[Elecraft] Kpa500 lcd display issue

[Jack Brindle]

Andy; Your analysis was correct. Somehow the LCD ADJ value became set to 100. KD5SPX was able to resolve the issue by figuring out the exact keypresses needed to access the menu setting and lower the value.

The range of the value is 0 to 100, with the default being 30. This value sets the duty cycle of a PWM in the microcontroller that is connected to the LCD controller’s Contrast input. At 100 the LCD segments will be shown as grey, but the value should be readable, although it may be difficult to distinguish the exact segments that should be illuminated. There is not much contrast between the grey segments and the black ones. 

The easiest way to correct this situation is to reset the parameters by holding the EDIT button while powering up the KPA500 using the front panel button. Wayne did find a way without resetting the parameters. My hat’s off to his tenacity in succeeding with that method.

73!
Jack, W6FB


> On Apr 14, 2020, at 10:25 AM, Andy Durbin <a.durbin at msn.com> wrote:
> 
> Given that the "test pattern" may be caused by an extreme LCD contrast setting I'd suggest checking the contrast voltage that is derived from PWM signal VCONTRAST.    Contrast voltage is available of "TP2" which is connected to LCD pin 55 (VLCD).
> 
> The schematic shows VLCD range is 3 - 6.5 V.   I see a good display with LCD ADJ set anywhere between 0 and 30 so I would guess VLCD between 3 V and 4 V would give a readable display.
> 
> 73,
> Andy k3wyc
> 
> 
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