- Samsung NP350V5C laptop repair - 2 Updates
- SMPS wall wart failure. - 8 Updates
| M.Joshi <M.Joshi@eternal-september.org>: Jun 08 08:29AM Hello all, I am trying to repair the above Samsung laptop which just produces a series of clicks when you press the power button? I have tried powering up without the battery and removing any residual capacitor charge by depressing the power button for 1 minute with neither the battery nor the AC adaptor connected. The battery seems to be charging which indicates that the main 19V input rail is functional. Looking at the LA-8862P PCB schematic for the laptop, I cannot seem to work out what the B+ voltage rail is and where it is generated? Also, there is mention of a TPS51125 in the Power Tree block diagram but it does not appear in any of the circuit schematics later on? Any pointers would be much appreciated. Thanks. |
| Ken <Ken@invalid.com>: Jun 08 09:38AM -0500 M.Joshi wrote: > it does not appear in any of the circuit schematics later on? > Any pointers would be much appreciated. > Thanks. You may well have a problem that requires opening up the laptop, but I would try another power supply before doing that. I have seen many laptop that fail due to lack of current when under load. In fact I purchased one for parts that the owner said would not power up, but all it needed was a power supply. It has been working fine for over two years now. |
| "David Farber" <farberbear.unspam@aol.com>: Jun 07 12:04PM -0700 M Philbrook wrote: > fail in this manner for routers, I replaced my 3 times, now I have a > transformer 60hz type and works great... > Jamie Hi Jamie, I did replace the faulty cap. As far using a 5 watt zener diode, the original one is 3mm long and 1.4mm in diameter. That would seem to be in the under 1 watt category. Also, please see my corrections to my original post. The zener diode is paralleled by the filter cap, not the power diode. Thanks for your reply. -- David Farber Los Osos, CA |
| John-Del <ohger1s@aol.com>: Jun 07 02:29PM -0700 On Sunday, June 7, 2015 at 11:47:39 AM UTC-4, David Farber wrote: > -- > David Farber > Los Osos, CA Basic crowbar zener. Meant to protect the device powered by the supply in case the supply runs away. |
| Jeff Liebermann <jeffl@cruzio.com>: Jun 07 02:37PM -0700 On Sun, 7 Jun 2015 12:04:01 -0700, "David Farber" >The zener diode is paralleled by the filter cap, not the power diode. If the zener is there strictly for protection, the power supply should work normally without it. Have you tried using it without the zener? If it's in parallel with the output, it's likely some voltage slightly over 5V, such as 5.6v or 6.8v. If the zener is expected to short upon overvoltage, I would guess(tm) that a low power zener would be more appropriate than one that can handle the power. I've had my share of 5v 2A power supplies blow up. I don't recall if they were made by Jentec, but when I replaced the usual bulging capacitor(s), most would not recover. I never bothered to troubleshoot further and just recycled them. Thanks for the hint about the zener. -- 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 |
| "Arfa Daily" <arfa.daily@ntlworld.com>: Jun 08 01:01AM +0100 "John-Del" <ohger1s@aol.com> wrote in message news:22d3f51e-41b6-4f4c-a893-c2199ff79e6d@googlegroups.com... >> Los Osos, CA > Basic crowbar zener. Meant to protect the device powered by the supply in > case the supply runs away. That would be my feeling for the purpose of it, too ... Arfa |
| "Arfa Daily" <arfa.daily@ntlworld.com>: Jun 08 01:09AM +0100 Also, please see my corrections to my original post. > The zener diode is paralleled by the filter cap, not the power diode. Although strictly speaking it is correct no matter which way round you say it, that still comes across sort of wrong, as though the zener has some primary function, and that of the filter cap is secondary. It would be better to say that the filter cap is paralleled by the zener, implying that it's the zener that has the secondary function. Probably just me splitting hairs though ... :-) Arfa |
| "Mark Zacharias" <mark_zacharias@labolgcbs.net>: Jun 07 08:23PM -0500 "Arfa Daily" <arfa.daily@ntlworld.com> wrote in message news:j35dx.855892$I97.187416@fx31.am4... >> -- >> David Farber >> Los Osos, CA 1. Cap develops ESR. 2. High frequency AC waveform appears on the desired DC output. 3. Circuit interprets as low DC - attempts to compensate. 4. Actual DC runs away. In the Panasonic example, the 14 volt line would go to 35 volts. 4. Zener shorts. 5. Ideally this throws off the "Q" of the circuit so much that it simply stops oscillating. Power supply stops but does not blow up. "Ideally". The old Panasonic switchers still usually fried the primary circuit switching transistors in this scenario. Remove the shorted zener, replace the cap, observe the voltage at that point, replace with an appropriate zener. For example, Panasonic put an 18 volt zener across the 14 volt line. If your rated output is 5 volts, maybe a 6 volt zener. Mark Z. |
| "David Farber" <farberbear.unspam@aol.com>: Jun 07 06:31PM -0700 Arfa Daily wrote: >> -- >> David Farber >> Los Osos, CA Hi Arfa, I agree with you regarding the phrasing. Your way does sound better and it is splitting hairs. (-: I was wondering what would happen if the choke were placed before the capacitor and zener diode. Wouldn't the choke filter out the spikes and then make the zener diode unnecessary or at least less likely to short? Thanks for your reply. -- David Farber Los Osos, CA |
| Phil Allison <pallison49@gmail.com>: Jun 07 09:52PM -0700 David Farber wrote: > I was wondering what would happen if the choke were placed before the > capacitor and zener diode. ** A choke would present a high impedance in series with each current pulse from the switching tranny - causing a big drop in the voltage appearing on the electro cap. > Wouldn't the choke filter out the spikes and then > make the zener diode unnecessary or at least less likely to short? ** The zener (probably 6.2 V) conducted heavily and failed short when the electro went high ESR and caused the peak output voltage to go high. An electro that has developed high ESR cannot smooth the current pulses being delivered by the switching tranny and diode, so the output wave has continuous high peaks with a low *average* value. The control loop responds to the low average and tries to correct it by making each current pulse stronger, which only makes things worse. In short, the output electros in a SMPS are critical to it operation and in many cases there in nothing to prevent the output voltage going high when they wear out. I have seen serious damage done to 5V logic when this happens. ... Phil |
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