Playing with crt's

[dr pepper]

I was planning on making this crt a vector monitor controlled by a pic, the issues are the bandwidth and feedback arrangement of the deflection amps and the fact that tv crt's are not linear on one side, current amps pretty much negate being able to use the original linearizing choke, maybe a diode/resistor on th ei/p might correct it, might just try it as is and see what its like.
I just bench tested some tda2050's, into an resistive load I get over 100kc's, not sure how thats going to be into a yoke coil, might not even be stable.

Back to burning tubes, apparently atari vector monitors have been known to blow holes in the mask, pretty serious amount of electrons.

 

[Nigel Goodwin]

Back to burning tubes, apparently atari vector monitors have been known to blow holes in the mask, pretty serious amount of electrons.

If left on high brightness for an extended period it would certainly damage the shadow mask, it's only a very thin piece of metal, and 30-40W of energy on a small area will soon overheat it.

 

[dr pepper]

Well at least theres a safety mechanism, if the electrons burn a hole in the glass the loss of vacuum would stop emmision before it burns a hole in someone :-(

 

[dr pepper]

Well having got the beam to burn the tube I moved on to deflecting it.
The vertical coils were ridiculously high inductance and because of that very slow, so I have removed the stock 900 turns and wound on bifilar 100 turns, this gives me a combined inductance of 400uH, with a tda2050 driving the coil in current feedback mode I get full scale deflection at 8khz with a +-25v supply.
Horizontal is a little bit slower.
When my 2 dacs show up in the post I'll write code to display a square box and see how it looks, looks probably not going to be fantastic.
I read somewhere that putting the 2 sides of horiz or vert coils in series instead of stock anti parallel decreases inductance and speeds them up, how does that work then?, I thought chokes in series increased the inductance, or is it some mutal inductance thing.

 

[Nigel Goodwin]

The vertical coils were ridiculously high inductance and because of that very slow

That's because they are designed to work at 50/60Hz

 

[dr pepper]

Yes probably lot ofwindings for efficiency.

 

[dr pepper]

Well I used my 'scope clock as an xy source for the monitor.
This shows the importance of slew rate, the x defelction amp blew up si I replaced the dead tda2050 with a la6500, the latter only has 0.1v/us slew rate, and you can tell as the dots that represent the hours are just wiggly lines.
The colours are washed up as here the tube is running without the convergence and purity magnets, the deflection module probably isnt in the right place either, but it shows it doesnt take that much for an xy monitor to work, just the blue cathode is connected.
The out of round bottom left is dues to a magnet missing on the cover of the deflection coil pack.

 

[dr pepper]

I connected up a tda7265 stereo amp to the xy coils and it is much better.

However as th epic shows I get squiglles at 12, 3, 6 and 9 o clock positions, I think this is due to cross talk, at these positions one of the axes has just gone to zero and the other to max, I suspect that the coil that has gone to zero is ringing and the ringing voltage is being conducted to the other axis.
Might be due to the layout being breadboarded.
There is 47 ohm resistors across the coils to damp ringing

I'm going to try dc offset, then maybe connect the amp i/p's to a square wave and 'scope the coils to see what going on.

 

[dr pepper]

Sorted now, the squiggles on 12,3,6, and 9 are sposed to be there, they looked wrong as the correction magnets being missing is messing up the screen making them look like errors, they look ok on my 'scope in xy mode.
Fair amount of warmth from the stereo amp, but when you look at the size of the 'sinks on a amplifone vector monitor it makes sense, the amplifones are hooge.

The text actually looks really good, just like 70's arcade vector graphics.

Might bash this into a bit of ply to hold it, and work on a pic program to show some graphics, maybe the intro screen from night driver.

 

[dr pepper]

Probably a question for you nige.

I marked up the yoke and the convergence magnets assy and put them back the same, however some magnet looking stickers fell out between the yoke and the tube, and now all back togther I cant get the convergence to be correct all across the screen.
I have a vague recollection of convergence strips, bits of tape with some kind of metal on the end, you sort of shove them behind the yoke till the colours look ok.
Couldnt find any on ebay, can I make some of these?

 

[Nigel Goodwin]

I marked up the yoke and the convergence magnets assy and put them back the same, however some magnet looking stickers fell out between the yoke and the tube, and now all back togther I cant get the convergence to be correct all across the screen.
I have a vague recollection of convergence strips, bits of tape with some kind of metal on the end, you sort of shove them behind the yoke till the colours look ok.

Presumably it's a PIL tube (Precision In Line)?, they are assembled and aligned in the factory during manufacture, and there aren't any adjustments - the scan coils are supposed to be permanently bonded to the tube.

The only CRT's (in anything remotely 'recent') that required alignment were the Sony Trinitron tubes - which weren't PIL, and required complicated setting up, including tiny magnets on strips which slid inside the scan coils.

 

[dr pepper]

It has 3 gun sinline, like old sets had and I think thats how trinitron were isn tit, but the set is less than 10 years old.
There is 6 rotating convergence magnets and what looks like a purity magnet at the back of the tube, and there were half a dozen white strips stuck to the scan coils I just checked they have ferrous bits of cheese stuck to them.

Having just degaussed the tube the colour is now all blue as it should, so maybe running it a few times without magnetized it, I did have dc through the coils on more than one occaison.

 

[atferrari]

Hola Dr P,

This thread of yours sparked my interest. I had no idea how a CRT was driven.

Found two (possibly too dated) application notes, 861 & 656 from National Semiconductors, where I could start understanding something of what is being discussed here. Interesting.

 

[Nigel Goodwin]

It has 3 gun sinline, like old sets had and I think thats how trinitron were isn tit, but the set is less than 10 years old.

Not quite - 'old' sets had delta tubes, in-line were the more 'modern' types - and after a fairly brief spell of requiring alignment became PIL tubes, which needed no alignment. As I mentioned, the sole exception was the Sony Trinitron - which presumably wasn't able to be manufactured as a PIL device?.

The first PIL tubed set in the UK was the Thorn 9000 series, yet another ground breaking set from Thorn - not only a PIL tube, but also a 'Cyclops' circuit - utilising the same transistor for both PSU and LOPT. It also had the most advanced SMPSU up to that time, allowing a huge voltage range of operation.

 

[tvtech]

Hi Nigel

Some proper "Telefunken" sets also used the Cyclops design....TX805 chassis comes to mind. Original S2000 was the chosen switching device.

Waay later then Thorn though. Thorn always innovated...and others followed. And improved.

As far as I can remember, Thorn is an innovative Company that has always lead from the front

Regards,
tvtech

 

[Nigel Goodwin]

Hi Nigel

Some proper "Telefunken" sets also used the Cyclops design....TX805 chassis comes to mind. Original S2000 was the chosen switching device.

Don't know about 'proper'

The TX805 was a Ferguson (Thorn/Thomson) chassis - after Thomson had bought Ferguson out

Nothing 'Telefunken ' about it, presumably Ferguson technology with the Cyclops type design, following many years of Thorn TX chassis.

https://english.electronica-pt.com/electronica-search?find=TX805

Waay later then Thorn though. Thorn always innovated...and others followed. And improved.

As far as I can remember, Thorn is an innovative Company that has always lead from the front

Unfortunately 'was' not 'is'

 

[dr pepper]

So this no mark set tube presumably is a trinitron then?
It did have stuck on magnets, not on the tube, on the scan coil pack, I dont know where they knew to stick them, unless the scan coil pack was checked on another machine first and setup, its just hose clamped to the tube.

I'm able to get pure blue now at least, and it looks like all the non linearity has come out positioning the horiz and vert coils, I expected a lot of pincushion, but there doesnt seem to be a lot, maybe its due to only a 14"screen, that said I dont have means to check an xy monitor, I'm thinking of a simple square shape generator using a 4017.

AT if theres any help you need playing with crt's just shout, I mananged it and I've never messed with them before.

 

[tvtech]

Hi Nigel

Some proper "Telefunken" sets also used the Cyclops design....TX805 chassis comes to mind. Original S2000 was the chosen switching device.

Waay later then Thorn though. Thorn always innovated...and others followed. And improved.

As far as I can remember, Thorn is an innovative Company that has always lead from the front

Regards,
tvtech

I know Nigel. I just chat here with you and Spar from time to time. So nice to know that I am not the only one that has walked that long road.
My road is longer than yours though..

You know...I am wearing out. Impossible under these circumstances...

I am not a Machine that is meant to be hammered day in and day out with fixing other peoples broken stuff....

Eight Years is a lot considering where I am.....no enjoyment..no fun...no life.
Work, work, work. And the posting here.

So, as a tvtech, a hard road....

For the record here in Africa....Stupidity and ignorance is a killer.....as a white person who is honest and treats black customers fairly...

They KEEP COMING BACK. I WANT THEM TO TAKE THEIR TV'S AND STUFF TO THEIR OWN PEOPLE FOR REPAIRS AND LEAVE ME ALONE.

FFS..How easy is that????

Sorry for shouting.

That's how I feel about this mess...that I work my Butt off fixing rubbish that they never cared for anyway.....

I have been asked numerous times to put up a FB page by friends. I have alienated them by rather choosing to help the "customers here".

Has it been worth it = no.

At least I know now after Eight Years in this Crappy place where Spiders bit me, crappy place....not worth it.

You guys think you have seen it......

I kid you not.

And that as tvtech is all I have to say

Huge rant.

Regards,
tvtech

 

[atferrari]

AT if theres any help you need playing with crt's just shout, I mananged it and I've never messed with them before.

Always scared by the so many warnings about HV in CRTs , I never messed with them, and now, I think is a little late to start. Aren't they vanishing from Earth? It seems that I always try to catch up with old techniques.

Gracias anyway.

 

[dr pepper]

There are still 100's of 1000's of them, allthough they are on the way out, there are places that do nothing but re-process tv tubes.
There is still plenty of time to play if you like.

The hifgh voltage fear is healthy however, I have been zapped from a flyback, not that bad, but when itsattached to a tube which is effectively a capacitor its much more deadly, but so long as you earth out the ht before you unlplug the anode cap its not so bad.

Pulling telly's apart takes me back to being a kid.

Hey Tvtech there is a solution, put your prices up just a bit, one of 2 things will happen, your customers will stop comming back as much which is what you want, and if they do keep comming back you'll have more beer money.
Its very difficult in the uk to find anyone that will be straight with you, most just want your readies these days.