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dbGrafx Booster is CSync'ing!

posted Jan 29, 2015, 5:21 AM by René Richard   [ updated Jan 29, 2015, 5:23 AM ]
Early on I discovered that my first revision of the dbGrafx Booster had a flaw in the Sync circuit (or lack thereof). I may be guilty of sometimes designing first rev PCBs a bit too quickly and not looking to check if SYNC is 0.7Vpp or TTL-level. Needless to say, it didn't work reliably as the equipment I have to convert RGB to YPbPr is expecting TTL Sync. Even if I had equipment which wanted 0.7Vpp it would still not work reliably because the signal needs to be buffered once out of the console in order to function properly.

I tried a few circuits with NOT Gate amps to produce a quick and very low delay Sync pulse but nothing seemed to operate to my liking. Finally, I decided I was fighting a losing battle and decided to order a few LM1881 sync separators. These are purpose-built chips which take in the CVBS video signal and output a TLL CSync pulse - DONE! I simply built the exact circuit found on page 7 of the datasheet and it works flawlessly (as it should!).

Now, the next step is to pull out my RGB to SCART gear and test if this will pass the test - stay tuned!