At last I resolved to test the charger/battery system to sort out what is going wrong, so I opened the dso and connected a couple of multimeters to the system.
I started with a depleted battery, i.e. I waited until dso turns off
the voltage on the battery, once disconnected was a few tens of mV (bad thing I suppose)
then I connected to the circuit and the LT4054 started giving 76 mA (another bad thing… shouldn’t be 500 mA, at least at start, with battery low?). immediately after chargeing started, battery voltage is 3.4 V
after about 15 minutes, battery voltage approaches 3.7 V and charge current start to decrease, with fluctuations between 0 and 76mA, that could be the way the charger works, I don’t know…
in 20 minutes charging current is 0, charging has stopped (third bad thing, the battery cannot be charged fully with 20 minutes @ 76 mA!)
last: if I turn the dso on, the charging current becomes something like -70 mA, i.e. the dso draws current from the battery. this explains why I found that with the instrument on, not only the battery didn’t charge, but it depleted instead!
these problem, I think, could originate from a defective battery that does not “take charge”, or a defective LT4054, or both… but after these tests, I do not know what else to do, so please help me getting my dso working!
thanks again