[Premium-Rx] Cubic R-3030

[Heinz Breuer]

Hello,
I got several very helpful emails, thank you all.
I increased C2 with a 4.7 uF electrolytic soldered directly to pins 7 
and 10 of U2 keyboard encoder. 99% of my keyboard problems are now gone.
I also perfomed a memory reset "RCL" dot dot 911 "ENT" as suggested by 
Frank WA1GFZ and the left receiver with the AGC problem came back to 
life. I had probably stored some invalid parameters when I recycled the 
power once too often.
I still face the intermittend failure in one preselector unit. I will 
open it up and resolder a couple connections as a start. Otherwise I 
have to built an extender first to be able to take some measurements.
vy 73 Heinz DH2FA, KM5VT



Am 12.07.2012 19:48, schrieb Tisha Hayes:
> Interesting, I just did a long write-up on this on one of the other lists
> (maybe Harris or one of the mil receiver sites in the past day or two) and
> you are correct about the debounce.
>
> Back in the 80's I designed this test-set that had a flat front with
> membrane keys for data entry and optioning. After a few years they were
> coming back with extremely worn out "enter" keys and the trouble ticket was
> about multiple key entries when pressing keys. I had to go back and design
> a little adder board that went between the display panel and the logic card
> that put an RC circuit debounce onto the 4 x 8 scan lines of the keyboard
> to logic board interface. After I finished the design one of the service
> techs came in and saiid, "well, I have just been changing this 2.2 uFd cap
> to a 4.7 uFd cap"... it was the capacitor that made up the RC circuit on
> the keyboard decoder circuit. Thank goodness someone was actually looking
> at what I had designed and wondered what that capacitor was for, he had the
> fortitude to go read the chip data-sheet and saw what it was for.
>
> Either solution would work, his was better for it's elegance. In the future
> I added RC integrators and Schotky buffers so I had some EMI isolation and
> was always pulling the line to VCC with a resistor so it was not at a high
> impedance state on the logic lines.
>
>
>
>
> --------quoted------------
> ...  There are two issues with the keypads, firstly that the value of the
> keybounce suppression cap in the interface module is too low, and secondly
> that
> the keypad plastic overlays become detached from the keypads and bulge in
> the middle because they are held in place by machine cut double sided tape
> that  has a relatively small contact area on the thin frames separating the
> individual  keys.
>
> Issue one is dealt with by increasing the value of C2 in the Panel
> Interface Module from 3.3uF to somewhere closer to 10uF.
> This cap goes from pin 7 of U6, the 74C923 Keyboard Encoder to ground, and
> I found it easier to leave the existing capacitor in place and fit another
> in parallel across the top of the IC and soldered to the actual IC pins. I
> used 6.8uF but 4.7 uF would probably be ok too, or perhaps it was the other
> way  round it was a few years ago now:-)
> ----------------------------
>