HP 21 Woodstock Missing Decimal Point

[Sanjeev Visvanatha]

3-2-1 Detach!

I had some time, and luck to get the plastic bubble cover off the PCB holding the LEDs. With a very sharp Exacto blade, I lifted the very thin 'mushroom' head from the stakes holding the bubble cover in place.

While working, the best optical magnification I could get was about 5x. It was sufficient for me to confirm that the tiny wire is connected to the PCB, but detached from the LED.

I took a digital photo, which shows it rather well. The offending digit is the second from the top of the photo (click to enlarge):

(01-07-2016 12:03 PM)emece67 Wrote:  Sometimes, inspection with a watchmaker's lens can give a clue if the tiny aerial wire connecting the offending dot to the PCB strip is damaged. If it is still attached to the dot, but otherwise broken or desoldered from the PCB, it may be repairable by soldering a new (thicker) wire to the PCB and soldering it to the remaining tiny wire. Use old Sn/Pb mix to solder, as the tiny wire does not support well the high temperatures needed by modern mixes.

Indeed, I think I would have more confidence in repairing a situation as you describe. As it is, it appears the tiny wire is detached from the dot, which I think is beyond my skill level to repair

(01-07-2016 08:44 AM)jebem Wrote:  Another much easier option would be to ask Panamatik for a display replacements here.

But of course if you really are into diy (like myself), you can buy 3 HP QDSP-6064 7-segemnt bubble LED chips, then totally remove the old leds from the PCB and hard-wire thee 3 new chips in place.

And thinking speed of repair and lower costs, Panamatik offering is a safe bet and very competitive price against any other options that I mentioned.

Panamatik's replacement display is a very good option in this case. I was not aware that he had devised this neat solution!

If there were single digit, 7 segment LED's available, I may be able to affect a repair with my skills. Doing the tiny soldering several times over is probably going to end up badly for me!

As it is, I have a personal machine. When there is no decimal point displayed, I know it is after the first digit!