Thanks for the answer Tim,
Always good to know that we can test the tweak with differents tests rigs to be able to check the increase of the video BW with confidence.
I've passed some time to probe the HD_DEC video outputs of the 30K with a good oscilloscope (500MHz analog). I've discovered that there is two different VDAC option inside the unit :
- One is with the use of IC1001 (JCP8037) HD_DEC internal VDAC (COMPY/COMPCR/COMPCB signals),
- One with an external video DAC optionnal IC (IC801=JCP8029 not populated in my unit) a small 80-pin LQFP package chips.
I've checked the PCB and found that COMPY/COMPCR/COMPCB signals from HD_DEC VDACs are all in Unity Gain (x1) with Sync. measured at 316mV. That's a good new since there is no need to change the current to voltage conversion resistors (R1021/R1022/R1023) on the PCB to add the tweak
Hope the use of HD-DEC internal VDACs is also major in your units
I've also checked the "1080_H" signal states :
Playing 480i tape -> "1080_H" = 0V
Playing 480p/720p/1080i tapes -> "1080_H" = 3.3V
Then Q836 is inverting the polarity of this signal ("1080_L") with 10.5V amplitude.
Just another information : The MPEG2 HD transport stream is decrypted through a specific JVC IC (JCP8044) but unfortunatly, the decrypted TS buses (links to IC1201/IC1001/IC601 BGA) are buried in the inner layers of the digital circuit board : no access in any case for security reason
I've updated the schematic to reflect the change of Pr
/Pb bandwith to 18MHz(HD)/9MHz(SD) and "1080_L" amplitude.