sure there is no parts that are getting way too hot because they are damaged? Smells are often a symptom of things like overheating transistors, too high voltage, shorted resistors. It can be pretty damaged but still work, but make alot of heat.I found a simple transformer that had some insulation damage in it, ran at 120C doing nothing, but it did work OK.These CRT PCB are like a forest of upright verticle resistors and capacitors too, hard to clean that crap.

author: Psi
author_rank: Super Contributor
timestamp: December 21, 2024, 08:50:58 am
content: You may find it just needs a really long run-time for the small to dissipate. Like 7 days of 24/7 operation fully up to temp.Obviously you'd have to do this somewhere else so the smell doesn't annoy you, and there may be a fire risk leaving it unattended for that long, so consider carefully.But if you just turn it on and use it for a few hours a day it may take a really long time to burn-off the smell.

author: CRTguy23
author_rank: Contributor
timestamp: December 21, 2024, 09:05:39 am
content: Quote from: coppercone2 on December 21, 2024, 08:48:23 amI would still have to check the boards for any parts that are overheating. What I can say is that my boards didn't start smelling until I began working on them. When I first re-flowed all the solder joints, it only smelled a little from the flux that was left on the boards. I left the flux on there for a year and the smell wasn't much of an issue. The boards didn't start smelling really bad like I'm describing until I attempted to clean the flux off them a few weeks ago. Maybe a temporary solution would be to just wrap some plastic wrap around the back of the TV casing where there are ventilation holes. It seems like this would trap the smell in. I only use the TV once in a while but it's my childhood set so want to keep it.

author: Psi
author_rank: Super Contributor
timestamp: December 21, 2024, 09:47:16 am
content: Yeah, if you can find a friend with a thermal camera you can track down if anything is getting crazy hot and causing the smell.