82002A Battery Charger voltages



#2

Hello,

My Battery Charger AC Adapter has following output voltages
: center pin (-) to the (+) pin : +5.33vdc
/center pin (-) to the unmarked pin : +15.75vdc

The HP35 calculator works just fine in standalone with its battery pack.
However, it just want to display a row of ... dots when powered by the AC adapter.
Any helps would be very appreciated,
Many Thanks,
Pyerre


#3

I am pretty sure you can download an ascii-art schematic for
this type of charger from somewhere on this site. If not, then e-mail me and I'll send it to you.

The 35 should run off the charger even without a battery pack (the 2 outputs from the charger are a constant-voltage supply, supposidly 4.2V, for the logic, and a constant current supply to charge the battery. The battery is disconnected from the logic when you connect the charger).

Most likely the output from your charger has excessive ripple. The voltage looks fine, but you'd not see ripple on a voltmeter. Again most likely the 400uF electrolytic capacitor on the charger PCB has dried up. Try replacing it (a 470uF is fine).


#4

Many thanks for your advices.
I'd replaced the filter capacitor, even the old one has the ESR ~0.35, considered as still good, and the charger has no significant ripple at the output.
I don't know why, but the display dimmed with a row number of dots.
The HP35 still works fine with its own battery pack.
/Pyerre


#5

Have you checked the output voltage and ripple when it's connected to the calculator (turned of, of course)?

Have you got the schematics yet?


#6

With the adapter connected, the output voltages at the battery contacts are about +5.0vdc, ripple ~6.0mVac

anh remains unchanged even turn the calculator on.

I've got your (HP82011) schematics here :
http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/articles.cgi?read=390

and beleive it's the same for the 82002A.

Many Thanks,
/Pyerre


#7

Does it behave in the same way if you plug the charger into the calculator _without a battery pack installed_ (it is quite safe to do this on a 35, I have read the schematics..)

Have you checked the various voltages inside the calculator when the charger is connected? At least Vbsw at the logic-to-keyboard connector and the Vss and Vgg lines on the testpoints?


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