Fault finding

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Fault finding

Postby Harry Dalek » Tue Feb 16, 2021 9:44 am

I am posting this up as i had a problem with the monitor and good to share the fix .
Sad as it is nothing lasts for ever and things brake ,so i will post up there what i found for a future repair for me or any one else .
To start off with i was noticing the raster lines were looking a little glitchy which i put down to a poor earthing grounding some where but all looked ok on this front testing. Started to get worse focus at times was going in and out a touch and i then lost just the line raster altogether ,and lastly lost all raster no CRT light at all .
Well one problem at a time i looked into first why i had lost line sawtooth oscillator IC702 replaceing the ic702 didn't help ! all the circuit seemed fine ,it came down to removing the input syncing to 6c input ic604 output...the line oscillator sawtooth fired up right way doing this so Ic 604 was faulty! replacing this ic all was fine again here .
3BP1 NBTV Sawtooth 3.gif

circuits.jpg


On to looking into why i had no raster light at all at first i went with replacing the opto coupler as past monitors this tended to be be a problem at times but testing it it was fine, next i looked into if the 24 volt zener ZD902 had died in this case 2 12v zeners in series for the same result but testing out side circuit both were working fine but showing 4 to 6v across them in the monitor circuit bit random next looked into D901 and ZD901 both again tested ok then i moved on to looking at the grounding side of the HV circuit the resistors
R901 tested fine and the focus resistors again were ok ,next the 470k R903 ..here i use 2 2 watt resistors for the same result the first in the series was testing good but the second was open circuit so here was the problem no grounding in the HV circuit ,but as it went open it must of been sparking inside it as i found in past monitors any sparking to ground tends to kill the 4538 ics not the first time !
At least this was the cause a bad resistor after replacing every thing back to normal just have to resolder some parts in neat and get back to working on adding the panel controls ..lost week back on track now.

VCR139A NBTV Initial 1-Model.gif
Attachments
P1070661.JPG
P1070668.JPG
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: Fault finding

Postby Harry Dalek » Tue Feb 16, 2021 3:44 pm

Not really a fault but i noticed i have not been able to repeat the higher line rate frame syncing as before as is ,not till i worked out the level need to be increased and i can see it does frame sync but i need to work on the contrast and brightness as doing this the image is washed out ..result good for frame sync not for image result ..so will be working on the this .
Using Free NBTV program as is the monitor is happy up to 36 line after that the frame syncing go's unless i increase the volume to the monitor its more washed out and more volume needed as i increase the line rate to higher numbers to get the frame syncing .
The brightness and contrast do need some balancing as there's little lower level control .
I tried 30 line 5 and 6 frame videos this works ..more problems the higher end of displaying
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: Fault finding

Postby Steve Anderson » Tue Feb 16, 2021 5:10 pm

Wow! I'd forgotten I did that stuff, less than four years ago, senility, it creeps up on you!!

Somewhat surprised you're able to get it work at other rates than those I envisaged...that's seemingly without modifications, no doubt about your abilities!

Failures, well, using re-cycled components as you often do, that's bound to happen, but I'm pleased to see someone doing it! I'm guilty of not doing so.

I'm at a bit 'stuck' at the moment. I have the SSTV-TV/VGA thing to do, maybe an updated 'ROM-scanner' and a blend of the 'ROM-scanner' and a CRT display in a single unit. Maybe. Decisions, decisions...(Later) Oh! and the NBTV PC-based DC-coupled record/playback device...that's in addition to 'real work' and my other passion - flying! Perhaps at this point I should also mention the wife...

Steve A.

Coming back on-topic, it'll be the SSTV-TV/VGA thingy first, the DC-coupled recorder second, then (perhaps) the updated 'ROM-scanner', with or without the display...but I'm open to other suggestions...

The updated 'Rom-scanner' is a concept, stores 1024 images in the same format as Ralph's (8k-byte each), maybe four/five DIL/SOIC/SOIJ chips, one 28-pin DIP/DIL device (the micro), the others smaller, nothing exotic.....though it could be simplified if you don't mind a PC-based solution with a smaller 'adapter' rather than a stand-alone device. The stand-alone version would be my preference though.
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Re: Fault finding

Postby Harry Dalek » Tue Feb 16, 2021 7:33 pm

Steve Anderson wrote:Wow! I'd forgotten I did that stuff, less than four years ago, senility, it creeps up on you!!


Well it sure does when you look at something you have made and wonder how you did it and what go's where takes a while to catch up to it again .

Somewhat surprised you're able to get it work at other rates than those I envisaged...that's seemingly without modifications, no doubt about your abilities!


Well your design Steve its a good one ..its getting there again ,the new scope and its frequency meter sure help and show what's happening .

Failures, well, using re-cycled components as you often do, that's bound to happen, but I'm pleased to see someone doing it! I'm guilty of not doing so.


Yes the resistor failing and your comment was pretty much was on my mind when i found the fault today just a bit harder to find a large wattage resistor locally but you take the risk and this time it was a faulty .
Of late i have found most of the time you make some thing that works put it away next time you use it its gone faulty i would blame my self but its the same for any thing a good percentage of electronics works a few years ago next fire up a few years later something has gone in it ..i think you have to power these things pretty regularly .

I'm at a bit 'stuck' at the moment. I have the SSTV-TV/VGA thing to do, maybe an updated 'ROM-scanner' and a blend of the 'ROM-scanner' and a CRT display in a single unit. Maybe. Decisions, decisions...(Later) Oh! and the NBTV PC-based DC-coupled record/playback device...that's in addition to 'real work' and my other passion - flying! Perhaps at this point I should also mention the wife...

Steve A.


Hahaha Life does get in the way some times you go down one path you turn and go into another as here i want my phonoVision recorder player to do more than 32 line 30 line perhaps 48 might be possible with FreeNBTV program i can test its top range might even do a bit more SSTV with it but here i need a monitor to view the play back the Narrow band Television results so back on this CRT project need and ended up big than i thought working on the panel and what's possible to display with it again!

Just see on your front what you feel like doing can always go back to it or work a bit on each and keep the dish washer empty the wife likes that :lol:


Coming back on-topic, it'll be the SSTV-TV/VGA thingy first, the DC-coupled recorder second, then (perhaps) the updated 'ROM-scanner', with or without the display...but I'm open to other suggestions...


Well i liked the 625 line thing but VGA is OK to i am rusty on this but you could do both with circuit below and what your outputting from to the Vga monitor i think ?
b5476e0933bcbf89319fe4dc35727033.jpg
b5476e0933bcbf89319fe4dc35727033.jpg (24.54 KiB) Viewed 7977 times

viewtopic.php?f=8&t=2548&p=23342&hilit=mode+line+program#p23342
Playing around with the mode line program above with correct settings you could every one happy but that was a PC and this is different so just in case ?

The updated 'Rom-scanner' is a concept, stores 1024 images in the same format as Ralph's (8k-byte each), maybe four/five DIL/SOIC/SOIJ chips, one 28-pin DIP/DIL device (the micro), the others smaller, nothing exotic...


Well that sounds good to ! a lot of projects to mind at once ,i think more than 2 would be hard to juggle ...perhaps get onto the CRT project the others are similar give you time to think about them more .
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: Fault finding

Postby Steve Anderson » Tue Feb 16, 2021 8:01 pm

Harry Dalek wrote:Well that sounds good too! I think more than 2 would be hard to juggle

Yep. Now (I think) I'm around the 'blockage' [1] I had with the SSTV up-converter the others will fall into place in time. I do feel duty-bound to complete the SSTV-TV/VGA first though. The others, well, we'll see...they are somewhat embryonic at this stage...though an interesting distraction over the past while...sometimes you hit an impasse, "How in the heck am I going to do this?" I hope I've found it! It's as if the brain's digestive system works on it, in my case often while I'm asleep, a 'Eureka' moment..though not to be said in the same breath as Archimedes or Einstein...

Interesting to note both those gents surnames start with a vowel, so does mine, nah!, forget it Steve...

Steve A.

[1] Maybe constipation would have been a better word?
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Re: Fault finding

Postby Harry Dalek » Wed Feb 17, 2021 8:17 am

Steve Anderson wrote:Yep. Now (I think) I'm around the 'blockage' [1] I had with the SSTV up-converter the others will fall into place in time. I do feel duty-bound to complete the SSTV-TV/VGA first though. The others, well, we'll see...they are somewhat embryonic at this stage...though an interesting distraction over the past while...sometimes you hit an impasse, "How in the heck am I going to do this?" I hope I've found it! It's as if the brain's digestive system works on it, in my case often while I'm asleep, a 'Eureka' moment..though not to be said in the same breath as Archimedes or Einstein...

Interesting to note both those gents surnames start with a vowel, so does mine, nah!, forget it Steve...

Steve A.

[1] Maybe constipation would have been a better word?


Well the up converter is pretty much done to finish off or large percentage but does not stop you thinking about the others on a to do list as you say they will fall into place ,have to do what you feel like too so some thing different to the above is always good ,perhaps do a topic on the forum for them all here and see if it evolves least you can go back to it if it go's any where as they are all interesting ideas.
All this keeps the mind active all in the same boat here ,i always find doing some thing very different to the last idea is more enjoyable you have not done a CRT one for a while .
On my topic i am going to have a look brightness and contrast controls today we are in lock down again last day of a week of it i think so have some time today to ponder and poke around :wink:
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: Fault finding

Postby Harry Dalek » Wed Feb 17, 2021 10:45 am

I have worked out the multisystem framing for this monitor worked out all i had to do was make R622 variable on ic604B just lowing the resistance a touch for different higher line rates over 36 line the framing works now the main trimmers on ic605a coase and fine can stay as is, seems to work so far up to 64 line very well..the jump in the short wav video is due to repeating the video.
So i think all i have to do is switch in a pot using a 500k over the 82k to lower it resistance and adjust it for framing depending on the line rate switch it off if need be for 32 line and under.
My thoughts are why be stuck with a one system monitor when you can have many
64 line below
Attachments
circuits (1).jpg
P1070678_x264.mp4
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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: Fault finding

Postby Harry Dalek » Wed Feb 17, 2021 12:53 pm

I found the monitor will frame in the 100 line or more range so far tested of cause Bandwidth is not there for a great image but this good to see the syncing is there ! .
Didn't adjust the aspect ratio here pretty much need to increase image size higher you go pushing it with this little CRT ..well does show Steves circuits have no problem for a wide syncing range .
I would think a video of the correct bandwidth would display rather well think the opamps have the bandwidth .
32 line
P1070689.JPG

50 line
P1070681.JPG

100 line
P1070696.JPG
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: Fault finding

Postby Steve Anderson » Wed Feb 17, 2021 1:28 pm

Well I'm surprised they continue to operate well away from the frequencies they were designed for, I must have had a good day that day! I don't recall as it was five years ago as noted on the circuits.

I would guess the bandwidth limitation will be set by the opto-coupler arrangement, mainly on the output (CRT) side and to a lesser extent the op-amps used. Overall a bandwidth of 30-50kHz is probably the limit, perhaps a bit less. I think I checked it to around 15kHz but didn't go any further.

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Re: Fault finding

Postby Harry Dalek » Wed Feb 17, 2021 5:35 pm

Steve Anderson wrote:Well I'm surprised they continue to operate well away from the frequencies they were designed for, I must have had a good day that day! I don't recall as it was five years ago as noted on the circuits.

I would guess the bandwidth limitation will be set by the opto-coupler arrangement, mainly on the output (CRT) side and to a lesser extent the op-amps used. Overall a bandwidth of 30-50kHz is probably the limit, perhaps a bit less. I think I checked it to around 15kHz but didn't go any further.

Steve A.


Yes the years go quick ! On the syncing side this is pretty good range wise

It always originally had no problem with detecting the line sync on wide range of line rates at all ....this is the first time i have looked into the framing side and it really is just a minor change to get to do as shown ,when i have time it would be nice just to know its limits on the high end as is .

OH the Opto coupler bandwidth is lower than expected , i think it would be higher than 15khz since 64 line looks ok more than likely using all the pcs audio bandwidth ,i suppose there might be better opto couplers for this .
Any case interesting
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: Fault finding

Postby Steve Anderson » Thu Feb 18, 2021 12:43 pm

Harry Dalek wrote:OH the Opto coupler bandwidth is lower than expected , i think it would be higher than 15khz since 64 line looks ok more than likely using all the pcs audio bandwidth ,i suppose there might be better opto couplers for this. Any case interesting

Yes, the output bandwidth from the PC will dictated by the sample rate and type of file. If your PC can generate/handle 96kHz sampling the bandwidth will be half of that, 48kHz. Most (mine included) are limited to 48kHz sampling, i.e. 24kHz of video bandwidth. It is, by laptop standards, getting old now, nearly five years, but still does all I require.

Opto-couplers can be improved in bandwidth to an extent, but the simple circuit in the CRT application above does impose some limits. A short (glass)fibre-link is one answer, but the optical components for high-speed aren't as cheap as an opto-coupler and generally logic devices, not linear, requiring an A-D and a D-A plus all the support stuff.

A short RF link (a few cm) is another option, a few micro-watts is enough, but interference could be a problem, and more complexity added.

Those are what spring to mind at the moment, there are surely others...

Steve A.

The dual (one LED, two photodiodes) opto-coupled device in the attached datasheet (IL300) claims a bandwidth to 200kHz and excellent linearity. (Implying a rise/fall time of 1.75us). Worth considering. But the CRT grid-drive arrangement mentioned above would also need an overhaul.

There are other very similar devices that go up to 1MHz or more...

IL300 2.pdf
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Re: Fault finding

Postby Harry Dalek » Thu Feb 18, 2021 8:15 pm

Steve Anderson wrote:
Opto-couplers can be improved in bandwidth to an extent, but the simple circuit in the CRT application above does impose some limits. A short (glass)fibre-link is one answer, but the optical components for high-speed aren't as cheap as an opto-coupler and generally logic devices, not linear, requiring an A-D and a D-A plus all the support stuff.


I recall i think your experiments a while back you were testing this ?

A short RF link (a few cm) is another option, a few micro-watts is enough, but interference could be a problem, and more complexity added.


mmm this a new one to me

Those are what spring to mind at the moment, there are surely others...


Well induction ..the transformer passive modulation is another i used a while back perhaps using a audio transformer would be a simpler smaller idea if a mains transformer has no problem to transfer the video at NBTV bandwidth you would think a transformer dedicated to audio would be as good or better wider ? has any one done a frequency test to test these things frequency range ?
Some times simple ideas old inventions still can out class todays inventions i am still amazed at magnetic amplifier's what you can do with copper wire and steel.
I suppose its really similar to a RF link AF link at least :wink:
Here's a passive modulation test a cyclops photo i did at 128 line the mains 50hz transformer i think is doing better than the opto might be worth check be no great circuit change i could just wire in the transformer for either cathode or control grid modulation and hook the opto back as a temp brightness control something to think about .
IMG_0612.JPG
IMG_0612.JPG (142.25 KiB) Viewed 7884 times


viewtopic.php?f=15&t=2641&hilit=passive+modulation

Edit
Audio transformers using sheet steel cores, such as those used in vacuum tube amplifier circuits to match the high impedance of the tube to the low impedance of the speaker, have a bandwidth of 20Hz to 20kHz, RF transformers made using ferrite or even air cores can have bandwidths of 1MHz-30MHz.

Sounds like with a simple idea you could out do an opto coupler as far as transfer of the frequency side of it with a bit of experimentation .

Steve A.

The dual (one LED, two photodiodes) opto-coupled device in the attached datasheet (IL300) claims a bandwidth to 200kHz and excellent linearity. (Implying a rise/fall time of 1.75us). Worth considering. But the CRT grid-drive arrangement mentioned above would also need an overhaul.

There are other very similar devices that go up to 1MHz or more...

The attachment IMG_0612.JPG is no longer available


Yes 200khz is a big improvement not really a drop in replacement but interesting for sure
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: Fault finding

Postby Steve Anderson » Fri Feb 19, 2021 12:39 am

Harry Dalek wrote:Yes 200khz is a big improvement not really a drop in replacement but interesting for sure

Yes, but they're smaller and not prone to external magnetic fields or a transformer's size, weight or cost[1]. Plus opto-coupled arrangements are easily DC-coupled, no headaches with LF performance, a bugbear of NBTV and SSTV.

Steve A.

[1] I'm always thinking of commercial applications...
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Re: Fault finding

Postby Harry Dalek » Sun Feb 21, 2021 3:22 pm

Steve Anderson wrote:
Harry Dalek wrote:Yes 200khz is a big improvement not really a drop in replacement but interesting for sure

Yes, but they're smaller and not prone to external magnetic fields or a transformer's size, weight or cost[1]. Plus opto-coupled arrangements are easily DC-coupled, no headaches with LF performance, a bugbear of NBTV and SSTV.

Steve A.

[1] I'm always thinking of commercial applications...


Yes that is a good point about the opto coupler ,i will put that one the back burner for now and look into if i can find a wider bandwidth version for the future .
For what i am up to here the lower bandwidth video is all needed but i am curious to improve things for a future monitor 100 lines over .
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: Fault finding

Postby Steve Anderson » Sun Feb 21, 2021 6:39 pm

Harry Dalek wrote:...for a future monitor 100 lines (or) over .

Well, it all depends on the bandwidth required. Which is dictated by number of lines (OK set at 100 for now), Aspect ratio, (WxH), and frame rate. Plus to an extent sync arrangements.

Say 100 lines, 1.5 Aspect Ratio and 12.5 fps. So that implies 150 line pixels. 100 lines at 12.5fps. 100 (lines) x 150 (pixels) x !2.5 (fps) = 187,500 pixels per second, a bandwidth of 93kHz. Add in a fudge-factor of 15% for syncs = approx. 105kHz. You see the problem...

The electronics isn't the problem, the storage and retrieval could be...and we haven't even touched on the audio to go with it.

The bandwidth required goes up with the square of the resolution required, all other things being equal...

Steve A.
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