zx spectrum +2 video (composite)

[640KB]

I'm currently working on a +2 (grey) and have a couple of questions i'm hoping someone can help me with. The +2 is now working and can run software just fine, but the background colour on the menu at startup is bright white instead of grey. This happens on both the RF and on composite (pin 1 and 2 on DIN). Anyone had this problem? I'm suspecting it might be a problem with the conversion from composite to hdmi rather than an issue with the spectrum.
Also i'm puzzled with the voltage on the composite out signal. The signal is around 4 V, which I haven't seen before. I'm used to composite signals between 0 - 1 V, but looking at the schematics from the TEA2000 to the Din socket it seems like this is intentional?

[1024MAK]

The composite video output does rely on the TV/monitor having a 75Ω termination resistor (that presents the correct load). If unloaded, the voltages will be higher. Also Sinclair computers don't produce video signals that fully comply with the standards, that includes the voltage levels.

Having said that, I can't remember what a normal machine actually produces. How are you measuring it?

The bright / non-bright is set by the inputs to the TEA2000 chip. So are the other colours correct or wrong?

Mark

[640KB]

The voltage is measured between ground and LK4 without a monitor connected. Also measured directly on the composite cable (unplugged). When I run the composite signal through an old VCR before inputting it to the upscaler, things actually look alot better than running it directly to the upscaler. The output from the VCR is around 2.8 V. Other colours seem fine especially when running the signal through the VCR first.

[Guesser]

You must have a load connected when measuring as it forms part of the circuit. It's also a video signal so the only way to sensibly measure it is with an oscilloscope.
The video should be on the order of a volt between the sync tips and peak white but there's probably a large DC offset.

[PeterJ]

I'm locking this thread as the user has asked for their account to be deleted.

It seems unusual to ask for assistance, get help and then delete your account.

Peter