HP-33C/34C Power Supply or Other Damage?

[aj04062]

If the AA pack in inserted in reverse (with the switch one), does that blow a part on the power supply board or does it damage the RAM, ROM or CPU?

If it does blow a replaceable part on the board, what?

[John R]

(10-31-2014 11:12 PM)aj04062 Wrote:  If the AA pack in inserted in reverse (with the switch one), does that blow a part on the power supply board or does it damage the RAM, ROM or CPU?

If it does blow a replaceable part on the board, what?

Here is a discussion of that very topic (along with other battery-related topics).

I have momentarily inserted a Spice battery pack backwards without resulting in any damage to the calculator.

[aj04062]

Yeah, I saw that thread. It gave me confidence that what I did may not have damaged it, but I did this and it did do something to the unit. What I don't know is what.

If you plug the unit in with the AC Adapter, the screen will respond with PR Error and then randomly display "0s" and other numbers.

Maybe it was finally time for it to give up the ghost.

As Randy said "Be aware that the 30 series units do not offer any internal reverse polarity protection. A shorted transistor or other damage in the power supply is possible." Can anyone point to me where that would be, what part?

[Hans Brueggemann]

adam,
i'd say that a "Pr Error" is actually a good sign of still some life being in the unit. had similar effects because of the amount of supply ripple when accidentially using the charger without having the NiCads installed. after inserting them, the calc worked just fine with the charger.

hans

[aj04062]

That's what I suspect as well, but I think something in the DC Power supply circuit has failed as there is no life when on battery power.

Could it be the transformer on the PS board? If it is a transistor, which one should I look for in the circuit?

I have the circuit diagram from HPCC, but wondering who else may have encountered the same problem before to give pointers.