Eric, Please consider taking a few high quality pictures and submit this (as an article) to RB for publishing.
Kevin Custer > I did a little further digging with the RC96, and discovered the > following... > > The SELECT 1 line which controls the CD4053 (U9)RX audio gate control > pin behaves as follows: > > When the controller is in carrier access modes (COP07, 08, or 09), > the pin never changes state with or without a COS and/or PL signal > present. It is always low, allowing audio to pass. > > When the controller is in PL access mode (COP10), the SELECT 1 line > becomes high when no signal is present, thus blocking rx audio from > passing. When only an active COS signal is presented, it remains > high. When only an active PL signal is applied, it still remains > high, and no audio passes. However, when both COS and PL active > signals are applied, the SELECT 1 line becomes low, and audio is > allowed to pass. The line remains low even when COS then dissappears, > and stays low until the PL signal ceases. Basicly, both COS and PL > are needed to open the audio gate, but only PL is needed to keep it > open. > > Fortunately, there is an easy fix. > > I simply bent up pin 9 of the 4053 IC (U9) so that the pin is removed > from the socket. Conveniently, there is also a board solder/feedthru > connection for pin 9 (SELECT 1) just to the right of the IC socket. I > simply soldered in a 1N4xxxx series diode, anode connecting to the > aforementioned thru-board hole tied to pin 9, and the cathode to pin > 9 of the 4053 IC itself. Next, I installed the cathode of a second > diode to pin 9 as well. The anode of this second diode connects to > the COS signal coming out of the ULN2804 input buffer IC (U5) at pin > 18 (this is also the same signal appearing on pin 3 of the optional > ADM connector location). > > The two diodes are simply used to fully isolate the SELECT 1 and COS > signals from each other. > > Now, when the controller is in any of the three COS modes, the SELECT > 1 signal has no effect, but the newly connected COS signal switches > the 4053 audio gate to track with COS. > > When the controller is in PL mode, the SELECT 1 signal controls the > audio gate so that audio only passes when both COS and PL are > present. Since this mode is already working properly via the SELECT > 1 signal to track COS (along with PL), the newly installed COS signal > is simply "paralled" with the original SELECT 1 signal, and > effectively has no bearing on the control at that point. > > > Now, the controller will effectively mute rx audio properly no matter > which receiver mode is selected (COS or PL). I successfully tested > the RC96 on a Micor receiver feeding approx. 1Vpp into the controller > with absolutely no blowby whatsoever. Full muting. > > > This mod will work on the RC85 as well. With the simple installation > of two $0.05 didoes, the ACC controllers will now accept unmuted rx > audio without a problem. > > Eric > KE2D
