Contrast control too sensitive

Contrast control too sensitive

Postby lusoman » Wed Jul 01, 2015 3:07 am

I build my 062 over the weekend, and thought initially that there was a problem with the LCD, since I can get it completely blank or completely dark, but not the right contrast in between.

When it's dark I can see four icons top right - a battery icon, and up-arrow, a circle with two diagonal light lines, and a triangle pointing upwards.

If I turn the LCD trimpot INCREDIBLY slowly, I see the screen flash very briefly with the graticule and some numbers plus a DC indication, but I can't get it to stick there - it always overshoots to completely light or dark, depending on which way I'm turning the trimpot. I estimate that it goes from completely dark to completely light in less than 1-2 degrees of rotation.

I've checked all the test points on the board with a good multimeter, and they all seem fairly close the the values in the troubleshooting guide, though not spot on (see below).

Any help would be appreciated

TP1: 0.00V
TP4: 8.21V
TP5: 4.98V
TP6: -6.14V
TP7: 8.20V
TP8/9: 0.00V
TP12: 2.49V
TP13: 5.67V
VEE: -4.86V
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Re: Contrast control too sensitive

Postby jye1 » Wed Jul 01, 2015 9:12 am

Please check soldering of POT1 and pin 3 of LCD module. Check voltage at LCD pin3 with a voltmeter to see if you can get a steady change while turning POT1. If not POT1 is possibly defective.
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Re: Contrast control too sensitive

Postby lusoman » Thu Jul 02, 2015 12:56 am

jye1 wrote:Please check soldering of POT1 and pin 3 of LCD module. Check voltage at LCD pin3 with a voltmeter to see if you can get a steady change while turning POT1. If not POT1 is possibly defective.

Soldering at POT1 is fine. The voltage at LCD pin 3 does not change smoothly. It seems to only take the values +0.4V or -5.0V.
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Re: Contrast control too sensitive

Postby jye1 » Thu Jul 02, 2015 12:53 pm

Suggested solution 1:

Use another pot (2 - 10K) to set contrast to desired setting. Substitute the pot with two fixed resistors.


Suggested solution 2:

Contact JYE Tech at jyetech@163.com for a replacement of the defective trimmer.
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Re: Contrast control too sensitive

Postby lusoman » Fri Jul 03, 2015 1:10 am

Thanks.
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