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Intermittent power on problems with 2465B
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Mark Hatch
I have a tek 2465B (serial# B077725, so could have the infamous SMD cap issues) that sometimes does not start.
Typically, this is in the morning, and after I hit the switch 2-3 times, it starts. This afternoon, I fetched it from my workshead where it had to live for a few days (it has been raining in No Cal last few days), and I must have had to pound on the button at least 30x before it finally started. Subsequently, no problems, started up the first time after ever power down. (tried this about 8x tonight). When it doesn't power on, no fan, no front LED's nothing.... Made me think that I had not plugged it in. Read about the "ticking" state on startup, but could not hear any ticking (but perhaps I should ask someone with better hearing...) As far as I know, there has been no power supply re-cap. Once it starts, seems to work fine for its age. I saw where some folks had to replace the power switch, but that sounds like a hard failure to me and not an intermittent problems. Suggestions to start? Thanks Mark
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Hi Mark,
I would start by recapping the PS, the intermittend not starting makes me feel it's in there. The SMD caps on the A5 board would cause all sorts of funtions on the frontpanel not working as they should, including brightness, trace position, even calibration, etc. Just my 2 cts, Leo
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Jean-Paul
Mark:
Doubt it is the A5 SMD cap, BUT that MUST be checked and fixed on any old 2465B. Any relation to the mains voltage, Check turn on with a variac? Suggest to open it and fix, and NOT exercise repeated on/off cycles. Have had issues in SMPS PSU startup ckts. Kind Regards, Jon
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Mark Hatch
I was hoping not to have to recap.... But it sounds like that is where this is going.
I will just order the A5 SMD caps to have on hand when I dig through it instead of waiting for another order thru Digikey. They are cheap enough. So, my understanding is that the power on is thru the LVPS board? So that is on the list to recap. What about the A1 Board? Except for the 2nd tear down, wonder if I should do these in a separate pass to reduce error source... Regards, Mark
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Chuck Harris
On SMD caps:
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Take the cover off of your scope. Set it on the bench CRT side of the chassis down, A5 board up. Find the 4 SMD caps, and look at the solder joints that hold them to the circuit board. They should remind you of shiny little mirrors. If they are milky or hazy in appearance, the caps have leaked and must be replaced PDQ. If you need further proof, take a fine tipped soldering iron, tin it, wipe it off, and touch one of the solder joints on one of the caps. If the smoke that comes off of the joint smells like dead fish that are swimming in a bucket of used automotive antifreeze, the capacitors are bad. As to recapping the supply: The job is quite easy, but you do have to get the supply out first. You have to remove all of the obvious screws, and unplug all of the obvious plugs first... look in the manual for instructions. The whole job gets easier if you remove the screws that hold the fan side of the back panel to the chassis. Contact me off list if you want the job done for you. -Chuck Harris Mark Hatch wrote:
I was hoping not to have to recap.... But it sounds like that is where this is going.
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Mark Hatch
Chuck,
Thanks for the advice! Saw your earlier work on getting the 2018 cap list up dated. Thank you for that work too! I am going to give the re-cap a try (love the dead fish analogy on those SMD caps!) Any recommendations on LVPS and A1? I assume I should do both as the caps are the same age. I am sure that you would do both at same time. But as a Tek newbie, I was thinking I would do one, check my work and then go back. Realize there might be some duplicate tear down and re-assembly. Just trying to not juggle too many variables at once. BTW: are you the 2465b cap reseller on ebay that is located in San Antonio, TX? I can order from digikey, but rather support contributors to the community when possible. Regards, Mark
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Chuck Harris
I recommend that you leave the A1 board alone. It is very
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difficult to remove without damaging something, and the capacitors on the A1 board are rarely bad. I would say never bad, but I am sure someone would argue that point. They don't really do all that much anyway. The important capacitors on the A1 board are all ceramic or film type. I would buy from Mouser or Digi-Key. There are a lot of really bad counterfeit capacitors being sold as main brands over the internet. You can trust Mouser and Digi-key (or you can trust no-one). To simplify life, all of the 250uf 20V and 180uf 40V can be replaced with one value: 330uf 50V. It is a similar sized capacitor, and works well. Use United Chemicon, or Panasonic. All of the 100uf caps can be 50V. I am reluctant to use capacitors that are drastically smaller than the originals in size, regardless of their parentage. At an equal value of capacitance, and ESR, a larger capacitor will stay cooler, and last much longer. Generally, a higher voltage capacitor of the same value will have a lower ESR value, and a higher ripple current capability. -Chuck Harris Mark Hatch wrote:
Chuck,
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Jean-Paul
To Chuck, perfect advise as always.
A few notes please: 1/ PSU fail to turn on is likely NOT solved by a recap of the PSU. Caps failure are rare but ESR goes up and C down as the electrolyte dries out. The rectifiers sometimes fail. 2/ Suggest the OP get the excellent PDFs of the manuals for the exact SN range of the unit, and examine the A5, and PSU troubleshoot flow chart. Sources of complete (FREE) service PDFs: https://w140.com/tekwiki/wiki/2465B#Manuals https://bama.edebris.com/manuals/tek/2465b/ 3/ Removal of the PSU is easy, (note all connector and cable positions and screw lengths!) for troubleshooting, the switcher, startup and regulation need loads to work. 4/ The A5 SMD cap corrosion is terrible, if present the entire board needs cleaning and examination as other parts and traces are affected. See the many threads on this. The A5 later SN have a Dallas NVRAM to hold CAL constants, with embedded lithium battery that eventually fails. TEST 04 FAIL 05 on self test. You MUST see the threads on A5 NV RAM, replace, socket, reprogram and CAL. Afterwards a full CAL is highly recommended! Mark, 2465/7B are GREAT scopes and the LAST CRT scopes TEK ever made. A prefect melding of analog design and digital control. If well restored and cared for they will serve for decades! Just the ramblings of an old retired EE! Bon Chance, Jon
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David Campbell <k_8_b_y_p@...>
Re. recapping 2465B
Youre on the cusp of learning the *hard way* why advice to NOT replace caps is extremely bad. Out of the multiples of semi load after semi load of equipment I worked on "back in the day" (very high volume consumer electronics from tube to fine pitch SMT)Ive seen too many electrolytics and some tantalums go 'knees up' and leak, explode, literally take off like rockets and stick in a ceiling 8 feet up, blow confetti across the room, destroy power supplies and even turn power transformers into smoking piles of tar and iron. And do circuit board damage... Only a* FOOL* thinks they can get away with NOT recapping and I do mean ALL of the caps. Its a crap shoot, a losing gamble to trust any old cap. Its a false Meme from the antique radio world that says "I can get away with not replacing caps/ just testing them" That Meme is from the world of working on an old AM broadcast or SW receiver and attempting to keep it as near "stock " as possible. The adventurous remove old caps and hide new ones inside. The foolish ignore old caps... Its EXTREMELY bad practice in anything worth keeping, such as high end equipment like Tek. Its a second Fools Errand and false meme to play the "bring it up on a variac" or "Ill reform a 50 year old cap." Delusional. The "bring it up on a variac" meme was for finding shorts that were hiding in equipment with linear power supplies where just turning the thing on instantly blew the fuse. It is NOT a valid or useful procedure for dealing with old caps, no matter how hard the True Believers want it to be. Ignore those advising anything but a total recap. *They wont be paying for the damage their foolish advice causes.* This is (presumably) high end, near scientific Tek (and other) test equipent. If its not worth $100 in caps and a days work, why bother? Just throw it in the dumpster. Signed, replaced more leaky, shorted and open caps than " theyll" see in 5 lifetimes...,
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Tom Lee
Let's see your stats for Tektronix equipment. I have never seen tants from Tek gear eject into ceiling tiles. I reject any dogma that is uninformed by relevant data.
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-- Prof. Thomas H. Lee Allen Ctr., Rm. 205 350 Jane Stanford Way Stanford University Stanford, CA 94305-4070 http://www-smirc.stanford.edu
On 1/5/2021 13:56, David Campbell wrote:
Re. recapping 2465B
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Chuck Harris
Histrionics, I love it!
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You must live in an alternate universe from the rest of us. I would rank electrolytic capacitors as being the second least reliable part in modern electronics, narrowly being bumped from first place by incandescent light bulbs... But, I know of something that leaves even more damage in its wake than bad electrolytic capacitors: People who are not skilled in electronics construction and repair, replacing good parts they heard someone on the internet say might be bad. I have been a practicing electrical engineer for 40 years now, and I have seen just about every sort of part failure that can happen over that time, but I have not seen electrolytic capacitors take off like rockets and stick in a ceiling 8 feet up. The closest I have seen to that is back when I used to do my annual December 7th sacrifice of a Japanese electrolytic capacitor in honor of those who lost their lives on Pearl Harbor day. Those were hooked directly across the power line, and blew instantly. Your hyperbolic warnings will probably do more damage in the long run than the capacitors you rant against. -Chuck Harris David Campbell wrote:
Re. recapping 2465B
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I hate to interject into this very interesting and exciting thread which I am finding much more interesting than CNN, but one thing does concern me. That is I have spent many hours searching for a trouble when the answer was far simpler. I would want to make absolutely certain that the problem wasn’t in the AC side of things. I would take off the cover and set up to both measure the ac inside the scope and use a probe or clip lead to jumper the switch. If it doesn’t help no harm no foul. But I would certainly check these two things before ripping the poor scope apart. Jm2¢.
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Roy Thistle
On Tue, Jan 5, 2021 at 03:36 PM, John Williams wrote:
for my 0.01 dollar worth... it was an intermittent power cord... when I had dozens of "good" ones... but not the imagination to imagine that could be the problem. Lesson learned... I hope.
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Mark Hatch
I *really* appreciate all the views here. Lots to think about.
I am ok with replacing the LVPS e-caps and those x2's too. And it will be good to look at the infamous SMD's on A5. Haven't done that yet and I *really* should... In terms of simpler solutions, anybody think that it could be the power switch on the front? When it first started acting up, I thought sticky relay. But threw that idea out the window when I found no relay in power lines. Having worked on boat anchors (like I suspect most of you), right after e-caps the next set of problems are caused by dirty/corroded switches. And given that the last (and worst) incident was after I had to put the scope in my shed during are most recent set of rain storms here in No Cal it got me wondering. The shed is dry, but I suspect it still would be damp over that 2-3 days. Perhaps that could lead to corrosion on the switch contacts? Or am I just having wishful thinking.... I did see in the archives that the switches do go bad, but nobody mentioned intermittent powers. Reading between the lines it sounds like the switch failure was something hard. Currently, the scope is behaving itself and turning on with the button push like it should... Would be nice if it failed hard instead of playing "hide and seek" with me.... Regards, Mark
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Bob Albert
I am late to this party but I fixed one smilar unit by replacing the power FET in the switching power supply. Perhaps yours has a similar problem.
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On Tuesday, January 5, 2021, 04:29:44 PM PST, Mark Hatch <mark2382@hotmail.com> wrote:
I *really* appreciate all the views here. Lots to think about. I am ok with replacing the LVPS e-caps and those x2's too. And it will be good to look at the infamous SMD's on A5. Haven't done that yet and I *really* should... In terms of simpler solutions, anybody think that it could be the power switch on the front? When it first started acting up, I thought sticky relay. But threw that idea out the window when I found no relay in power lines. Having worked on boat anchors (like I suspect most of you), right after e-caps the next set of problems are caused by dirty/corroded switches. And given that the last (and worst) incident was after I had to put the scope in my shed during are most recent set of rain storms here in No Cal it got me wondering. The shed is dry, but I suspect it still would be damp over that 2-3 days. Perhaps that could lead to corrosion on the switch contacts? Or am I just having wishful thinking.... I did see in the archives that the switches do go bad, but nobody mentioned intermittent powers. Reading between the lines it sounds like the switch failure was something hard. Currently, the scope is behaving itself and turning on with the button push like it should... Would be nice if it failed hard instead of playing "hide and seek" with me.... Regards, Mark
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Roy Thistle
On Tue, Jan 5, 2021 at 01:57 PM, David Campbell wrote:
I don't fully understand why one is making such a general anecdotals claims... unless... 1) it is an "err on the side of caution" type admonition. 2) it is on the "recommendation" of some YouTube presenters. 3) it is meant as sarcasm. For 1) I'd think... but won't claim.... that many of the individuals available to make sufficient use of 1) might cause more damage to PCBs than cure, when "replace all" replacing capacitors. For 2) Some YouTube presentors are making a similar claim ("to replace all capacitors.") Some of those YouTubers, however, are also selling "intruments" to "detect" capacitor failures... which raises my suspicions of a confict of interest. For 3) If so... then point taken... though, sarcasm taints the message... as there are many individuals ...highly trained, and highly experienced in Tektronix equipment... opining on this forum... who may have seen "similar" things... but would not posit such general claims.
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Bob Albert
I have always been opposed to 'recap' actions. The cost, labor, and possibility of error are all too great. As is often (but not always wisely) said, if it ain't broke don't fix it.
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Electrolytic capacitors, particularly in power supply circuits, are a different story, but not that much. I often will leave those alone if they are working well, and I have had very few problems. And of course, just because a part is brand new doesn't mean it's also good. If you enjoy soldering, go for it. Bob
On Tuesday, January 5, 2021, 05:10:43 PM PST, Roy Thistle <roy.thistle@mail.utoronto.ca> wrote:
On Tue, Jan 5, 2021 at 01:57 PM, David Campbell wrote: I don't fully understand why one is making such a general anecdotals claims... unless... 1) it is an "err on the side of caution" type admonition. 2) it is on the "recommendation" of some YouTube presenters. 3) it is meant as sarcasm. For 1) I'd think... but won't claim.... that many of the individuals available to make sufficient use of 1) might cause more damage to PCBs than cure, when "replace all" replacing capacitors. For 2) Some YouTube presentors are making a similar claim ("to replace all capacitors.") Some of those YouTubers, however, are also selling "intruments" to "detect" capacitor failures... which raises my suspicions of a confict of interest. For 3) If so... then point taken... though, sarcasm taints the message... as there are many individuals ...highly trained, and highly experienced in Tektronix equipment... opining on this forum... who may have seen "similar" things... but would not posit such general claims.
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I have never had to replace caps in any of the 2400 series that I have had come through here, including the 2465A that I now use. I have also rarely had to replace a cap in any of the hundreds of 500 series that have been on my bench. I believe that when manufacturers changed from wet electrolytics to dry the problems with caps largely ceased. Luckily I have never had a dry cap “shoot up to the ceiling.” I have had a number of capacitor failures in 321 series, probably due to heat and the lack of fan cooling. I do have an old family radio though that I am afraid to turn on due to the possibility of rocketry. (grin)
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Jean-Paul
John: "when manufacturers changed from wet electrolytics to dry the problems with
caps largely ceased" The cap issues are mixed up a bit: a/ Certain types tantalum caps had poor seals especially in early SMD parts days, eg the notorious A5 board corroding leaky bypass caps. b/ All "electrolytic" or ELCO caps use a water based electrolyte. The issue is drying out by loss of water over the years, causing low C and high ESR. This is a function of: 1/ End seal design, greatly improved in recent decades. 2/ Application eg soldering technique 3/ Operating temperature and time 4/ Internal temperature rise due to ESR and ripple current 5/ Cap tem rating eg 85 C or 105 C or even 135C. Note that the temp rating means that at that external temp and with rated ripple current, 50% of the pars will exceed ESR or C after 1000 or 2000 hours! In other words limited life! 6/ Quality of mfg eg cheapo junk Chinese no name vs major brands eg Rubycon, Nichicon, United Chem Con, etc. So the cap life and need for replacement is not a simple question! In decades of SMPS design and manufacture we specified 105 C and 135C lytics and bought from the US firms like Sprague, then the Asian firms mentioned above. For TEK scopes, they used good quality parts, so very seldom are the lytics defective in PSU BIG exception is the 2465/B A5 control board SMD corroded caps, bad SMD seal design! I just replaced a 9 uF 150V lytic in 7603 backplane 50 V filter, corroded at one end. RE "exploding" lytics: Yes I had a few in 100-1000W SMPS, it was always a backwards +/- error Bon Chance, Jon
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Jean-Paul
Mark I have never seen an intermittent power switch on any,Tektronix scope, but have seen the power connector plastic shaft mechanically come off.
I suspect a marginal part in the PSU start-up circuit. If you look at the service manual the power supply troubleshooting flow chart is very good for diagnosis. Jon
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