Beko 12.1 chassis tuning doesn't stop on strong signals

grahamaaron · Guest

Hi all,
This Beko 14213T (chassis 12.1 with UHF only) just continues to scan over all signals. Changed the STV8223, thinking it was not dipping the AFC line to the micro very much (only changed by 100mV on the 2.7V DC level, as measured on DVM). Didn't help. Checked the capacitors that were related to a tuning drift fault, as recommend by the legendary plamensl (thanks for your many contributions if you are reading this, you've been a huge help to many I'm sure). I am now starting to think the Micro (IC401) is informed of video presence via the I2C bus, from IC151 (STV2116A).
Any thoughts appreciated.

grahamaaron

Found out a little more. The I2C bus controlled Video Processor chip has an output registor read, during the tuning scan process. 1 bit of this read cycle represents the Video Indenitication. I have spent a little time trying to scope that bit to try to see if the micro is to blame. Does anyone know for sure whether this Video Indentication is the mechanism that is used to tell the onscreen control micro to stop the scan?
another question I have, if this is indent the mechansim used, then what is the AFC line to the micro for? It comes from the IF STV8223 IF system IC.
Fine tuning?