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"Kenny" <me@privacy.net>: Feb 03 06:57PM "Miguel Giménez" wrote in message news:n8q2rt$1iml$1@gioia.aioe.org...   Hello   I'm trying to repair a dead LG 32LS570S LCD screen. The backlight work OK, all the power supply voltages are nominal and the unit turns on and off via the remote or the keypad, but there is no image. The service manual says "change the main board", but first I want to ask here if this is a known fault.   Thank you   -- Saludos Miguel Giménez   You didn't say if you have sound and channel change etc. Service manual's here if it helps. http://elektrotanya.com/lg_32ls570s-zb_32ls570t-zb_chassis_ld22e_mfl67360915.pdf/download.html   Kenny Cargill

"Miguel Giménez" <me@privacy.net>: Feb 04 05:25PM +0100 El 03/02/2016 a las 19:57, Kenny escribió: > You didn't say if you have sound and channel change etc.   No sound, but I don't know if the device is properly tuned (it's not mine and comes from another repeater area).   The channels may change, but I can't see the change.   I already had the service manual you pointed (thank you), but an special remote is needed for almost any test. I followed the debugging procedere until I arrived to "change main board".   Thank you.   -- Saludos Miguel Giménez

Cursitor Doom <curd@notformail.com>: Feb 04 01:59PM Hi all,   I'm now working on a different Philips scope which 'died' suddenly for no apparent reason. Here's a summary of the key points:   The smps section had power in, but nothing coming out. I checked the smps outputs for shorts/low-res. One output marked 45V was trying to feed a board with an input resistance of only 6 ohms. I located the board in question. There were several multi-pin connectors around the edge of it running off to other parts of the scope. Now it turns out the smps runs perfectly fine when *one* of these connectors is pulled from the board. With the suspect connector's plug disconnected, the aforementioned 6 ohms shoots up to about 15k and life is great. *BUT* (and here's the thing) the resistance looking into the suspect plug (which has only two wires) is several megohms. And yet this very high resistance, when plugged into the board causes such a voltage drop that the smps shuts down! How is this even possible? I keep thinking there must be something simple I've overlooked, but can't think what it might be. If anyone has experienced something similar in the past and remembers what the underlying issue was, then that could be very helpful! Thanks.

Pat <pat@nospam.us>: Feb 04 10:26AM -0500 On Thu, 4 Feb 2016 13:59:27 -0000 (UTC), Cursitor Doom >If anyone has experienced something similar in the past and remembers >what the underlying issue was, then that could be very helpful! >Thanks.   Regarding "How is this even possible?", I can think of two things. One is mechanical - plugging that 2 wire connector in causes a short near the socket. Can you unplug the other end of that cable and see if you get the result? The more likely cause is a voltage on that two wire cable turns on a transistor or some other device hard wihich then shorts the incoming line from the power supply due to a bad part somewhere else on the board. Good luck.

Cursitor Doom <curd@notformail.com>: Feb 04 03:42PM On Thu, 04 Feb 2016 10:26:46 -0500, Pat wrote:   > is mechanical - plugging that 2 wire connector in causes a short near > the socket. Can you unplug the other end of that cable and see if you > get the result?   Already tried and eliminated, thanks.   The more likely cause is a voltage on that two wire > cable turns on a transistor or some other device hard wihich then shorts > the incoming line from the power supply due to a bad part somewhere else > on the board. Good luck.   That's what I was wondering. If my DVM on resistance range doesn't use enough voltage to switch such a transistor or diode into conduction, then that could account for it. I'll try it again with an old-style AVO.

MJC <gravity@mjcoon.plus.com>: Feb 04 04:08PM In article <n8vlfv$7l5$1@dont-email.me>, curd@notformail.com says...   > ... *BUT* (and here's the thing) the resistance looking into the suspect plug > (which has only two wires) is several megohms. And yet this very high > resistance, when plugged into the board causes such a voltage drop that > the smps shuts down! How is this even possible?   It's rather easily possible if the current draw is non-linear with voltage. After all, the further the circuit deviates from a simple resistor the more likely this is!   Apart from brutal ideas like providing the suspect plug with a very beefy PSU and watching to see what burns up, I don't see what alternative there is apart from gradual splitting off of parts of the circuit...   Mike.

Cursitor Doom <curd@notformail.com>: Feb 04 04:12PM On Thu, 04 Feb 2016 16:08:38 +0000, MJC wrote:     > Mike.   "Current blasting"? It would have worked in this instance, but I've found the problem with my good old trusty AVO which confirmed my previous suspicions. People often go on about how modern DVMs are great because they don't turn on pn junctions, which is all very well, but there are odd times when that is precisely what you *do* want the meter to do! This was one of those. Thanks, guys.

N_Cook <diverse@tcp.co.uk>: Feb 04 12:10PM Definitely PbF used, but nothing obviously wrong in the way of ring cracks etc. "digital" checking of caps (with fingers) a Sanwha SD, 47uF 450 V , C16 designation ,would move like that situation of pad and pin fully soldered over so you cannot see the metal of the pin at all, but there is movement of the cap as the pin is moving fully enclosed in a PbF solder "socket". Ground back the solder on both pins to show discontinuity of metals and still no movement seen. A physical break inside the cap on one pin of 'D' anode supply to the preamp, of the R/C, B to E HT chain. I've yet to hear back from owner , how much hum there was.

Trevor Wilson <trevor@SPAMBLOCKrageaudio.com.au>: Feb 04 06:58AM +1100 On 3/02/2016 11:31 PM, Mark Zacharias wrote:   > This thing took approximately five whole days worth of bench time.   > I'm going to spend a very generous amount of time patting myself on the > back for this one.   **All for an amp worth, what(?), $300.00? It can be a bugger of a business. How much can you charge your client? $200.00?   On the flip side, I did a couple of really ancient (ca. 1972) Accuphase amps recently. The client was willing to spend around $700.00 on each. He bought them for a song and they typically sell for a couple of Grand on eBay.     -- Trevor Wilson www.rageaudio.com.au   --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus

John-Del <ohger1s@aol.com>: Feb 03 01:53PM -0800 > Any more recent successs stories to brag about?   > C'mon, don't we all enjoy patting ourselves on the back, really?   > Mark Z.   Okay, one more. True story... This wasn't so much a difficult repair as it was the circumstance. 1980, hot summer day and my new girlfriend (who would be my wife) is having her HS graduation party when her parent's early 70s tube Magnavox console blacks out in a cloud of smoke leaving a clean horiz line. I was 21 at the time and looked younger, but of course being a TV tech I was asked to look at it. I pulled the chassis out and the area around the vert centering control was pitch black. That and the cigarette smoke and wood stove deposits made seeing what else was burned nearly impossible.   I borrowed the garden hose and a bottle of Fantastik (TM) and soaked the bottom of the chassis and rinsed so it sparkled, then left it out front in the hot sun. Later in the afternoon I put in two 10 ohm 5W resistors in place of the vert cent control and put it together, touched up the height and lin and it worked fine for a few more years.   When my father in law tells the story, he said that when he saw me hosing out the TV guts in the front yard he was thinking "oh sh$t I'm going to have to buy a new TV tomorrow".

"Mark Zacharias" <mark_zacharias@sbcglobal.net>: Feb 04 05:09AM -0600 "Trevor Wilson" <trevor@SPAMBLOCKrageaudio.com.au> wrote in message news:dhf4nvF7fagU1@mid.individual.net...   > --- > This email has been checked for viruses by Avast antivirus software. > https://www.avast.com/antivirus   After an initial assessment, I gave the customer an approximately 300.00 estimate.   Midway through the process I advised him it would be more.   Billed out at 400.00.   He hasn't picked it up yet, but it's part of a set with the preamp, tuner, cd, and cassette so I'm not too worried.   Yeah - these days you take what you can get.   I was pretty confident I could fix it, but one problem kept hiding behind the last one, and oscillation problems kinda turn my knees to jelly.     Mark Z.

"Mark Zacharias" <mark_zacharias@sbcglobal.net>: Feb 04 05:16AM -0600 "John-Del" <ohger1s@aol.com> wrote in message news:78c200c3-b710-43b0-8002-8fbb178d0c17@googlegroups.com...       >When my father in law tells the story, he said that when he saw me hosing >out the TV guts in >the front yard he was thinking "oh sh$t I'm going to >have to buy a new TV tomorrow".       Same thing happened to my younger brother when our family was visiting the family of the older brother's wife.   Zenith TV died. My younger brother, who was either still in tech school or early in his career, tore the set down to bits and pieces right there on the living room floor, puzzled over it a bit, the light came on, ran down to the Zenith distributor, picked up a part, got back over there and finished the repair.   Two families (not to mention the two brothers) were sweating bullets on that one.     Mark Z.

thekmanrocks@gmail.com: Feb 04 03:16AM -0800 John-Del wrote: "When my father in law tells the story, he said that when he saw me hosing out the TV guts in the front yard he was thinking "oh sh$t I'm going to have to buy a new TV tomorrow".     Good story with happy ending! Nowadays most folks won't let me adjust their PICTURE menus for them, let alone go component level. Sets are so reliable today, with consistent image quality, yet people wonder why they burn out after only 3-5 years.   Backlit TVs(LCD, LED) require a backlight to be seen, and very often this setting, along with the others, are left in factory/showroom mode, shortening the life of the appliance. Getting set owners to understand this basic fact, along with the benefits of correct setting of the basic adjustments(brightness, contrast, color, etc), is well-nigh impossible! A $300 full calibration is often not necessary to achieve these goals.

frank <frank@invalid.net>: Feb 04 10:08AM Hi all,   I've got this really old TV test signal generator to repair. I've found a very poor copy of the service manual from a well known internet site (elektrotanya). Does anyone, by chance, have a readable copy of that manual around? Thanks in advance   Frank IZ8DWF

"David Farber" <farberbear.unspam@aol.com>: Feb 03 10:14PM -0800 I'm servicing a Gateway GM5260. It uses an Intel DP965LV motherboard and it has Windows XP installed. It also has this habit of freezing randomly. Then you are forced to hold in the power button to shut it off. Here is the interesting part. When you power it back on after it freezes, it will ALWAYS shut down about 1 second after the power button is pressed. If you restart it second time, usually it will power up fine. Occasionally, it will take a third try to keep the power on. If the computer goes through a normal shut down, the power up process always works the first time. I've swapped the RAM, video card, and power supply, and it made no difference. The only hardware issue I can find is that in the system bios, there is a value in the hardware monitor called, +1.5V and it hovers around 1.298V. I have inspected the caps and they don't look or test bad. The CPU and motherboard temps are normal. Has anyone experienced this type of problem before?   Thanks for your replies. -- David Farber Los Osos, CA

Jon Elson <jmelson@wustl.edu>: Feb 03 03:27PM -0600 Tim R wrote:     > I got a better look yesterday. It's a street light, no camera. Besides, > I see the flash when I'm stopped at a red light, so the cross traffic > would have a green.   It is a worn-out lamp. When they get old, they start to run hot and the ballast cycles power every few minutes. The repeated starting, maybe 10 times an hour, increases the wear on the lamp. When they get really bad, the ignitor can't strike the arc, and so the ignitor keeps trying. The strobe effect, maybe a couple flashes a second, is the ignitor trying to get the lamp to restart.   Jon

Tim R <timothy42b@aol.com>: Feb 03 06:28PM -0800 On Wednesday, February 3, 2016 at 4:26:44 PM UTC-5, Jon Elson wrote: > strobe effect, maybe a couple flashes a second, is the ignitor trying to get > the lamp to restart.   > Jon   You could be right. I need to get a better look at this one.   It doesn't sound like that to me, because a lamp that old shouldn't stay normally lit most of the time. It should be burned out trying to start most of the time. But I haven't heard a better explanation either.   I might call the city engineer and just ask.

Jon Elson <jmelson@wustl.edu>: Feb 03 03:23PM -0600 > application right now. In fact I am pretty sure I could do it with SCRs > and not too many other components. But then what ? Maybe some presets for > equipment where things are still set by voltages ? Actually, you could make the neon lamps, themselves, be the storage element. Connect one side of all the lamps together, and tie to B+ with one resistor. Have individual resistors to ground on each lamp. Short each individual resistor with the select pushbutton. When you press this button, all other neons will go out, and the selected one will light, and stay lit when you release the button. Now, a circuit detects which of the individual resistors has voltage across it, and selects the desired function. Definitely cheap, and will work for a while. Eventually, the neons will get far enough out of balance to cause problems.   Jon

Chuck <ch@dejanews.net>: Feb 03 04:39PM -0600 >Something has to momentarily cut the current to all the other neons, likewise if you tried to make this in logic, it would most likely be a bunch of bistable flip flops but with a bit different gate arrangement.   >Hell, I now wonder if neons is not maybe the best way to do it even today. There is only one main dropping resistor to all of them, when you hit the switch or whatever YOUR neon pulls more current and is fired, the other ones cannot fire because of not enough voltage.   >There may be a nifty way of doing this with SCRs. I just can't think of an application right now. In fact I am pretty sure I could do it with SCRs and not too many other components. But then what ? Maybe some presets for equipment where things are still set by voltages ?   No It was a Large Scale CMOS chip. Maybe made by NEC. (NEC codes worked with some AOC sets.)   --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus

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