Broken HP 71B. Where to start?

[Seirin-Blu]

Hello,

I'm very new to the world of vintage calculators and come from the land of vintage mechanical keyboards. I recently found a broken HP 71B and am a little bit puzzled on where to start. I cleaned the corrosion off of the battery contacts and opened it up to see if there were any exploded capacitors (there weren't). There seems to be a bit of corrosion on the band between what I assume is the motherboard and display/keypad that I cannot seemed to clean of without damaging the cable. Is there something I can short to turn it on from the motherboard and check? Or should I just list this on ebay to someone who knows what they're doing more than I?

[Maximilian Hohmann]

Hello!

I think that a broken HP-71B is difficult for anybody to repair. Listing it on eBay could however be of interest to someone who needs a spare keyboard or display, so I guess it won't take long to sell.

Two easy fixes that I can think of:

1. Sometimes when the HP-71B was turned off for long periods it requires a very long press (several seconds) of the ON key to come back to life. This is always the first thing I try.
2. Depending on the production year some HP-71Bs come with battery connections that are not made by wires soldered to the PCB but simply the back end of the battery springs that touch a gold plated area of the PCB. I have had contact problems with one of these in the past and ended up by soldering the contact springs to the pcb. The springs are rather difficult to solder though. For testing purposes you can solder wires to the PCB directly and power the calculator from a 6V DC power supply.

Otherwise the service manual can be accessed from here (in case you haven't already downloaded one): http://www.hpmuseum.net/exhibit.php?hwdoc=118

Regards
Max

[KimH]

Welcome!

The situation you describe here is not uncommon, the acid from the batteries went on
It’s journey an you are forced to repair the damage….

The connection between the keyboard and the CPU is not designed for when acids starts to wander…

I have soldered more than a handful - making them work again, but this does require some experience. Not a lot, but some.

If you are keen with a soldering iron and thin wires, you can make it work. If not, put it back on the market.

(03-22-2022 11:44 PM)Seirin-Blu Wrote:  Hello,

I'm very new to the world of vintage calculators and come from the land of vintage mechanical keyboards. I recently found a broken HP 71B and am a little bit puzzled on where to start. I cleaned the corrosion off of the battery contacts and opened it up to see if there were any exploded capacitors (there weren't). There seems to be a bit of corrosion on the band between what I assume is the motherboard and display/keypad that I cannot seemed to clean of without damaging the cable. Is there something I can short to turn it on from the motherboard and check? Or should I just list this on ebay to someone who knows what they're doing more than I?