HP Forums
Classic HP LED failure diagnosis - Printable Version

+- HP Forums (https://archived.hpcalc.org/museumforum)
+-- Forum: HP Museum Forums (https://archived.hpcalc.org/museumforum/forum-1.html)
+--- Forum: Old HP Forum Archives (https://archived.hpcalc.org/museumforum/forum-2.html)
+--- Thread: Classic HP LED failure diagnosis (/thread-195756.html)

Classic HP LED failure diagnosis - aj04062 - 09-16-2011

I have a 65 that has a non-lighting minus sign. Upon dis-assembly, it can be observed that the Cathode 1 segment does seem to light very faintly when the CHS key is pressed. The minus sign does not light.

Upon additional testing, when the battery drains and all the decimal points light up, the Cathode 1 decimal point DOES LIGHT UP. This leads me to believe that it is likely the LED Module and not the Cathode driver.

does anyone concur with this diagnosis?

Re: Classic HP LED failure diagnosis - Kees van der Sanden - 09-17-2011

Hi aj4062

I agree with your diagnosis. If the Cathode 1 digit decimal point lights up at low voltage conditions, the cathode driver does his job.
A failing LED segment in the module can be the root course.
The module contains only a matrix of LED diodes and no control electronics.
The specifications can be found here.
Desolder the module and check all segments with the diode test of a multimeter.
Failing segments in classic series LED modules is a common problem.

Re: Classic HP LED failure diagnosis - aj04062 - 09-17-2011

Thanks for the confirmation Kees!

Just wanted to see if anyone else comes to this conclusion before I spend the time to desolder and replace that module.