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Thread: Connecting an Arcade PCB to a CRT TV

  1. #11
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    I'm pretty happy with how this monitor displays so I'm going to leave it at that for the time being. It's good enough for a test bench monitor.

    Moving on to the next TV (JVC model AV-14A3) which was the first one I grabbed.



    It has an MN1873287JL1 and an NN5198K on the chassis.





    I did a bit of hunting around and found a TV service manual for a JVC 21" that uses both of these chips so in theory the circuits should be similar.

    https://drive.google.com/file/d/1kz_...w?usp=drivesdk

    The plan is to confirm what voltage is coming out of the Ys (pin29) blanking pin then disconnect the Ys and OSD RGB lines and supply the required voltage to the Ys line and feed in the RGB from the arcade PCB.
    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. #12
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    I worked out today one of the tvs I planned to RGB mod uses y u v so that one is a dud. A nice 29 inch trinitron. Please keep sharing. Helps others get into it

    Sent from my HTC 2PZF1 using Tapatalk

  3. #13
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    I managed to find the correct service manual for this TV which made things a lot easier.

    JVC AV-14A3


    This chassis uses surface mount as well as though hole components and the traces are really hard to follow, fortunately the schematic filled in the blanks. This is the poverty pack version so there are a number of components that were missing and it took a little while to work everything out.
    This TV also uses blanking so I had to work that side of thing out.

    So I found the OSD RGB and Ys (BLANK) outputs from the MN1873287JL1 (MICOM) controller and confirmed it was supplying 4.2v when blanking.



    The signals ran to where the RGB Switch IC would have been if populated.
    The deluxe version of this TV has an RGB Switch IC but that wasn't populated on this unit, the 0Ω SMD resistors and jumpers allowed the signal to pass through.




    From there the signal goes to the NN5198K (Jungle Chip).



    The basics of the mod are the same as the previous TV with the addition of finding +5v for the blanking input and this time I added resistors tied to Gnd on the input to reduce the intensity of the image, I'll add that to the previous TV and that should get the image looking right.

    The mod was done at the RGB Switch IC location on the PCB as it was easier to solder the RGB input wires into the empty through holes where the chips RGB outputs would have been (pins 4-14-15).



    The four links/0Ω resistors were removed at Y371-Y374 so the OSD output from the MICOM controller is disconnected.
    RGB from the PCB passes through a 470Ω resistor on each line and after the resistor they are tied to ground through a 220Ω resistor on each line.



    +5v was picked up from the voltage regulator output and connected to the Ys BLK location on the pad where the emitter would have been at Q371 SMD transistor.



    Sync and Ground are connected to the AV Input at the back of the TV.

    This TV holds it's memory so when it's switched off and back on it always returns to AV Input.

    This is how it looks with the DK PCB connected...





    If it was going in an arcade cab I'd probably swap the resistors out with pots for finer adjustment but good enough for a test bench monitor.
    I think I'll add in a 4PDT switch to reverse the mod so I can plug Composite signal B&W games into it when I have them on the test bench as well as reversing switches on each deflection coil so I can flip/rotate/mirror the image depending on how the output of the PCB is oriented. Terra Cresta is 180 degrees opposite to Donkey Kong for example.

    Deflection Coil Reversing Switch Mod



    The next TV to mod will be a 20" for my LAI Space Invaders cocktail that has been waiting for a monitor.

    Last edited by Kaizen; 11th June 2019 at 01:55 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

  4. #14
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    Mate, great stuff, very interesting read. Thanks for the effort of writing it all up too.

  5. #15
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    Are you using caps on the rgb and sync to protect your Arcade boards? I think you put them in reverse polarity to work as a filter. Not 100% sure.

    Sent from my HTC 2PZF1 using Tapatalk

  6. #16
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    This chassis has them just before the signal goes into the chip.




    Will look into it for the other TV.
    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

  7. #17
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    Good stuff, there's a massive thread on the shmups forum about RGB modding CRT TVs if you haven't seen it yet. The 8bit guy has a pretty good video about RGB modding a samsung set as well.

    If you are planning to use arcade boards, you'd probably want to attenuate your sync level:
    Arcade boards often have sync going up to the TTL level (5Vpp) the sync expected on these consumer TVs should range between around 0.2-1Vpp, feeding a TTL sync in the AV in might work but you are most likely wearing out the electronics.

    There's no easy way to measure your sync level without an oscilloscope, but one safe way I found to attenuate is to use the well documented attenuation of Csync for the megadrive as it outputs Csync at TTL:
    https://www.retrorgb.com/csync.html


    The above video explains it well, specifically at 5:44 (timestamps does not work on the link above)

  8. #18
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    You're on the right path with the mod, but you don't need to sacrifice OSD, @MarkOZLAD and Syntax hav developped a "OSD Mux" method where resistor values are changed so RGB and OSD voltage together match the voltage expected by the Jungle chip, I've done a few myself and it looks and works pretty much like factory except for the need for blanking switch to enable RGB.

  9. #19
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    Connecting an Arcade PCB to a CRT TV

    @djcalle You can just hardwire blanking for arcade so no need for a switch.

    If the TV wonít startup in AV there are tricks. Follow the AV circuitry and youíll likely work out a way to trick the set into having AV feed into the tuner CVBS. Sometimes by redirect, sometimes by tricking an AV switch.


    Sent from my iPhone using Aussie Arcade

  10. #20
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    Oh and @Kaizen thanks for promoting the old OSD snip method....Just another audience for me to re-educate! :-)

    If you need a primer on the OSD mux method drop me a PM. Itís generally easier to do and you donít lose the OSD.


    Sent from my iPhone using Aussie Arcade

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