HP 71b repair advice - won't power on with batteries or on AC adaptor

[KimH]

(07-13-2021 01:55 AM)dmh Wrote:  

(06-11-2021 06:40 AM)KimH Wrote:  Pretty much what I expected it would look like.

Some gentle application of vinegar to get rid of all the corrosion (watch out for possible bridging between traces and components, use a loupe).

The “flange” for the zebra is probably held by corrosion as well, again vinegar is you friend.

Then on to the soldering…

I have repaired at least a handful that way, none failed to work.

Tip: use two different colors of wire alternating, it helps avoiding mistakes in the sequence.

Hi KimH,

So I opened my other dead 71b and it is very clean with only slight damage to the zebra and barely any corrosion and have soldered the 2 halves together with wire wrap wire but still no go.

Do you have any other suggestions / advice?

Thanks

Hi there,

Without having anything in front of me it is really hard to give suggestions here.

I have looked at my notes and I have repaired 6 machines which were „like yours“ and all of them came to life, I have yet to see one which was completely dead.

Note that even the tiniest of damage on the zebra can be fatal, the contact is critical. The display-part which is welded also has zebras, which might be your issue, but as said, I have yet to see one of those situations.

One test which could be done is to see if there is power on the front-module ports when having batteries. The first and last pads/contacts are those where the power can be found. The battery voltage or a bit less (around 5 volts) should be available even when OFF.