On Wed, May 2, 2018 at 4:55 PM, J. Alexander Jacocks <jjacocks@gmail.com> wrote: > All, > > I've asked a number of places, but I thought that I would get the thoughts > of the fine folks, here, as well. > > I have a C128DCR NTSC that has issues with signal level on chroma, from the > video connector. Signal levels seem to be just fine at the RF connector, > and the picture is fine, from that connector. From the video connector, to > a modern TV or monitor, the picture is excellent quality, but monochrome. > Checking the output pins on the video connector, the level is very low, on > the chroma signal. > > I have changed: > 1) VIC-II (8564) > 2) Clock generator (8701) > 3) Crystal (NTSC/14 MHz) > 4) RF modulator according to the schematic, there're two jumpers that select different levels of the chroma signal: J10 and J11 and associated resistive divider R13-R14. I would check these components as second step after having excluded EMI42 filter. The filter should have basicly 0 ohms dc resistance between input and output and basicly infinite resistance between either input or output to GND. Of course, you should make sure the "about 0 ohms" dc resistance is present from the J10/J11 jumpers to the chroma output pin too, to rule out any track/solder problem. Almost all you changed, couldn't have been the problem judging from the tests you describe. I would have first checked with another monitor/TV. HTH Frank IZ8DWFReceived on 2018-05-02 18:00:02
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