Film-Tech Forum ARCHIVE: Diode stuffing for Nonsynce 4:2:4 decoding on cp55

This is topic Diode stuffing for Nonsynce 4:2:4 decoding on cp55 in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Gordon McLeod (Member # 33) on 06-08-2010, 07:48 PM:

Does anyone have the diode stuffing handy to set the cp55 nonsync input to 4:2:4 matrix decoding with sub
The units have been stuffed for the DA20 method of SR and there is a signal appearing on the output LED of the cat 150 but the output card only shows the hard left and right
I can't seem to find the schematic or notes for the cat 243

Posted by Steve Guttag (Member # 268) on 06-09-2010, 06:06 AM:

The CP55 ONLY routes L/R to L/R...not 2:4 decoding except for Center and Surround.

Steve

Posted by Tony Bandiera Jr (Member # 2365) on 06-09-2010, 03:14 PM:

Isn't there some sort of backplane mod to get 2:4 decoding? Maybe switching the N/S in where the SRA-5 would normally go?

I'm sure Sam would know of a way to do it.

Posted by Pete Naples (Member # 761) on 06-09-2010, 04:07 PM:

It's been a few years, but I've gotten round this succesfully.

With a SRA5 installed the good (DA20) way, I connect my pro-logic souce to the SRA5 Non-Sync terminals, then with a simple toggle switch and a bit of wiring, you put the DA20 into 'SR OUT', by breaking the sens/control line between the SRA5 and the CP55.
With the CP55 in Format 05, the SRA5 routes it's Non-Sync input straight into the decoder.

Watch out for DC or spikes on the SRA5 Non-Sync output. The VCA doesn't like that, and those chips are getting rare now. A colleague came up with a resistive scheme to protect it from such things, I don't have the details handy, sorry.