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janetnkansah1@gmail.com: Mar 08 11:12PM -0800 Pls My Toshiba laptop Statellite C855-S5356, When switched on boots up to the bios stage then the screen will change to some multi-checker boxes (as if using a scratched DVD in a DVD player)then the screen will go off for about 10 seconds then it will repeat that process(on and off)but takes a longer time to come on again each successive time. I tried an external monitor but there was no display. I removed the harddisk but the problem remained the same, remove the battery-same. I will be happy if l can get some help here. Thanks

janetnkansah1@gmail.com: Mar 08 11:19PM -0800 Pls My Toshiba laptop Statellite C855-S5356, When switched on boots up to the bios stage then the screen will change to some multi-checker boxes (as if using a scratched DVD in a DVD player)then the screen will go off for about 10 seconds then it will repeat that process(on and off)but takes a longer time to come on again each successive time. I tried an external monitor but there was no display. I removed the harddisk but the problem remained the same, remove the battery-same. I will be happy if l can get some help here. Thanks

Ken <Ken@invalid.com>: Mar 09 06:30AM -0600 > display. I removed the harddisk but the problem remained the same, > remove the battery-same. I will be happy if l can get some help here. > Thanks   Try removing and cleaning the RAM.

Chris Jones <lugnut808@spam.yahoo.com>: Mar 09 03:09PM +1100 On 08/03/2016 05:53, Jeff Liebermann wrote: > not conduct electricity very well and will in fact cause > resistance issues and eventually failed connections."   > etc...   This stuff is for putting on contacts: http://www.electrolube.com/products/contact-lubricants/sgb/contact_lubricants/   If it is in a dusty environment, it would be a good idea to seal out the dust from the switch or connector. I believe that modern automotive connectors tend to be sealed with o-rings or similar.   I would not use silicone grease, oil or gel near anything electrical with relays etc. for the reasons that Tauno Voipio explained in the S.E.D. version of this thread.

DaveC <not@home.cow>: Mar 08 11:04PM -0800 > This stuff is for putting on contacts:   http://www.electrolube.com/products/contact- lubricants/sgb/contact_lubricants/   Fercryinoutloud! Have you seen the product selection guide for those? ::   http://www.electrolube.com/pdf/electrolube-product-selector-brochure.pdf   I went cross-eyed at the first chart.

Phil Allison <pallison49@gmail.com>: Mar 08 11:20PM -0800 DaveC wrote:     > This research found that simple mineral oil reduced contact resistance > dramatically:   > http://www.te.com/documentation/whitepapers/pdf/p154-74.pdf   ** The "Conclusions" section backs up what products like WD40 have been claiming for decades.   --------------------------------------------------   CONCLUSION   We have shown that all of the more commonly used non-noble contact materials experience large increases in resistance during fretting action (small amplitude cyclic motion). The results of our tests were such that a warning could be issued concerning the indiscriminate use of such materials in applications where fretting action could occur on electric contacts as a result of vibration, mechanical motion, or differential thermal expansion. Resistance increases noted during fretting action are felt to be due to trapped wear debris composed mainly of oxides. This process is commonly referred do as "fretting corrosion." Lubrication has been identified as a very good deterrent to fretting corrosion; the important mechanisms imparted by lubrication are postulated as: first, a reduction in wear; second, that the treatment aids in the selfcleaning and flushing of wear debris from contacts; and finally, and perhaps most important, liquid lubricants have the ability of excluding oxygen from the contact, thus preventing oxidation of wear debris and freshly exposed contact material.   --------------------------------------------------   .... Phil

Jeff Liebermann <jeffl@cruzio.com>: Mar 08 11:23PM -0800 On Wed, 9 Mar 2016 15:09:49 +1100, Chris Jones   >This stuff is for putting on contacts: >http://www.electrolube.com/products/contact-lubricants/sgb/contact_lubricants/   Link for the USA: <http://www.electrolube.org/products/contact-lubricants.html>   The web page says it's for putting on contacts but offers no explanation of how it works or what's in it. The MSDS pages say "contact the factory". At least that TDS is available. Picking one version (CO70 oil) at random: <http://www.electrolube.com/core/components/products/tds/044/CO70.pdf> I see that the active ingredients are a "Blend of synthetic fluids", which is a rather useless description. I guess you'll just have to rely on the word of the manufactory that the contact oils and greases actually do something in an unspecified manner.   >If it is in a dusty environment, it would be a good idea to seal out the >dust from the switch or connector.   That's always a good idea. I used to maintain the processes controllers at a canning plant. If any kind of dust or aerosol got into the contacts, the switching current would burn the solids to a crisp. Eventually, that would produce a layer of insulating carbon. We eventually pressurized and locked the NEMA enclosures, which ended that problem (and others).   >I believe that modern automotive >connectors tend to be sealed with o-rings or similar.   Probably true. Lets see what they look like: <https://www.google.com/search?q=automotive+connectors&tbm=isch> Oddly, I don't see any visible o-rings, but they might be hidden inside the connector. There also seem to be a few molded rubber seals.   >I would not use silicone grease, oil or gel near anything electrical >with relays etc. for the reasons that Tauno Voipio explained in the >S.E.D. version of this thread.   <https://groups.google.com/d/msg/sci.electronics.design/j4LskBMCJ7w/Rbjrl1LAIQAJ> If you have an army of assemblers using silicone bearing hair spray in close proximity to your switch contacts, you should switch them all to Brylcreem, also known as the "greasy kid stuff", which is based on mineral oil and bees wax. <https://kitsadnauseam.wordpress.com/2009/05/25/greasy-kid-stuff-the-brand-that-viral-marketing-built/>       -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann <jeffl@cruzio.com>: Mar 08 06:59PM -0800 On Fri, 4 Mar 2016 05:37:53 -0800 (PST), Tim R <timothy42b@aol.com> wrote:   >I had on what we called triwall neoprene.   I couldn't find anything by that name, but did find these: <http://www.mapa-pro.com/our-gloves/protections/disposable/p/g/trilites-994.html> It's a mix of latex, neoprene, and nitrile. These might be the ones, but the chemical chart at: <http://www.mapa-pro.com/our-gloves/protections/disposable/p/g/trilites-983.html#chemical_chart> doesn't show that it's resistant to any chlorinated hydrocarbon solvents.     -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558

Cursitor Doom <curd@notformail.com>: Mar 08 04:48PM Well, I've replaced all the flaking capacitors and still no improvement. A number of people have been suggesting I remove the two resonant caps (the 30n ones) from the primary circuit and test them. I didn't have any expectation that this would achieve anything since they tested good in- circuit, but as we're running out of ideas now I did remove them this afternoon and they both tested at 31nF a piece and no signs of any physical damage. I then subbed a couple of common-or-garden mylars of the same value in their places and re-swept for changes in resonance. Result was no change in resonance - but a slightly better Q(!!) Also checked the two 10Meg resistors whilst I was at it and they were fine, too. So I can only think of making up Dimitrij's winding tester and looking for signs of any turns shorting in the main transformer. I'm coming to the end of the amount of time I'm prepared to spend on this psu as it stands. I'm more and more tempted to mothball the key parts of it til next year then rebuild it as a conventional non-res converter to a fresh design. TBH, I'm not prepared to still be testing this thing after the end of this week, so if anyone has any last-ditch ideas, now's the time to toss 'em into the mix. Speak now or forever hold your peace. Thanks, all.

JC <Chipbee40_SpamNo@yahoo.com>: Mar 08 12:35PM -0500 On 3/8/2016 11:48 AM, Cursitor Doom wrote: > the end of this week, so if anyone has any last-ditch ideas, now's the > time to toss 'em into the mix. Speak now or forever hold your peace. > Thanks, all.   I have no idea what you now consider to be wrong with the PSU. Apart from a resistor that in your opinion runs too hot even though its well within its rating I seem to recall amidst your ramblings that the voltage rails are correct?   It seems to me that the only fault was the diode which was pretty obvious from the beginning. (Always check for previous repairs).   You persist in not using the correct manual, refuse to test it with an appropriate load and won't put it in the scope to see if the scope actually functions.   If you just want to discuss switching supply design go buy some control chips or an evaluation kit and build some.

legg <legg@nospam.magma.ca>: Mar 08 12:33PM -0500 On Tue, 8 Mar 2016 16:48:05 -0000 (UTC), Cursitor Doom >the end of this week, so if anyone has any last-ditch ideas, now's the >time to toss 'em into the mix. Speak now or forever hold your peace. >Thanks, all.   Waste of breath.   RL

Cursitor Doom <curd@notformail.com>: Mar 08 06:43PM On Tue, 08 Mar 2016 12:35:07 -0500, JC wrote:   > from a resistor that in your opinion runs too hot even though its well > within its rating I seem to recall amidst your ramblings that the > voltage rails are correct?   Yes, they're fine. It's not *my* opinion that this is a poor design! I posted the schematic to s.e.d and the designers there told me that. I've said all along I know nothing about this type of PSU so I defer to those better qualified. Having said that, the widespread evidence of charring and soot residue that appear even worse in real life than in the photos would seem to indicated that that is not a happy board. The rest of the scope's boards are still pristine showing no sign of repairs at all.   > It seems to me that the only fault was the diode which was pretty > obvious from the beginning. (Always check for previous repairs).   Nothing obvious about it! - apart from the rather poor replacement technique. The problem with that replacement was very subtle inasmuch as it wasn't recovering quickly enough at 20kHz. Nevertheless it was still capable of functioning as a viable rectifier right up to 500kHz.   > You persist in not using the correct manual, refuse to test it with an > appropriate load and won't put it in the scope to see if the scope > actually functions.   All the recent tests have been carried out using the actual scope itself as a load - can't get any better than that. I won't put it in the scope until that resistor is running cool. It's proximity to other temperature sensitive components like diodes and its siting deep within the scope uncooled lead me to believe that it is running far hotter than it should be - and will be even worse in situ. That *might* just be a design flaw, but I doubt it.

Cursitor Doom <curd@notformail.com>: Mar 08 09:31PM On Tue, 08 Mar 2016 12:33:50 -0500, legg wrote:   > Waste of breath.   Yeah, I know what you're thinking - your suggestion still hasn't been adopted. I've been giving it more thought and I've come up with a brainwave.   This is a 2W resistor. If it's trying to dissipate more than 2W as I strongly believe, something's definitely wrong. The problem up until now has been measuring the dissipation, because we can't use I^2*R or variations thereof because of the highly noisy/irregular waveform. So... Here's the clever bit: Measure exactly how long it takes at present for the resistor to reach say 50'C. I believe it's around 1 minute, but get the exact time. Then let it cool completely back to the room ambient temperature. Remove from circuit. Attach to bench power supply and by means of trial and error, set the voltage across the resistor to raise it's temperature to 50'C in 1 minute (will obviously require several attempts, but no matter). Read off the voltage level which produces this outcome, then just do V^2/R to find W and see if it exceeds 2W. I'll do it first thing tomorrow!

Julian Barnes <jb9889@notformail.com>: Mar 08 10:08PM On Tue, 08 Mar 2016 21:31:25 +0000, Cursitor Doom wrote:   [snip] > I'll do it first thing tomorrow!   Finally it gets *really* interesting. >:-}

Jeroni Paul <JERONI.PAUL@terra.es>: Mar 08 03:10PM -0800 Cursitor Doom wrote: > off the voltage level which produces this outcome, then just do V^2/R to > find W and see if it exceeds 2W. > I'll do it first thing tomorrow!   Good test. It would be more straight to plug the right voltage to make it dissipate 2W, for 20 ohm that would be 6,3V and check what temp results in 1 minute. You could use another identical resistor for the test if you have one lying around to avoid unsoldering.

Dimitrij Klingbeil <nospam@no-address.com>: Mar 09 12:20AM +0100 On 09.03.2016 00:10, Jeroni Paul wrote: > make it dissipate 2W, for 20 ohm that would be 6,3V and check what > temp results in 1 minute. You could use another identical resistor > for the test if you have one lying around to avoid unsoldering.   There's no need to unsolder, neither to actively avoid unsoldering. That resistor is connected through a diode on the board. Just apply the proper polarity signal, and the diode will take care of the isolation.

Cursitor Doom <curd@notformail.com>: Mar 08 11:58PM On Wed, 09 Mar 2016 00:20:35 +0100, Dimitrij Klingbeil wrote:     > There's no need to unsolder, neither to actively avoid unsoldering. That > resistor is connected through a diode on the board. Just apply the > proper polarity signal, and the diode will take care of the isolation.   Thanks for the tips, guys, they will both save me time. I'll work out the appropriate voltages for 3, 4 & 5W too and that'll save even more time.

JC <Chipbee40_SpamNo@yahoo.com>: Mar 08 07:38PM -0500 On 3/8/2016 4:31 PM, Cursitor Doom wrote: > off the voltage level which produces this outcome, then just do V^2/R to > find W and see if it exceeds 2W. > I'll do it first thing tomorrow!   OMFG

JC <Chipbee40_SpamNo@yahoo.com>: Mar 08 07:59PM -0500 On 3/8/2016 1:43 PM, Cursitor Doom wrote: > posted the schematic to s.e.d and the designers there told me that. I've > said all along I know nothing about this type of PSU so I defer to those > better qualified.   Yes, I read your posts on sed, you didn't tell them this was a Philips scope, and some replies implied Philips made televisions, jeez.   Philips/Fluke made excellent test equipment and many products beat Tektronix into the ground but being European never made it across the pond in large numbers. I've worked in both design and repair facilities and the folk who couldn't repair ANYTHING were the design guys because they always spent 3 days criticizing the original design, another week debating it with their colleagues and then gave it to a repair tech to fix (in about 30 minutes). You obviously fit into the design mentality, so good luck and give the scope to someone who will appreciate it.

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