- Scope keeps blowing fuses - 14 Updates
| three_jeeps <jjhudak@gmail.com>: Oct 25 10:45AM -0700 On Monday, October 24, 2022 at 2:12:12 PM UTC-4, Peter W. wrote: > I kinda-sorta think that will do it. KISS and all that. > Peter Wieck > Melrose Park, PA Ditto.....I was going to suggest this but some ppl want to find *the* problem. For *vintage* stuff, it makes no sense to me, Replace all the caps, check all resistors. Having a solid power supply is critical for the rest of the unit to work properly, so why screw around with replacing only one bad component? As long as you got it apart.....Do you really want to revisit this later when another cap dies? |
| Cursitor Doom <cd@notformail.com>: Oct 25 07:33PM +0100 Here we go, gentlemen, the finished "repair" on the PSU board: Before (the faulty RIFAs are arrowed since they're a bit hard to spot) https://disk.yandex.com/i/9VID9SDCNLoxQw After (the new replacements are not arrowed, since they're blindingly obvious) https://disk.yandex.com/i/uHJW9u33lWACVQ It's just awful, isn't it? |
| Jeff Liebermann <jeffl@cruzio.com>: Oct 25 12:42PM -0700 On Tue, 25 Oct 2022 19:33:00 +0100, Cursitor Doom <cd@notformail.com> wrote: >obvious) >https://disk.yandex.com/i/uHJW9u33lWACVQ >It's just awful, isn't it? I've done worse. I don't like the exposed hot wires, but since you're the only person likely to be working on the scope, it's probably an acceptable risk. I suggest you tack the capacitors to the PCB with a little REMOVABLE glue, such as hot melt glue or non-acetic-acid RTV. -- Jeff Liebermann jeffl@cruzio.com PO Box 272 http://www.LearnByDestroying.com Ben Lomond CA 95005-0272 Skype: JeffLiebermann AE6KS 831-336-2558 |
| JC <Chipbee40_SpamNo@yahoo.com>: Oct 25 03:43PM -0400 Cursitor Doom wrote: > obvious) > https://disk.yandex.com/i/uHJW9u33lWACVQ > It's just awful, isn't it? Probably won't fit back in the scope cos of the IEC filter. Tons of info out there on this power supply and how to fix: https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/150/ |
| Cursitor Doom <cd@notformail.com>: Oct 25 09:38PM +0100 On Tue, 25 Oct 2022 12:42:51 -0700, Jeff Liebermann <jeffl@cruzio.com> wrote: >I've done worse. I don't like the exposed hot wires, but since you're >the only person likely to be working on the scope, it's probably an >acceptable risk. Thanks, Jeff, I thought you'd tear me a new arsehole! >I suggest you tack the capacitors to the PCB with a little REMOVABLE >glue, such as hot melt glue or non-acetic-acid RTV. In an ideal world and all that. Sadly, we both know that's not going to happen, Jeff. :-( |
| Cursitor Doom <cd@notformail.com>: Oct 25 09:39PM +0100 On Tue, 25 Oct 2022 15:43:14 -0400, JC <Chipbee40_SpamNo@yahoo.com> wrote: >> https://disk.yandex.com/i/uHJW9u33lWACVQ >> It's just awful, isn't it? >Probably won't fit back in the scope cos of the IEC filter. It does actually fit back in again - *just* about. >Tons of info out there on this power supply and how to fix: >https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/150/ Many thanks for that indeed. |
| Cursitor Doom <cd@notformail.com>: Oct 25 09:54PM +0100 >for embarrassing field failures after 20+yrs. >X2 caps are desiged for 'impedance-limited' applications and >are tested at around 1KVAC/1500VDC. Do you know why these caps usually have their self-resonant frequency marked on the side of them? That's always puzzled me. |
| three_jeeps <jjhudak@gmail.com>: Oct 25 02:19PM -0700 On Saturday, October 22, 2022 at 2:34:59 PM UTC-4, Cursitor Doom wrote: > >Melrose Park, P > These are X2 caps and supposed to fail short. However, for whatever > reason, they both failed open. Fail short...really? Why would you want a cap that is across the supply line to fail short? Just to make sure the fuse blows? It is my understanding that X and Y capacitors experience line spikes, and will endure multiple small breakdowns over the years as a result of this stress. They fail open because local heating caused by a microscopic dielectric breakdown results in polypropylene melting, which seals off the "edge" of the breakdown. Is this not correct?? |
| Cursitor Doom <cd@notformail.com>: Oct 25 10:38PM +0100 On Tue, 25 Oct 2022 14:19:38 -0700 (PDT), three_jeeps >Fail short...really? Why would you want a cap that is across the supply line to fail short? Just to make sure the fuse blows? >It is my understanding that X and Y capacitors experience line spikes, and will endure multiple small breakdowns over the years as a result of this stress. They fail open because local heating caused by a microscopic dielectric breakdown results in polypropylene melting, which seals off the "edge" of the breakdown. >Is this not correct?? No idea if that's the failure mechanism or not. However, if you read my orginal remark, I did say they are *supposed* to fail short, which makes pretty clear that was the intention of the manufacturer even if they were not successful in many instances. |
| Rayner Lucas <usenet202101@magic-cookie.co.ukNOSPAMPLEASE>: Oct 26 01:04AM +0100 In article <4696384c-8b39-4bae-a924-81096d9b3da0n@googlegroups.com>, pallison49@gmail.com says... > ** Rifa PME271 X2 caps are still made and widely available. > Strangely they are also the most expensive X2 caps on offer for no > good reason. I got a handful of brand new PME271 Y caps a few years ago, for reasons that I'm sure can't possibly have been good ones. All of them have developed a couple of small cracks in the casing, just from sitting unused in a parts box. So if anyone was wondering if they'd fixed the defects in the design at any point in the last 40+ years, apparently not. > IME Rifa X2s are notorious for catching fire and filling the room with > acrid smoke. Happened twice, right in front of me, first case was a > room heater and the second with a portable TV. Yep, they're a menace all right. These days I pre-emptively check any mains-powered electronics from the 80s and 90s for them, which thankfully meant I got them out of my Tek 2445A before they popped. Wish I'd been more alert with the 2235A; I spent ages cleaning sticky brown crud out of the crevices of that one. And then there was the HP spectrum analyser where I thought I'd saved myself a heap of trouble by extracting all eight(!) Rifa capacitors from its power supply. Plugged it in, and half an hour later a thick cloud of truly foul phenolic smoke poured out. Opened it up to find that it had blown part of the case off its power inlet. Turns out that Schaffner filtered power inlets can *also* contain Rifa (or very similar) caps, concealed inside a metal casing and potting compound just to add extra force and noxious smells to the eventual and inevitable explosion. I'm pretty sure anyone who works on older electronics eventually develops their very own rant about these accursed objects. Rayner |
| legg <legg@nospam.magma.ca>: Oct 26 08:34AM -0400 On Tue, 25 Oct 2022 19:33:00 +0100, Cursitor Doom <cd@notformail.com> wrote: >obvious) >https://disk.yandex.com/i/uHJW9u33lWACVQ >It's just awful, isn't it? You could probably have leadformed the new parts to suit. My guess is you just prefered to solder from the comp side. RL |
| Cursitor Doom <cd@notformail.com>: Oct 26 04:15PM +0100 >My guess is you just prefered to solder from the comp >side. >RL It's really not my thing. When people say, "Just recap anything suspect" and there might be fewer than half a dozen to do, the prospect still fills me with horror. If they only knew how ironic the "Just" bit strikes me in suggestions like that. |
| "Peter W." <peterwieck33@gmail.com>: Oct 26 08:57AM -0700 > suspect" and there might be fewer than half a dozen to do, the > prospect still fills me with horror. If they only knew how ironic the > "Just" bit strikes me in suggestions like that. The problem with vintage equipment, however well designed and well built, is that parts within it age. Typically, items that are approaching, or exceeding 30 years old will have some marginal parts within. Further, if those parts are 'common' as in "many of them", if one fails the others will not be far behind. Some truisms: a) As in the Holland America commercials - Time is a precious commodity. b) Most (not all) hobbyists are not limited by cost constraints for a few parts. So, a US$20-or-equivalent investment to save a valuable item is not outrageous. c) Most of the effort in repairs is 'getting to it' - the taking-apart, the testing, documenting, and then reassembly. d) The actual repairs take very little time. So, when whatever the device might be, when it is taken apart, *THEN* is the time to refurbish the entirety to the greatest extent possible - to avoid having to repeat the process if nothing else. Analogy: the engine in your vehicle spins one (1) bearing. You would replace _ALL_ of the bearings, as the incremental cost of the additional bearings against the cost of the tear-down is tiny, and the rewards significant. There is a school of thought that suggests that repairs are made only to the minimum necessary. Subscribers to this theory are the ones that one sees stranded on the side of the road in a blinding snowstorm. Your power-supply went through a traumatic event - and it is supplying a complex and expensive piece of equipment. Consider it in that light. As to soldering and technique - time and repetition will give you more confidence. Peter Wieck Melrose Park, PA |
| "Peter W." <peterwieck33@gmail.com>: Oct 26 08:57AM -0700 That would be Viking.... |
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