PCEGT replace with 3.5inch TFT LCD

[turbokon]

Always test first before installing

[famiac]

Hm alright. My roommate has a controller board for the same monitor. I'll test it using his.

Always test first before installing

Yeah, i was just overconfident.

[Keith Courage]

I have gone through this many times myself. The screens look the same on the outside but with different parts inside. So no good way to tell from looking at the unit if it will work or not before buying. I think I buy and return maybe 50% of all the screens I get. Just have to keep testing till you find a good one.

[thesteve]

my last buy was 4 screens from the same listing
2 worked 2 didnt
returned the 2 and of the replacements 1 works 1 doesnt

[wilykat]

Is there a way to test LCD before taking it apart? Hook it to a PCE/TG16 or other old systems with 240p composite output and run a game?

[thesteve]

that works great
i tested them by hooking them to a DUO
sometimes the ones that dont work on the express still work on the nomad, so you want to test on something using the 6260 video source

[Vimtoman]

Heres one I had bought. It has an add on which alows you to use a potentiometer for contrast or color.

http://www.buy-lcd.com/index.php?route=product/product&product_id=10133

Just ask for the P version.

Tested and works OK with composite.

This is a direct replacement for the 2.4" screen.

They also do a 4" version for the LT and a 3.5" too.

They do also have VGA versions but I've not tried those.
I was thinking that maybe it could be a RGBS.

[famiac]

So i tried it with a different controller board, but all i got was a white screen if the composite was connected
If it wasn't connected, i got a black screen/off

Does it have to do with how the stepdown is bypassed?
Should i just buy a new LCD?

[Vimtoman]

Looks like it's not compatible. I would just change the display.

[Keith Courage]

Order a new LCD and test before taking it apart so you can return it if you have to.

[famiac]

Crap. Does anyone have an LCD that they confirmed working?

[famiac]

Progress?
I connected the LCD controller board using a 12V psu, and it works. (only on its original lcd)

The image is noticeably less sharp than the scrolling one, but i might settle for it.

Does anybody know why it works with 12V input but not when the buck IC is bypassed? It must have something to do with other components requiring the 12V, but has anybody figured out how to bypass the 12V on this board specifically?

[thesteve]

that board supplies VGH and VGL from the pulse on the bucking chip through a diode/cap multiplier
http://pcengine.freeforums.org/express-gt-composite-t179-10.html
pics showing how to make it work

[wilykat]

Can you try tapping off the middle pin of the power switch? That is 8-9v unregulated power from either DC in jack or batteries.  (middle pin is because NEC wired the switch a bit strange. When viewing the PCB with the switch solder spot up, left and middle are connected when the switch is "OFF" and middle and right is connected with switch is "ON", the right pin goes to the regulator circuit and middle is unregulated input.

If it still doesn't work, you got unlucky All the LCD I've tried always worked from either regulated 5v or from unregulated 8-9v

[famiac]

Wouldn't that reduce battery life? Maybe not dramatically

To turn down the 24V clockwise, that would mean turning it clockwise, right?