Spectrum 128K: distorted picture with composite to vga converter
I'm trying to get my 128K Spectrum (toastrack) to work with a vasmon3 composite to vga converter, but all I get is a distorted image on the VGA monitor. (the osd of the converter is rocksteady and crystalclear)
The converter is working fine with any of my 48K boards.
The RF output on the 128K is working fine on a LCD t.v.
I compared the composite video signals of the 48K and the 128K with my antique 10MHz oscilloscope.
The output voltage on the 128K is about 4 V DC max and signal swing 2 V tt.
The output voltage on the 48 is about 4 V DC max and signal swing 1 V tt.
The blanking part (chroma) is about 300mV (=conforming to spec.) on the 48K.
It is less than 100mV on the 128K and I suspect that to be the problem.
Is this low voltage of the blanking part normal for this machine and could it cause my problem ?
And if not normal, what can I do to fix it ?
Shorting R134 (75 Ohm) has no effect.
I already tried L3 on pin 10 of the TEA2000 with no effect.
L5 is also without effect.
Power on pin 11 is about 10,7 volt and the 12 volt signal is about 11.8 volt.
Picture of the problem:
https://picasaweb.google.com/lh/photo/krPHzSMcbQ6bEkSBxc4GKWvEyy9_oMMADQ4qTRJyUkY?feat=directlink
The converter is working fine with any of my 48K boards.
The RF output on the 128K is working fine on a LCD t.v.
I compared the composite video signals of the 48K and the 128K with my antique 10MHz oscilloscope.
The output voltage on the 128K is about 4 V DC max and signal swing 2 V tt.
The output voltage on the 48 is about 4 V DC max and signal swing 1 V tt.
The blanking part (chroma) is about 300mV (=conforming to spec.) on the 48K.
It is less than 100mV on the 128K and I suspect that to be the problem.
Is this low voltage of the blanking part normal for this machine and could it cause my problem ?
And if not normal, what can I do to fix it ?
Shorting R134 (75 Ohm) has no effect.
I already tried L3 on pin 10 of the TEA2000 with no effect.
L5 is also without effect.
Power on pin 11 is about 10,7 volt and the 12 volt signal is about 11.8 volt.
Picture of the problem:
https://picasaweb.google.com/lh/photo/krPHzSMcbQ6bEkSBxc4GKWvEyy9_oMMADQ4qTRJyUkY?feat=directlink
Post edited by Knik on
Comments
I'll have to order a new one and see if replacing it helps.
I also made a picture of the PAL signal from the computer.
https://picasaweb.google.com/lh/photo/no4sFiCiBNQVRElPzP0vatMTjNZETYmyPJy0liipFm0?feat=directlink
Chroma seems too small and it's also quite dirty on the slope corners.