My HP-67

[Kroni]

Dear forum members,
as a young man - this is almost 50 years ago! - I purchased a new reimported HP-67.
Later on during my work a HP-41CX was my calculating tool given to me by the company.
Meanwhile I have retired and I had a look at my beloved HP-67 but it has some issues:
- the rechargeable battery - it had already been exchanged - was dead. I replaced it by a new one.
- when I connect the original HP power supply I can see that on each LED unit the vertical segments on the right side do not work.
- even the power supply is connected charging does not take place
My search for a service manual of the unit was not successful except of a sketch of a schematics and a CAE job of the processor PCB.
In first step I have checked the voltages of the power supply and could find 5,2/16,2 Vdc. Is - especially 16,2 V - correct?
Thank you for your feedback in advance, best regards
Nick

[teenix]

(10-23-2024 08:41 AM)Kroni Wrote:  In first step I have checked the voltages of the power supply and could find 5,2/16,2 Vdc. Is - especially 16,2 V - correct?

Battery should be around +5VDC
Vgg should be around -12VDC
Vcc should be around +6VDC

Check for corrosion damage if the battery was in the calculator whilst stored. If so, this will need to be cleaned.

Check the pins at the bottom of the CPU board that connect to the keyboard. The display information goes through these, so if they are corroded or not making proper contact, the LED segments may play up as described.

Maybe if it has been sitting for a long time, some of the capacitors have failed and is giving improper voltages from the power supply.

cheers

Tony

[BobVA]

Welcome!

The fact that the problem with the display is in all the digits is probably good news, as it indicates the difficult-to-find LED displays are probably OK and the problem is outside it, in a connection or driver.

If you were measuring the output voltages of the wall charger, that sounds about right. (The 16v you measured is actually a constant current supply, dedicated to charging the battery.)

You'll have to be comfortable disassembling the calculator and doing electronics repair to proceed any farther.

+1 on Tony's suggestions! The display is directly above the battery and there may be corrosion-damaged traces on that part of the display/keyboard PC board, which will need to be repaired. And you should inspect/clean the connections between that board and the CPU board. A less likely possibility is that the segment driver IC has failed.

You might want to check out one of the tutorials on repairing the HP-67 card reader, such as: this one using O-rings and this one using silicone tubing, to see how to disassemble / reassemble the calculator if you decide you want to try a repair.

[Kroni]

Hello all,
there are no corrosion issue but I am still struggling with the internal power distribution on my HP67.
The rechargeable battery seems to be connected correctly since when charging it the voltage increases. When doing a measurement without the charger on pin 20 of IC 1826-0322 the voltage is present. But still the part can not be switched on!
In the adjacent drawing that I had found in the internet on page 6 in area "chassis wiring" there seems a link between the outermost pins of the connector (The center is GND.). And doing the connection manually the part works ...
Having investigated the wiring, the PCB and several components up to now I am unable to find an error ....
Does anyone have idea how the outermost pins are linked to each other?
Thank yo for answering and best regards
Nick

[teenix]

(10-25-2024 10:58 AM)Kroni Wrote:  Does anyone have idea how the outermost pins are linked to each other?

There is a gold plated connector that normally shorts the two outer pins when the charger is removed. This connects the battery to the power switch. This short is removed when the charger is plugged in and the charger supplies power to the calculator through one of the pins and charges the battery through the other.

If it works when you manually short the pins, the calculator should work whilst on charge.

If the shorting bar is not present, then that would explain why it is not working. If the bar is there, then it might have a bit of corrosion on it and if cleaned may fix the problem.

Pin 20 of the sense IC is normally connected directly to the battery +ve.

Image shows the gold connector.

cheers

Tony

[Kroni]

Dear Tony,
thanks a lot - this was a very helpful hint!! I was not knowing where this clip belonged to?!
Putting it to the correct position now the HP67 is switched on!

Again thanks a lot and best regards

Nick

[teenix]

Nice :-)
I hope many years of use follows.

[Kroni]

Regarding the display problem (both vertical segments righthand do not light) I did some measurements with my portable scope and I assume the IC 1858-0050 (CA3082) seems to have two damaged paths affecting segments b and c.
I took captures of the base and emitter pins of two working (d end e) and the two non-working segments.
Prior measurement I tried to fill the display on 10 positions with "8".
Based upon the pictures do you agree to assumption?

Best regards from Nick

Sorry, but since I can not attach multiple files - so I wiil include these in further postings.

[Kroni]

next picture

[Kroni]

further picture

[Kroni]

final picture

[teenix]

I have attached a scope image of segment (b), 1V 500uS per division. Segment (c) is the same. This was captured at pins 9(c) and 10(b) of the bottom row of board to board connectors. (Pin 1 is most left looking down at CPU circuit board) I'm not sure what the larger pulse is.

These would match up with pins 6(c) and 10(b) of CA3082.

If you have a 3V power supply and a 1K resistor and some leads you can test the LEDs directly.

You will have to strip the keyboard from the calculator.

Hold the -ve power supply lead to pin 1 of the LED display module (pin 1) This will connect to the common cathode of the 5th digit in the module.

One end of the 1K resistor connects to the +3V supply. Touch the other end of the 1K resistor to pin 12 and then to pin 3 to light the (b) and (c) LEDs. If they light, then the problem is in the driver IC or from the CPU connections or from the ROM 0 IC.

You should get the same scope signals shown in my image from ROM 0 IC pin 3 (b) and pin 4 (c)

cheers

Tony

[Kroni]

Dear Tony,
thank you for your reply and the work you did!
I just checked at ROM0 all pins and all signals are present. BUT: most signals as yours have a peak amplitude of 3V, but pin 3 (B) shows 5V and pin 4 (C) shows 6 V. To my opinion this can happen if the load to these pins is different compared to the other. I checked the array and it shows on all positions around 33k each.
I forgot to mention that already the day before I checked with my multimeter the two affected LEDs on one segment and I could recognize that they have been illuminated on a quite low level.
So as before mentioned I suspect the CA3082 to be the "bad boy" - do you agree?
Best regards from Nick

[teenix]

(10-27-2024 12:40 PM)Kroni Wrote:  So as before mentioned I suspect the CA3082 to be the "bad boy" - do you agree?

It is possible that an internal transistor has failed.

cheers

Tony

[Kroni]

Dear Tony,
after having replaced IC 1858-0050 by an RCA CA3082 the display now is working perfectly (refer to picture). BUT: I was struggling against an intermittent fault! Segment A on all digits sometimes worked sometimes not. Finally I found the root cause: the pins on the CA3082 have been quite long, so I shorted these and now it works! Possibly this is an interesting hint for other, who exchange an IC.
Now I only have to care for the card reader and its rotted transport wheels.
Best regards from Nick

[teenix]

Congratulations, all your hard work paid off :-)

[BobVA]

Good news! Thanks for sharing!