2015-02-22 - ZX Spectrum +2 Issue 1 board, no composite video output on RGB connector

Got this machine from a large batch last month.

It's a somewhat rare issue 1 board (most +2's have an issue 3 board).

Problem
no video output using the composite video signal from the RGB port.

Bad 12V
Measured pin 11 of the TEA2000 which should be around 12V. There was only 1.46V.

Mostly the ZTX650 is dead when there is no 12V, TR9 on the +2.

Soldered out the ZTX650 and tested it on one of my testboards (a 48K): not working.

Replaced the ZTX650 with a ZTX651: video works.

Bad 5V
Still there was a strange horizontal black glow visible.

Measured 5V: was 6.2V. Probably the 78S05 ('S' is the 2A version).

Tested one 78S05 (with heatsink) from another +2: everything was fine.

Replaced the bad 78S05 with a new one.

Improved composite video
Detached video from audio to improve picture quality (cut one leg of C31).

Happy ZX Spectrum +2 again!