NBTV Scope Evolution

Forum for discussion of electronic television. Generally, stuff to do with CRTs and not using mechanical displays.

Re: NBTV Scope Evolution

Postby Harry Dalek » Sun Aug 09, 2015 6:23 pm

Well i hooked the circuit up again today to the crt scope and unfortunately even with the pwm on the frame sawtooth i am really just getting a distorted raster when the audio is raised .

I will be checking my work again for any mistakes ,the frame width control is a little tight and the black level control is the same needs to be set in the dead middle for any pwm to to added to the frame sawtooth .

OH well back to fault finding .
Attachments
IMG_0039.JPG
The frame sawtooth
IMG_0039.JPG (69.62 KiB) Viewed 7299 times
IMG_0032.JPG
Line sawtooth
IMG_0032.JPG (69.8 KiB) Viewed 7299 times
MVI_0059_mpeg4.gif
The frame sawtooth with pwm
MVI_0059_mpeg4.gif (3.71 MiB) Viewed 7299 times
MVI_0054_mpeg4_Segment_0_mpeg4 (2).gif
testing the raster had the video right down as it distorts the scan ,think i can see at least some sync bars
MVI_0054_mpeg4_Segment_0_mpeg4 (2).gif (3.91 MiB) Viewed 7299 times
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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Harry Dalek
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Re: NBTV Scope Evolution

Postby Steve Anderson » Sun Aug 09, 2015 9:51 pm

I can't even begin to guess what's going on there! It seems the ramp waveform is OK, so that's a start...now, the output of the op-amp which is fed from the 'Video Gain' pot and the diode from the 'Black level' control transistor. This (right on the output pin) should be much as the same as on the wiper of the 'Video Gain' pot but elevated by the voltage set with the 'Black Level' control. Make sure you haven't got inverted video.

The output of the Schmitt NAND 'Shift Oscillator' (which feeds the 56k resistor) should be a 12V p-p constant square waveform at around 30-40kHz. It shouldn't 'wobble' that much with video modulation - best if it doesn't wobble at all.

Turn off the source of video completely, make sure that you get a varying duty-cycle square-wave at the output of the Schmitt NAND gate that feets the 1k mixing resistor as you vary the 'Black Level' control.

Let me know how you get on.

Steve A.

It's odd that Jeremy has drawn the NAND gates (both versions) as NOR gates, that confuses me sometimes. As I understand things the sketch below is correct for both standard and Schmitt versions.
Attachments
Gates 1.gif
Gates 1.gif (4.34 KiB) Viewed 7294 times
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Steve Anderson
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Re: NBTV Scope Evolution

Postby Harry Dalek » Mon Aug 10, 2015 7:41 pm

Hi steve

OK i am looking at my circuit again now testing the power supply to the 4093 shift oscillator .

I am using a switchable voltage power pack..... results are when the circuit is on 6 volts the shift oscillator runs higher 42 khz on 12 volts it drops to 30 khz ....interesting .

So i am in range here ,as the voltage is raised the frequency drops the amplitude of the squaure wave increases pretty much to what the voltage is to the circuit ...the pf capacitors that turn it into a triangle wave at 30khz this drops the amplitude to about 2 volts/

There is slight spiking to the square wave but i don't see a problem on the triangle wave after .

So to me it looks ok ....

i am useing a cd4093be for the shift oscillator and i have grounded all unused inputs as jeremy recommended.

If you think this looks ok also i can move onto the opamp ....i am using a ua386pc i am not sure if there is a difference to the recommended Lm348 ?

I have run out of time today to do any more testing but i will look into the video if its inverted or not .

i did notice when using the Black Level control depending on the settings the video will raise or lower in polarity position to the setting of the trimmer more positive or more negative but as i said for some reason i get not pwm out of the 4093 unless its centered ...still need to look for mistakes some where else ,i will try and do more testing after work tomorrow .

I will try and show also next pwm out of the 4093...that should look less messy with it added to the sawtooth in the post above.

It's odd that Jeremy has drawn the NAND gates (both versions) as NOR gates, that confuses me sometimes. As I understand things the sketch below is correct for both standard and Schmitt versions.


OH ! i would be worried if he had not said what the ics were ...

Thanks for the help there i'll do those tests .
Attachments
IMG_0061.JPG
circuit on 6 volts
IMG_0061.JPG (114.99 KiB) Viewed 7286 times
IMG_0065.JPG
the triangle wave 30 khz
IMG_0065.JPG (103.49 KiB) Viewed 7286 times
IMG_0066.JPG
my power supply
IMG_0066.JPG (88.58 KiB) Viewed 7286 times
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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Harry Dalek
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Re: NBTV Scope Evolution

Postby Harry Dalek » Tue Aug 11, 2015 7:30 pm

OK Steve i did the tests below

Turn off the source of video completely, make sure that you get a varying duty-cycle square-wave at the output of the Schmitt NAND gate that feets the 1k mixing resistor as you vary the 'Black Level' control.


The 2 videos are

video 1 the Schmitt NAND gate that feeds the 1k resistor ..................looks ok bit jumpy which i think is caused but the 12 hz ramp feeding back up the resistor .

video 2 i am adjusting the black level control either side of the middle of its adjustment ..about in the middle the 30 khz square ware appears theres no real neat adjustment of this as i would think it should be if the black level is what i think a brightness adjustment ? the main input of the video trimmer would be contrast ?
sorry on this one trying to adjust the trimmer and film at the same time .

Black level npn trany is a c547
frame pnp BC558
line pnp BC559

If i find any thing else that might be different i will jot it down.
Attachments
MVI_0068.gif
MVI_0068.gif (5.9 MiB) Viewed 7277 times
MVI_0074_x264.gif
MVI_0074_x264.gif (15.09 MiB) Viewed 7277 times
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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Harry Dalek
"Fester! Don't do that to 'Thing'"
 
Posts: 5364
Joined: Fri Sep 26, 2008 4:58 pm
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