I investigated the datasette port... it seems to only drive less than 9V DC... I *really* wanted to use it for S-VIDEO power, but 6V DC (?) is not enough!
Err, sorry, I don't understand what is your question... ideas? Well, I used 9V AC from UserPort to create 12V DC for my S-VIDEO adapter... it works for me but (maybe) because it draws very little power (about 64 mA). In other words I get 12V DC with a simple circuit from the 9V-AC of the user port to make video work... I never got S-Video to work from the Cassette-Port (voltage too low... 6V DC?)
Ah I totally missed the zener diode CR 301. Well that explains my problem with cassette/s-video, so thank you!!
Looking at schematic from Zimmer's, there I don't see a reason it should fail with only +5V.
But from the original C128 schematics (I tried to capture image, but Windows 8 sucks), the Z80 clock line is driven by +12V line. I don't own DCR so I can't say for sure which schematic is accurate... BUT if your DCR does use +12V like my flat C128 then that would explain the problem. (Remember the Z80 starts the computer, no matter what mode you select... no Z80 = black screen)
Captured schematic from C128 PRG and highlighted +12V line to Z80
Last Edit: Jan 6, 2015 7:13:48 GMT by hydrophilic: Added schematic
I was hoping, I find here min. 1 man who knows the function of the C128DCR. With +12V, but without U109 = machine start OK. With +12V, but without U112 = machine start OK. With +12V, but without U60 = machine start OK. With +12V, but without U57 = machine start not OK. This normal. www.zimmers.net/anonftp/pub/cbm/schematics/computers/c128/manual/83.gif I will find the reason.