HP-71B LCD Problem! How Common?

[Raymond Del Tondo]

(02-17-2019 02:00 AM)rprosperi Wrote:  

(02-17-2019 01:46 AM)Namir Wrote:  The atual seller is working through a clearance vendor on eBay. That vendor wrote me and said that after I informed him about the LCD problem, he tested two more new HP-71B units he had AND FOUND THAT THEY HAD TEH SAME LCD PROBLEM!!! He claims that this is a common "bug" based on what he found on the Internet!!!!!!!!!!!!!! Not sure I am buying it!

I call BS. It is extremely unlikely that multiple units have the same unheard-of before now problem; it's not even likely the vendor bothered to test the units, he's just coming up with an excuse to not swap you a good unit for the bad one you have. Ask the vendor to send you links where he "found" this information; when he can't, I'd demand a swap for another unit, which I suspect will miraculously self-heal on its way to you.

It *may* get a problem to all 71B units which have the same type of interconnection between the LCD and the pcb, namely the bacon strips. These tend to dry out over the decades, and shrink in consequence, leading to contact losses. It's the same as with the bacon strips on some HP-41 units, in the Voyagers, and in the Pioneers. The gold ring zebra strips are way better in that respect.
And here we come to the next problematic interconnection part of the HP-71B: The zebra strip between the upper and lower half of the case. Although they usually work fine, I have seen some which don't work reliably, leading to strange patterns on the LCD, in the best case. In worse cases, the unit simply won't work.

If more than one of those NOS 71B units has the same problem, then it simply happened as stated above.
Although many of the different HP calcs are over-engineered in various respects, they all have weak points, in this case the cheap bacon strip connectors.

EDIT: The Pioneers don't use a bacon strip for interconnection between the main pcb and the keyboard. The Pioneers use a foam pad (w/o electrical lines) which presses a foil pcb to another pcb. The effect is the same: A shrinking foam pad leads to loose contacts.