HP-34C Won’t Power Up

[stevenme]

My 34c no longer powers up, no display at all. It was working and I think I can narrow it down to two (stupid) things that I did just before it stopped working.

1. I noticed the traces on the circuit board were worn where the connector plugs in and I was attempting to use the charger to power the 34c without the battery pack installed.
2. While installing a rebuilt battery pack I may have allowed the voltage to the 34c to be reversed momentarily
   

I know a bit about hardware so I know either could have caused damage. I was wondering if incorrect polarity or a voltage spike could damage the 34c? If so is this something that can be fixed with off the shelf components and a soldering iron? Thanks,

Steve

[Dave Frederickson]

The Spice Low Power repair kit will solve your problem.
http://panamatik.de/html/hp_low_power.html

[mfleming]

(02-21-2021 10:11 PM)stevenme Wrote:  I noticed the traces on the circuit board were worn where the connector plugs in and I was attempting to use the charger to power the 34c without the battery pack installed.

He's dead Jim.

[stevenme]

(02-23-2021 01:11 AM)mfleming Wrote:  

(02-21-2021 10:11 PM)stevenme Wrote:  I noticed the traces on the circuit board were worn where the connector plugs in and I was attempting to use the charger to power the 34c without the battery pack installed.

He's dead Jim.

Was it that I connected the AC charger without the battery installed that killed it? Just wondering for future reference. Thanks!

[Steve Simpkin]

(02-24-2021 10:47 PM)stevenme Wrote:  

(02-23-2021 01:11 AM)mfleming Wrote:  He's dead Jim.

Was it that I connected the AC charger without the battery installed that killed it? Just wondering for future reference. Thanks!

Yes. Unfortunately HP engineers used the batteries as a voltage regulator in the HP-2x (aka Woodstock family) and HP-3x (aka Spice family) models. Trying to operate these models from the AC charger without the batteries installed usually instantly destroys the ACT chip at a minimum. This can also occur if the batteries are making a bad connection (for example, due to corrosion) or if one of the batteries failed in an open state. The manuals for the HP-2x had somewhat dire warnings against doing this at the beginning of the manual and in the battery charging section. The HP-34C manual only hints at not to use the AC charger without batteries installed on page 270. Not good considering the almost certain damage that would occur.

[mfleming]

(02-24-2021 10:47 PM)stevenme Wrote:  

(02-23-2021 01:11 AM)mfleming Wrote:  He's dead Jim.

Was it that I connected the AC charger without the battery installed that killed it? Just wondering for future reference. Thanks!

Pardon my tongue in cheek reference to Star Trek, The Original Series (ST:TOS). Yes indeed, your ACT chip is likely fried. Some models in that condition offered for parts on The Bay do show some lit LEDs, so there may be an off chance that a loose connection saved your electronics. It's worth a try if you have the case opened to trace back from the battery contacts to some exposed trace internally. I don't know enough to help but others might.

Good luck.

[stevenme]

(02-25-2021 02:22 AM)mfleming Wrote:  

(02-24-2021 10:47 PM)stevenme Wrote:  Was it that I connected the AC charger without the battery installed that killed it? Just wondering for future reference. Thanks!

Pardon my tongue in cheek reference to Star Trek, The Original Series (ST:TOS). Yes indeed, your ACT chip is likely fried. Some models in that condition offered for parts on The Bay do show some lit LEDs, so there may be an off chance that a loose connection saved your electronics. It's worth a try if you have the case opened to trace back from the battery contacts to some exposed trace internally. I don't know enough to help but others might.

Good luck.

Hard to believe they are so fragile. I’ve had the case half way open, but I haven’t had the nerve to pry open the front. Even though it’s dead, cosmetically it’s in good shape, so I’d hate to completely destroy it!

Other than the upgrade kit I suppose the only way to fix it is with the guts of another working 34c, since the parts are no longer stocked.