HP-65 weird display behavior

[albertofenini]

Hi everyone

we need a bit of advice on this ...
this is an HP-65 display board the behaves like this no matter what logic board
we use, since the same logic boards are working fine in their own units we
assume that is the display board with some problems :
beside an obvious degradation of the first left led block,
for every digit lit (except when the number 2 is shown) it also lits the
next h segment (decimal point) and the next c segment.
What could it possible be and what could we possibly check ?
Thanks in advance !!!

pictures : HP-65 weird display behavior

[teenix]

It looks like the 'c' segment causes the problem, so might be a short in one of the LED modules, on the pcb or perhaps a faulty anode driver.

cheers

Tony

[albertofenini]

Hi Tony
You mean that the faulty c segment can turn on also the g segment ?
By the way, if we remove the first from the left block
will the others work ?
Take care !

[teenix]

(06-26-2020 06:11 AM)albertofenini Wrote:  Hi Tony
You mean that the faulty c segment can turn on also the g segment ?
By the way, if we remove the first from the left block
will the others work ?
Take care !

Its possible, but also could be the anode driver decoding.

Maybe the replaced inductor is faulty as well.

The other displays will work if one module is removed, however I am not sure if it will damage the cathode driver chip because the inductor current will have nowhere to discharge when trying to drive the removed LEDs. I think Harald had problems of this nature when developing his Classic replacement board.

I created some information about this in my Classic notes document.

http://www.teenix.org/ClassicNotes.pdf

cheers

Tony