Blew Up My First Oscilloscope!!! - Page 1
Forum section: electronics / testgear

author: PixieDust
author_rank: Frequent Contributor
timestamp: February 27, 2019, 06:50:32 am
content: Woops, not sure what happened. I was going through the first chapter of my oscilloscope manual and all of a sudden I heard frying/sizzling and then a tonne of magic smoke (I'm guessing a large capacitor). (It was still working while I was pulling the power chord out).The only thing that I didn't do according to the manual was have probes inserted. But no measurements were even required up to this point in time. The manual was mostly just going through using all the menus and knobs and buttons.The frying happened when I got to the section of triggering (went though some basic things in Vertical and Horizontal controls). After pressing Auto, I pressed the Trigger->Mode button and then I cycled through the various modes and then boom!What on earth happened? Anyone have any ideas?

author: ataradov
author_rank: Super Contributor
timestamp: February 27, 2019, 07:10:00 am
content: Most likely not your fault. This is an old device, capacitors are all dried up by now.Disassemble it and see what exactly is blown.

author: DaJMasta
author_rank: Super Contributor
timestamp: February 27, 2019, 07:17:58 am
content: Yep, no input on the front and it's quite unlikely it was you. Most likely adjusting the controls was coincidental, but maybe a setting turned on something which was not happy to be on. The next step is definitely to sniff around and find the smoked bit.

author: Ice-Tea
author_rank: Super Contributor
timestamp: February 27, 2019, 07:20:58 am
content: Unless you ignored a voltage selector at the back (or the rating itself) most likely not your fault..

author: Keicar
author_rank: Regular Contributor
timestamp: February 27, 2019, 07:23:20 am
content: Schaffner line filter perhaps?

author: Fungus
author_rank: Super Contributor
timestamp: February 27, 2019, 07:32:26 am
content: Quote from: PixieDust on February 27, 2019, 06:50:32 amIt's old. Probably some component teetering on the brink that just happened to die while you were touching the front panel.

author: PixieDust
author_rank: Frequent Contributor
timestamp: February 27, 2019, 07:40:03 am
content: Thanks guys, will sniff around a bit. Smells like burn wood, doesn't smell chemically. I thought it might be dust, but when I opened it, there wasn't much dust to be found. Most of the unit is relatively clean. There was dust in spots, but none of it looked burnt.I certainly didn't mess up the voltage rating.I'll look for damaged capacitors or Schaffner filter.

author: med6753
author_rank: Super Contributor
timestamp: February 27, 2019, 07:47:13 am
content: RIFA capacitor on the primary most likely.

author: VK5RC
author_rank: Unknown
timestamp: February 27, 2019, 11:09:42 am
content: Don't forget Tektronix's excellent fault finding in a oscilloscope paper - from the 70sEdit' couldn't get the ###### link to work (on a phone)Google Tektronix Oscilloscope TroubleshootingApol, Rob

author: PixieDust
author_rank: Frequent Contributor
timestamp: February 27, 2019, 11:10:21 am
content: Quote from: med6753 on February 27, 2019, 07:47:13 amLooks like we have a winner. You guys are too good.Quote from: VK5RC on February 27, 2019, 11:09:42 amThat link doesn't work for me?

author: Wolfgang
author_rank: Super Contributor
timestamp: February 27, 2019, 11:55:34 am
content: As there is no crater in your desk its probably a lighter case. I would bet on wearout rather than misuse.

author: HalFET
author_rank: Frequent Contributor
timestamp: February 27, 2019, 11:57:35 am
content: Quote from: PixieDust on February 27, 2019, 11:10:21 amTry it without the "&..." part:https://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

author: lordvader88
author_rank: Frequent Contributor
timestamp: February 27, 2019, 03:42:00 pm
content: I just learned what RIFA caps are myself, and I have a Tek 2430A scope. I had it apart before, when I knew a lot less. Soon I should take it apart again and have a nice look around. Same with my Tek2215

author: tggzzz
author_rank: Super Contributor
timestamp: February 27, 2019, 05:00:03 pm
content: Quote from: lordvader88 on February 27, 2019, 03:42:00 pmThose delayed action smoke generators are in many many pieces of equipment of that era. They should be replaced, and replaced on sight if there is any cracking in the transparent outer case.They are also buried inside many IEC connector mains filters, especially Schaffner filters.

author: PixieDust
author_rank: Frequent Contributor
timestamp: February 28, 2019, 01:21:59 am
content: Quote from: lordvader88 on February 27, 2019, 03:42:00 pmThis is what happens if you don't:Exactly what happened to me, was on for about 10 minutes and then started smoking like a chimney!Quote from: tggzzz on February 27, 2019, 05:00:03 pmThanks for the heads up.According to Dave's video:They can look fine after they go. But I think that's the case if you pull the plug quickly. Mine were sizzling for a good 5-7 seconds. Then it becomes apparent that something is wrong because there's more time to do damage.

author: tooki
author_rank: Super Contributor
timestamp: February 28, 2019, 04:47:02 am
content: What amazes me is that Kemet is still manufacturing those awful things. (Kemet bought up Evox-Rifa years ago.)For example, here’s the datasheet for the exact series shown in the preview of Dave’s video above:http://www.kemet.com/Lists/ProductCatalog/Attachments/322/KEM_F3011_PME271M_X2_275.pdfLike... ugh.

author: David Hess
author_rank: Super Contributor
timestamp: February 28, 2019, 04:57:21 am
content: Quote from: Keicar on February 27, 2019, 07:23:20 amOr the paper-film RIFA X and Y capacitors.

author: tooki
author_rank: Super Contributor
timestamp: February 28, 2019, 05:14:29 am
content: Quote from: David Hess on February 28, 2019, 04:57:21 amYou’re about a day late.It was already confirmed to be those, hence the ensuing discussion of them.

author: james_s
author_rank: Super Contributor
timestamp: February 28, 2019, 06:03:14 am
content: Quote from: tooki on February 28, 2019, 04:47:02 amPerhaps they have been improved?Also it's worth noting that the ones that are failing now are mostly more than 20 years old, while not ideal I have a hard time being upset over 20+ year old components failing. I had one burn up in the power supply of an Apple IIe years ago, it made a bunch of stinky smoke but it didn't really cause any collateral damage.

author: Zenith
author_rank: Frequent Contributor
timestamp: February 28, 2019, 01:21:36 pm
content: Here are two Rifa 2200pF Y class capacitors which are probably over 20 years old, but are unused and have been kept in reasonable conditions. Both are cracked in the same place. The crack underlines the Rifa logo and goes up just short of the corners and there's a similar crack on the back. It looks to be an age related thing.There are loads of X and Y rated capacitors of the same age which don't have this class fault.

author: james_s
author_rank: Super Contributor
timestamp: February 28, 2019, 04:47:09 pm
content: Well I'm not arguing that they're the best or anything but they're still old. It's unknown whether the currently manufactured ones will exhibit the same fault, one can hope they've been improved.

author: duak
author_rank: Super Contributor
timestamp: February 28, 2019, 06:23:09 pm
content: Some 2200 series scopes also have problems with some 470K or so 1/4 W resistors in the focus circuit. If the the scope is apart, look for a group of resistors with a bit of space around them. The PCB itself might also look a bit stressed. If I remember correctly, Tek used 5 or so of them in series to handle a 1 KV or so potential.Cheers,

author: tooki
author_rank: Super Contributor
timestamp: February 28, 2019, 06:33:21 pm
content: Quote from: james_s on February 28, 2019, 06:03:14 amValid points to be sure, and I did consider that (somewhat) without mentioning it before.My hunch, though, is that they haven't been changed, or else they'd have changed the part number.Quote from: Zenith on February 28, 2019, 01:21:36 pmThe local mom-and-pop electronics store/living museum has bins of Rifa caps that are cracked, for sale. o_O

author: JohnPen
author_rank: Regular Contributor
timestamp: February 28, 2019, 06:44:43 pm
content: High value Resistors with high voltages across them used to be a problem with the old CRT TV years ago. The focus potential used a chain of high value carbon resistors, often in the Megohm range, and they used to shift dramatically in value as they aged. Sometimes down by several Megs other times similarly upwards. High voltages across resistors, particularly the carbon based ones, are definitely not very good for them.

author: Zenith
author_rank: Frequent Contributor
timestamp: February 28, 2019, 07:37:00 pm
content: Quote from: tooki on February 28, 2019, 06:33:21 pmThey caused no problems whatsoever for the OEM or the first owner.The manufacturer didn't find they caused production rework or warranty claims.The first owner wasn't likely to keep the unit for more than ten years, and there weren't many post warranty problems, which the maker wouldn't particularly want.Rifa had a successful product which they'd had to pay to have certified with UL and the rest.No one, who mattered, cared what was going to happen 12 years plus down the line, and probably still doesn't.

author: Gyro
author_rank: Super Contributor
timestamp: February 28, 2019, 07:40:46 pm
content: The USP of the Rifa caps is higher dV/dT rating than Polypropylene, that's why they still use them.

author: Calambres
author_rank: Frequent Contributor
timestamp: February 28, 2019, 07:43:03 pm
content: Someone should start a database of appliances using those infamous RIFA caps!

author: tautech
author_rank: Super Contributor
timestamp: February 28, 2019, 07:45:45 pm
content: Quote from: Calambres on February 28, 2019, 07:43:03 pmYou'd be amazed how large it would be, they were used in a very wide range of mains powered gear.

author: Zenith
author_rank: Frequent Contributor
timestamp: February 28, 2019, 07:53:23 pm
content: Quote from: JohnPen on February 28, 2019, 06:44:43 pmIt's often forgotten that resistors have a voltage rating which you can exceed without exceeding the wattage, and if you do you alter the behaviour of the resistor. Carbon composition resistors tended to drift high after a few years anywayI've seen special high voltage resistors in old scopes, which I think were quite long with a spiral carbon film track. They weren't that reliable, but people tried to replace them with the porcelain bodied 1/4 watt carbon composition resistors which died very quickly. Farnell and others used to stock modern metal glaze resistors rated for 3kV or so, I don't know if they still do. I never had any problems when I used them as replacements

author: David Hess
author_rank: Super Contributor
timestamp: February 28, 2019, 08:10:53 pm
content: Quote from: duak on February 28, 2019, 06:23:09 pmThe 2213/2215 used carbon composition resistors in the focus resistor chain. The 2235 and 2213A/2215A, which are really a different but related series from the 2213/2215, also used carbon composition resistors in the focus resistor chain. Oddly enough the 2236, which was released at the same time as the 2235, uses high voltage film resistors instead (or at least the service manual says) and I think all of the later instrument do also.Quote from: Zenith on February 28, 2019, 07:53:23 pmI did some research on this in connection with the 2235 series several years ago and found evidence that the high voltage film resistors Tektronix used to replace the carbon composition resistors in the high voltage circuits eventually became the Vishay VR25 and VR35 series of high voltage film resistors which have good pricing and availability now.

author: Electro Detective
author_rank: Super Contributor
timestamp: February 28, 2019, 10:39:10 pm
content: Ha, just copped the same RIFA PITA myself on a kitchen appliance... operating in magic smoke modehad all the symptoms of a burnt out motor aka 'toss it time'Still, I opened it up for parts scavenging purposes and what a MESSbrown gunk EVERYWHERE,the RIFA must have popped during the loud motor running, then started to smoke gradually.Folks, the smell was unbelievable, I had to work on the sucker outdoors with gloves and lots of residue free contact spray and toothbrush to loosen and wipe up the all crud.If you don't mop up all of it, it will smell like forever, what the hell is in those stinkers ?Amazingly the bridged resistor across the Live/Neutral legs and the small 250volt blue cap thingy with one leg to earth/ground were both unscathed and like new, tested and re-usedRepaired kitchen appliance is 30 years young, nice clean motor, heavy duty switch work, hopefully should see another 30 with the new X2 cap in thereFWIW Jaycar and Altronics in Australia regions have X2 replacements and cheap, smaller in size, and apparently no quality comebacks over the years.I got the the same value 0.1 that was on the trashed RIFA so as I could reuse the same resistor and cap combo with it,not sure what the difference would be with other X2 values,more or less suppression at 50 hz, is bigger better, etc ?

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: March 01, 2019, 08:15:01 pm
content: just another load of fried Rifas going back...

author: Electro Detective
author_rank: Super Contributor
timestamp: March 01, 2019, 10:01:17 pm
content: Why the RIFA label and not REEFER ?That is how they eventually perform, right ?

author: PixieDust
author_rank: Frequent Contributor
timestamp: March 02, 2019, 03:44:38 am
content: Does anyone know how to remove these plastic screws? They appear to be quarter turn to loosen them, but then they don't pull out easily after that. Should I be pulling harder?If you turn it 180 degrees, they make the receptical bulge out again, making them increase in diameter and hence hold the board in place.Scrap that, they just need to be turned, not removed.

author: PixieDust
author_rank: Frequent Contributor
timestamp: March 02, 2019, 07:31:08 am
content: Job done! Replaced the two RIFA with some 100nanoFarad ones. Not 0.068microFarad but I'm hoping it should work. Re-assembled it, turned it on and passed all the tests.The replacement capacitor in the image is of a different value, but the one I installed is of the same form.

author: med6753
author_rank: Super Contributor
timestamp: March 02, 2019, 10:06:25 am
content: The absolute value doesn't really matter. Just as long as they are X2 caps which they are.You're good to go.

author: Twoflower
author_rank: Frequent Contributor
timestamp: March 02, 2019, 10:17:22 am
content: Isn't that thing on the left side of the picture a line-filter that's also notorious to fail?

author: Gyro
author_rank: Super Contributor
timestamp: March 02, 2019, 11:13:17 am
content: Quote from: med6753 on March 02, 2019, 10:06:25 amThere's no reason why you can't substitute X1 capacitors of course - they just have a higher voltage withstand rating.

author: PixieDust
author_rank: Frequent Contributor
timestamp: March 02, 2019, 11:30:25 pm
content: Thanks everyone for your help.

author: Electro Detective
author_rank: Super Contributor
timestamp: March 04, 2019, 10:39:28 pm
content: Whoahold up guys, there is a slight difference between X1 and X2 suppression capacitorsX2 bridge across Live and NeutralX1 are placed in lineAlso if an X2 has an associated resistor and cap with it (and or other parts) I am assuming the manufacturer has chosen the values to tune in a certain bandwidth to suppressor whatever the result required for that particular power input circuit.i.e. till certain that 'any value will work' I reckon it's a better punt to wack in the original X2 valueFWIW: a worthy Youtube to watchif someone buys up on different value X2 caps and tests them in the same circuit to see what actual effect/difference they make.In the meantime, I'll keep replacing old RIFAS with the same values the manufacturer installed...less thinking

author: Gyro
author_rank: Super Contributor
timestamp: March 04, 2019, 10:59:13 pm
content: Quote from: Electro Detective on March 04, 2019, 10:39:28 pmNo, X1 capacitors are rated for L-N use, they just have a higher peak voltage withstand rating (<4kV) versus <2.5kV for X2. They tend to be used more in industrial gear and 415V three phase but it's perfectly acceptable to substitute them in if you have some around (I happen to have more X1s than X2s in my drawer).http://www.kemet.com/Lists/Filestore/EvoxRifaRFIandSMD.pdfhttps://www.allaboutcircuits.com/technical-articles/safety-capacitor-class-x-and-class-y-capacitors/X1s won't affect filtering performance if they are the same value.

author: Electro Detective
author_rank: Super Contributor
timestamp: March 05, 2019, 08:26:49 am
content: I haven't looked into it too deep (yet) and just roll with straight up same value replacementsstill I don't understand why all the cap values available, and X1 and X2 voltage ratings, rather than a 'one size fits all' approachThey must have a reason for the different cap values

author: Gyro
author_rank: Super Contributor
timestamp: March 05, 2019, 11:56:16 am
content: In a word, cost.X2s are a bit cheaper than X1s.X1 caps are also slightly bigger physically, although they often share the same lead pitch.Theoretically an X1 cap should last longer in a mains application as its higher withstand voltage causes it to self-heal (and hence lose capacitance) less. Hence they tend to be used more in industrial applications - though I've spec'd them in consumer gear before now.P.S. There are also even lower rated X3 caps but I've never seen one.

author: PixieDust
author_rank: Frequent Contributor
timestamp: September 28, 2023, 12:30:38 pm
content: Well, I repaired the scope and used it a handful of times to complete a small project and then put it into cold storage. It has been sitting idle ever since then. I turned it on just now for the first time since it’s last power off almost 5 years ago now and… more magic smoke. I was hoping to use it to learn electronics on something that wouldn’t be too expensive to blow up in case I made a mistake, but it seems like I should just get a new scope when I finally move on to electronics on serious basis. I’m starting to realise that old gear is just now worth the hassle.

author: DavidAlfa
author_rank: Super Contributor
timestamp: September 28, 2023, 02:16:47 pm
content: Only 12 years? Rifa caps usually fail in 25yr+ equipment!

author: metrologist
author_rank: Super Contributor
timestamp: September 28, 2023, 07:41:26 pm
content: Could be something else but if it's the same component, at least you have practice replacing it

author: DavidAlfa
author_rank: Super Contributor
timestamp: September 28, 2023, 07:58:51 pm
content: "Rifa" in spanish is adrawraffle ticket, usually sold locally by kids for their summer school trip, or in parties, charity events... where there's usually 1st, 2nd and 3rd prices, could be anything from paid vacations to Christmas baskets ( With cheese, ham, wine...) or just a moderate amount of cash like 3000€.So it's actually pretty hilarous when these go boom, you literally won the "rifa".

author: Fungus
author_rank: Super Contributor
timestamp: September 28, 2023, 09:00:23 pm
content: Quote from: DavidAlfa on September 28, 2023, 07:58:51 pm"Raffle ticket" en Inglés.

author: DavidAlfa
author_rank: Super Contributor
timestamp: September 28, 2023, 10:06:48 pm
content: Aha,wasn't sure which to use, both made sense to me

author: p.larner
author_rank: Frequent Contributor
timestamp: September 29, 2023, 02:53:08 am
content: i had one go nuclear in a big 5v 90amp smps,i just removed it and the psu still worked ok.

author: Swainster
author_rank: Frequent Contributor
timestamp: September 29, 2023, 03:08:06 am
content: Quote from: PixieDust on September 28, 2023, 12:30:38 pmCould be the line filter this time - it was mentioned during your original repair. At least some line filters have RIFAs inside them (looking at you, Schaffner). Other than that, I feel your pain. I love old test equipment (and old cars), but sometimes you just want it to just do its $&^$@ job

author: PixieDust
author_rank: Frequent Contributor
timestamp: September 29, 2023, 03:08:40 am
content: Well I suppose I didn't actually see any magic smoke. But the magic smell was unmistakable. It can't be the RIFAs this time since I replaced them with a non RIFA component. So unless the components I replaced went bad in just 5 years, it must be something else. I'll have a look at it, but I have a feeling it's above my pay grade to repair it this time.

author: PixieDust
author_rank: Frequent Contributor
timestamp: September 30, 2023, 12:41:54 pm
content: Well, that was easier than I thought.Where's Wally?Capacitor $8. That's one expensive little thing.The nose lead the way.

author: David Hess
author_rank: Super Contributor
timestamp: September 30, 2023, 11:25:40 pm
content: Quote from: PixieDust on September 30, 2023, 12:41:54 pmAn exact axial replacement was not required.

author: PixieDust
author_rank: Frequent Contributor
timestamp: October 01, 2023, 05:52:05 am
content: Thanks David. Noted.