NBTV Television Analyst

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Re: NBTV Television Analyst

Postby Steve Anderson » Wed Apr 29, 2020 4:31 pm

Harry, I suggest you stop for the day. I'm trying to put together an explanation how this all works, but it may take me some time...

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Re: NBTV Television Analyst

Postby Harry Dalek » Wed Apr 29, 2020 4:39 pm

Steve Anderson wrote:Harry, I suggest you stop for the day. I'm trying to put together an explanation how this all works, but it may take me some time...

Steve A.


Ok wait til i hear back ...
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Re: NBTV Television Analyst

Postby Steve Anderson » Wed Apr 29, 2020 7:53 pm

Right, here goes...

First we'll remove the opto-coupler, transistor, CRT and R905.
Breakdown 1.gif
Breakdown 1.gif (4.77 KiB) Viewed 1270 times

Next simplify the three resistors and one pot at the top of the drawing into a single resistor. You can forget the focus current, it's just a few micro-amps.
Breakdown 2.gif
Breakdown 2.gif (6.89 KiB) Viewed 1270 times

From this we can work out the voltages and the chains current draw...some components are at high voltages, but that doesn't matter, it's the voltage the device 'sees' that counts.

Part 2 next. Any questions so far?

Sorry about the text..nothing I can do about it really...no, I'll start over, but have a look at the above...Text problem fixed! Quickly too!

I've rounded the numbers to integers to remove the rather useless decimals.
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Re: NBTV Television Analyst

Postby Harry Dalek » Wed Apr 29, 2020 9:08 pm

Steve Anderson wrote:Right, here goes...

First we'll remove the opto-coupler, transistor, CRT and R905.


OK baby steps

Ok high voltage negative in one end ground the other a circuit in action ...the zeners and diode used to drop the voltage so the 75 v zener drops the 1520 by 75 volts or around that i see that in the readings ..the diode used as high ohm a resistor ?and a further 5 volt drop with the other zener ...thats what i am thinking ,so this circuit would have the crt on full on i am thinking with this circuit as is .

Breakdown 1.gif

Next simplify the three resistors and one pot at the top of the drawing into a single resistor. You can forget the focus current, it's just a few micro-amps.
Breakdown 2.gif

From this we can work out the voltages and the chains current draw...some components are at high voltages, but that doesn't matter, it's the voltage the device 'sees' that counts.\
Part 2 next. Any questions so far?


MMM yes could you use resistors here ? ..Zener do keep the voltage constant i suppose .

Also why the needed 75 volts drop i know it was less for the vcr139A only 24v this i am not sure about no idea really as the input hv negative can change a bit as i am doing but voltage out of the zener would vary too always a 75 volt drop to what ever input voltage i am supplying it but crt seems ok perhaps focus control position varies ..i recall you mentioning on the 3bp1 before we started the zener would have to be at least 60v could it be higher than 75v ?

....the diode in914 i mentioned what i thought it might be there for ? i can see you are dropping the voltage a touch to cathode and more by the time it gets to the focus control / understandable to supply the crts needs

Sorry about the text..nothing I can do about it really...no, I'll start over, but have a look at the above...Text problem fixed! Quickly too!

I've rounded the numbers to integers to remove the rather useless decimals.


No No this is good i would like to understand what i am building txt is fine this is interesting its interesting to build some thing but i do like to know what i am doing thanks for explaining !
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Re: NBTV Television Analyst

Postby Steve Anderson » Wed Apr 29, 2020 11:48 pm

Harry Dalek wrote: ...the zeners and diode used to drop the voltage so the 75 v zener drops the 1520 by 75 volts or around that i see that in the readings ..
Just like resistors, zeners have a tolerance, usually 5% at a specified test current, if the current is different to the test current that adds or subtracts to/from the final value. I always assume 10% for zeners.

MMM yes could you use resistors here ? ..Zener do keep the voltage constant i suppose.
Well zeners are a poor-mans regulator, put it this way - it's far better than a resistor which has no regulation at all. Though doubtless a Chinese company would 'try it on'. Not recommended!

Also why the needed 75 volts drop?
Grid cut-off (no trace at all) is specified in the datasheet at a certain negative voltage measured from the cathode, there is rarely a tolerance quoted, so -75V on the grid is sure to kill the beam current for this type of CRT. There's no point in increasing the -ve voltage, once the beam is cut-off, it's cut-off.

...the diode in914 i mentioned what i thought it might be there for ? i can see you are dropping the voltage a touch to cathode and more by the time it gets to the focus control / understandable to supply the crts needs.
It's there to stop the grid going positive relative to the cathode, that's all, it's not obvious - I'll come back to it later on.

The -1520v will vary with CRT brightness and a few other factors, it's partly due to the voltage doublers used in the power supply. Also if your 240v mains goes up by 2v (someone switching something off in the house) the -1520v will increase to -1532v. It's nothing to worry about. Even the 240v coming into your house will 'wobble' a bit as neighbours switch things on or off.

Part 2 tomorrow...

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Re: NBTV Television Analyst

Postby Harry Dalek » Thu Apr 30, 2020 10:01 am

Steve Anderson wrote:Just like resistors, zeners have a tolerance, usually 5% at a specified test current, if the current is different to the test current that adds or subtracts to/from the final value. I always assume 10% for zeners.


That i didn't know i thought they were a bit better tolerance wise .

Well zeners are a poor-mans regulator, put it this way - it's far better than a resistor which has no regulation at all. Though doubtless a Chinese company would 'try it on'. Not recommended!


i mentioned it as control voltages for old scope crt circuit's just used a chain of them ..ok we needed regulation here

Grid cut-off (no trace at all) is specified in the datasheet at a certain negative voltage measured from the cathode, there is rarely a tolerance quoted, so -75V on the grid is sure to kill the beam current for this type of CRT. There's no point in increasing the -ve voltage, once the beam is cut-off, it's cut-off.


Yes looking now at the data sheet says between -45 for -1500 supply and to -60 for a -2000 volt i looked on the collector of the now mpsA94 its voltage range reading across the 47k here it is 0 to bit over 69v here adjusting the opto.

the diode in914 i mentioned what i thought it might be there for ? i can see you are dropping the voltage a touch to cathode and more by the time it gets to the focus control / understandable to supply the crts needs.
It's there to stop the grid going positive relative to the cathode, that's all, it's not obvious - I'll come back to it later on.
[/quote]

Ok thats a good reason but that one was confusing for me .

The -1520v will vary with CRT brightness and a few other factors, it's partly due to the voltage doublers used in the power supply. Also if your 240v mains goes up by 2v (someone switching something off in the house) the -1520v will increase to -1532v. It's nothing to worry about. Even the 240v coming into your house will 'wobble' a bit as neighbours switch things on or off.

Part 2 tomorrow...

Steve A.


The input supply voltage does vary to an adjustment of the opto ic ....80v difference to a raster on or off i think i was thinking may be this is a problem but it is stable once set ...
Very good Steve this does help this is interesting
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Re: NBTV Television Analyst

Postby Steve Anderson » Thu Apr 30, 2020 2:49 pm

Next bit...using a simplified part of the CRT circuit,you'll see where this is going in a while...
Breakdown 3.gif
Breakdown 3.gif (5.11 KiB) Viewed 1245 times

We know quite a lot already, the supply voltage, the transistor type and the resistance values. We need to work out those items that end with a '?'.

First, let's attack the zener bit. The supply is +12V, the zener is 5.!V so the junction of ZD1 and R2 is +6.9V. What's the current through the pair, that's determined by the value of R2 and the voltage across it. So we have 6.9V/10,000=690uA. So we now have Iz & Vb.

The voltage between the base & emitter of a conducting transistor is usually between 0.6 & 0.7, I use 0.7 - it's near enough for devices like these. But in very low current stages it ca be closer to 0.5V, and in power devices often over 1.0V.

So we now have the emitter voltage as 6.9+0.7=7.6V.

Again the supply is +12V, the emitter voltage is +7.6V, what's the emitter current? (Ie)=12'-7.6=4.4V. R1 is 1k so the emitter current is 4.4mA (Ohms law). What's the base current? This particular fictional ZTX558 has a current gain of 200. So the base current is 4.4mA/200=22uA. This adds to the current through R2, but it's small and can be ignored in this case, but not always.

What's the collector current? There's 4.4mA in the emitter, 22uA in the base, so what current is left has to come out of the collector. the base current is so small we'll call the emitter and collector currents equal. So the collector current is as near a damnit the same at 4.4mA. This leads us to this...
Breakdown 4.gif
Breakdown 4.gif (5.56 KiB) Viewed 1245 times

Now a transistor is a current-operated device, it generally doesn't care a rats a**e about voltage unless excessive. Notice in the text before there was no reference to voltages regarding the transistor, only currents. What voltages there are are mostly derived from currents. I said previously, "You need to think in terms of current, not just voltage".

Now, a 1k resistor has been inserted in the collector lead, the collector is a current source, not a voltage source, always remember that. With the 1k resistor inserted (R3) the collector voltage rises due the current through the resistor by 4.4V. There is some interaction between collector votage and the current, but it's usually small enough to be ignored in these low-power stages. The collector current is the same at 4.4mA even though the collector-emitter voltage has been reduced by 4.4V

Now, what happens if we change the value of R1? Lets change it to 2k2...here's the result...
Breakdown 5.gif
Breakdown 5.gif (5.7 KiB) Viewed 1245 times

So, the only voltage that has changed is the voltage across R3, but there's more changes than one change in terms of current as can be seen. Currents again!

Lets substitute R1 with a current source. A current source will try and keep the current the same no matter what the voltage. Think of a regulated power supply, it tries to keep the voltage constant no matter what the current. This is just the other way around, it tries to keep the current constant no matter what the voltage is.

We'll go back to the 4.4mA example with a 4.4mA current source replacing R1...
Breakdown 6.gif
Breakdown 6.gif (5.96 KiB) Viewed 1245 times

Everything is the same as before except a current source is used instead of a resistor. What happens when we alter the current source?...
Breakdown 7.gif
Breakdown 7.gif (6.27 KiB) Viewed 1245 times

Again same as before...so why bother?

What's a good current source? A transistor. And in this case a phototransistor, the output part of an opto-coupler.

More to come...

Steve A.

Think current, voltage is a result of current. Current is the flow of electrons, hence the name electronics...

All of this is a simplification, there are other factors to be considered, but hopefully this is a beginning.
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Re: NBTV Television Analyst

Postby Harry Dalek » Thu Apr 30, 2020 6:51 pm

Thanks for another full explanation Steve , understanding the circuit may help or should working out why there's a problem i know you were pointing at the PNP HV transistor here .
Your very good at the explanation on the working of your circuit i can see you really know your Elelctronic's ! ,i am very lacking on the current side of things the current readings i am seeing are more calculations more than direct readings yes ..and for current direct readings we have to brake the circuit to check at these points if the circuits shown were to be tested with a amp meter .
Only thinking if what should be is actually happening again about this Transistor .

What's a good current source? A transistor. And in this case a phototransistor, the output part of an opto-coupler.


So i can see we are working more with current than voltage here so you have worked it out here with the supply voltage and resistance in the circuit the resulting currents should be


Think current, voltage is a result of current. Current is the flow of electrons, hence the name electronics...

All of this is a simplification, there are other factors to be considered, but hopefully this is a beginning.


I am trying to understand how you came about the idea for this as its good to know whats happening in the circuit make's things safer building it ,and i hope i we can work out why there's a problem and also there's always as well a next time if you have an interest and a spare CRT so the next build for me i will know a lot more all the had work would of been done here .

I had an idea today and it was why don't i just double check this circuit in the past monitors just in case i missed something ,found my 3bp1 Anderson but no power cable ! arrrr what have done with it ...next i found the devil monitor it had the cable but the 12v transformer is out in the in that power supply i forgot about that i am not winning here ..
so i got no where today

The ztx558's used here were from a batch that were used in the binocular so i think it must be ok i have now swapped over to the mpsA94 i put in a socket for now to save the soldering testing a transistor ,as far as voltage across the zener is similar results .

Do resistors change current when warmed up ? just wondering if the larger 2w 230 470k could cause this problem with the Zener ... :roll:
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: NBTV Television Analyst

Postby Steve Anderson » Thu Apr 30, 2020 7:55 pm

Harry Dalek wrote:Do resistors change current when warmed up ? just wondering if the larger 2w 230 470k could cause this problem with the Zener ... :roll:

They do, by how much depends on what the resistance material is, carbon composition, carbon film, metal film, wirewound and many others. But in all cases it's not enough to cause any real upset in these types of circuits. Much more variation with temperature is found in the semiconductors - by a huge amount, but you try to design out the consequences of that variation. In these circuits there is some temperature dependency, but in normal human-friendly environments you can forget about it.

An extreme 'domestic' example is electronic ignition in a car. It must start in Northern Sweden in winter where the temperature may be -40C, yet the same model has to cope with outside temperatures of +50C stuck in a Bangkok traffic jam where the temperature inside the engine bay might be over 90C. That is a tough requirement to meet.

Then think of Aerospace - even more extreme! The Silicon used in most semiconductors starts to melt at around 150C. Pure silicon melts at around 1400C, but the silicon used in semiconductors isn't pure. It's deliberately 'doped' with other elements to produce the P and N regions.

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Re: NBTV Television Analyst

Postby Harry Dalek » Thu Apr 30, 2020 9:58 pm

I know it should work as is just trying to think of tests to find the problem

mmmm...not the resistors due to heating ... I wonder if its worth building this on a board just to see the result again same or correct /

what about Parallel Transistors Current Sharing more to see the result ?

And since we are talking current i am not sure what the transformer is i would guess at 10 amp by size supplying the rectifier circuits and i am using a transformer saturable reactor for ac control here i never thought of the current situation would be changed i wonder if the CRT current needs are being effected ,i wouldn't think so only if the transformer was to small.

I could just hook another high ac transformer up to this and see some thing else i could try .

Its funny how its working correctly very nicely in fact in what it displays even with the anomaly but if the 5v zener should not vary and all the parts work mmm i will try some thing changing the current rating of the 75v zener i know it worked fine on the binocular i had 2 for both crts
Last edited by Harry Dalek on Fri May 01, 2020 12:47 pm, edited 1 time in total.
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Re: NBTV Television Analyst

Postby Steve Anderson » Fri May 01, 2020 12:44 pm

Not being 'funny', but it's best to try and find what's wrong with what you have in front of you. Changing things, "Oh, it might be this." without any reasoning is just throwing one more variable into the mix. It's a bit like, "My car won't start - I'll check the brakes." Extreme, ridiculous, but done without reasoning what the problem actually is.

..."what about Parallel Transistors Current Sharing more to see the result ?"...not sure what you're trying to say here, but the fact remains that this worked fine on three previous builds - why not this time? That's the crux of the matter. There's no point in changing things, something is simply wrong here. not as it should be.

"I wonder if its worth building this on a board..." I was going to suggest a a new build, using genuine components, on fresh new board, from the circuit diagram, and NOT copying the existing build. i.e. Start from step one, do a layout on paper first, make sure it's correct and build from that. Don't re-use any components, and ban any Chinese made stuff.

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Re: NBTV Television Analyst

Postby Steve Anderson » Fri May 01, 2020 1:28 pm

Harry Dalek wrote:I am trying to understand how you came about the idea for this...

When I was about eight I got a Meccano set for Christmas, and I still have it! (For those that know what Meccano is). All sorts of mechanical bits and pieces, I-beams, flat plates, axles, gears, nuts and bolts, even a clockwork motor! Link follows...

https://en.wikipedia.org/wiki/Meccano

Putting a circuit together is much the same, you use the appropriate part to fit what's required. That's a simplification, as often the 'magic part' you need doesn't exist, so you dream up an alternative - mechanically you'd fabricate the part you need. That often is the hardest part.

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Re: NBTV Television Analyst

Postby Steve Anderson » Fri May 01, 2020 1:39 pm

Harry before you do the re-build I'd like you to check one last thing - check the voltage across the photo-transistor, does that behave in a similar manner to the 5v1 zener?

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Re: NBTV Television Analyst

Postby Harry Dalek » Fri May 01, 2020 1:54 pm

Steve Anderson wrote:Not being 'funny', but it's best to try and find what's wrong with what you have in front of you. Changing things, "Oh, it might be this." without any reasoning is just throwing one more variable into the mix. It's a bit like, "My car won't start - I'll check the brakes." Extreme, ridiculous, but done without reasoning what the problem actually is.


thinking out aloud still more than any thing ... yes silly


..."what about Parallel Transistors Current Sharing more to see the result ?"...not sure what you're trying to say here, but the fact remains that this worked fine on three previous builds - why not this time? That's the crux of the matter. There's no point in changing things, something is simply wrong here. not as it should be.


True and i used the same 5 volt batch Zeners and 558 transistor that's why it is confusing .

"I wonder if its worth building this on a board..." I was going to suggest a a new build, using genuine components, on fresh new board, from the circuit diagram, and NOT copying the existing build. i.e. Start from step one, do a layout on paper first, make sure it's correct and build from that.

Steve A.
[/quote]

Something tried today was use a 5w 75 v zeners and they worked on the binocular monitor i just changed the 1 w to a 5W here to see and i got about the same result across the 5.1 volt zener its stays at 5v mostly ....checking the opto 10k brightness control nothing changes till i get to 5.24k ground to wiper 4.14 k wipper to positive so around higher end of brightness very similar to readings using the 1 watt..
So most of the working raster levels that 5v zener stays in range only on higher brightness does that voltage start to change

i then tried the NEC 2561 opto i used on the past working monitor and same results ...

The way i built the original 3bp1 the little circuit is a known working board i might just grab that and we can see ...i keep thinking when i got about to this 5.1v zener test on the other monitors i don't know if i adjusted the opto brightness control to see the results either end of the pot .. i know i was always more worried about the 75v zener ...we would know for sure with a known circuit built already better than rebuilding it
Last edited by Harry Dalek on Fri May 01, 2020 2:00 pm, edited 1 time in total.
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Re: NBTV Television Analyst

Postby Harry Dalek » Fri May 01, 2020 1:57 pm

Steve Anderson wrote:Harry before you do the re-build I'd like you to check one last thing - check the voltage across the photo-transistor, does that behave in a similar manner to the 5v1 zener?

Steve A.


ok i i will have a look ! never know...

across the opto trany below

Edit 0.15 to 5.28v......

across the opto led 0 v no raster 1.11v full brightness

may be 3.3k value on the opto led was increased the 5v across the zener would stay in rage i think
Last edited by Harry Dalek on Fri May 01, 2020 2:39 pm, edited 4 times in total.
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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