Need help identifying a capacitor on PT Engine GT

[grahf]

I know its not technically a mod (well it will be, once i start my replacement LCD proect). I just got this broken PC Engine GT in the mail today, and set about removing all the old electrolytic capacitors. Im hoping to fix the sound problem this way, as well as the battery problem.

While removing one of the shields, i accidentally knocked an SMD capacitor off the board. The problem is that i completely lost it.  Also, there are no markings on the other smd caps, so i dont know how to tell what it was. I have another PC Engine GT that is fine. Is there any way to test the value?

Here are links to two full size scans:
http://my.opera.com/grahf/homes/albums/363...20board%202.jpg
http://my.opera.com/grahf/homes/albums/363...20board%201.jpg

And here is a closeup:

[NFG]

Unless it causes trouble I wouldn't worry about it.  There's every chance it's a filter cap to smooth out the power.  There's not really any easy way to tell what it was, it's unmarked and you can't easily tell what it was without removing it from another LT (you'd have to beg me, really).

[grahf]

Thanks lawrence. It turns out it works fine, so it probably was a filter cap. I will take your advice and leave it be for the time being.

Now on to the actual mod. Im going to replace the LCD in this GT with one from a Hip Gear Screenpad. Ladyada has a nice portable using one http://www.ladyada.net/make/gamegrrl/make.html , and a lot of people over on the benheck forums use them. For the record, it looks WAAAAY better in person than in the pics.

I have the board all stripped down to just LCD and control board. Its a fraction shorter than the original GT lcd, and i dont think the resolution is much higher. BUT, its about 3x as clear as the original lcd. Power consumption is also much lower, and it will run on as low as 5v. I had it hooked up and powered off the GT motherboard already, with a composite input coming in from my Duo for testing.

The problem is that its only composite input, and im pretty sure the display driver IC does the composite -> RGB conversion internally. So i think at this point my best bet is to try to build an RGB to composite encoder using another CXA1645. Once i get my first one finished for my DUO that is. Any comments welcome.

[NFG]

The GT has the same composite components as any other TG.  You need only a few small cheap components (caps, resistors, etc) to get it.  It might be easier to figure this out than put in a power-sucking chroma encoder.

[grahf]

I didnt realise it was that easy, but its starting to make sense after a few hours of backtracing on my coregrafx.
Im fairly certain it goes through a resistor, capacitor, antother resistor coupled to ground and then goes to pin 30. I cant post from home, so this is all from memory.

Ive prodded the GT a bit, and it appears as pin 30 has no connection, which would make sense. I'm going to try this out when i get my order of resistors in the mail. Thanks for the insight lawrence.

[grahf]

No success, but i missed something. Ive been having a little trouble with following traces due to the heaving coating in some spots on the CoreGrafx board.

It appears pin 30 goes through a transistor, which im assuming is being used to boost the voltage. There also is a small array of resitors beside that, which i cant tell if any of them are involved. I need to do more experimenting. I really dont want to scrape up my CoreGrafx if i dont  have to.