Repairing a ZX Spectrum 128K +2 (serial no U-043583) - Part 3

In part 2, I used a CART to HDMI adaptor as my LG TV does not like the composite video output from my spectrum 128K +2 but now I get a ghost image effect which is not present on the RGB output.

Composite video display with shadow

I got the oscilloscope out and started probing the composite video circuitry.

Spectrum 128 2+ composite video circuit

TEA2000

The TEA2000 is the IC in the spectrum that takes the RGB output from the ULA and generates the composite video output. Let's check it out.

The TEA2000 requires a 12V input on pin 11. I measured a fairly steady 10V which is a bit below 10.8V in the minimum spec in the datasheet. I do not think this is the cause of the ghost image so I will come back to look at the 12V supply later.

TEA2000 pin 11 12V input - 10V measured

 
The ramp input on pin 15 looks okay to me.

TEA2000 pin 15 ramp input

I measured the output on pin 6 which looked in spec but I am not sure if this is what the signal is supposed to look like or not.

TEA2000 pin 6 composite video output

I measured resistors R32 and R31 in-situ and they both measured the correct resistance according to the circuit diagram. Diodes D1 to D11 also seem okay when measured in situ and C3 is not shorted.

I can't see any obvious fault so will need to keep looking.