View Full Version : GB-A1000 PLL Adjustment

23rd February 2015, 13:21
Can anyone explain the PLL adjustment procedure for me please?

The PDF with the jumper settings give the following:

To adjust the flicker fixer on clock frequency of the Boards: !
1. Placing jumper X7 left
2. turn on computer
3. Adjust with trimmer capacitor C59 (right under X7) still image
4. Insert jumper X7 right
5. Adjustment through trim resistor R26 (right next to X7)

There's a few things unclear about all that...

1. Adjust and Adjustment - what am I adjusting for? Is the to improve picture quality? position? other? noise with a scope maybe?
2. when moving the jumper from left to right - still with the computer on?
3. If I remember when I've done this in the past, at point 3 - "Still Image", I had a black / blank screen. I'll try again, but if so, this makes the "what am I adjusting for" question all the more relevant.

I'm just a little confused with this procedure and i don't have a particularly good picture when using the VGA out. I have clearly vertical bands visible on the screen for all but the grey workbench background. The purple of the KS screen is particularly noticeable. I'm thinking it may be that my adapter isn't grounded / shielded well or something, but I don't know if it may be this adjustment might help.