Jump to content
Due to a large amount of spamers, accounts will now have to be approved by the Admins so please be patient. ×
IGNORED

Connecting an Arcade PCB to a CRT TV


Recommended Posts

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.

 

ij8wAMX.jpg?1

 

n0NIu5f.jpg?1

 

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

 

K96fbkA.jpg

 

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

Edited by Kaizen
Link to comment
Share on other sites

  • Replies 129
  • Created
  • Last Reply

Top Posters In This Topic

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.

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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.

 

Z0djFj3.jpg

 

I'll cut the traces from the OSD out and see what voltage the BLANK has when displaying the OSD.

Link to comment
Share on other sites

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.

 

muMuy8C.jpg

 

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.

Edited by Kaizen
Link to comment
Share on other sites

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.

 

ct3ZDLX.jpg

 

 

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.

 

wbAHjMH.jpg

Edited by Kaizen
Link to comment
Share on other sites

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).

 

KEuAmLc.jpg

 

vsrJhU0.jpg

 

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.

 

WGlxAZr.jpg

 

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.

Edited by Kaizen
Link to comment
Share on other sites

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.

 

E2cHTpA.jpg

 

It has an MN1873287JL1 and an NN5198K on the chassis.

 

Le9nREe.jpg

 

yuwQzR0.jpg

 

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_TSJklwzDS9mG_LEK2uElbwkvJJies/view?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.

Link to comment
Share on other sites

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.

 

ale1JdL.jpg

 

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.

 

zkqBdIb.jpg

 

 

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

 

zAvQFQS.jpg

 

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).

 

CJ11Lxe.jpg

 

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.

 

PlnonxP.jpg

 

+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.

 

HkvWUxp.jpg

 

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...

 

O2E7p4N.jpg

 

uNG6g5V.jpg

 

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

 

5XO8LtE.jpg

 

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

 

I0R6S5u.jpg

Edited by Kaizen
Link to comment
Share on other sites

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)

Link to comment
Share on other sites

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.
Link to comment
Share on other sites

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 won’t startup in AV there are tricks. Follow the AV circuitry and you’ll 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

Link to comment
Share on other sites

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. It’s generally easier to do and you don’t lose the OSD.

 

 

Sent from my iPhone using Aussie Arcade

Link to comment
Share on other sites

Thanks @MarkOZLAD, will shhot you a PM.

 

After a steep learning curve I've found this mod quite a simple alternative to using an arcade monitor, one thing I see as being a challenge for use on an arcade cab is not being able to adjust H and V position.

 

 

 

PlnonxP.jpg

 

After a bit more research it looks like a 10uF cap should be added inline added and the 220 ohm resistor should be 75 ohm, is that correct?

Link to comment
Share on other sites

This will provide you with H and V positional adjustment.

 

AU $40.86 | New Arrival Adjustment of picture position Converter Adjustable converting board connect to any JAMMA for adjust Image Position

https://s.click.aliexpress.com/e/clF9bDpQ

 

Cool! Are you familiar with that circuit Frank? I assume there’s an IC on the underside.

 

 

Sent from my iPhone using Aussie Arcade

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.

×
×
  • Create New...