| Electronics > Beginners |
| Does this circuit even make sense? |
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| hermitengineer:
The pinout question depends: Can two parts with the same part identifier (2N3904 in this case) have different pinouts? I would hope for the sanity of a repair guy that they would always be pin compatible. Anyway, you wanted the whole schematic, so here it is. The output format is SECAM. I've tried to understand and identify each stage, but that doesn't guarantee that the descriptions are accurate. |
| Mechatrommer:
why the fuck the 74LS624 designer made it so hard to understand what is RNG? Range Input? or Random Number Generator? what a random generator doing in a VCO? :palm: |
| hermitengineer:
--- Quote from: Mechatrommer on October 27, 2019, 07:14:57 am ---why the fuck the 74LS624 designer made it so hard to understand what is RNG? Range Input? or Random Number Generator? what a random generator doing in a VCO? :palm: --- End quote --- Well from what I've seen on my multi-system TV, it almost seems random :D Well, I just got a used test pattern generator today that can output NTSC, PAL, and SECAM. The TV responds properly to PAL/D and NTSC/M, but fails to detect SECAM/L over RF. It can detect it and properly switch through A/V though. Maybe that's a limitation of the TV. I wish I could find the manual for it. Anyway, it appears that the output frequency is determined on the graph page of FC vs RNG. But yeah, it would be nice to know what "RNG" stands for. |
| ataradov:
--- Quote from: hermitengineer on October 27, 2019, 07:52:54 am --- But yeah, it would be nice to know what "RNG" stands for. --- End quote --- It says right in the datasheet that it is a "range input". |
| AVGresponding:
As ataradov says, it's on the datasheet... So it looks like the transistor is being used to switch the 4u7 cap in and out of circuit to alter the frequency range of the VCO. Given that the transistor gate connects back to the VSECAM connection and SYN (synchronisation?) pin on the (CPU?) IC it looks like a region selection for PAL/SECAM maybe. |
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