On Wed, May 2, 2018 at 11:12 AM, Francesco Messineo < francesco.messineo@gmail.com> wrote: > 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. > Frank, I did indeed check with at least 2 TVs, and both showed the same issue, so it's not the TV/monitor. I will open up my 128DCR this evening, and check the levels on those resistors and jumpers. I didn't think that any of the parts were the problem, except for the RF modulator, which since the levels are low after the modulator, I thought might be faulty. Thanks! - AlexReceived on 2018-05-02 18:02:11
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