PX-8 power supply. Was: Epson PF10 problems

Tony Duell ard at p850ug1.demon.co.uk
Tue Dec 27 16:10:53 CST 2005

> >Do remember there are no regulators in the PX8 PSU. The power supply must 
> >be close to 5V (4.8V is OK), not a random unregulated one. You may well 
> >do a lot of damage with the latter.
> >  
> >
> The standard adapter for the HX-20, PX-8 and PX-4 delivers 6 V DC at 
> 600ma. If you use a regulated 6 V or lower power supply, the machine may 
> work, but batteries will not be charged. At 

For the <nth> time, I am talking about running the machine from a bench 
supply _without having a battery pack installed_. Rechargeable sells are 
too expensive for me to buy a set just to test a machine (and these sub-C 
tagged cells have to be soldered up into the right pack, you can't buy a 
few and move them between devices easily, unlike, say, AA cells). And I 
don't use the machine often enough that I would get anything like a 
reasonable life out of a pack of cells.

Yes, I loose the memory and configuration when I turn the supply off. 
This is not a problem for me testing it. If I start using it seriously, 
I'll buy the cells.

> http://www.xs4all.nl/~fjkraan/comp/hx20/adapter.html you can find some 
> more info on proper power supply.

Now what does 6V, 600mA really mean? There are at least 3 reasonable 
explanations of those figures (and a lot more unreasonable ones) : 

1) The open-circuit voltage is 6V, the short-circuit current is 600mA

2) The open-circuit voltage is 6V, the rated output current is 600mA

3) One point on the I,V curve, hopefully near the point where the adapter 
will be used, is 600mA, 6V.

Now, I wonder what the actuall I,V curve of that adapter is. And I wonder 
how critical it is (knowing that HP chargers were designed to have poor 
regulation, and the charger circuit depended on this. Yes, I have 
measured the I,V curves of many HP calculator chargers). 

I have seen the (your?) web page which gives a hand-drawn schematic of 
the Epson adapter. IIRC it's a 2-diode 'biphase' full wave rectifier. I 
assume this was the one built into a case with a European mains plug.

With my PX8/PF10 I got a wall wart, which may be something to do with it, 
it may not (some other items included in that lot on E-bay had nothing to 
do with the machine, but were useful to me anyway). It's in a case with a 
UK 13A (BS1363) plug on it. It has a bridge-type full-wave rectifer. Of 
course it's very possible that different designs were used in different 

I have not put the mains on it yet. But it would be useful to know what 
the 'correct' adapter's I,V curve is before risking my machine (I can 
easily measuer the curve for this one).

Incidentally, do you know if the PX4, PX8, PF10 and HX20 all use the same 


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