[QuadList] Shinybow SG-3680 RGB-to-CVBS, Y/C Converter Funny

[Steve Burgess]

Hi folks

Attached are pics of both sides of the (rather nice) PCB for this eBay.co.uk-sourced SB-3680 RGB-to-CVBS, Y/C converter (serial: 20048001106).

It uses a KA2198BD encoder chip wired for PAL operation (pin 7 grounded) and a 4.43MHz crystal oscillator employing a Schmitt-trigger inverter.

Inspection reveals that R1 and C5 are not fitted, which means the 4.43MHz subcarrier is not reaching pin 6 of the KA2198BD – so no wonder I am having problems with the chroma output.

Also, the KA2198BD datasheet says that for PAL the components connected to pin 17 should be 82uH and 15pF whereas 100uH and an unmarked capacitor are actually fitted; if the capacitor is 20pF, these values are what the datasheet says should be fitted for NTSC operation.

Weird.

eBay seller swears blind it was working ok but decided not to return as paid next-to-nothing for it and was curious to get to the root of the problem.  I’ve e-mailed Shinybow in Taiwan.

Steve Burgess
retired, ex-BBC/Channel 4 UK
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