Author Topic: You can always try the hard way first.....  (Read 12766 times)

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Offline oztules

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You can always try the hard way first.....
« on: February 23, 2012, 04:16:31 pm »
This is a rehash of a time where in the the remote isolation, you decide to have a go just to see.... Not what a sensible person may do.

Those of you who have a reasonable electronics background may not want to see this, or it may cause nightmares for the rest of your time.
Enjoy if you can....

=====================================================================

Sometimes people expect you to do what appears to be simple to them, but is a problematic to me.

If you can load batteries into a torch, you obviously know all about electronics and can fix anything with a switch on it.....

Where do they get these ideas.

I'm posting this, just to give some hope to older fogies like me who have done limited electronic trickery in their time as a hobby..... and get tired of all the new fangdangled electronic thinggies... and how they are built, and how are you gonna fix em when they fail....

So.....
A sorry looking local looked me up, and asked if I would look at his computer screen. I figured it was a CRT type, and accepted the challenge. Yes I said, figuring if it wasn't the EHT transformer, I had a better than fair chance of fixing it.

The owner and the screen dutifully turned up and it turned out to be a very new looking 20 odd inch LCD device. I went cold to the core... cursed things, I bet they use those hard to see and even harder to get hold of surface mount bits and pieces. I was about to tell him to take it to the tip as I didn't feel too confident about it at all, but before I could get it out, he couldn't help but tell me that.... so and so said I could do it no problems etc. etc.

I was cornered by local legend and vanity.... egad.

Well, I shuffled off to the shed with it, mumbling things about Gordon and his proclivity for surface mount things... and anyone else who encouraged them....

I figured that at least the power supply would be through hole, and probably the fault would be there, and barring exotic components I didn't have, we'd still carry the flag.... Most of the satellite decoders, dvd players etc so far have through hole power supplies, and surface mount after that....we live in hope.

Electrolytic capacitors deserve special mention. They are built to fail.... and do with monotonous regularity..... maybe thats the cause in this case......just them.... if so, an easy fix may be on the way.

It took ten minutes to find out how to open the damn thing. What ever happened to a few well placed screws. It was all very cunning... but with patience and good management (and a few swift thumps), it came apart.

I didn't take any photo's at this stage, as I didn't think it would ever go again. The blown fuse, and black smoke marks across the board almost encouraged me to put the cover back on and call the owner..... but I just couldn't help but look in wonder at all the little bits and pieces too small to see almost, and marvel at how they must do these things.

Well, we'd gone this far, so how does it work anyway.

Popping off the screen and wiring harness to it, we find this...... the screen carries a mountain of very intricate whoop arse looking gear, and I ain't ever tackling that. All made in China by robots... no person could hope to do it.

 593-0

Actually, the bottom of one of those boards has been butchered, as this is after the ordeal, not before....

My heart sank, as I didn't recognise any of those little bits as normal stuff. I pulled off the top board, and cheered up some.... there was at least some through hole bits to look at:
594-1

You can see that there has been a fair amount of butchery there too... no before shots I'm afraid.

The black marks have been cleaned up some. The Fet was blown up, the fuse was blown, and ...... where was the PWM chip.....

The PWM chip was one of those cursed surface mount things...yes, on the hard to see side of the board and surprise surprise, 320v going through one of them just leaves a smudge and some leads and burnt plastic.

Things looked grim about now, and I vowed to look at it some time later, and tipped all the bits back into the rear frame and let it sit for a few days... and then some.

Some days later, I decided to trace out the tracks away from the 8 pin pwm site, to see if I could guess what the part may have been. The 320v from the rectifier went straight to the chip.. pin 8 in fact. This told me that the chip was one of those "greenie" chips, which used the HV to bootstrap direct, and then turn it off and run from the tertiary field, rectified and then used as vcc... pin 6?. Output was pin 5, ground pin4 and feedback pin2.... etc. This narrowed it down.

The second green pwm chip I researched was an ld7575... and it matched pin for pin. I was shattered, I couldn't track one down anywhere.... I needed a plan B.

Looking at the data sheet for the 7575, we find a typical simple flyback circuit looks like this :
* 3.jpg (14.93 kB. 500x261 - viewed 3360 times.)
I did another quick trace, and whilst it wasn't the same at all, it sported an opto isolator, transformer with tertiary winding... and well.....that was enough bits to make a supply with.

I grabbed the trusty 3842's  (pwm chip) out of the box, and proceeded to graft it onto the board... this was the tricky bit. Their entire PWM was built on the surface mount side, and 20 odd components used less room than a postage stamp.... what to do.

The big smoothing capacitor took up a lot of real estate on the top side of the board, so I resolved to use this space, and put the capacitor elsewhere.... anywhere..and a few (what I felt) unnecessary components were turfed out all together.

It now looks like this
596-3

You can see the capacitor was prized off the board and repositioned (where some other stuff used to be), the bridge was moved back a bit, and the 3842 through holed into a socket... (not very confident are we??). A few more holes and a few bridging wires, and we have half of it built. On the other side it looks just as woeful:
597-4

I scratched all the surface mount stuff off the board with a razor blade, and scratched all the tracks off as well. With some filthy soldering and slapping the bits on, I was finished. I replaced the Fet from out of a computer monitor from the tip, and last but not least, I wired up a rudimentary bootstrap circuit (80k resistor and 18v zener)......The bootstrap is the two messy looking resistors between the transformer and the fet.

598-5

After this, the tertiary should take over..... and it didn't. The 3842 I had (gotten cheaply from Rockby) didn't turn on until 16v... and the tertiary winding was only 12v...dammit... 16v wins, and the tertiary doesn't get a look in.

I'll worry about that later, the bootstrap will carry it until we find out if the rest of the thing works.

It was modelled around this circuit here:

599-6

Obviously were running it at 320v not 17v... but close enough...

Well it was time for the quick check around the board to see if all was well..

3 electro's were down from 1000uf to about 50uf. This is what appears to have o/loaded the fet which then blew everything up.replaced these and moved on to the 2000v screen supply PWM.... surpirse suprise.

At least this although surface mount, used a surface mount tl494... home territory. I used a 14v supply to mimic it's input voltage. The oscilloscope showed the oscillator was functional, and by driving the dead time pin down, the 2000v hissed into life for a few seconds. I tracked down who was turning me off, and bypassed that (the computer on the other board controls this chip for brightness, sleep etc.)... satisfied with this.... it was time to switch on.... and I was greeted with this.....

600-7

Feeling pretty smart about life now aren't we.......... and then it went blank...and then the panic sets in, I go over it all , and all seems fine. Switch it on, and it works and stops again.

These smart damn machines, I had forgotten to give it some video drive, so it switched itself off after 20 seconds.... nothing wrong at all perhaps.

I had found an old laptop at the tip....
601-8

After fixing it up (idle Fet), and tossing aside the screen/lid, and cleaning it up,  ( yes that is it in it's cleaned up state), loaded up some software (Linux Ultimate2) and tried again.... this time it was all different..... but we will have to start another section as we have used up 9 pics thus far
Flinders Island...... Australia

Offline oztules

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Re: You can always try the hard way first.....
« Reply #1 on: February 23, 2012, 04:26:58 pm »
Well pic three didn't work
602-0
Flinders Island...... Australia

Offline oztules

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Re: You can always try the hard way first.....
« Reply #2 on: February 23, 2012, 04:31:59 pm »
Just to see how it looks when it has drive.....

603-0

And for more busy stuff on the screen.... like this:

604-1

So, there is hope for those Neanderthals out there, who like me rue the passing of valves, and then sort of rue the passing of transistors.... and are less than impressed about the surface mount stuff.... if you stick to your guns, and smash out some extra space... we can still fix somethings.

But for how much longer.


Now I'm not sure if I am allowed to do this.... so wolv kill it if not... but Dinges gave the following comment on it...it's apt I think.

Dinges
"You know how occasionally when driving you see a bit of roadkill lying on the road in the distance? And as you get nearer you think to yourself that you shouldn't watch all that blood and gore? And that you then decide not to watch it, but will look straight ahead ignoring it? And that when you are getting really close to it you can't help but watch anyway? And how, as you are watching, you already regret doing so?

That's how I felt reading this post....

Some of the pictures in this story will be etched into my mind till my dying days. The stuff of which nightmares are made - the kind where you wake up in the middle of the night, soaked in sweat, screaming for mercy.

There should be laws against such butchery. Once convicted, said persons should be forbidden to ever own a soldering iron again, or come within a 50m radius of one, on pain of banishment to a remote settlement - Van Diemensland or one of its islets perhaps?


Peter. (dreads to think what mischief Oztules could achieve with a crystal, a PL504 and a transformer) "


He says it all really.



.....................oztules

Flinders Island...... Australia

Offline Wolvenar

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Re: You can always try the hard way first.....
« Reply #3 on: February 24, 2012, 12:25:40 am »
Oh I remember that background image , ubuntu ultimate edition!!

BTW..
I dont consider this you and Dinges called  "Butchery" a bad thing.
It's many times a way of life for some with the skill, but for whatever reason lacking resources or funding..
Its also a crucible of/for discovery..

I love stuff like this, and do my share of it... now where did I put those pics like that  ::)
Trying to make power from alternative energy any which way I can.
Just to abuse what I make. (and run this site)

Offline Norm

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Re: You can always try the hard way first.....
« Reply #4 on: February 24, 2012, 11:26:01 am »
I'll go along with you W.....
What the heck....it was broken anyhow ?
Norm.

Offline ghurd

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Re: You can always try the hard way first.....
« Reply #5 on: February 24, 2012, 04:02:26 pm »
"a mountain of very intricate whoop arse looking gear"
is exactly the moment I snap the cover back on and label the item "unrepairable".

Nice job on the repair!
It looks fine to me.
Always looks better with the cover replaced.
G-

(PS- Tell Peter "Click... Click...")

Offline Wolvenar

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Re: You can always try the hard way first.....
« Reply #6 on: February 24, 2012, 04:28:31 pm »
Similar experience , but no hacks needed

The black capacitors needed replacing.. It is a common problem in this set. It is also a VERY poorly designed power supply. I have had to replace these caps twice now. The next time around I will be redesigning this circuit. These caps are a bit on the limit of what they should do.





And back to life.

Trying to make power from alternative energy any which way I can.
Just to abuse what I make. (and run this site)

Offline oztules

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Re: You can always try the hard way first.....
« Reply #7 on: February 24, 2012, 04:52:12 pm »
Ghurd:
I almost recollect that it was a number between 2 and 4 ..... or three to be more precise ;D

Do Gas caps in the northern hemisphere go anticlockwise to click ? :)... click click click.


Nice one wolv.... caps are a pain in the bejeezers. Good to get to them before they stress the power switches... and bang.
Some of the power inverters I have had to work on have huge banks of caps.... and I always look at them as an accident waiting to happen..... but what the heck, they work for a good while generally.

I have had some success about a year ago..... the wives 60" telly went on the fritz.... serious problem here... she lives for her telly.
.....
It had a ballast board to drive the HID projector globe intergrated into the computer.... Didn't know if it was the globe or the board or the computer control... so with the bits from an old florescent tube body,and the ballast transformer from it as well, I made a makeshift HID driver. It proved the board was at fault.
Funny thing is the home brew one is still in the tv, as it works so well, and she runs it for 12hrs a day..... so by choosing the ballast tranny to be a bit smaller I have pulled the wattage usage from 120W down to about 95 total W.... and she hasn't noticed.. te he he. Uses the neon from the starter with a cap and bits to make the 6000v for startup.

Never know what you can do till you have an angry wife wanting her telly fixed.

And I now have a spare new board for it that will never get used. >:(

....................oztules
Flinders Island...... Australia

Offline tomw

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Re: You can always try the hard way first.....
« Reply #8 on: February 24, 2012, 05:43:35 pm »




Nice video capture from "The Fifth Element"! ;)

Tom
Do NOT mistake me for any kind of "expert".

( ?° ?? ?°)


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I thought that they were angels, but much to my surprise, We climbed aboard their starship and headed for the skies

Offline Wolvenar

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Re: You can always try the hard way first.....
« Reply #9 on: February 24, 2012, 06:13:36 pm »
Oz Is that a DLP TV you were describing?

I have a nice projector here that one day I have to troubleshoot.
I am almost sure its in the high voltage supply, as I replaced the bulb.
It will fire the bulb for a split second a couple tries over, then go into shutdown.


Yet another TV repair I did some time ago if you have not seen it.
http://www.anotherpower.com/board/index.php/topic,12.0.html

I should get some images of my first *major* electronics related project where I built an entire old style console television set,
woodwork and all .
--<edit>---
This tv was built in about 1993.. before that I guess I had done minor cb radio repair, and gotten my first b/w TV from a scrap pile and fixed a couple minor solder issues with it in 1986.. ( yeah anyone knowing my age might wonder about that, but its true. )
--</edit>---

I have repaired more televisions now than I care to count   :-\

Again, seems a lot of us are electronics nuts.

Tom, yep nice catch. One of my favorite movies.
Trying to make power from alternative energy any which way I can.
Just to abuse what I make. (and run this site)

Offline oztules

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Re: You can always try the hard way first.....
« Reply #10 on: February 24, 2012, 07:28:54 pm »
Hi Wolv
It is an SP-61L2HX, Widescreen Samsung

The symptoms you describe are saying ballast board in bold letters.

When the computer starts the globe up, it waits for a power good signal (+5v for mine). If it does not get this signal, it will shut down, and after a few attempts, shuts right down.

If you fake the power good signal, it will run until the globe itself shuts down... (something HID does on it's little ownsome when it is pushed too hard... don't know how this happens... magic ) . My bet is yours is over driving the HID and it knows it.. so the ballast shuts off as it is outside limits preset in the on board cpu.

mine look like these two units ( old and new (but not used):
610-0
 Instead  replaced the shot one with two of these 40 watters:
611-1

If you do do this, you will need to fake the power good, and put in a relay to turn the HID on and off  when the computer says so. ( i used a transistor and relay for on off from the  computer. 240v or 110v from the power input to the relay to drive the HID and ballast. Use a neon in parallel to the globe .. seriesed with a capacitor.

On start up, the HID is high impedance, so the cap will drive the neon to flash. When it does it will also generate a high voltage pulse in the ballast, and that ignites the HID. It will then become very low impedance, and the ballast will current limit it.

One drawback is if a power interruption occurs, the globe will not ignite while it is stinking hot. It needs a few minutes to cool before restart.
If it had 28000v startup, then hot start is no problem..... 6000 gets it going while it's cool.

But your sounds like hundreds of others... the ballast mucks up after a few years, the iron ballast will last a very long time.
Would be nice to see your pics of the old TV.

Edit: I am considering trying a 12v car HID and ballast, as they are dirt cheap, and see if 50w will do for night viewing. (only use the biggy at night). Will have to wait another few thousand hours for this globe to fail first though. The plasma gap is very small in these projector types to get a sharper image, ( light seems to all come from one point) The car HID are a longer arc, and may have less resolution.... we'll see.


...............oztules


"Again, seems a lot of us are electronics nuts."....... no just one of us is nuts, but I have fun anyway ::)
Flinders Island...... Australia

Offline ghurd

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Re: You can always try the hard way first.....
« Reply #11 on: February 24, 2012, 09:27:46 pm »
I almost recollect that it was a number between 2 and 4 ..... or three to be more precise ;D

Do Gas caps in the northern hemisphere go anticlockwise to click ? :)... click click click.

That why the "..." after only 2 clicks.
Very impressed anybody would remember that banter from so many years ago.

Hemispheres related to the proper direction of clicking?
I can't say for sure. 
It gets complicated, especially with the conversion from the real number 3 to the metric equivelent of the number 3.
I am in the nothern hemisphere.  You are in the southern hemisphere.  I am in the western hemisphere, while you are in the eastern hemisphere, my Toyotas were either designed or manufatured in either the eastern or western hemisphere, and Peter is so very close to the Prime Meridian, that I am not sure if clockwise or anticlockwise would have the same meaning in this situation.

BTW, I am impressed you guys will put forth so time and much effort to fix them.
Habitat For Humanity's 'reuse' stores (donated used stuff) have flat panel TVs for $40 or less, flat panel monitors for $15, and they can hardly give away a CRT unit.  The disposable economy based on sending all the money to China or OPEC saddens me.
G-

Offline Wolvenar

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Re: You can always try the hard way first.....
« Reply #12 on: February 24, 2012, 09:56:47 pm »
I never find those kind of deals around here.
 
Our local thrift stores are run by not for profit and employ disabled. They always get first shot at that kind of stuff, so it is very rare any will get out on the shelves. Surrounding towns have different reason and people, but similar circumstances, where the employees get first shot, all in an area that 95% have incomes that are considered well under what the gov. considers poverty.
 
Normal CRT you see on garage sales offered for free.. but LCD and anything considered a large screen carry a prime $ tag.

Trying to make power from alternative energy any which way I can.
Just to abuse what I make. (and run this site)

Offline oztules

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Re: You can always try the hard way first.....
« Reply #13 on: February 24, 2012, 10:21:40 pm »
Certainly not like that here either.... but thats to be expected.

Ghurd, that rotten telly cost me $8000 about 10 years ago. I have nursed it along, and it has to run for another 40 years to get any value out of it at all I reckon. However the boss insists on 60 inches as a minimum for her viewing pleasure.... even though she's asleep most of the time it is running....... don't ask, I just obey ;)

That being the guide lines I have to work within, no other technology uses so little power for such a beautiful huge picture.... and I will see if I can get it usefully less.... maybe  40- 60w??? The latest 60" leds are $3000, and use <160W... bad both ways. (plasma 500w but cheaper)...

I can now buy these things on ebay for $100 not working..... but it costs the earth to get them over here in 1 piece.... so I bought 2 for $110, and got my son to pick them up, pull the boards out of them and send them over.... this darn thing will work for a long time to come.... and the worst component.. the ballast is solved.
The main supply does not drive much power at all now, as the DC supply to the ballast is no more... now it is straight AC, so if I replace the caps on the spare boards... chances are it will work for a long time to come.

Great plans can always come undone in spectacular fashion.... but this time I think I'm doing ok.



....................oztules
Flinders Island...... Australia

Offline ghurd

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Re: You can always try the hard way first.....
« Reply #14 on: February 24, 2012, 11:36:29 pm »
I never find those kind of deals around here.

Last time I was at the reuse store, I almost bought an "all-in-one" 15~17"(?) CRT TV with built-in VCR and DVD player for $10?
Plenty of generic LCD 'puter monitors in the 19~21" class for cheap too (not powered up, so maybe had defects).

They also had 20% of damaged leftover $3 P-Trap parts priced at $5, so it could be the pricing person at that place has no idea what he is dealing with.

don't ask, I just obey ;)

Great plans can always come undone in spectacular fashion.... but this time I think I'm doing ok.

Understood.
And I think you are doing just fine.

G-