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I was looking at the service manual of the HP97 from the DVD set

By looking at different schematics, I have the strange feeling
that the HP 82031A charger (see page 5-1) is only a 220V to 12.8V AC transformer.

See also the figure 5-10 for HP 82037A schematic diagram page 5-3/5-4

Can someone confirm this or I completly mis-read this doc ?

Thanks in advance

Yes the charger is just a transformer see schematic figure 4-10 on page 4-15 you will see the charger input goes directly to a bridge rectifier. I use the North American 110V charger 82059 the output of it is rated for 8VAC 3VA.

In page 2-5, and figure 2-10 it is said that

"the ac adapter/recharger is a transformer that drops the line voltage to 12.8 Vac at the input terminals of the calculator"

So is it 8 Vac or 12.8 Vac ?

Elsewhere we can find other reference for topcat adapter such as
82066B 8 Vac for 7 Watt

A 220 V to 12 Vac rated 1A is easy to get, a 8 Vac isn't ...

Near as I can tell the chargers all have a rated output of 8VAC 3VA. The unloaded output is about 12.8VAC but drops to about 9.7 VAC when connected to a 97 with a good battery pack and drops to about 8.7VAC when the 97 is turned on.

Thanks for the info,

I will try with a linear 9 V ac 3,5 VA adapter. The drop from the transformer at 8,7 V under load should be ok ?

It's a mascot 8310 (see http://www.mascot.no/?CatID=1179)

I would suspect that will be ok, it is a little lower than what I observed with the HP charger. A lower input voltage would be better than higher at worst it would not be able to maintain the battery voltage and charge the batteries, but with 8.7Vac input that should not be a problem. A fully charged battery pack with good cells should be about 5.5 to 6 VDC.