(1) Errors in the PC board design
You can find these by referring to the ExpressPCB layout for Revision L. While it's easy enough to fix these mistakes in the ExpressPCB program, we present the design as-is so you can see the board in the form we had manufactured.
(1.1) R933 (above the IR3y05) does not quite touch the ground plane. This is easy to fix with a wire bridge.
(1.2) Pin 48 of the MN83803A(K/L) does not quite touch the ground plane. This is also easy to fix with a wire bridge.
(1.3) The BNC connector's lugs that connect it to the ground plane on the top side of the board (as they should) are made right over the positive supply rail on the reverse side of the board-- so if you solder the BNC connector in place without modifying the board, you will solder the positive supply directly to ground, shorting it out.
The fix for this is easy: cut the trace of the positive supply line so it does not touch the BNC connector's mounting lugs; then solder a wire reconnecting the separated sections of the positive supply line.
A dremel with grinding bit is ideal for cutting the supply trace. If you want to make a through-hole connection to reconnect one end of it with the other, you can just as easily use the dremel to shave off some ground plane on the top of the board, over the supply trace, and drill a hole there to place your wire.
(1.4) The plating that mounts the FPC connector going to the LCD is positioned in a way that on one side of it, one of its two 'feet' will bridge the VDD to Ground, shorting out the power supply.
You will readily see this when you situate the FPC connector in its position on the board.
This problem can be solved easily by dremel too-- or with a straight razor blade, as I discovered (I discovered the problem after I had returned the borrowed Dremel to its owner). Just shave away some of the plating from the area that connects to the collector of Q901, and pins 14 and 19 of the LCD, taking care not to damage adjacent traces. Hollowing out a rectangular portion of this surface leaves little space to solder the 'foot' of the FPC connector to, but will prevent a power supply short circuit.
My own revision that fixes this and other errors is revision 'M' (slcdm.pcb). Julie Porter had no part in this revision, so any mistakes remaining in it, or newly introduced to it, are entirely mine.
(2) Mislabeled parts
You can avoid putting the wrong parts down by following the schematic diagram to the PV-950-B camcorder, supplied as a supplement to the repair manual for the PV940 and PV950 camcorders.
(2.1) C911 is labeled 0.01 but the schematic specifies 0.1 microfarad.
(2.2) C919 is labeled 0.047 but the schematic specifies 0.47 microfarad.
(2.3) C937 is labeled 0.1 but the schematic specifies 1.0 microfarad. This is probably not a critical value, being a bypass capacitor in a circuit designed for DC functionality.
(3) Unlabeled parts
These are not really mistakes. We left the values up to the user. However, since Sharp shows some specific values in their data sheets for the IR3y05, we thought we'd give them so you will have some guidelines in choosing values.
(3.1) R24 : Recommended value is 33k.
(3.2) VR25: Recommended value is 33k.
(3.3) R26: Recommended value is 33k.
Since 33k trimmer potentiometers seem hard to come by (do they exist?), another group of values seems appropriate for this circuit. This is the on-board voltage reference circuit for the IR3y05's pin 28, which sets the DC offset of the outgoing RGB video. For this reason, I'd suggest a multiturn precision trimmer if possible.
I can't seem to find a current specification for pin 28 (output DC control), and only a 'typical' voltage rating is given for it (the acceptable range would be between ground and the absolute maximum value given for this pin, Vcc2). Therefore I'll guess that its input impedance is high enough that we don't need to worry about the impedance of our voltage source.
For this reason, I'll guess that values of 20k for all three values (R24, VR25, and R26) would suit just fine. Any combination yielding the adjustment range the user wants will probably work.
Click here to return to the LCD project main page.
Click here to return to my home page