HP65 Extreme Makeover S/N 1333S07557 - Advice requested

[teenix]

(05-22-2019 10:06 PM)[kby] Wrote:  No advice but i’ll Be interested in what you find out and others say. I have a -65 with a (perhaps only vaguely) related issue: Works fine except for a faint ghosting of some segments in LED 3 (I think—maybe 4) if they are lit in LED 8-kby

The energy in the inductor for each LED segment has to be completely discharged before the cathode driver is sequenced to the next LED digit. If this doesn't happen, then the remaining inductor energy is passed to the next LED and the 'bleeding' that you see takes place. This means the timing between the ARC, anode and cathode drivers has to be quite precise.

Why it happens only on one or two digits might suggest a higher than normal resistance for the inductor discharge path. This is normally from the inductor, through the LED segment, out through the LED digit common cathode pin and into the relevant cathode driver and then to ground.

Look for dirty looking solder joints or corrosion around the display and the drivers. It could be the corresponding transistors inside the cathode driver are showing their age and are not passing the inductor current as well as they should.

cheers

Tony