[Premium-Rx] RA6790/GM display madness

[Nick England]

Update for the archives and the next person who encounters this.

Dan Rae suggested that the pin to the LCD backplane might have been bent
and not making socket contact, as he had observed similar display
strangeness on a 6790 he repaired. That seemed like an excellent theory,
but alas, my BP pin was making good contact with the socket.
I ended up replacing the whole display panel, but I suspect Dan was correct
and there was an internal break from pin to backplane.

Side note- when replacing the front panel, it drove me batty trying to plug
the keypads back into their connectors. Flexible plastic is not the easiest
thing to force into a recalcitrant connector. Some Deoxit as lube and a
little exercising of the contacts did the trick....I hope.

Cheers
Nick and his now very happy RA6790/GM

On Mon, Apr 19, 2021 at 2:23 PM Nick England <navy.radio at gmail.com> wrote:

> While I am waiting on Mouser to send me some parts to (maybe) fix my AGC
> problem, I started investigating the LCD display problem on this
> receiver.....
>
> The indicator LCD display panel is fine - dark characters on a light
> background
> The frequency LCD panel shows the following -
> CW mode - freq is 00850000 Hz
> http://www.navy-radio.com/rcvrs/racal-display-CW.JPG
> AM mode
> http://www.navy-radio.com/rcvrs/racal-display-AM.JPG
>
> 1) The segments are all ON-OFF inverted!
> When it should be displaying a 0, the center horizontal bar is dark, the
> others are light. Looking at the LCD signals, the dark segment is in phase
> with the BP backplane signal and the light segments are out of phase.The
> manual says in-phase is OFF and out of phase is ON. What am I missing???
> 2) All segments are pretty dark in any mode but CW. There is still some
> contrast but the "light" segments are only a little lighter than the
> "dark". My oscilloscope shows no timing or voltage difference between CW
> and AM/USB/LSB. The only difference is that the BFO digits aren't blanked.
>
> I'm feeling either stupid for ignoring something blazingly obvious or
> incredibly puzzled - What the heck is going on!
>
> Nick England K4NYW
> www.navy-radio.com
>
-- 
Nick England K4NYW
www.navy-radio.com