Injecting video in DuMont RA-102?

[Phil Nelson]

OK, more data. Injection with the BK Analyst does work, after all (don't ask me what happened before). I lifted the 1N34 video detector diode from the junction of R53 and pin 4 of the video amp, injecting at that point with the Analyst's video output control set at midrange and the polarity positive:



(Excuse the rotten handheld photo; the set is propped on its side. The RA-102 actually has better linearity than appears here -- I think my Analyst is due for a service visit of its own.)

That image is stable and has decent resolution. In the unwelcome side effects category, the Contrast control is now completely inoperative. And increasing the Brightness control only makes the picture bloom, as seen here:



For kicks, I tried injecting a signal from my Philips PM 5518 TV pattern generator. I guess the polarity is wrong. The image is negative, with awful sync (the correct image would be a white circle on a black background):



Same deal when I inject video from a DVD player:



For comparison, here is that same DVD menu page when I was experimenting with audio injection and the video was coming through the antenna:



To summarize, I guess a signal roughly the same strength as the BK Analyst output will work at that injection point. The disabling of the Contrast control is a bummer; there is only a narrow range of adjustment on the Brightness control where the picture is watchable, with no contrast adjustment at all.

Regards,

Phil Nelson