Sinclair ZX80 / ZX81 / Z88 Forums

Hi,

I got a TC 2068 which has a problem and I wonder if any of you can help me.

Blue, yellow, black and white colors are fine, but the other ones give weird colors. Red, Magenta Green and Cyan are all wrong.

I didn't made any tests yet (not sure what tests I can do - I can't find info on internet about TC2068 diagnostics).

Thanks in advance

Shots bellow:

I'm in the process of replacing all the capacitors in the video circuit, but have to pause as there's a couple missing from my inventory

Hi,

Nice board and all IC's socked. Anyway, when you finish re-cap, all colours should be back to normal. If not, check continuity of traces between the SCLD (ULA) and 22uF capacitors and between these capacitors and the PAL encoder (MC1377 type) inputs.

I would suggest cleaning both RCA connectors (TV and monitor outputs) because they look very dirty and rusty. 1000 grit wet sandpaper would do the job.

Bear in mind that any TS/TC2068 has a flaw in the design. BRIGHT is visible in BLACK, so TC2068 shows 16 colours instead of 15.

For diagnostic purposes you can you any diagnostic ROM available on the net and the demo called "Timmy" (https://www.pouet.net/prod.php?which=64102). For my own purpose and testing AY in any Timex machine I've cracked DiagROM I hope Phill wouldn't mind (https://www.youtube.com/watch?v=dC0ZgcBu8rQ).

Thank you for your comment. I'll try everything after the recap