HP-67 advice needed



#8

Dear All,

I'm restoring an HP67, which was in bad to very bad conditions.

Battery contacts missing, very dirty and with a lot of oxidation.

I've cleaned the keys, the faceplate, and put all the electronics

in some vinegar for few hours.

I have recovered a couple of new battery contacts from an HP97

power pack and I have put some pieces back together.


I'm using a working HP-67 for the troubleshooting.

If I install the working board in the cleaned keyboard this is what
I get



Would you think of a bad soldered pin on the cathode or anode drivers or something more serious ??

Also, the back of the keyboard plate had some corrosion and has been partially recovered, now it looks now like :




Could this also be responsible for the bad display ??


If I put the cleaned board



into the working HP67 all I get
is the low battery led turned on.

I'm planning to do some seriuso rework in this unit,

desoldering everything an polishing the pcb, unless you have

a better idea.


As always, thanks in advance for any suggestion given

take care, Alberto


#9

Sorry that I cannot offer any tips or help.

But I couldn't resist offering some admiration. That is one deep dive. I wish I had the skills and patience to do the same.

#10

Can you light all the LED modules? I had a 65 with a similar problem, but it was only one module that was bad.

I'd have to go back to the schematic on the module, but I'd suspect a bad module.

#11

Use a better test value, key in 8888888888 EEX 88 CHS

If you cannot enter the test value, check for operation of the bottom 4 x 4 grid of keys on the keyboard: all numeric keys and the 4 basic math functions. Start troubleshooting any inoperative keys looking for open traces as the keyboard scan lines and display cathodes are multiplexed.

Don't forget this: HP-67 Internals

#12

What is that symbol on the lower left corner ?... mine has an HP symbol there (I think).
That board sure looks terrible :(.

#13

ciao a tutti

first let me tell that I'm able to light all the segments, and all
do look like the first three shown in the picture.

As far as for the display, I have desoldered both the drivers and
soldered them back again, but it didn't change a bit

I'll try to do what Randy suggests, but as far as I could remember, keys were operating correctly.


I have stripped all the components from the PCB :





and with the help of a 600 sandpaper and water, carefully tried to bring some connectivity back






I have then resoldered all the components back.

Red circles show damaged traces and I will restore those connections with a very thin isolated wire later.

However, using it as it is, in the working unit I have, it behaves
exactly like yesterday ...

I think I'm going to keep the case as spare parts .... :) but I'll do any test that you would suggest

take care and thanks again Alberto


#14

We have a misunderstanding due to the terms you have used.

A classic display has 15 digits. There are 3 LED packages of 5 digits each. Each digit has 7 segments plus the decimal point.

The original picture you posted has "0.00" displayed but each digit that is illuminated is missing segments c, e and f. If every digit illuminates but it is missing the same segments (c,e and f), the problem is open traces or bad transistors within the 1858-0050 IC on the keyboard assembly. It would be a simple matter to test each transistor with an ohmmeter using Tony's information on the 67 Internals article that I referenced in my previous post.

You may also find this of some help: http://www.classiccmp.org/calcmuseum/clasdisp.htm


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