Trying to revive a HP67 (Dead on arrival)

[Hugin]

Hello,

I recently bought an HP67 from an older gentleman who seemingly used it until a few years ago. He then stored in in his desk for when he might need it again. And just to make sure the calculator would be ready when he needs it, he left the charged batteries inside.

Now, years later I got it and yes... its a damn mess. One of the battery contacts was completely rotten away (literally) and the long "connecting PCB" next to the battery tray was covery in corrosion as well as the charging port.

Today I spent nearly five hours cleaning, manufacturing a new battery terminal and then hooked it up to my lab supply (tried 3.5-4v).
According to the PSU (hooked up the the battery terminals) it draws 270mA when switched off, which drops to 150mA when switched on, which I consider to be rather weird.

So I guess the first thing to start with would be the power supply-components but I have no real clue, where they are. Also I didnt find any helpful repair flowchart.

Does anyone have an idea where to start from?
I have a lab PSU, a good multimeter, time and general electronic knowledge but not about how to fix calculators/vintage computers.

Any help would be appreciated, I realy hope that the HP67 might become my new EDC-calculator at university.

Thanks a lot already!
Oh and I live in Germany so my English might be slightly incorrect, but I am trying my best.

[teenix]

It is possible that corrosion has affected the sense board (long one you mention). This board has a direct connection to the battery, so if it is faulty, it might explain the switched off current, which should be zero, unless batteries are installed in which case there might be some charging current visible on the lab supply.

Leave the sense board unplugged from the CPU board. If the sense board is faulty, it could damage the CRC chip on the CPU board.

There are two red wires connected to the board. One to the motor, the other to the battery.

Disconnect the one to the battery, you might be lucky, as sometimes these wires can be unplugged, otherwise unsoldering is required. See if the switched off current is now zero. If so, the sense board has a short (corrosion) or possibly the sense IC is faulty.

If the switched off current is still there, then you need to check under the keys circuit board around the circuit traces for the power switch. This will require further disassembly of the calculator.

It is also possible that the card reader has a "gummy" wheel problem and will need some repairs. You can check this by looking ate the gear and worm drive connected to the motor. You might see some "mess" where the drive roller contacted the magnetics cards to pull them through the reader.

If you manage to fix this fault, then it might be wise to replace the 47uF 16V tantalum capacitor as a faulty one can sometimes interfere with the reading of cards. It is located at the 1 o'clock position from the power supply coil. (Polarity sensitive - be careful)

If you would like to make a new sense board, I have a zip file here. Inside is another zip file that you can send to a PCB manufacturer (like PCBway) and get some boards made quite cheaply.

cheers

Tony

[Johnboy]

And of course Tony Duell's schematics might be handy : https://www.hpcc.org/cdroms/schematics5....c/hp67.pdf

Cheers,
John