NBTV Television Analyst

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Re: NBTV Television Analyst

Postby Harry Dalek » Mon Apr 27, 2020 7:57 pm

Steve trying to get my head around it but while checking as you were saying check the resistor chain i checked resistance between the top of the 5.1v zener to the other duplicate not in use and there was a very high resistance well over a meg and a half or so i should written it down but i can't do much with the kids running around this time of night thinking wise ! :roll: i can only think its via its resistor chain then via ground back up via the other circuits resistor chain to its zener theres no where else its connected even the ztx558 trany has not been replaced yet nothing hooked up it .
I was not expecting resistance between these two zeners ... but via ground connection makes sense ...so i don't think this is the problem i thought i would mention what i found ..
I have not got time yet to check the board again tonight for dry joints but that resistor chain seems fine via connections ..

It is a nagging problem to want to know why and checking is good ,never hurts to double triple check ..i have looked at the boards circuit here so many time i think i could build if from memory now . :wink:
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Re: NBTV Television Analyst

Postby Steve Anderson » Mon Apr 27, 2020 8:09 pm

Keep at it - when you have a quiet moment - there's no panic rush on this.

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Re: NBTV Television Analyst

Postby Harry Dalek » Mon Apr 27, 2020 8:18 pm

Steve Anderson wrote:Hang on! Something ain't quite right here. Your measurements added to the drawing are 'odd'. The posting of 26th April shows one end of the 220k resistor as -1400V, the other as -1430V, 30V of difference, a current of only 136uA. Whereas the focus pot end of the same resistor shows +388V (I assume relative to the cathode)...so that's about correct at 1.76mA.


Yes positive readings there via cathode not ground ...ground for all the high negative readings
OK i will double check that for sure tomorrow ..

Get the tube at a reasonable brightness with the best focus you can and check again. Don't move/bump the controls as you do so.


So it does not matter just any where best focus ,i found over all its best to focus the tube at the dim end and you get the range i showed in the video a while back if i focus best to the brightest end it go's out of focus in the lowest brightness ...any way will do ...

68k parallel with 1M is about 63k, so no problems there.


Thats good can replace to dead on 68k when i have time...but seems fine for all the voltage range i have tested it on ,i will not play around just keep it as it is so we can work out the anomaly.

I will have check tomorrow now Steve ,just helping the kids with some school work and thanks for looking into this for me any advice to make it better is a good thing .
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Re: NBTV Television Analyst

Postby Steve Anderson » Tue Apr 28, 2020 12:48 pm

Harry Dalek wrote:...and thanks for looking into this for me any advice to make it better is a good thing .

Well, I drew the circuit so I feel it's only fair that I should at least try to help in sorting out any problems with it. Plus we'll both learn from the exercise - others too hopefully.

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Re: NBTV Television Analyst

Postby Harry Dalek » Tue Apr 28, 2020 4:46 pm

Steve Anderson wrote:
Harry Dalek wrote:...and thanks for looking into this for me any advice to make it better is a good thing .

Well, I drew the circuit so I feel it's only fair that I should at least try to help in sorting out any problems with it. Plus we'll both learn from the exercise - others too hopefully.

Steve A.

Hi Steve i was going to send the results as i took some readings this morning but i was not to sure as some voltages some the meter readings where changing on the 3rd digit which i found a bit strange .,switching it on just now i think the 75 volt zener has gone again -1520 might be to high for it ..may be i was seeing that zener pack it up its not like a wire yet but its showing a much lower voltage across it ...crt raster is just staying on and the opto adjustment is just putting it in and out of focus a bit ...i have a few spares of the 75v zener i will replace now drop the high negative a bit .

Yes i am interested in how if works here and glad you are too ...BTW have you even made this circuit for your past monitors i was thinking yes ,that's a reason keep using your circuit and you learn more from mistakes than from your successes ...Yes i keep forgetting others are viewing out there...

readings took this morning below i wanted to also double check the hv positives if i had them the right way around ...i was a bit rushed had to go to work
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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 Harry Dalek » Tue Apr 28, 2020 5:34 pm

OK i replaced the 75 v zener and its working again i also for now dropped the supply voltage a bit just in case ....with a raster full brightness on and completely off the supply voltage changes -1410 +310 crt off 1350 +300 crt on this is what it is at the moment ..the positive is a too low but i can increase this just dropped every thing for safety for now.

What i was meaning to ask regarding the A2 side is i can see on the 3bp1 data sheet the positive side should be at least 430v to a max of 575v ..what is the range of the deflection amplifier with the ztx transistors are rated 400 volts i can go much higher on the positive side but i might have to drop the voltage to the deflection amplifiers feeding a higher voltage to the A2 circuit ..i don't want to brake the deflection amplifier which is using the same supply at the moment ..

I can see its a bit like a juggling voltages here getting the right voltages for focus without over heating any thing or this case braking the 75 volt zener ,the crt can run higher voltages but have to be careful factors like itsa hand made circuit layout for space and that does change every time you make it only human!.
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Re: NBTV Television Analyst

Postby Steve Anderson » Tue Apr 28, 2020 6:32 pm

The A2 voltage is stated as minimum 1500V to a maximum of 2000V - measured from the cathode (as all CRT data sheets are). Here it appears to be around 1600V, so that's OK (with the Astig pot mid-way).

I don't see any point in raising the deflection supply voltage, they were fine on the previous build. Anyway, the deflection isn't the problem here - don't compound the problem by introducing another variable. This is a focus/grid problem. Until the 5V zener issue is fixed there's no point in making things worse.

Steve A.

With the revised voltages above there's 1.7mA through the 220k resistor, somewhat better than yesterday's few hundred microamps. So something has changed, Is it stable across the 5V zener now? Is R904 really 47k?
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Re: NBTV Television Analyst

Postby Harry Dalek » Tue Apr 28, 2020 7:15 pm

Steve Anderson wrote:
With the revised voltages above there's 1.7mA through the 220k resistor, somewhat better than yesterday's few hundred microamps. So something has changed, Is it stable across the 5V zener now? Is R904 really 47k?



No the 5 volt Zener is still changing with the opto ,and the 47k is showing 47.1K in circuit ...

Would disconnecting the CRT and doing the test work you think ? crt would be the load yes ? with out a load perhaps different result just thinking ..i can change to another crt mid week if need be to see.

The 75 and 5.1v zeners are 1 watt each is that a problem ? looking back i checked with the original 3BP1 Anderson build you mentioned the 5v zener 5V/0.3W that's lower than what i am using but i replaced it with a smaller wattage 5.1v zener the other day with same results ..
5.1V 1N4733 1 Watt Zener
75V 1N4761 1 Watt Zener
Last edited by Harry Dalek on Tue Apr 28, 2020 7:36 pm, edited 1 time 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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Re: NBTV Television Analyst

Postby Steve Anderson » Tue Apr 28, 2020 7:31 pm

Harry Dalek wrote:No the 5 volt Zener is still changing with the opto ,and the 47k is showing 47.1K in circuit ...

Would disconnecting the CRT and doing the test work you think ? crt would be the load yes ? with out a load perhaps different result just thinking ..i can change to another crt mid week if need be to see.

The 75 and 5.1v zeners are 1 watt each is that a problem ?

There's no harm in disconnecting the CRT, it could be defective, though I don't see how, it;s basically working.

The 1W zeners should be OK.

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Re: NBTV Television Analyst

Postby Harry Dalek » Tue Apr 28, 2020 7:59 pm

Steve Anderson wrote:There's no harm in disconnecting the CRT, it could be defective, though I don't see how, it;s basically working.

The 1W zeners should be OK.

Steve A.


Yes running out of ideas this might be a silly idea but could you replace the 5v zener with a 5v reglulator ? thinking to keep it at that voltage .. would it explode ?
I can build the circuit as to your design but how the zeners are working with these high voltages my understanding is lacking i just know whats expected in and out sort of with out getting into to much trouble with it .

Could you explain not just for me but for any one else interested here from opto slowly light switching its transistor on ,its control of the circuit via its parts .. as in just lighting the CRT part via the CRT circuit

Copying most of us can do its nice to learn more
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Re: NBTV Television Analyst

Postby Steve Anderson » Tue Apr 28, 2020 11:46 pm

You can't use a 78xx type of regulator here as is quiescent current (with no load) is greater (about 3mA) than all the current in the chain, around 2mA. It's not a problem with the zener, it's just showing us that the current isn't enough to reach the zener point. The current is being 'stolen' somewhere and at this distance it's hard to figure out where. Often you need to think in terms of current and voltage is secondary.

This circuit worked fine on your previous build, there's no reason why it shouldn't work here. I still think it's the ZTX558. Are these from a cheap Chinese batch again? If so they may be fine with the low volts in the meter when measuring hFE, but perhaps at these higher voltages they give up.

I'll get to the other points in the morning. I need to make an important (and probably long) call to the UK in a short while.

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Re: NBTV Television Analyst

Postby Steve Anderson » Wed Apr 29, 2020 1:13 pm

Harry Dalek wrote:...I can build the circuit as to your design but how the zeners are working with these high voltages my understanding is lacking i just know whats expected in and out sort of with out getting into to much trouble with it. Could you explain not just for me but for any one else interested here from opto slowly light switching its transistor on ,its control of the circuit via its parts .. as in just lighting the CRT part via the CRT circuit


Sorry Harry, not quite sure what you're asking for here...

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Re: NBTV Television Analyst

Postby Harry Dalek » Wed Apr 29, 2020 2:21 pm

Steve Anderson wrote:You can't use a 78xx type of regulator here as is quiescent current (with no load) is greater (about 3mA) than all the current in the chain, around 2mA. It's not a problem with the zener, it's just showing us that the current isn't enough to reach the zener point. The current is being 'stolen' somewhere and at this distance it's hard to figure out where. Often you need to think in terms of current and voltage is secondary.


Well today i stopped a jaycar electronics and stocked up on a few more 5.1v 75v 12v zeners the 5 volt ones are showing ok but so was the 75v for a time changing it with one from a new batch will show once and for all if it is that or not .

This circuit worked fine on your previous build, there's no reason why it shouldn't work here.


Yes 3 times infact the 3BP1 Anderson then the A for Andrew Tasmanian devil and the Binocular so i agree some thing is up some thing is wrong ..i am the builder so it comes down to me myself and I ! no one else .

I still think it's the ZTX558. Are these from a cheap Chinese batch again?


No not cheap i could only get about 6 problem here is the other mpsA94 type giving same results ...i will take some readings see if changing this transistor makes a difference ,i am crossing my fingers the new 5 volt zener fixes first .

If so they may be fine with the low volts in the meter when measuring hFE, but perhaps at these higher voltages they give up.


Yes perhaps i an no expert on all this so i have no clue .

I'll get to the other points in the morning. I need to make an important (and probably long) call to the UK in a short while.

Steve A.
[/quote]

Well i will do some more tests see what happens this afternoon i have a few things now i can try .
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 Harry Dalek » Wed Apr 29, 2020 2:55 pm

Steve Anderson wrote:
Harry Dalek wrote:...I can build the circuit as to your design but how the zeners are working with these high voltages my understanding is lacking i just know whats expected in and out sort of with out getting into to much trouble with it. Could you explain not just for me but for any one else interested here from opto slowly light switching its transistor on ,its control of the circuit via its parts .. as in just lighting the CRT part via the CRT circuit


Sorry Harry, not quite sure what you're asking for here...

Steve A.


Sorry i must sound stupid here but i don't understand this HV CRT circuits workings (just that part )i just know what to do to make it work there's a difference .

Pretty much i mean how does the opto ic with the temporary brightness control .....control the high voltages with the ZTX558 and zeners ...if it was the first time i saw this circuit and if it was any one but yours i would never try to build this because as i would be worried it would explode .

As you increase the led light in the ic i would think it allows voltage via the collector and emitter to pass but at the voltages in this circuit i don't understand why it is not killed and the ZTX558.

If i didn't know any better i would expect the zeners to go in an instant well they do if you push them with to high a voltage very much so the 75v one .

Any case when i used to work at BHP and as a chemical plant operator i used to make benzene ...we had to write up standard procedures on the plants operation at the end because no one apart from us knew how to run it ! so if we operators left there were drawings of what go's where but how it works there was no information at all just word of mouth from one operator to the next ! ...reason for a standard procedure ...so with the circuit i see where it all go's but how it should work there is no information apart from wanted set points as we used to say at the Gas processing plant .

After all that back to testing i have disconnected the CRT i will test the circuit as is if any difference ...i will report back
Last edited by Harry Dalek on Wed Apr 29, 2020 7:00 pm, edited 1 time 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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Re: NBTV Television Analyst

Postby Harry Dalek » Wed Apr 29, 2020 3:35 pm

With the CRT disconnected the voltage across the 5.1 volt zener is showing 4.8v and 5.3 v other end of the opto adjustment 0.8 0.4 swapping the reading probe placements...mmmm 5.3v should not be happening i think

With it back connected the 4.8 and 5.3 are the same but 0.4 0 is lower

i will change the 5 volt zener now see what happens bit of luck i just had a faulty one

EDIT...changed the 5.1v zener same result so its not the zener not the CRT

Took the ztx558 out reading across zener 4.8v 5.3v checking reading either side of it no change adjusting opto led makes sense

Changing the ztx558 with mpsA94 across zener readings - 5.08 +5.08 crt raster off ....-0.21 +0.21 crt raster fully on ...thats a bit different i like the same reading at least either side

I adjusted the focus right to the other end of the swipper its not effecting the 5.1v zener readings same as above so its not that .

next took opto ic out reading across zener still 5.08 crt raster off no adjustment again makes sense correct
Last edited by Harry Dalek on Wed Apr 29, 2020 4:33 pm, edited 1 time 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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