High incidence of DOA LCDs

[mikeincinci]

Has anyone else experienced a high level of DOA (dead on arrival) 420 LCDs for use with the T100MD1616+?  For 6 years I never had any problems, but in the last 18-24 months, I've had about a 20%-30% DOA rate, about ten total.  I sent a batch of bad ones back for testing last year, but found Mr. Yew's response unsatisfactory.  They are cheap, so I currently order extras each time, treating them as disposable.

I have never had one fail in use.

Mike

[support]

When is the incident? We shipped thousands of LCD420 every year but did not notice high rate of DOA or return in general.

Did you purchase through a distributor? Would like more details about your issue. Please email purchase details to sales@tri-plc.com so that we can look into it.

To ensure that the LCD is not killed while installed in the panel from any electrical short circuit etc, you may like to test the LCD on a desktop with a good PLC when you first received the goods. This way you can confirm if the LCDs are working when you first receive them.  

Please ensure that power to the PLC is turned OFF before you plug in the LCD to the PLC as the LCD or the PLC could not tolerate hot-plugging/unplugging.

[mikeincinci]

I do have a test fixture for these with a known good PLC and a regulated power supply.  I have years of experience with these and use common sense and good electrical work practices, such as ESD prevention and connecting equipment unpowered.  At least one of the LCDs arrived with a dead backlight, but most have issue with the display showing some random block pattern.  I test the display first, and if it is ok, then I test the backlight.

We order through a non-stocking distributor, CaliTech in Louisiana.  Our recent LCDs shipped to us directly from somewhere in California.

I am hesitant to reopen this issue with sales because of my experience last time.  Your manufacturing and test processes do not issue/track serial numbers or issue individual test reports.  I am leaning toward having a third party (distributor) perform testing in accordance with our QA program before sending to us.  
Do you have any such QA-testing distributors already?  CaliTech has expressed a willingness to do this testing for a minimal additional charge.

[support]

I checked our record and I believe I've found the correspondence we had with yourself and Calitech regarding your case.

Our record shows that Calitech returned to us 1 unit of LCD420 in April 2007 claiming LCD has no backlight. However, when we tested the LCD backlight it worked without any issue. It worked at both 12V and 24V DC. We have emailed the report to Calitech to be forwarded to the customer but we are not sure if they have followed up with you about the fact that the LCD had no problem.

Calitech subsequently returned to us 1 unit of T100MD1616+ PLC and 4 LCDs that purportedly from you in August 2007. It was suspected that the PLC's LCD port could be the what was damaging the LCD. However, we tested the PLC and connected our own LCDs and everything worked well so the PLC was working perfectly. However, the 4 returned LCD had indeed suffered some kind of electrical damage.  Since you were aware of and have applied good electrical work practices to handle the PLC and LCD,  it is a bit puzzling and we can only conclude that some unknown factors during the installation have damaged the LCD. We can fully understand if you may not be convinced  by it because unfortunately not everything that could go wrong is always obvious.  Thus to-date we have only received 5 units of LCD420 from you and 1 of them is a working unit (the complaint was no backlight on this unit) and only 4 damaged LCD420.

All our products undergo 100% testing in the factory before packing for shipment, so to ensure that what you received are indeed functional unit, It is a good idea to appoint Cali-tech or a third party to do a test prior to installation.  At least we can eliminate the possibility of something happened during transportation in the aircraft (zapped by cosmic ray??? - just kidding).