[Premium-Rx] Cubic R-3030

[FRANCIS CARCIA]

Hi Heinz,
Great news on the fix. The preselector should be easy to fix after you determine whic channel has a problem.
If it is the decoder it will be more than one. Go through all the second functions and adjust them to make sure good data is stored when you change modes. Yes rapid power cycles can cause bogus data is stored.
Frank


________________________________
From: Heinz Breuer <hbreuer at debitel.net>
To: premium-rx at mailman.qth.net 
Sent: Thursday, July 12, 2012 2:14 PM
Subject: Re: [Premium-Rx] Cubic R-3030

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:-)
> ----------------------------
>

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