Author Topic: Getting a picture on a mini camcorder CRT  (Read 4125 times)

0 Members and 1 Guest are viewing this topic.

Offline QuantumplateTopic starter

  • Regular Contributor
  • *
  • Posts: 135
  • Country: gb
Re: Getting a picture on a mini camcorder CRT
« Reply #25 on: May 28, 2023, 12:04:17 pm »
Please connect your scope probe to pin 1 at the tube base and post a photo of the scope trace of the video there.
Pure D.C. 0.75v as shown.
I
 

Online wasedadoc

  • Super Contributor
  • ***
  • Posts: 1268
  • Country: gb
Re: Getting a picture on a mini camcorder CRT
« Reply #26 on: May 28, 2023, 12:16:22 pm »
Aren't you wondering why this is not the video signal you stated you saw at the emitter of Q904?
 

Offline AndyBeez

  • Frequent Contributor
  • **
  • Posts: 837
  • Country: cx
Re: Getting a picture on a mini camcorder CRT
« Reply #27 on: May 28, 2023, 08:07:09 pm »
It's all there in the service manual - just remove the dot from the end of your link.

The 'composite' input is actually a luminance signal that originates from IC 201.

The service manual shows the expected scope traces for the EVF board.

RTM :popcorn:
« Last Edit: May 28, 2023, 08:10:01 pm by AndyBeez »
An iPhone is held together by glue. A Boeing 737 Max 9 is held together by angels.
 
The following users thanked this post: Quantumplate

Offline QuantumplateTopic starter

  • Regular Contributor
  • *
  • Posts: 135
  • Country: gb
Re: Getting a picture on a mini camcorder CRT
« Reply #28 on: May 28, 2023, 08:08:19 pm »
Aren't you wondering why this is not the video signal you stated you saw at the emitter of Q904?
Sorry, life got in the way for a bit after whacking the photo up.
Pins 3 and 5 are also putting out straight d.c. when they should be sawtooth waves of course for the vertical deflection. Pin 1 i'm not sure what should be emerging there, but these are all the chip vertical sync section so there's the problem - new chip needed i would assume. Luckily a couple of places still sell them.
Why do you think pin 1 should be the video signal?
 

Offline QuantumplateTopic starter

  • Regular Contributor
  • *
  • Posts: 135
  • Country: gb
Re: Getting a picture on a mini camcorder CRT
« Reply #29 on: May 28, 2023, 08:39:20 pm »
Aren't you wondering why this is not the video signal you stated you saw at the emitter of Q904?
Sorry, life got in the way for a bit after whacking the photo up.
Pins 3 and 5 are also putting out straight d.c. when they should be sawtooth waves of course for the vertical deflection. Pin 1 i'm not sure what should be emerging there, but these are all the chip vertical sync section so there's the problem - new chip needed i would assume. Luckily a couple of places still sell them.
Why do you think pin 1 should be the video signal?
Sorry, misread your instructions - i posted about pin 1 of the ic. You meant the tube connector point to see if that was working.
 

Online wasedadoc

  • Super Contributor
  • ***
  • Posts: 1268
  • Country: gb
Re: Getting a picture on a mini camcorder CRT
« Reply #30 on: May 28, 2023, 09:04:16 pm »
Aren't you wondering why this is not the video signal you stated you saw at the emitter of Q904?
Sorry, life got in the way for a bit after whacking the photo up.
Pins 3 and 5 are also putting out straight d.c. when they should be sawtooth waves of course for the vertical deflection. Pin 1 i'm not sure what should be emerging there, but these are all the chip vertical sync section so there's the problem - new chip needed i would assume. Luckily a couple of places still sell them.
Why do you think pin 1 should be the video signal?
I already told you (in Reply #5) which places to scope for the video signal.  There is nothing amiss with the vertical deflection - the evidence for that is in front of your eyes when you look at the CRT screen.  If you want to scope the vertical sawtooth it is on pin 5.  Unless and until you find there is no inverted video coming out of the chip on pin 14, you have no reason to think the chip needs to be replaced.
« Last Edit: May 28, 2023, 09:14:36 pm by wasedadoc »
 

Offline vk6zgo

  • Super Contributor
  • ***
  • Posts: 7525
  • Country: au
Re: Getting a picture on a mini camcorder CRT
« Reply #31 on: May 29, 2023, 12:28:03 am »

I already told you (in Reply #5) which places to scope for the video signal.  There is nothing amiss with the vertical deflection - the evidence for that is in front of your eyes when you look at the CRT screen.  If you want to scope the vertical sawtooth it is on pin 5.  Unless and until you find there is no inverted video coming out of the chip on pin 14, you have no reason to think the chip needs to be replaced.

I think that should be pin 13.

The DC voltage on Q903 collector & Q904 emitter is important, as it is -10v derived from the centre tap of the FBT secondary via a rectifier & C914.
I have had strife with "derived" supplies like that in the past-----the filter cap fails either O/C, when you get unfiltered half wave
rectifier crud, or S/C when you pretty much get "zilch".
 

Offline EPAIII

  • Frequent Contributor
  • **
  • Posts: 988
  • Country: us
Re: Getting a picture on a mini camcorder CRT
« Reply #32 on: May 29, 2023, 02:05:07 am »
EDIT: I read the rest of the thread. And eliminated my suggested starting place. Good luck.


Base band video, composit video, NTSC video, and PAL video are all terms that mean a video signal as would come from a camera which is just that, a CAMERA and nothing more. They usually do have sync and the color reference burst added to the combined waveform/signal. These terms, keeping in mind the differences between NTSC and PAL, all mean a signal that combines: black and white video information, a color subcarrier that contains the color information, the vertical and horizontal sync signals, and the color "burst" which is the timing reference for decoding the encoded color information. These signals do not contain audio. Base band audio, monaural of stereo, would be the accompanying audio signal.

Base band video signals are commonly carried on 75 Ohm, coaxial cables with connectors like BNC and RCA. But almost any other kind of connector can also be used.

When the base band or composit video signal AND the base band audio signal(s) are modulated on an RF carrier, you then have what is commonly called an RF signal. And it contains everything that a TV monitor needs to display both a picture and the sound.

RF, modulated signals are commonly carried on 50 Ohm coaxial cables with type F, BNC, or many other kinds of coaxial connectors.

You may notice that I listed BNC connectors for both base band and RF signals. But, since two different coaxial cable impedances are used for these two, the BNC connectors are also NOT the same. BNC connectors actually come in three varieties: 75 Ohm, 50 Ohm, and Non Continuous (not specified) impedance. The third of which is, perhaps, the most common.



Even so, either NTSC or PAL format video into the viewfinder module from a 210 or a 210E should give something visible on the tube.

Why are you using a cable with those Belling-Lee coax plugs?  The video signal from the DVD player into the viewfinder needs to be baseband not RF.  Your mention of "channel frequency o/p of the dvd player" and "fixed channel i/p of the viewfinder crt" is nonsense.

Thanks for helping with my education on this. I've always skipped over analogue tv theory until now. And the only connectors i've ever used on the back of tvs/vcrs/dvds have been Scart connectors. 

What are the 210 and 210e you referred to? You lost me there.
I checked in the manual and it's pin 3 for video which i've wired up so that's all good. I did try inputting a signal without the converter box too when i initially hooked everything up two weeks ago.

I have that old coax cable there because i thought i would be plugging it into the rf out of an equally old vcr recorder. That didn't give a picture other than white so i moved on to the dvd player. Having soldered the pin to the wire I've left it like that and have to use adaptors to join it to a phono rca cable.
So i'm using the rca Video out socket from the dvd player.  Is that a baseband signal?
I thought it was rf out tuned to channel 36 for an analogue tv to decode, hence my utter confusion. Still confused actually as i don't see any other connection options from my dvd player. I've looked up baseband, but in all the analogue tv theory sections in my books the only signal in town is the rf composite video/audio signal, so i'm none the wiser yet.

 I do appreciate your efforts though!
« Last Edit: May 29, 2023, 02:13:10 am by EPAIII »
Paul A.  -   SE Texas
And if you look REAL close at an analog signal,
You will find that it has discrete steps.
 
The following users thanked this post: Quantumplate

Offline QuantumplateTopic starter

  • Regular Contributor
  • *
  • Posts: 135
  • Country: gb
Re: Getting a picture on a mini camcorder CRT
« Reply #33 on: May 29, 2023, 08:50:04 am »
Aren't you wondering why this is not the video signal you stated you saw at the emitter of Q904?
If you want to scope the vertical sawtooth it is on pin 5. 
I did and there's no sawtooth (reply #28), hence chip not working?, despite the white wash on the screen...which i know doesn't make sense.
 

Online wasedadoc

  • Super Contributor
  • ***
  • Posts: 1268
  • Country: gb
Re: Getting a picture on a mini camcorder CRT
« Reply #34 on: May 29, 2023, 10:49:10 am »
I think that should be pin 13.
Typo. Yes, pin 13 is inverted video out to the discrete transistor Q903.
 

Online wasedadoc

  • Super Contributor
  • ***
  • Posts: 1268
  • Country: gb
Re: Getting a picture on a mini camcorder CRT
« Reply #35 on: May 29, 2023, 11:13:47 am »
Don't know why you are hung up on the chip being faulty.  It is the also the horizontal oscillator which provides drive out of pin 16 to Q902.  Q902 cannot oscillate by itself.  If Q902 was not switching on and off there would be no horizontal scan, no final anode voltage and no heater current.  From what you have described seeing on the tube screen all those three are present so the chip is not dead.  The chip also contains the vertical oscillator and output power to the vertical deflection coils.  If that was not working the raster would not cover the screen height.

Please use the scope on pin 13 of the IC. Is inverted video there or not? If yes, put your scope on the the grid pin of the CRT.  That is pin 1 of W901. See the PCB layout on page 4-50 of the Service Manual.  Is erect video there?
 
The following users thanked this post: Quantumplate

Offline QuantumplateTopic starter

  • Regular Contributor
  • *
  • Posts: 135
  • Country: gb
Re: Getting a picture on a mini camcorder CRT
« Reply #36 on: May 29, 2023, 02:31:04 pm »
Please use the scope on pin 13 of the IC. Is inverted video there or not? If yes, put your scope on the the grid pin of the CRT.  That is pin 1 of W901. See the PCB layout on page 4-50 of the Service Manual.  Is erect video there?
Yes, and yes - both present.
I promise you that there are no sawtooth waveforms on pins 3 or 5, just d.c. So the vertical sync section of the chip is kaput, even though the rest seems fine.
 

Online wasedadoc

  • Super Contributor
  • ***
  • Posts: 1268
  • Country: gb
Re: Getting a picture on a mini camcorder CRT
« Reply #37 on: May 29, 2023, 04:34:53 pm »
Please use the scope on pin 13 of the IC. Is inverted video there or not? If yes, put your scope on the the grid pin of the CRT.  That is pin 1 of W901. See the PCB layout on page 4-50 of the Service Manual.  Is erect video there?
Yes, and yes - both present.
I promise you that there are no sawtooth waveforms on pins 3 or 5, just d.c. So the vertical sync section of the chip is kaput, even though the rest seems fine.
Please post two photos showing the screen at two significantly different brightness levels.
 

Offline QuantumplateTopic starter

  • Regular Contributor
  • *
  • Posts: 135
  • Country: gb
Re: Getting a picture on a mini camcorder CRT
« Reply #38 on: May 29, 2023, 04:57:14 pm »
Please use the scope on pin 13 of the IC. Is inverted video there or not? If yes, put your scope on the the grid pin of the CRT.  That is pin 1 of W901. See the PCB layout on page 4-50 of the Service Manual.  Is erect video there?
Please post two photos showing the screen at two significantly different brightness levels.
Three here - 1st is crt unpowered.
 

Offline QuantumplateTopic starter

  • Regular Contributor
  • *
  • Posts: 135
  • Country: gb
Re: Getting a picture on a mini camcorder CRT
« Reply #39 on: May 30, 2023, 09:42:38 am »
Just musing on whether the problem may be C907 connected to the V.OSC part of the ic. I tried measuring it in situ of course, and my trusty B&K capacitance meter gave the readout you get when shorting the probes. Ok, so maybe pins 6 and 7 are connected internally i thought - but not according to my continuity test.
 

Online wasedadoc

  • Super Contributor
  • ***
  • Posts: 1268
  • Country: gb
Re: Getting a picture on a mini camcorder CRT
« Reply #40 on: May 30, 2023, 12:04:23 pm »
There are two conflicting pieces of evidence and a third that appears unrelated.

1.  No sawtooth waveform points to no vertical scan.

2.  Screen lit up evenly from top to bottom suggests there is vertical scan.

3.  Irrespective of vertical scan or not a changing voltage (ie video) on Q904 emitter should be making visible changes to screen brightness.

Before you go to the step of changing the IC it would be best to get a definitive answer about vertical scan.  There is one test I can think of.  On a display with a vertical amplitude (ie height) or shift control one could adjust it to bring the top and/or bottom of the raster into view.  Sharp transitions between the middle lit area and top and/or bottom unlit area of the screen would be proof of vertical scan.

Your viewfinder has no such control. It would of course be possible to reduce the scan current by increasing the value of some resistor such as R915 but that is a tiddly surface mount one.  Prefer not to try to swap that out (and back in again afterwards) especially if awkward to get at.

I suggest the less invasive method of trying to use a magnet to shift the electron beam travelling down the tube.  This would act like a shift control and bring edge of illuminated area into the visible part of the screen.  A bar magnet would probably be more effective than a horseshoe one but whatever you can lay your hands on.  Just experiment with moving it around near the deflection coils yoke and see if you can get a horizontal edge or one of the corners visible.  If you see sharp transition then vertical scan is happening,  If you see a slow soft transition I would suspect a problem with CRT voltages causing a very defocused electron beam illuminating the whole screen.

« Last Edit: May 30, 2023, 12:28:51 pm by wasedadoc »
 

Offline AndyBeez

  • Frequent Contributor
  • **
  • Posts: 837
  • Country: cx
Re: Getting a picture on a mini camcorder CRT
« Reply #41 on: May 30, 2023, 02:11:09 pm »
I suggest the less invasive method of trying to use a magnet to shift the electron beam travelling down the tube.

The simplest fault finding techniques are often the best :-+

You could also try videoing the CRT with a mobile phone. Experiment with frame rates if they are available on the movie app. The result should be be a flickering or strobing display. Again, this with show the raster is doing something.
An iPhone is held together by glue. A Boeing 737 Max 9 is held together by angels.
 

Offline QuantumplateTopic starter

  • Regular Contributor
  • *
  • Posts: 135
  • Country: gb
Re: Getting a picture on a mini camcorder CRT
« Reply #42 on: May 30, 2023, 02:45:00 pm »
Time to say i appreciate your tenacity!
Right, so, couple of pics to look at:
1st one is with power to the EVF dropped from 5v to around 3.5v. I get about the top 1/6 of the screen illuminated, fuzzy as hell, but with evidence of moving shapes/brightnesses as the dvd plays. Just thought you'd like to know.
2nd pic is pin 4 on connector CN902 - horizontal coil, showing around 50v pk-pk. Not a sawtooth though is it?

I tried the magnet trick with my telescopic screw retriever. No sharp transitions to be seen, just very gloopy soft transitions.
 

Offline QuantumplateTopic starter

  • Regular Contributor
  • *
  • Posts: 135
  • Country: gb
Re: Getting a picture on a mini camcorder CRT
« Reply #43 on: May 30, 2023, 03:11:44 pm »

You could also try videoing the CRT with a mobile phone. Experiment with frame rates if they are available on the movie app. The result should be be a flickering or strobing display. Again, this with show the raster is doing something.
Nice idea!...sadly 20 year old phone here, or should i say happily.
 

Online wasedadoc

  • Super Contributor
  • ***
  • Posts: 1268
  • Country: gb
Re: Getting a picture on a mini camcorder CRT
« Reply #44 on: May 30, 2023, 03:12:02 pm »
Time to say i appreciate your tenacity!
Right, so, couple of pics to look at:
1st one is with power to the EVF dropped from 5v to around 3.5v. I get about the top 1/6 of the screen illuminated, fuzzy as hell, but with evidence of moving shapes/brightnesses as the dvd plays. Just thought you'd like to know.
2nd pic is pin 4 on connector CN902 - horizontal coil, showing around 50v pk-pk. Not a sawtooth though is it?

I tried the magnet trick with my telescopic screw retriever. No sharp transitions to be seen, just very gloopy soft transitions.
You will not see a voltage sawtooth when probing the horizontal deflection coil.  At horizontal sweep rate the inductance of the deflection coil dominates its resistance.  So voltage step gives an approximation to sawtooth current.  It is the current which generates the field which deflects the beam.  The step is the long flat bit along the bottom of the scope trace.  The other end of the coil is at +ve supply.

Can you do a better close-up of the CRT screen when running at reduced voltage and video playing?

I have attached the datasheet for the IC.  Would be interesting to see the waveform on pin 8.
« Last Edit: May 30, 2023, 03:36:48 pm by wasedadoc »
 
The following users thanked this post: Quantumplate

Offline QuantumplateTopic starter

  • Regular Contributor
  • *
  • Posts: 135
  • Country: gb
Re: Getting a picture on a mini camcorder CRT
« Reply #45 on: May 30, 2023, 04:19:23 pm »
Time to say i appreciate your tenacity!
Right, so, couple of pics to look at:
1st one is with power to the EVF dropped from 5v to around 3.5v. I get about the top 1/6 of the screen illuminated, fuzzy as hell, but with evidence of moving shapes/brightnesses as the dvd plays. Just thought you'd like to know.
2nd pic is pin 4 on connector CN902 - horizontal coil, showing around 50v pk-pk. Not a sawtooth though is it?

I tried the magnet trick with my telescopic screw retriever. No sharp transitions to be seen, just very gloopy soft transitions.
You will not see a voltage sawtooth when probing the horizontal deflection coil.  At horizontal sweep rate the inductance of the deflection coil dominates its resistance.  So voltage step gives an approximation to sawtooth current.  It is the current which generates the field which deflects the beam.  The step is the long flat bit along the bottom of the scope trace.  The other end of the coil is at +ve supply.

Can you do a better close-up of the CRT screen when running at reduced voltage and video playing?

I have attached the datasheet for the IC.  Would be interesting to see the waveform on pin 8.
Fraid i can't - comes out too overexposed. It looks like only one horizontal line repeated multiple times.

Pin 8 is doing weird things to my scope. The central 0v beam stays where it is, plus the thin d.c. line shown pops up...
 

Online wasedadoc

  • Super Contributor
  • ***
  • Posts: 1268
  • Country: gb
Re: Getting a picture on a mini camcorder CRT
« Reply #46 on: May 30, 2023, 04:31:44 pm »
Pin 8 is doing weird things to my scope. The central 0v beam stays where it is, plus the thin d.c. line shown pops up...
Scope is not triggering properly.  Maybe timebase is set too fast.  Should be 5ms.
 

Offline QuantumplateTopic starter

  • Regular Contributor
  • *
  • Posts: 135
  • Country: gb
Re: Getting a picture on a mini camcorder CRT
« Reply #47 on: May 30, 2023, 04:59:17 pm »
Scope is not triggering properly.  Maybe timebase is set too fast.  Should be 5ms.
[/quote]
Yes, you're right, wasn't expecting to go that slow.
 

Online wasedadoc

  • Super Contributor
  • ***
  • Posts: 1268
  • Country: gb
Re: Getting a picture on a mini camcorder CRT
« Reply #48 on: May 30, 2023, 05:56:57 pm »
Vertical oscillator is running OK.

When you measured the voltages on the IC pins did you actually measure pin 4 or did you just assume it was GND because the schematic shows that? And could you recheck that -0.4 volts on pin 6?  I cannot figure out how/why there would be any negative voltages.
 

Offline QuantumplateTopic starter

  • Regular Contributor
  • *
  • Posts: 135
  • Country: gb
Re: Getting a picture on a mini camcorder CRT
« Reply #49 on: May 30, 2023, 06:17:00 pm »
Vertical oscillator is running OK.

When you measured the voltages on the IC pins did you actually measure pin 4 or did you just assume it was GND because the schematic shows that? And could you recheck that -0.4 volts on pin 6? 
Yes i measured pin 4 and got 12mV.
Checked pin 6, now getting 1.5v. Not sure what happened earlier - apologies.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf