CM7000 converter box missing S/P DIF? circuit that feeds the "Not Used" RCA jack

[wa2ise]

Popped the lid off my CM7000, and "ohmed" out the traces in the area of the missing parts that feed the "Not Used" black RCA jack. The below diagram appears to be what is missing. Of course I don't know what the values of the missing resistors and caps are, but as SPDIF levels are around 1/2 to 1 V at 75 ohm impedance, and the feed from the chip is probably 0 to 3V, and with the two emitter followers in series, RD61 is probably 150 ohms, and RD62 is probably 150 ohms. CD29 is probably 0.1uF, RD60 is probably 1K, and RA7 around 100 ohms. CD26 is a bypass of the 5V supply. There's a space for RPR1 near the RCA jack, but I don't know why it's there, and I think I can safely ignore it. CD30 is probably a roll off cap of something like 50pF, you probably could ignore it. QD10 is a PNP, and QD09 an NPN, any general purpose ones should do.



This all assumes! that the SPDIF from the STx7707 is in fact active, and not been turned off via SW or such. If I had a scope handy, I could easily tell.

Standard disclaimers and YMMV. I haven't tried to build any of this yet...

[andy]

000

[wa2ise]

Does anyone know where I could buy one of these boxes with a coupon?

This place has them: http://www.solidsignal.com/prod_disp...p?prod=CM-7000 and when you place the order, you can key in your coupon's number.

Incidentally, this box uses a video filter chip that I "invented" about 10 years ago, when I worked for MicroLinear. Looks like ST second sourced it. This chip takes Y and C from the DACs, and creates composite video for the yellow RCA jack, and another composite signal with a notch at 4.5Mhz, and group delay pre-dostortion, to be fed to an RF modulator.

[wa2ise]

I installed this circuit, and it seems to be producing signal at around 3Mhz, and at 1.5Mhz (as heard on an AM radio). I think that matches: 3.072 Mbit/s (48 kHz sampling rate, which I think is what they use with HDTV. I don't have a SPDIF receiver here, so I can't tell yet if it really works or not!

Someone over at this forum http://www.avsforum.com/avs-vb/showt...004274&page=18
Built a similar circuit, and got SPDIF, but it was always muted.

If there's no solution to that, I'll just jumper out CD29 and change resistors RD61 to 75 ohms and RD62 to 2K, and remove RA7. The Y output of the STV6433 filter chip will now feed the base of QD10, thus making this circuit a baseband video line driver, to feed luma only to a modulator to drive my antique B&W TV sets. Thus "Not Used" becomes an RCA jack with Y out on it.