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TV Video Problems (Got Color!) — Parallax Forums

TV Video Problems (Got Color!)

blittledblittled Posts: 681
edited 2009-09-06 10:48 in Propeller 1
I set up the circuit for TV Video on a breadboard and everything works fine. Then for some reason the output goes to black and white only. I checked the connections with a voltmeter and it checks out. I finally resoldered the connections on a female header on a PSM board that I connect to the resistors to and the color came back. After awhile the screen goes black and white again and I can't get the color back. I think I still may have a bad connection. What resistor combo causes black and white only?

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Post Edited (blittled) : 9/5/2009 2:45:01 PM GMT

Comments

  • potatoheadpotatohead Posts: 10,261
    edited 2009-09-04 04:17
    Have you checked your clock reference? If it's not a crystal, then you will have color problems due to accuracy problems.

    Pretty sure it's the 270 ohm that adds the chroma signal in.

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  • VIRANDVIRAND Posts: 656
    edited 2009-09-04 07:45
    Sounds like inaccurate or loose crystal, nothing else except maybe bad video cable (or antenna if you used one).
    Touch the crystal and see if that makes the color come and go.
    Check the chroma frequency in the program DAT; It should be 3579545 for NTSC American analog TV or something else for PAL.
    For one inaccurate crystal maybe try adjusting for a single project's board by changing the crystal frequency in CON
    or the chroma frequency in the tv object parm DAT sections in the program by a small amount from -3000 to 3000.

    Edit:Also, crystal must be very close to the propeller chip and best soldered in. Long wires make the crystal inaccurate.
    It might help a lot to put 10pF caps from crystal wires to ground, although I heard they are already inside the Propeller.
    Do you have a bypass capacitor across and close to the Propeller power input?
    Are all 4 VCC and VSS pins connected to the power?
    Does your 3.3V power supply Voltage Regulator require a over 100uF capacitor that's missing across it's output?
    The color comes from one pin through a resistor and it's very unlikely to have intermittent color from a wrong resistor.
    Again, bad video connection or if you are experimenting with transmit antenna it's likely to have intermittent color.
    (^Home made board troubleshooting ideas added)

    Post Edited (VIRAND) : 9/4/2009 8:11:31 AM GMT
  • blittledblittled Posts: 681
    edited 2009-09-04 11:03
    Thanks for all the input. I'm using the 10 pin header from a Propeller System Module so crystal placement and trace lengths are not the issue. I also wired up another Propeller to the TV output with no problem. I do think it may be the header connection to the PSM. I'll look for a cold solder joint at the 270 ohm resistor connection. I'll also change the video cable.

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  • RaymanRayman Posts: 14,849
    edited 2009-09-04 12:13
    Uh oh... I hope it's not a bad connection at the Prop or the crystal... If the resistor checks out, try pushing down gently on the crystal and then the prop. Also, if you can, try to see if the crystal pins of the Prop are soldered down good. I usually test all the PSMs for good video ever since I had a bad contact once... But, one could have slipped through...

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  • RaymanRayman Posts: 14,849
    edited 2009-09-04 12:16
    On the other hand, if you have color when you first turn it on and then if fades away, that sounds like some other problem...

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  • RaymanRayman Posts: 14,849
    edited 2009-09-04 14:22
    Make sure you have a good ground connection to the RCA connector from the PSM too...

    PS:· Are you saying that you have the same problem with the breadboarded Propeller?· Or, that it works with the breadboard but not with the PSM?

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  • blittledblittled Posts: 681
    edited 2009-09-04 16:10
    The breadboard propeller works great and gets color. I'm thinking of redoing some things since it has become a nest of 24 gage solid wires. I'll make my own ribbon connectors and see if that works since I'm sure I'm getting a bad connection somewhere. I'll post my results.

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  • blittledblittled Posts: 681
    edited 2009-09-05 02:38
    Ok I tested things out. This is the setup:

    Female header soldered on the 10 pin header breakout. I then use a Parallax Breadboard RCA Connector. The resistors are 1K, 560, 270 10% tolerance 1/4 watt. The connection between the breadboard and PSM: Short 24 gauge wire from the RCA Connector ground and the ground on the 10 pin header. A servo 3 conductor cable with 3 pin headers to plug into the resistors on the breadboard and the female header.

    Results:
    Black and white screen. Pressing on the crystal does sometimes bring back the color. But then in about 3 minutes it loses color until pressed again. I tried resoldering the two pads on either side of the crystal and it only brings back the color for about 3 minutes.

    Is this something that can be easily repaired with a 15 Watt Soldering Iron and a 30 Watt desoldering iron with a squeeze bulb? Thanks for all your advice.

    Rayman: The PSM is definitely an awesome device and I'm very impressed you take the time to build and test every board. This may be a poor connection but I've learned from personal experience those are always the hardest to track down since they can work sometimes and sometimes not depending on the mood of the circuit [noparse]:)[/noparse]. Reminds me of when you take a car into the shop due to a noise and it doesn't make it for the mechanic. [noparse]:)[/noparse]

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    Post Edited (blittled) : 9/5/2009 2:46:03 PM GMT
  • blittledblittled Posts: 681
    edited 2009-09-05 04:54
    I just noticed something. When I first apply power it holds the color the longest. As it warms up each tap on the crystal causes it to remain holding the color shorter until it no longer will show color. Is this a sign of a bad crystal since it seems to drift out of color synch?

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  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2009-09-05 14:47
    Blittled

    On PAL I have noticed that the background colour beating can be minimised/masked by altering the frequency quoted in _xinfreq. On one of my bds the xtal was about 1.5KHz lower than the marked 5.000MHz. Obviously a small error could have been introduced by measuring it but when 4_998_500 was used the chroma was better. With regards to your problems, if I used numbers further away in either dirrection colour lock was lost.

    Try some numbers and see what happens. The mass produced xtals are never exact, for better acuracy you pay more.

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  • blittledblittled Posts: 681
    edited 2009-09-05 14:49
    It turned out to be an inaccurate crystal. I still need to home in on the correct frequency to get the color correct but it holds the color now.

    Rayman: It's no big deal to have the crystal off a little. I was wondering though if it's easy to replace the crystal? Hmmm..... I got a couple 6.25MHz crystals lying around [noparse]:)[/noparse].

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  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2009-09-05 14:56
    Thats good. By varying the _xinfreq figures either side and the choosing the centre you should effectivly be measuring what the freq really is. Delay timings sould be more acurate too.

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  • RaymanRayman Posts: 14,849
    edited 2009-09-06 00:52
    Huh... I've never heard of that kind of failure before...
    Sounds like you can solder though... If you PM your address, I'll mail you an new crystal.

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  • blittledblittled Posts: 681
    edited 2009-09-06 02:14
    I'm not sure the laws of physics apply where I live! I just tried the video driver at 5MHz and everything works perfect! I have the PSM firmly mounted now so there isn't any movement of the wires. The wires in the header must have been just loose enough to be sensitive to the slightest movement and I was testing it without being mounted.

    Rayman: Thanks for the gracious offer. I don't think I need one now but if I do I have a couple of 5 MHz crystals so I'll use one of them if it happens again.

    Thank all that helped and gave me suggestions during my "false" alarm. Don't let my ramblings discourage anyone from buying a PSM. It is a very useful platform to work from and Rayman does quality work. I would recommend one to anyone.

    The crystal may not be off but I feel like I'm a little off [noparse]:)[/noparse]

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  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2009-09-06 10:48
    It probably shows what a tricky thing it is to generate

    1) Video of NTSC/PAL
    2) Encode the chroma

    It was this that led me to the Prop path. AVRs have no problems with the mono or RGB but req encoder chips, which are getting tricky to get now and would req the same acreage of PCB that the rest of the project.

    So it is this is an ability of the Prop that has been so cleverly woven in, and it is not surpising that the frequencies have to be so finely set.

    All this assumes that the Xtal on your Prop isn't "slightly wrong, one way" and the Xtal in the TV's decoder isn't "slightly wrong,the othe way"

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