HP-71B LCD Problem! How Common?

[Namir]

I received an HP-71B claulctor from TAS. The machine is in very good phsyical shape. You can say it was not used much. Hoever, when I typed a series of 8s across the LCD, the LCD displaye dthem correctly for less than a second and then displays bar-like charcaters in the middle of the LCD.

How common is this? Have you seen such a problem. I sure have not!

I appreciate feeback!

Namir

[rprosperi]

Hi Namir,

I have a 71B that occasionally will have similar LCD issues, wherein the bottom few rows of dots turn-off along the full width of the display. Pressing down on the bezel below the LCD will usually restore the full LCD; thereafter, it may not occur for months or it might the next day.

Obviously some kind of semi-loose connection, it does not seem to be affected by bumping or positioning the machine oddly, or other handling effects. I can only guess, but I suspect environmental effects (temperature, humidity, ??) may explain the intermittent behavior.

Give it try and report results.

[Namir]

(02-17-2019 12:11 AM)rprosperi Wrote:  Hi Namir,

I have a 71B that occasionally will have similar LCD issues, wherein the bottom few rows of dots turn-off along the full width of the display. Pressing down on the bezel below the LCD will usually restore the full LCD; thereafter, it may not occur for months or it might the next day.

Obviously some kind of semi-loose connection, it does not seem to be affected by bumping or positioning the machine oddly, or other handling effects. I can only guess, but I suspect environmental effects (temperature, humidity, ??) may explain the intermittent behavior.

Give it try and report results.

I first discovered the ssue after inserting an HP-IL module and executing the VER$ command. The output was long enough to cover most of the LCD. Itshowed that the middle characters turning into intermittent vertical bars. I tried another HP-IL module and got the same thing! Then I typed 8s (with no HP-IL module plugged in) and saw the same issue. In between I took a battery out and put it back in. Same problem.

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 find that hard to believe UNLESS THEY ALL CAME FROM A BAD BATCH WERE THE UNITS SAT UNUSED AND THEREFORE LOOK LIKE NEW. That is why I am asking for others if they have seen the same problem.

Namir

[rprosperi]

(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.

[Namir]

(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.

I am asking the vendor for a full refund.

Namir

[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.

[Namir]

(02-17-2019 02:58 AM)Raymond Del Tondo Wrote:  

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

Raymond,

How many HP-71B have you encountered where part of the LCD characters appear as intermittent vertical bars?

Namir

[Raymond Del Tondo]

(02-17-2019 05:59 AM)Namir Wrote:  How many HP-71B have you encountered where part of the LCD characters appear as intermittent vertical bars?

Hi, there were three units of which I remember that effect. One of them could be repaired by replacing the interconnection between the upper and lower half with a suitable piece from another unit.
The percentage of units with that effect was small, given the many HP-71B units which went over my desk, but the general problem stays.
Interesting that in all cases it was one of the later units with changed interconnection

[Namir]

(02-17-2019 08:24 AM)Raymond Del Tondo Wrote:  

(02-17-2019 05:59 AM)Namir Wrote:  How many HP-71B have you encountered where part of the LCD characters appear as intermittent vertical bars?

Hi, there were three units of which I remember that effect. One of them could be repaired by replacing the interconnection between the upper and lower half with a suitable piece from another unit.
The percentage of units with that effect was small, given the many HP-71B units which went over my desk, but the general problem stays.
Interesting that in all cases it was one of the later units with changed interconnection

Thanks for the information.

Namir

[james summers]

Hi All

I think my HP71B has developed the same problem after being unused for a few years. I'm pretty sure when last used the display was fine.

Display after executing VER$


Display of my other (good) unit after executing VER$


Oblique view of my problem display showing some missing columns


Closeup of the affected area - display showing a sequential string of numbers with '2' to '6' affected


I'm guessing the best place to start looking is the bacon strip or the zebra strip? Mine is one of the plastic backed 71s.

Regards
James

[KimH]

I have several 71B on hand, all versions

2 of them have an issue like this - both are the later plastic-back versions

- one has a character which is messed up (some pixels)

- one has a “block” of the LCD being “faint”

I have not had the need to repair, but suspect this is the strip between the LCD glass and the main (fixed) board - another rubber Zebra adventure.

Not easy to repair, but should be possible if you can heat-stake.

If anyone has suggestions, I’d also like to hear them.

[Stefan_Titan2944A]

Hi,

a Zebra issue is unlikely.

The HP71B has two PCBs:
- IO PCB ( can be removed ) containing
Power Supply, RAM and IO ports
- Keyboard PCB ( hardly removable) containing
CPU, Keyboard, Card Reader, Display RAM and LCD driver chips

Both boards are connected via Zebra (old versions) or flex cable.
This connection is the System Bus - it will certainly not corrupt the display
due to missing connections.

The LCD itself is soldered on the Keyboard PCB.

The problem is most likely the LCD itself - connection of electrodes to
top and bottom glass substrates. Both glass layers are seperated by a
spacer layer, which shrinks. This may cause missing or additional lines.
Hence, when moderate external force is applied, missing lines usually
re-appear.

Use at own risk:
One of my HP71B had the same issue and was successfully
revived by moderately heating the LCD (hair drier). Try the areas
of issue first. Extend to the whole LCD if necessary.

- Stefan