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Display Contrast Issue with latest displays

Hi, we manufacture a legacy product that uses the 161A, it has done for many years with no issues at all.  All displays from the latest batch(es) we have received however have the self-same issue in that their contrast is really poor, (displays from the older batches of course work fine on the same driver boards),  Please see images below.

The printing on the back of the boards reads;

Original "good contrast" Display: 161ABABC.  RS REF:532-6335,  ROHS 1135C1135C10S

New “Poor Contrast” Display: 161ABABC,  E258078, ROHS 1747C1747B10S

We have tried adjusting the contrast using a 5Kohm multi-turn POT in place of R5; the contrast for displayed characters can be improved but in doing so we then introduce false activation of several columns of pixels both in the character fields that should be displayed and for characters fields where nothing should be displayed.

Any ideas?

Replies

terry_seacomp's picture
terry_seacomp
November 28, 2018

The date codes on these units are more than 6 years apart (35th week of 2011 vs 47th week of 2017). It looks like in the new LCDs the tolerance may be different/ lower than the older one. The condition you are seeing appears when the voltage to the LCD is too high. Perhaps this batch is on the lower range of tolerance and the normally supplied voltage is relatively too high for optimum contrast. Can you check this?

 

James Courtney's picture
James Courtney
November 29, 2018

Thanks for the info on the date coding nomenclature, it's very handy to know.

I am measuring the supply voltage at 4.95Vdc,

Also I just tried running it directlty from a Bench PSU, reducing the supply from 4.95Vdc in 0.05Vdc steps.  There was no visible contrast change at all until 3.90Vdc when the display/system shut down completely.

terry_seacomp's picture
terry_seacomp
November 29, 2018

Can you send your schematic to terry@seacomp.com? Where are you located?