NBTV Television Analyst

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Re: NBTV Television Analyst

Postby Steve Anderson » Fri Apr 24, 2020 1:45 pm

The ''rounding' of the the waveforms at the start/end is due to the input capacitance of the scope and those 'dangling' input leads. If you can, please use a better scope with proper probes. If you don't have 'proper' probes please try and invest in a couple of x10 probes and use a better scope. This current arrangement will only cause you grief in the future.

An example is here, not cheap but they should last years and save you a lot of heartache!

https://www.jaycar.com.au/cro-probe-cable/p/QC1902

There are many other sources too...

Here's an explantion of why scope probes are are a necessity ..

https://www.electronics-notes.com/artic ... probes.php

When you buy a new scope it always comes with a compliment of probes. But when buying second-hand often they're missing and/or broken.

"A tradesman is only as good as his tools." - whether that's true or not I'm not sure.

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Re: NBTV Television Analyst

Postby Harry Dalek » Fri Apr 24, 2020 2:48 pm

Ok Steve i will look into a probe for this scope ,i am only using it because i have to at the moment where i am i may have a spare probe laying around i will listen the connection to this i will look into
The project will be going out once this part of it is operational so i can build the rest of it .

i am fault finding around the crt circuit at the moment so far it all looks correct but it must be a mistake i will keep looking .
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 » Fri Apr 24, 2020 3:09 pm

Harry Dalek wrote:Ok Steve i will look into a probe for this scope...


Harry, not 'this scope', it only has terminals, you NEED one with a BNC input connector and a 1M input resistance/impedance. In addition DC/AC coupled (selectable) input.

The one you're using was probably aimed at classroom demonstrations and simple high-school stuff. The give-away is those input terminals, and probably AC only input coupling. As I said before, it's not up to the job - seriously!

What happened to the one we jointly fixed a few years back? If I recall it would more than do. Without something like that you'll be chasing your own tail, getting frustrated and wasting time. Sorry to be so strong on this point, but it is important.

It's like having a multi-meter that reads 6.7V when you know the output of a 7805 is 5V - useless!

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Re: NBTV Television Analyst

Postby Harry Dalek » Fri Apr 24, 2020 5:14 pm

OK Steve i will leave the scope stuff the better ones .
OH that other scope started to play up again after a while it works some times the trace go's a bit dimmer from time to time its hit and miss when it works again as we recall it got a nasty knock before i found it ,so i think there is a crack in the board every thing i saw i repaired apart from that it does work i just put up with it when i use it
I mainly use the good one in my work area in the garage when i am there i suppose every one uses those flat digital jobs these days i do live in the past a bit with the old CRT scopes i just like them.
On the project i took new readings to todays voltage adjustments ..all reading on parts same as shown.
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I also looked again at ZD101 5.1v zener voltage accross it ,it swings from O.18v to 5v on adjusting the brightness of opto led , the Zener reads similar to the unused Zener on the diode check on the multi meter ,i can only pull it out and see..all the rest of the circuit seems correct .
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 » Fri Apr 24, 2020 6:35 pm

It may be the ZTX558 has a short e-b...what's the grid of the CRT doing? -ve probe on cathode, +ve on the grid. It should swing from a couple of volts negative to almost -75V. If it doesn't try replacing the ZTX558. CRT cold I assume.

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Re: NBTV Television Analyst

Postby Harry Dalek » Fri Apr 24, 2020 7:24 pm

Steve Anderson wrote:It may be the ZTX558 has a short e-b...what's the grid of the CRT doing? -ve probe on cathode, +ve on the grid. It should swing from a couple of volts negative to almost -75V. If it doesn't try replacing the ZTX558. CRT cold I assume.

Steve A.


I will give that a look for sure Steve i must admit i didn't check for shorts in the transistor just looked if i connected it right in the circuit and every thing was going where it is in the schematic ,well checking the 558 seems fine same readings same as the unused one for the second crt ,checking the cathode grid test Steve adjusting the opto led pot..... zero to -74v the result so yes doing that
This is a tricky one mmmm but you know if and when its worked out we will never forget !
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 » Sat Apr 25, 2020 10:54 am

Another look at the wiring on the crt is going where it should ,i checked the 5.1 zener out of circuit with a 1k load resistor and a 12 volt power supply and coming up 5.1v as it should so the zener is fine.
Next looking at what is happening when the opto led is adjusted to the various test points shown below
The CRt starts to go out of focus with the trimmer supplying 4.6v to the opto led 3.3k resistor but the bright to dim part of the controlling is flawless .
I also tried replacing the opto and its fine .
The focus control works ..but i can adjust the crt to focus when its dim but increasing the brightness it will go out of focus same go's when fully bright adjust to a sharp focus it will go out of focus when i dim it visa versa ARRRRRRR head scratching
It seems better when i adjust the focus when its dimer it looks like the 470k which is 460k in my case should be increased but does answer why the 5v zener is changing voltage
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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 Steve Anderson » Sat Apr 25, 2020 11:13 am

Hmm...not easy to do this via 'remote control', i.e. I'm not actually there. Have you tried changing the ZTX558? If not, that's what I would do next...even if it 'reads' correct.

I assume you've checked resistors are actually the values they say they are.

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Re: NBTV Television Analyst

Postby Harry Dalek » Sat Apr 25, 2020 11:34 am

Steve Anderson wrote:Hmm...not easy to do this via 'remote control', i.e. I'm not actually there. Have you tried changing the ZTX558? If not, that's what I would do next...even if it 'reads' correct.

I assume you've checked resistors are actually the value they say they are.

Steve A.


Hi Steve Yes i will do that change the 558 ...not much left ready ...
Yes the values of what i have were posted in the crt schematic yesterday ,you will see 2 resistors are both 10k off which i can fix also yes those were all meter readings i don't trust the colour code much .
focusing the focus control when the crt is on the dimmer side sure helps you get a better range only gos bad out of focus now on close to maximum brightness.
Don't worry to much Steve i understand that suggestions at your distance are good enough i have got it going a few times before i know i can do it again ,the other day i had nothing now its nearly there.
i am right in saying the voltage across the 5.1 zener diode should be a constant 5.1v no matter what i just the opto led brightness too.
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 » Sat Apr 25, 2020 12:15 pm

Harry Dalek wrote:i am right in saying the voltage across the 5.1 zener diode should be a constant 5.1v no matter what i just the opto led brightness too.

Yep, that's correct.

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Re: NBTV Television Analyst

Postby Harry Dalek » Sat Apr 25, 2020 4:26 pm

Steve Anderson wrote:
Harry Dalek wrote:i am right in saying the voltage across the 5.1 zener diode should be a constant 5.1v no matter what i just the opto led brightness too.

Yep, that's correct.

Steve A.


Well i took out the ztx558 transistor and checking it i had the emitter collector wrong way around arrrr i thought that's it ! well guess what putting it in the right way around its worse no brightness control and the 5v zener still swings via adjusting the opto led,crt stays on full brightness .
i changed the 5v zener again and the little signal diode and the 75 volt all the same results so far .

i spent most of the day double checking if am i seeing what i am seeing ! i had another pnp 400v transistor i tried the mpsA94 it gave again the same results as the Ztx558 .

But checking on the meter i have it says both the transistors are BJT PNP's ..i looked at a ztx458 npn which i am using in the deflection amplifiers meter shows its a normal NPN ..i am wondering if this is the cause of my problems and why its working in reverse ? this type of transistor is not showing up in the data symbol if it matters at all ....only thing left i have not tried is adding 10k values to 2 resistors in the circuit .
Time for a rest and think about ...
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ztx558 reading
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mpsA94 reading
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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 Steve Anderson » Sat Apr 25, 2020 4:55 pm

Well, those two results (if correct) say those two transistors are as good as dead. Assuming you've got the pin-out correct and they really are ZTX558s. The hFE (current gain) should be at least 50, probably anywhere from 100-200 or more. If you mixed up the leads and applied the system voltage to them there's every chance that the b-e junction is buggered. The c-b handles up to 400V, but the e-b maximum is 5V - this is quite normal.

Time for some new ones, throw those two away.

Check any new ones for a good hFE before fitting them.

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Re: NBTV Television Analyst

Postby Harry Dalek » Sat Apr 25, 2020 6:39 pm

Steve Anderson wrote:Well, those two results (if correct) say those two transistors are as good as dead. Assuming you've got the pin-out correct and they really are ZTX558s. The hFE (current gain) should be at least 50, probably anywhere from 100-200 or more. If you mixed up the leads and applied the system voltage to them there's every chance that the b-e junction is buggered. The c-b handles up to 400V, but the e-b maximum is 5V - this is quite normal.

Time for some new ones, throw those two away.

Check any new ones for a good hFE before fitting them.

Steve A.


Those were new untested Steve i got a 2 batches a year ago i wonder if its another case of bad parts .
Now i know what to look for i can check the others , as far as how accurate the meter is on transistors i will test some other transistors and see if this meter is showing correct BC548 gain should be between 110 to 800 give me an idea if it reads correct or not .
The first transistor was a ztx558 next was a mpsA94 ...
Thanks advice Steve good to be pointed in the right direction i can look into this now ...
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 » Sat Apr 25, 2020 8:18 pm

Harry Dalek wrote:Those were new untested Steve i got a 2 batches a year ago i wonder if its another case of bad parts .

*Puts elbows on table and cups head into hands* This is the second time this sort of subject has come up in recent times, fake or defective parts. I won't repeat my diatribe of the last time, I'll just say, "DON'T BUY THIS CRAP"......because that's what it is.

How much is your time worth against all the savings you might have made? - except you didn't. How precious is quality time spent with your family instead of chasing around weeding out cheap defective components? OK, that's enough.

In this circuit you can replace the ZTX558 with a MPSA92/93/94 with no other changes being required. Pin-out might be different so check first and test the Hfe before fitting.

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Re: NBTV Television Analyst

Postby Harry Dalek » Sat Apr 25, 2020 8:38 pm

Steve Anderson wrote:*Puts elbows on table and cups head into hands* This is the second time this sort of subject has come up in recent times, fake or defective parts. I won't repeat my diatribe of the last time, I'll just say, "DON'T BUY THIS CRAP"......because that's what it is.


The meter i showed you is way out Steve my other multimeters transistor test are showing correct the ztx558 is showing a gain 174 ...never jump to conclusions this is not science testing testing testing ,well i did on the regulators get burnt with buying crappy parts that reminds me i need to get back to them !

Looking i got this
my friend!After query! Warehouse colleagues forget to re send the new package! This is our negligence! You can choose to have us resend or refund! Thank you! Sorry again!


In this circuit you can replace the ZTX558 with a MPSA92/93/94 with no other changes being required. Pin-out might be different so check first and test the Hfe before fitting.


The MpsA94 looked closest to ztx558 i could find ,had them for a year or 2 just got them out of interest ,never had a need to try them till now i always wanted to see now i know .

So next i forgot to look is if this meter is showing the correct pin outs to the other meters as i was trusting it .
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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