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Loose rivets
15th Jan 2018, 01:24
Fixed me little car, but then my favouritest little monitor went TU.

LG 1953 some 10 years old.

It was quite hard to split it open. A fingernail breaking job, but when it was open there was only one electrolytic that was bulging - and that was reading okay.

Powered it up while in bits and it ran! I know I've got to change the C's but for now I'll put it together for practice, thinks I. Bloody thing went wrong again, but worse. the C that's bulging shows 5v across it, and I kind of doubt it's just open circuit. Or, that being O/C would stop the thing turning on at all. Not even the power light by the switch. One will have to find one's thinking cap.

While I was working live and taking random readings, I came across 315 volts DC. Bloody Nora, didn't know these backlight tubes needed that. I assume that's what needs the volts????? Anyway, I pressed the off button and waited for voltages to decay. They didn't. I then got me AVO8 out and used that to drain the voltages. I didn't. I pulled the main power plug and the voltage dropped off with the AVO's 20,000 ohms/volt load.

So, sodding great voltage powered up year after year if one is not conscientious and turns it off at the mains.

I got an belt from my wife's camera flash years ago and that nipped, I imagine these circuits could pump out a serious OWIE. This morning I finally got around to splitting the pal's PANASONIC 40" I ran a thread about some weeks ago. What sort of voltages/power can I expect in that?

Oh, here it is: Don't know what I'm asking really. Obviously the sleeping tablets are kicking in. That, or the wine. Anyway, tomorrow is another day. Oh, again. I've got 4 Seiko Chronographs from when they were magnificent inside. All in bits. One's workload is becoming stressful. Wish I could do some work that's paid.

strake
12th Dec 2017, 08:09
Living as I do, in deepest SW France, I soon learnt that I had to become a jack-of-all-trades (master of none) to get anything done. TV repairing was added to my list a while ago. It goes without saying, 'fiddlin' wiv 'lectrics is danjerus'. In addition, your mates TV may be exceptionally unique but if you/he want to have a shot at it.....:
If you open the back, you will
probably find a direct satellite feed for Freesat which was unique at the time on this TV. You will also find a power supply board and a main AV board.
You could change each of those until you find the fault or just replace the lot for about £60. The sat input is a TNPA4661, the PSU, TNPA4677 and the main AV is a TNPH0756. If they are like other tv's they will simply attach with ribbon connecters but you can check this when you open the tv.
A search in Google on those numbers will turn up a number of suppliers on ebay and elsewhere.

llondel
15th Jan 2018, 03:02
Powered it up while in bits and it ran! I know I've got to change the C's but for now I'll put it together for practice, thinks I. Bloody thing went wrong again, but worse. the C that's bulging shows 5v across it, and I kind of doubt it's just open circuit. Or, that being O/C would stop the thing turning on at all. Not even the power light by the switch. One will have to find one's thinking cap.

Being open may well stop it operating. The capacitor (at least the big ones) is used to store charge when other bits of the circuit can't supply it, so if the cap isn't there, it may deprive circuitry downstream of suitable power. (OK, a simplistic explanation.) the ones that die are usually in the power supply, so either it'll be a mains input capacitor (typically rated 400V) or one of the main reservoir capacitors on the low-voltage side. Cheap ones are rated for 2000 hours when operated at their limits of voltage and temperature, but will usually last a fair bit longer when run below maximum.

If you're unlucky, a capacitor going pop will develop an internal short and take out something else due to excessive current. You can also find that a cooking capacitor still works well enough to handle the steady-state running condition but has dried out enough that it can't cope with the switch-on surge, which is why very often something fails to turn on even if it was working a short time before. I have managed to run some to failure without switching them off, usually in computer gear that runs 24/7.

Pontius Navigator
15th Jan 2018, 07:40
Llondel, thank you for that explanation which explains what I learnt from experience. I used to manage a pair of computer systems that ran 24/7 but where it was normal to shut them down for the 2 week Christmas break. One or other would usually fault on start up. Final year I left them running. No probs.

UniFoxOs
15th Jan 2018, 07:52
Most modern kit of this type is powered by a switch mode power supply. These rectify the incoming mains to DC, which will be the 315V or thereabouts. (Technically it will be the mains AC voltage times the square root of 2). This is then reduced to the voltage required by the components.

Problem is, if you want to have the TV or whatever turned on by remote control, the receiver and control circuit must be powered on at all times. Hence the voltage when powered off but plugged into the mains.

Note that there is no transformer involved, and a lot of circuits do not possess a drain resistor to discharge the 300 plus volts when the unit is unplugged, so this voltage is available and feeds back to the plug and can give one quite a good "pisser" as we used to call them when I worked in electronics. So don't touch the plug terminals on a wired-in mains lead, and don't unplug the IEC connector from the back of, for example, a PC and then pick it up with your fingers curled round into the IEC socket, unless you want to throw it across the room.

PN - leave them running and the several components that have degraded will ALL blow when you finally cycle the power, instead of the one that blows on a weekly power cycle. Makes them a bu66er to fix.

PS Why doesn't my spell checker show bu66er as an error?

yellowtriumph
15th Jan 2018, 09:15
I'm not sure what the question is you're asking?

Is this the model you're working on?

https://www.manualslib.com/manual/685073/Lg-Flatronl1753s.html?page=1#manual

If you could tell us the component circuit reference number of the bulging capacitor it would help. How are you checking whether the capacitors are ok or not? You need something like an 'ESR" meter to check them, and one of those needs a fair bit of experience to interpret the results.

Loose rivets
15th Jan 2018, 10:57
Thanks y-t

C212 in an LG W1952TQ

Trouble is, I'm working on a tiny dining table in a borrowed house. My two lovely hobby shops are probably a thing of the past. I left my Tektronics scope in Texas - and indeed my best AVO8. Oh, and a pair of long nosed pliers, the first tool I purchased as a nipper. 7/6d they were. Oh, and most of the watches I've restored, but that's another story.

I removed the cap and charged it via my AVO8, and then reversed the contacts and watched my needle rise and fall. Only used 1.5 volts however as I'm too mean to buy the 15v battery and haven't got round to making one since DVM's are almost a disposable item these days.

It is bulging, so will have to be changed, but when it is running the voltage is ~5v across it. I see people sell the kits to replace all the caps. One even supplied the soldering iron. I can't quite imagine anyone that doesn't have an iron being able to replace these - and do the rebuild. Even I wish I'd taken more photos for the rebuild. I just can't see how the metal cover is held SAFELY in place. It seems to just need the screen to press onto it. Ugg!

I always loved fault-finding, but rebuilding tatty bits of metal and plastic is a world-class chore. Especially in cars. How the heck do you get into the dashboard of a Bugatti?

What I'm not sure about is the fact that there's no light by the power switch when it does go wrong. However, all the buttons are on a 6 wire harness - clearly low voltage control of the mains in.

When it faults up, it's just as though it's been unplugged. If I catch it faulty I hope it's when the 300v has been depleted, and then I can check if that voltage comes back before turning on.

Worse thing is it's lying on my spare slumberdown - and I'm in need of a nap. One of those naps that old people take to make their brains work again.

yellowtriumph
15th Jan 2018, 11:41
Thanks y-t

C212 in an LG W1952TQ

Trouble is, I'm working on a tiny dining table in a borrowed house. My two lovely hobby shops are probably a thing of the past. I left my Tektronics scope in Texas - and indeed my best AVO8. Oh, and a pair of long nosed pliers, the first tool I purchased as a nipper. 7/6d they were. Oh, and most of the watches I've restored, but that's another story.

I removed the cap and charged it via my AVO8, and then reversed the contacts and watched my needle rise and fall. Only used 1.5 volts however as I'm too mean to buy the 15v battery and haven't got round to making one since DVM's are almost a disposable item these days.

It is bulging, so will have to be changed, but when it is running the voltage is ~5v across it. I see people sell the kits to replace all the caps. One even supplied the soldering iron. I can't quite imagine anyone that doesn't have an iron being able to replace these - and do the rebuild. Even I wish I'd taken more photos for the rebuild. I just can't see how the metal cover is held SAFELY in place. It seems to just need the screen to press onto it. Ugg!

I always loved fault-finding, but rebuilding tatty bits of metal and plastic is a world-class chore. Especially in cars. How the heck do you get into the dashboard of a Bugatti?

What I'm not sure about is the fact that there's no light by the power switch when it does go wrong. However, all the buttons are on a 6 wire harness - clearly low voltage control of the mains in.

When it faults up, it's just as though it's been unplugged. If I catch it faulty I hope it's when the 300v has been depleted, and then I can check if that voltage comes back before turning on.

Worse thing is it's lying on my spare slumberdown - and I'm in need of a nap. One of those naps that old people take to make their brains work again.

I see, here is the link to the service manual:

https://www.electronica-pt.com/esquema/monitores/lg-esquemas-monitores/lg-w1952tq-lm-84b-4681/

However, it does not show the power supply PCB which I imagine is where you are trying to tell us C212 is positioned. Given that the manual does not show either the power PCB or make any reference to C212 I imagine the PCB must be an LG stock item that they used(d) in many models and it probably has it's own service manual.

Is there any reference number on the power supply PCB itself?

I think you are going down the correct route of changing any visually faulty electrolytic capacitors, and personally I would change the lot especially if you have seen a complete repair kit for replacing them. An AVO is not much good testing caps in a switch mode power supply - which is what you have. Youtube has some dis/re-assembly videos but on the one I happened to see the power supply PCB did not look like the one you posted in your picture?

Edited to add after a bit of Googling, Now i am really confused. You say the monitor is an LG model, but the picture you posted of the internals shows a Panasonic PCB. (Part number TNPA4677).

Loose rivets
15th Jan 2018, 13:05
Huh!!!

Fail mode. 300v still there. Screen ribbon disconnected and fine. Connect, and fail. Several times.

Trying to put this together was a pain. The ribbons really hard to get in and out without stressing them. Put other end in last to make it easier and found it was going without failing. Mmmm . .

Maybe it switches off if the screen data is cut. Maybe the second end of the ribbon was dirty and plugging it wiped the surfaces. Maybe pigs can fly, but I'm looking at it now, so fingers crossed.


BUT, a strange thing happened while I was testing it on my Sony Vaio i7. I'd always thought the Vaio picture was [email protected] and now the monitor was also showing the same symptoms. What's strange about that? Well, the poorness of the picture is related to the viewing angle. This little LG has never had that issue, but now, supplied from the laptop, it had. One is bewildered that a repeatable vewing angle issue can come down a wire. It's almost as though the unwanted 3D-ness of the picture is electronically generated.

Believe me, I've spent ages on that Vaio, and written it off as one of the reasons Sony has given up on Vaio. I've tried the Nvidia control, and 'Let other programs control your picture' modes. Total rubbish picture..

So, some strange viewing angle effect is capable of being ported. Beats me.

Back to the big telly issue . . . after a snooze.

glad rag
15th Jan 2018, 17:52
Loose be careful!

Having had a number of belts over the years [mostly due to working to maintenance practices written by coco the clown and enforced with here's your P45 in Silicon Glen] I really don't like messing about inside todays electronics for just the reason you have shown; good safety compliant design bypassed for the price of a resistor from china.

Pontius Navigator
15th Jan 2018, 20:15
Unifox, the cards were about 18 inch square. Emery paper on the connector solved many problems. I am not convinced that last week's card wasn't swapped back in the following week. Not my job,I was just the switch monkey.

ImageGear
15th Jan 2018, 20:30
Emery Paper on a connector? not unless it is a 25Kv industrial transformer. If the connector is either copper, silver or gold contacts, it would give intermittent problems forever. Best thing to use would be a proper grey rubber pencil eraser. Nothing more is necessary. The pins on a PSU inline connector can be popped out with the correct tool but it can also be done with a small jewellers screwdriver. Emery paper would bring about oxidation and subsequent intermittent problems forever. (Unfortunately CTC is no longer available for cleaning said contacts properly. (Well it was hazardous to one's health.)

Imagegear

Loose rivets
15th Jan 2018, 21:51
Now i am really confused. You say the monitor is an LG model, but the picture you posted of the internals shows a Panasonic PCB. (Part number TNPA4677).

Ah, I have that effect upon people. The problem stems from trying to impress a strikingly pretty lady with my ability to not only repair her car, but also her television.

This evening's television perhaps elucidates, uncomfortably clearly, why at least for me, Ulysses and the address, Sandymount, Dublin, makes my recent interconnection with this universe at least vaguely understandable. It is thanks, more than a little, to Pprune members that I have this knowledge.

All of the above is said with a pronounced Irish accent.

I suppose I could have said, 'Ah, I have that effect upon people' Irishly, and left it at that, but it would not have explained how I, the son of a pig breeder - and that's on my marriage certificate thanks to my mother's feelings towards the man that left her with a little brat - could possibly know about matters electrical. Her father, Matthew, born in Sandymount in 1873 to the son of a Dublin handyman, was the GM of the Middleton Electric Traction Co before he was 30. I think I have that electrical wizard to thank for my understanding of smoke needing to be contained in electrical circuits - though I suspect he would have been perplexed by the tinyness of systems that control . . . systems, and the systems that they control.

I sometimes think it's better to let some of the smoke out, along with long magnetically curved sparks, when controlling large quantities of amps. But I digress. Perhaps, just a little. :}

The monitor is relaying the very essence of my thoughts to my neural networks this very moment, so it is the pretty lady's Panasonic television that will now make demands on my tediously diluted intellect, with no hint of reward you understand.

But that aside, it's odd that I had just been thinking of James Joyce, not 24 hours before seeing tonight's program about him, and am in my cups imagining what it would be like to be a real author. I'd downloaded Ulysses some months ago, but like many, or perhaps most, I'd promised to read it in small stages throughout the remainder of my life but had failed on that schedule. But now I'm resolved to put smoke, and the devices that contain it, on hold, and go back to the Martello Tower just south of Dublin, and a delightfully strange conversation .

yellowtriumph
15th Jan 2018, 23:40
Ah, I have that effect upon people. The problem stems from trying to impress a strikingly pretty lady with my ability to not only repair her car, but also her television.

This evening's television perhaps elucidates, uncomfortably clearly, why at least for me, Ulysses and the address, Sandymount, Dublin, makes my recent interconnection with this universe at least vaguely understandable. It is thanks, more than a little, to Pprune members that I have this knowledge.

All of the above is said with a pronounced Irish accent.

I suppose I could have said, 'Ah, I have that effect upon people' Irishly, and left it at that, but it would not have explained how I, the son of a pig breeder - and that's on my marriage certificate thanks to my mother's feelings towards the man that left her with a little brat - could possibly know about matters electrical. Her father, Matthew, born in Sandymount in 1873 to the son of a Dublin handyman, was the GM of the Middleton Electric Traction Co before he was 30. I think I have that electrical wizard to thank for my understanding of smoke needing to be contained in electrical circuits - though I suspect he would have been perplexed by the tinyness of systems that control . . . systems, and the systems that they control.

I sometimes think it's better to let some of the smoke out, along with long magnetically curved sparks, when controlling large quantities of amps. But I digress. Perhaps, just a little. :}

The monitor is relaying the very essence of my thoughts to my neural networks this very moment, so it is the pretty lady's Panasonic television that will now make demands on my tediously diluted intellect, with no hint of reward you understand.

But that aside, it's odd that I had just been thinking of James Joyce, not 24 hours before seeing tonight's program about him, and am in my cups imagining what it would be like to be a real author. I'd downloaded Ulysses some months ago, but like many, or perhaps most, I'd promised to read it in small stages throughout the remainder of my life but had failed on that schedule. But now I'm resolved to put smoke, and the devices that contain it, on hold, and go back to the Martello Tower just south of Dublin, and a delightfully strange conversation .

I think I'll bow out at this point.

Loose rivets
16th Jan 2018, 00:50
Oh, that's a shame, but remember this is Jet Blast and not the more sensible Computer section.

I like to think one can, and indeed I know they can, find the information they need while havin' a larf.

I'd like to think that one day I could emulate Davaar, though I'm going to need a lot of practice still.

One member wrote of Davaar, I love his posts. I don't know what the hell he's talking about, but love them. (something like that.)

Rossian
16th Jan 2018, 17:33
...... following Mr Joyce can take you down some very strange paths. "The Dubliners" is a rational mind at work, "the Artist as a Young Man" gives a few clues as to what is coming, "Ulysses" takes you into some of the stream of consciousness crap that some posters seem to produce at will, but for God's sake don't go to "Finnegan's Wake" in your present state - that way lies the final descent into insanity.
You have been warned!!

The Ancient Mariner

flash8
16th Jan 2018, 19:54
I don't know much (about anything..) but the old Servers I bring back to life from the 1970's (mainly PDP-11) usually have capacitor issues as the first port of call. Even 10 year old Motherboards that have failed Caps are the first place to look!

Once I blew a cap due to overheating (1U Modern Server was under my bed as it was very noisy and therefore didn't have adequate ventilation) ... heard a loud pop and smoke came from server... which still kept on running!

Loose rivets
16th Jan 2018, 21:34
but for God's sake don't go to "Finnegan's Wake" in your present state - that way lies the final descent into insanity.

Ah, oim thinking it is too late. Erm, to be sure, to be sure. My written Irish is not a patch on my granfather's - a snippet from a letter so well received that it was published in the local press:-


“Out here we have been having some stirring times. Our brigade’s baptism of fire came about quite early, and was a very impressive ceremony.
Herr Bosch’s pyro display on the occasion and during the week following was, we thought, rather startling, but presently our guns had a few words in the matter, and quelled the ructions . . .

Caught in bright moonlight between fronts.


. . . I clung to the soil of Flanders as if it had been a bit of “Ould Oireland.” whilst the Bosche’s bullets chirruped over us. Had our first officer—Lieutenant Maude—killed yesterday. Those snipers shouldn’t be given a chance by exposing oneself, as on both sides they make few mistakes".

Having had the skin taken off his nose by a sniper, I imagine it concentrated his thoughts on the matter.

A different reality, though I'm no longer sure what reality is - or of anything really. Capacitance works in the vacuum of space, whatever that might consist of. I'm strongly biased towards Quantum Loop Gravity, though I'm not sure how this would produce the Casimir effect. But back to capacitors and the material reality we think we live in.

It was thanks to Pprune that I changed the caps surrounding the CPU on my last motherboard. It cured the fault, though probably took a computer's worth of time cleaning the holes through a four layer motherboard. The new caps were advertised as immortal but as a result were so fat that the bunch took up 150% of the available space. Determination, and no regard for aesthetics, is what it took.