Strange fault with LCD/USB

[jb99]

I made a board with an 18F2550 driving a standard 2*16 line LCD module and using the USB interface to get data from a PC to display. It hardly seems worth posting the circuit, it's just directly connectly to the USB port and the LCD on the appropriate pins. It's powered from the USB and has a 0.47uF capactitor on the VUSB line. And a 20MHZ crystal and 2 22pF capacitors for the clock.

I have one LCD module which it works fine with.

I have a second different LCD module (different colour, very different board layout) which is working find as a display but when it's plugged in stops the USB from working properly. The PC recognises there is a device attached but fails to enumerate it.

I'm just wondering if anyone has any idea what could be wrong as it seems a very strange fault.

EDIT: More information - The USB bootloader on the board works with the LCD plugged in. It's only when this particuar display is actually used that it stops the USB from working properly, even though it seems to display the requested text perfectly well

 

[jb99]

Ok replying to my own post because I solved it.
The capacitor across the VSS and VDD on the PIC wasn't soldered properly. I fixed that and now it works.
A strange pattern of failures though that it caused. Ah well, the experience is good for next time!

 

[Hero.sl]

hey jb99, just found your post while searching.
I have a little question, but it is not related with your problem.
I'm planning to use PIC18F4550 to interface an OLED display to a pc. USB SIE will receive RBG information from the PC and they will be directed to OLED driver via the SPI port.
I want to know whether it is possible to receive data to the pic at the maximum speed of FS USB which is 12.00Mbps. Does anyone have experience on using USB PIC for similar application? Thanks in advance..