VDU not completely working; help?

[liamoc]

Hi, thanks for a great kit computer.

I've built a VDU and a black and white amplifier, and now when I plug the machine in and turn it on I get a sea of question marks, which suggests the video chip is working correctly.

Then I try (using the serial interface) to write to video memory in WozMon like so

8800: 00
8C00: 00
8000: 12 20 20 20

Nothing happens. Querying address 8000 returns FF. It seems like video RAM is not being mapped in? I have the VDU Base jumper set to the topmost one, i.e. 0x8000 and jumpers in VDU_EN, OSC_EN and on the lower positions of both INV_SEL and CSS_SEL. Is there something I should change here?

Edit: Oh, next time I turned it on, I got a sort of checkerboard pattern with 8x8 blocks of question marks and of @ signs (or backwards 6s?). When I write 00 to 8800 it turns into the normal sea of question marks

Edit: I also don't seem to be getting any results when I try to write to the locations of the LEDs (a000 etc.) on the joystick/digital I/O board. But I can at least read the state of those buttons OK.

[liamoc]

Nevermind, replaced the video RAM chip and all is well