HP 45 Charger`

[Milanomike]

Hi newbie here,

I have had an old HP 45 for years, which stopped working. After reading here, it seemed replacing the 400 uF electrolytic capacitor was a good first thing to do after cleaning the switch. I seemed to recall the display flickering for a bit some time back.

Took cover off the charger unit and noticed the resistor and diode on the side opposite the capacitor had clearly gotten hot. Checking resistor showed it to be open as it has separated from the lead.

So, anyone got a parts list for the charger or know the resistor value. Colors for the stripes are faded but I think I am reading 470 ohms, maybe a 1/2 watt resistor? As long as i'm there, anyone know what diodes I might need.

Sure would like the old 45 working again on my bench. Can't test otherwise as battery pack is long gone.

Thanks for any help here.

Mike

[AndiGer]

You can see here:
http://home.citycable.ch/pierrefleur/Jac...20unit.htm
or here where can find the link to the above
https://keesvandersanden.nl/calculators/...ic_charger

Andi

[Milanomike]

Andi,

Thanks for the info. The 2nd link looks like it tells me all I need to know, it lists the resistors, diodes, etc. I'll need to study it a bit as i'm not that great with schematics, but the unit isn't that complicated either.

Mike

[teenix]

(11-11-2018 01:53 PM)Milanomike Wrote:  Andi,

Thanks for the info. The 2nd link looks like it tells me all I need to know, it lists the resistors, diodes, etc. I'll need to study it a bit as i'm not that great with schematics, but the unit isn't that complicated either.

Mike

The main thing to note is the capacitor and the diodes are polarity sensitive and damage can result to the component, charger or worse, the calculator, if these are accidently installed in a reversed position.

cheers

Tony

[Milanomike]

Thanks for the help here. i'm aware of the polarity, just need to look closer and get the right bits.

[Milanomike]

OK, need a bit of help here.

I'm finally back on my HP 45 charge unit.

I need the 400 uF cap, no issue and the 470 ohm resistor,no issue, but I also want to replace the zener diode next to the resistor.

The schematic from above says to use a 1N4002, but the diode i have in there only shows 23097 on it.

I'm not shrewd enough in searching around to determine if this is equivalent to a 1N4002 or is a 5.1 volt (or any voltage) zener diode.

So, any help is appreciated, if i can order tonight, i can pick up locally tomorrow and hopefully have my old 45 working again.

Thanks.

Mike

[ijabbott]

1N4002 isn't a Zener diode, it's a rectifier diode.

Looking at the schaematic at https://keesvandersanden.nl/calculators/...ic_charger, D5 is a 4.7V Zener diode, and D1 to D4 are 1N4002 rectifier diodes.

Figure 8 at http://home.citycable.ch/pierrefleur/Jac...20unit.htm uses a 5.1V Zener, which is probably the one you want.

You definitely need a Zener diode of approximately the same voltage, as it is used to provide a reference voltage for the power supply circuit.

Probably any 5.1V Zener diode will do the job. It's not passing a lot of current in that circuit. An 1N4733A or a BSZ55C5V1, for example, should be more than adequate.

But I'll defer to those on this forum who have actual experience with these power supplies!

[Milanomike]

Thanks Ian, good info, I appreciate you looking at this.

[Milanomike]

OK, good news here!

I replaced the capacitor, it wasn't dead but it read almost 700 uF on my meter, not sure how much that mattered.

I replaced the broken resistor, the 470 ohm one and for the time being left the 5.1 volt Zener alone for the moment. Just wanted to see if she worked. I do have a Zener in case I need it.

Good news, she worked as soon as I pushed the switch, but then after using it a few times, the it started acting up, jiggling the switch could make it work or not, so I took it apart and carefully cleaned the switch contacts. All seems well!

In fact I cleaned it up and considering it took me thru undergrad and grad school, it doesn't look bad.

Starting to think I need to build a battery for it as the original leaked and is long gone.

Thanks for all the help.

Mike