Re: HP-33E Parts
Message #1 Posted by Tony Duell (UK) on 5 Sept 2001, 7:22 p.m.
What you have stated would appear to be impossible. The On/off switch in the 33E (and all other 3xE models) has
3 cotnacts. In the 'off' position all 3 are disconnected, in the 'on' postion all 3 are connected. One of them goes to the +ve battery terminal (and also to the output of the diode/resistor charger). One of them goes to the +ve input of the PSU converter (and thus powers the machine). The last one goes
to the other side of the resistor in the charger circuit, so that this resistor is shorted out when the machine is on (it thus increases the current drawn from the AC adapter, which is then both powering the machine and charging the batteries).
The 3 wires in the battery-terminal flexiprint are ground, charger AC output (the other side of the the charger socket is grounded) and the battery +ve terminal (again, the -ver terminal is grounded).
Sionce the power input to the converter is not available on the flexiprint, there is no way you can make the machine power up by shorting connections here.
I would guess there's a short between the +ve input to the PSU and the connection to the charger resistor (either on the PSU flexiprint, the keyboard/logic board, or the switch contacts). The result is that the machin attempts to run from
the battery via this resistor even when the switch is off. The current available might not be enough to get the PSU (or CPU clock?) started (hence the display is dark when you first put the batteries in) but it will keep it going.
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