PCEGT replace with 3.5inch TFT LCD

famiac · 10/27/2015, 06:09 PM

So i attempted this mod over the weekend. I wish i had seen this thread before. It would have saved me a lot of headache on saturday trying to figure out how to cut the case.

I've only got one problem:
The image scrolls vertically on the LCD.

Any idea what could be wrong ?

I'm using a BC548 rather than a 547.

wilykat · 10/27/2015, 07:40 PM

LCD is shit

I had the same issue and this one http://www.ebay.com/itm/181529434603 worked for mine.

famiac · 10/27/2015, 08:26 PM

Are you serious? Is it really the LCD or is it the controller board?

The LCD is glued in pretty tightly, so i'd like to avoid removing it

thesteve · 10/27/2015, 09:06 PM

well the vert roll appears to be the controller board, but its not defective, just incompatable

turbokon · 10/27/2015, 09:34 PM

A lot of those backup monitors are incompatible with low resolution.

turbokon · 10/27/2015, 09:34 PM

Always test first before installing

famiac · 10/27/2015, 09:38 PM

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

Quote from: turbokon on 10/27/2015, 09:34 PMAlways test first before installing

Yeah, i was just overconfident.

Keith Courage · 10/27/2015, 10:42 PM

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 · 10/28/2015, 01:23 AM

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 · 10/28/2015, 01:28 AM

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 · 10/28/2015, 01:36 AM

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 · 10/28/2015, 04:13 AM

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 · 10/28/2015, 06:31 PM

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 · 10/28/2015, 06:47 PM

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

Keith Courage · 10/28/2015, 10:36 PM

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

famiac · 10/28/2015, 11:22 PM

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

famiac · 10/29/2015, 02:24 PM

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 · 10/29/2015, 03:25 PM

that board supplies VGH and VGL from the pulse on the bucking chip through a diode/cap multiplier

https://www.tapatalk.com/groups/pcengine/express-gt-composite-t179-s10.html

pics showing how to make it work

wilykat · 10/29/2015, 05:33 PM

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 · 10/29/2015, 06:17 PM

Wouldn't that reduce battery life? Maybe not dramatically

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

thesteve · 10/29/2015, 10:35 PM

no CCW
read at the 22uf 35V cap

Keith Courage · 10/29/2015, 11:02 PM

Quote from: wilykat on 10/29/2015, 05:33 PMCan 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

I've always just tapped the middle pin of the on/off switch for power as well. Never had any issues.

famiac · 10/30/2015, 11:14 PM

Got it working! Thanks for the help, steve.

It would't work from unregulated power. I connected 5V, ground, VGL, and VHL as shown in the thread steve referred me to

thesteve · 10/30/2015, 11:58 PM

That was my thread on the other forum, from when I did that board

famiac · 10/31/2015, 01:27 PM

Yeah i noticed. Thanks

Keith Courage · 11/16/2015, 07:10 AM

Got 3 new screens in the mail over the weekend. They work just fine but what's weird is that if you turn the brightness past 60 everything gets super bright out of nowhere. Meaning the brightness will go up gradually as it should from 0-60 and then bam super bright. Almost like someone turned the brightness up all the way. No change whatsoever from 60-100. Just as bright as possible from 60-100

Anyone ever come across any screens like that before? Any fix for it or is it just a bad design to where I should return them?

In all honesty 50 for the brightness seems good enough so I may decide to keep them. Just thought it was odd that when I tested them I couldn't go past 60 on the brightness level without being blinded.

Vimtoman · 11/16/2015, 08:39 AM

You could try a resistor across the inner and outer pin of the pot
To change it from LOG to LIN or visa versa.

Keith Courage · 11/16/2015, 08:50 PM

There are no potentiometers. Just push buttons that control the brightness, contrast, tint etc.....

Vimtoman · 11/17/2015, 02:11 AM

Bummer.

You could try attenuating the composite video slightly using a half bridge resistor circuit.

Use a 100R multi turn pot and a fixed value of say 50R in series so it does not go any lower.

May work.

thesteve · 11/17/2015, 11:31 PM

the issue is in the software
you could return them or not have the buttons showing

12/23/2024: Localization News - Team Innocent

PCEGT replace with 3.5inch TFT LCD