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Thread: Connecting an Arcade PCB to a CRT TV

  1. #1
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    Connecting an Arcade PCB to a CRT TV

    I need a second monitor for my test bench, I've ran out of 14" arcade monitors so I thought I'd see if I could hack a CRT TV to display the RGBS from an arcade PCB.

    The Palsonic TV (Model 3499M) that I'm using has a TA8690 jungle chip and an ST6378B1/FLA controller IC.





    http://rokimservice.blogspot.com/201...a8690.html?m=1



    I've wired the RGB into the OSD inputs (pins 27/27/28)and the sync and ground to the AV connector at the back of the TV.
    It works except that the video seems to display inverted.
    My guess is that the OSD uses inverted video for some reason but there could be some other steps that I'm missing.
    I haven't cut the the traces from the OSD input so that may be interfering with the signal.

    Here's a video of it running Terra Cresta.



    How Terra Cresta should look...



    Any thoughts??
    @buttersoft
    Last edited by Kaizen; 10th June 2019 at 02:17 AM.
    Namco Starblade - Taito Cocktail 14" x 3, 20" x 2 - NZ SI PtII Upright - Chase HQ DX, Taito Top Speed - Taito Grand Champion - Taito Safari - LAI SI Head to Head Cocktail - SI Cocktail Clone x 2, Pong Clone x 3

  2. #2
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    Out of interest did you also do the blanking part? And are you pulling csync at the right level?

    Sent from my HTC 2PZF1 using Tapatalk

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    No blanking mod has been done, nothing else has been done as far as adding resistors etc.
    I have no experience with this stuff and am learning as I go.
    Will look up the controller IC and see if there is a blanking output next to the OSD output pins.
    Namco Starblade - Taito Cocktail 14" x 3, 20" x 2 - NZ SI PtII Upright - Chase HQ DX, Taito Top Speed - Taito Grand Champion - Taito Safari - LAI SI Head to Head Cocktail - SI Cocktail Clone x 2, Pong Clone x 3

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    I'm not completely either. Just doing the research to do the mod. But my understanding is you use the osd to inject your rgb. So blanking is necessary to tell the TV to use the osd. The reason I asked about sync is because I thought I K boards outputted HV, but likely the TV will only accept csync so therefore you would have to mix and I'm wondering if you'd also have lower the signal voltage.

    Sent from my HTC 2PZF1 using Tapatalk

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    I couldn't find a PDF for the ST6378B1/FLA controller but looking at the pinout for a few other similar ST chips it seemks they use the same pin locations for RGB-BLANK.



    I'll cut the traces from the OSD out and see what voltage the BLANK has when displaying the OSD.
    Namco Starblade - Taito Cocktail 14" x 3, 20" x 2 - NZ SI PtII Upright - Chase HQ DX, Taito Top Speed - Taito Grand Champion - Taito Safari - LAI SI Head to Head Cocktail - SI Cocktail Clone x 2, Pong Clone x 3

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    Good luck. I think it's such a cool mod and my thinking was this could be our arcade crt savior.

    Sent from my HTC 2PZF1 using Tapatalk

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    After reading the datasheet for the controller chip, the OSD can be set to positive or negative when programmed at factory.
    The BLANK pin is not connected.



    I followed the OSD outputs which each lead to a resistor then through a transistor to the jungle chip inputs.

    I lifted the three resistors on the output side and connected RGB to them first which gave me a barely visible image with just traces of blue showing but no white background.
    I then connected RGB to the other side of the resistors and got an image on screen that wasn't inverted but not perfect.
    The transistors are definitely inverting the signal.
    Some 25kΩ pots (all I had on hand with fly leads already connected) were connected inline on the RGB outputs from the arcade PCB and initially set to 1KΩ. When powered up the image was much better and I dialed them down to around 680Ω.
    Here's the result...



    I'll mount some 1kΩ trimmers on a Vero board for finer adjustment and hopefully that should sort it.
    Last edited by Kaizen; 10th June 2019 at 12:03 AM.
    Namco Starblade - Taito Cocktail 14" x 3, 20" x 2 - NZ SI PtII Upright - Chase HQ DX, Taito Top Speed - Taito Grand Champion - Taito Safari - LAI SI Head to Head Cocktail - SI Cocktail Clone x 2, Pong Clone x 3

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    So you didn't need to blank at all?

    How are you getting sync in there?

    Sent from my HTC 2PZF1 using Tapatalk

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    Quote Originally Posted by redferatu View Post
    So you didn't need to blank at all?

    How are you getting sync in there?

    Sent from my HTC 2PZF1 using Tapatalk
    The blanking was never connected so I left it that way, the Sync is connected to the AV connector (Video In) along with the Gnd at the back of the TV using an RCA connector.

    I mounted the 1kΩ trimmers on a PCB and connected them inline on the RGB output from the arcade PCB which allowed finer adjustment of the input voltage.

    I'm more familiar with what the colours on a DK PCB looks like so I swapped the PCB over to DK.





    I still feel like the brightness is up too much, I got a little improvement from backing off the drive on the neck board but I think the solution lies in the OSD Brightness circuit on the jungle chip.
    I'll trace the connection from pin 54 and see what it's connected to.

    Last edited by Kaizen; 10th June 2019 at 02:20 AM.
    Namco Starblade - Taito Cocktail 14" x 3, 20" x 2 - NZ SI PtII Upright - Chase HQ DX, Taito Top Speed - Taito Grand Champion - Taito Safari - LAI SI Head to Head Cocktail - SI Cocktail Clone x 2, Pong Clone x 3

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    I had a quick look at the where the OSD Brightness (pin 54) is connected to and it looks like it's just connected to Vcc through a 10kΩ resistor (set to maximum brightness).





    The two pots next to it are connected to pins 48 (AFT Output) and 52 (RF AGC Delay) so there doesn't seem to be any OSD Brightness adjustment as suspected.
    I'll connect a 10kΩ pot up to pin 54 as per the diagram tomorrow and see if I can get some control over the OSD Brightness.

    So here's the simplicity of connecting RGB to the TV, remove the three resistors (R868 - R872 - R860) and connect the RGB lines from the arcade PCB through 1kΩ pots (680Ω resistors would probably suffice) to the locations indicated by the coloured dots, Sync and ground simply connect to the AV In connector at the back of the TV.



    I'm guessing the only other step will be to add a pot in for the brightness control which I'll confirm tomorrow.
    One thing I didn't do was adjust the brightness through the OSD before starting so I'll add a toggle switch the swap between RGB In and the original OSD configuration though I don't believe it will have any bearing on the RGB (OSD) input brightness.

    The down side to modding this particular TV is that it doesn't hold it's memory so you have to push the On/Off button then select AV Input each time you turn it on. Not a big deal for a test bench monitor but not really suitable for an arcade cabinet.
    I've learnt a lot by going through the process and have plenty of other 14" CRT TV's to choose from, my current test bench arcade monitor is a bit flaky so I'll try doing a similar mod on another 14" TV.
    Last edited by Kaizen; 10th June 2019 at 02:40 AM.
    Namco Starblade - Taito Cocktail 14" x 3, 20" x 2 - NZ SI PtII Upright - Chase HQ DX, Taito Top Speed - Taito Grand Champion - Taito Safari - LAI SI Head to Head Cocktail - SI Cocktail Clone x 2, Pong Clone x 3

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