Tektronix 2430A DSO - CRT smell - Page 1
Forum section: electronics / repair

author: Personwithhats
author_rank: Contributor
timestamp: August 14, 2023, 10:20:51 pm
content: Hello,Recently acquired a 2430A DSO, it's working just fine but I've noticed a smell more pungent than normal coming out of it.I was hoping it was something obvious but atm it looks like it's the CRT - Smells like burnt dust or something.Most I know about CRT's is "High voltage beware" so didn't open it up further - I know it's not much info but if anyone has advice or other stuff I could check I'd appreciate itI'm just assuming it's the CRT due to the strange spotting on it. Performance wise everything seems to work.

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: August 15, 2023, 01:44:41 am
content: This looks like it was in an area of high moisture content it might or might not contribute to the smell.Many parts will outgas when heated, resistors and capacitors are known problems in these units andcan cause some of their own smells.Also not all of the capacitor failures are electrolytic some are other types and can fail slowly.I would not run any of these scopes without checking whats been done with what first.Jeff

author: Personwithhats
author_rank: Contributor
timestamp: August 15, 2023, 02:31:15 am
content: Quote from: Jeff eelcr on August 15, 2023, 01:44:41 amI've only had the budget for oscilloscopes/etc. recently. before that it was just PSU + DMM and winging it for some 3D printers and miscellaneous Arduino projects.Would you have any resources that I could check out?Common issues and signs, and especially how to safely decharge the CRT/other capacitors on the board so I don't risk blowing anything.I've done computer/PCB work before but not on anything this sensitive or high voltage.Thank you for your help

author: helius
author_rank: Super Contributor
timestamp: August 15, 2023, 05:21:23 am
content: 40 year old dust has a smell all its own. The CRT obviously has no smell any more than does a glass bottle, but the phenolic material that was usually used for circuit boards does have a distinct aroma, and potting materials (such as on the flyback transformer) can also outgas their unique perfumes. Some units that were "tropicalized" even have fungicidal coatings.

author: Psi
author_rank: Super Contributor
timestamp: August 15, 2023, 05:28:09 am
content: Yeah, old stuff, especially if it has not been powered on in ages, often has a smell when powered back on for the first time and and it warms up.This smell is often followed by a loud <bang> as something explodes.but that is not related to the smell at all, just that some parts have aged since it was last used and can no longer handle it so they explode soon after power on.

author: Personwithhats
author_rank: Contributor
timestamp: August 15, 2023, 06:49:18 am
content: Well, I used it for a few hours but it seemed to be getting awkwardly hot and smelly. Survived multiple power-ons.Any good video on how to service a CRT scope? Would maybe like to clean off whatever that residue is, without shocking myself

author: Personwithhats
author_rank: Contributor
timestamp: August 16, 2023, 02:57:47 am
content: I found the unexpected, yet inevitable, root cause of the smell.....No idea how the oscilloscope was functioningI might as well check some of the capacitors once I resolder this, will do once my ST42 come in.What are some good replacements for the film capacitors? And for other capacitors, just quality brands so I can future-proof repairs'n such.Is there a list of common caps that I can use for other repairs etc.?Also planning on using some chip quick no-clean halide-free flux to desolder, then some stannol no-clean trilence 2708 (it has some halides) for soldering new parts.That OK for fixing scopes? Or do I need something fully halide-free like ZV16 solder

author: helius
author_rank: Super Contributor
timestamp: August 16, 2023, 03:48:25 pm
content: To replace the RIFA metallized paper capacitor you should choose an X2 (I cannot read the safety class on it) polyester cap with the same lead spacing and ratings. The "Keeper" lithium battery may also need to be checked. Some battery chemistries are very highly corrosive and can leak. Be aware that if the battery fails or is removed then calibration can be lost. There is a procedure in the scope's service manual for doing this to avoid losing calibration.You can use any rosin based flux to repair a scope. The only areas critically sensitive to contamination are around the input amplifiers and/or prescalers. It's good practice to clean flux residue with a safe approved solvent, of course, but there is no need to go crazy.

author: elecdonia
author_rank: Frequent Contributor
timestamp: August 16, 2023, 03:50:05 pm
content: That melted capacitor in the plastic case is wired across the incoming AC mains. When these capacitors fail they tend to release copious amounts of foul-smelling smoke along with loud crackling and popping noises. This failure is more prevalent in devices powered by 230V AC mains. But it still happens to devices powered by 120V too.Older “RIFA” brand capacitors tend to develop cracks in their plastic cases. This leads to moisture absorption, internal corrosion, and electrical leakage. Eventually these deteriorating capacitors heat up and develop internal arcing. This arcing often initiates catastrophic failure with smoke, sparks, and popping noises. It may cause the device’s AC mains fuse to open.Many people choose to replace these “line filter” capacitors when they recondition older equipment. Note that there may be additional capacitors of this same type hidden inside the small metal boxes labeled “line filter” or “mains filter” which are often located where the mains cable or receptacle enters the chassis of the equipment.Search for these words and phrases to learn more:RIFA capacitorLine filter (or mains filter)Schaffner (popular brand of line filter)Magic smoke

author: Personwithhats
author_rank: Contributor
timestamp: August 16, 2023, 04:38:12 pm
content: Quote from: helius on August 16, 2023, 03:48:25 pmDo you know of any quality brands for capacitors? I'm not against paying a bit more, and ofc ordering from suppliers like TME/Newark/Mouser/etc.What kind of specs should I be looking for a in a 'good' capacitor? I doubt the caps I have lying around will last long, I just use them for prototyping.Also, is there a list of common caps that I can use for other repairs etc.?Quote from: elecdonia on August 16, 2023, 03:50:05 pmWill check , interesting

author: KE5FX
author_rank: Super Contributor
timestamp: August 16, 2023, 06:19:31 pm
content: The most important consideration when working on a 2430A is to provide adequate airflow to the main board on the underside when operating the unit with the cover off. You would also like to not get zapped by the CRT, but that's secondary to the damage that running without an external fan will do.Be sure to check out the guidelines in the service manual if you are not already experienced at working on this type of gear.