HP-67 Interface & Display Segment



I've just purchased a HP-67 thats in immaculate condition. Other than the card readers gummy wheel, and a display problem, it seems to function fine.

When I first switched the machine on, and performed some calculations, the LED display functioned OK. After about 30 seconds, one segment (top segment) on the 10th digit from the left flickered and then switched off. The next morning I switched the machine on and the segement was OK again, but after 10 seconds it switched off. Other than this the HP-67 functions without any problems.

I don't wish to open the machine and cause some irreversible damage, hence, does anyone have any theories as to what this could be. I think it could be an aged component, such as an electrolytic capacitor, but thats my theory and I may be barking up the wrong tree.

The other thing about this machine is that it has a 7-pin connector on the left of the top panel. The previous owner of the machine acquired the machine from a friend, hence, he has no idea what this was used for. Is this a printer interface?

I have not opened the machine yet, but will do so to repair the card reader and, hopefuly, the display problem. Only then I will know where the internal connections of the 7-pin connector are terminated. I can tell from the back of the machine that it has been very carefuly opened. Maybe it was opened to install this interface. Does anyone know whether HP installed interfaces on HP-67s on request. Furthermore, would anyone know what type of interfaces could be fitted to the HP-67.

Any help would be appreciated.

Thank you & Best Regards


I don't know if your problem is a contact problem, but it's easy to find out:
Turn the calculator on and wait till the display dies. Then you have to produce an electric spark near the calculator. Piezo-lighters can do this, or switch on the light.
With a piezo-spark about 10 cm from the device, I have "repaired" many devices (they work for some time, then quit again).
To switch on the light seems to work at greater distances, but no scientific proof yet.

Remember the old radios that sometimes lost the channel? Switching on the light worked as well as a hit by hand.

I think you should give it a try!


Hi Franz,

In the evening I will try the Piezo electric effect.

I have also tapped the calculator while it is switched on with no change to the missing segment. Is it possible that the bonding wire for the missing segemnt may have become loose?

The only solution to this problem would be to replace the 5 digit 7 segment display module. I don't think these are available anymore and would have to be retreived from a scrap calculator.

Thanks & Best Regards


If a single segment in only one digit is bad then the way the display is scanned in the HP67 means it almost certainly a bad LED module. If a whole digit or a segment in every digit is wonky then the problem would be in one of the display driver chips.



just to add to David's post that the "LED module" is a sealed unit with five complete digits (three of these compose the display). Thus, as David explained, if one segment is missing/flickering, it's more likely to be an internal problem. After the Classics (Woodstock, Topcat and Spices) the LED display as a whole is composed of a single unit. The HP67 is the exception: internally it's a mix of Woodstock architecture with a case and LED modules borrowed from the Classics.

My 2¢

Luiz (Brazil)

Edited: 11 May 2004, 1:34 p.m.


Hi Imran,

According some tips regarding HP-67 display problems, you can find a spare part for the anode driver. The 1858-0050-1D has the following spare part: CA3082 NPN transistor array (common collector), available in any Radio Shack. The cathode driver is an HP full custom integrated circuit 1820-1749.

Good luck,



Luiz mentioned that the LED modules were borrowed from the Classic series. What are the calculators in the classic series?

Do the classic series also comprise 3 of the 5 digit LED modules? Is the PCB that holds the LED modules identical to the one in the HP-67?

Would it be possible for me to purchase a classic series claculator and swap the LED modules or the LED PCB for the one in HP-67?

Is it also possible to purchase the LED modules from HP or compatible modules from another manufacturer? (as long as they don't cost more than purchasing a scrap classic series or HP-67)

What a life - thats 2 calculators I have with the same problem. (The other ones a HP-34C, for which a very kind forum member has forwarded me a replacement HP-34C, LED module in exchange for the defective one. I will keep everyone posted)

Thanks & Best Regards


The only source of replacement LEDs is another calculator. The HP35/45/55/65/67/70/80 all use pin compatible LED modules. They all have the same part number, but those with gold and silver leads have slightly different size digits. Best to keep them matched. Also there is a letter code digit on the back of each package that indicates brightness. I have seen them from "G" - "M". Try and keep them within a couple of letters for best appearances. The keyboard printed circuits are rather fragile. It is best to use a good vacuum desoldering station. You will probably have to remove the inductor package(s) to get to the LED pins. The inductor packages are not identical.. don't mix them up.


Nit-picky factoid: 67's don't have inductors on the display board. But those pesky transistors and resistors do get in the way.

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