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teenix · (This post was last modified: 03-18-2020 07:31 AM by teenix.)

Hi all,

Has anyone used the HP-97 from the charger only, with no battery connected?

From reading the user manual, it is supposed to be ok, but I was checking over the circuit and it appears that running only from the charger will place about 12V of rectified but unfiltered DC (ie. 100Hz or 120Hz half sine wave) on the supply rails.

The design has an overvoltage circuit which limits the "battery" voltage to a little over the maximum that the switch mode power circuit generates, but not sure what that would be with that sort of input without a battery.

I'm guessing that the card reader probably won't like it, and there won't be enough current to drive the printer.

Just wondering if it actually works at all.

cheers

Tony

Moggul · 03-18-2020, 08:02 AM

Mine did not like it at all.

When I got my HP-97 the battery did not hold any charge so when connected to the charger the calculator would disply just gibberish. Afeter I installed a fresh battery pack the calculator operated normally again.

teenix · (This post was last modified: 03-18-2020 11:33 AM by teenix.)

(03-18-2020 08:02 AM)Moggul Wrote: Mine did not like it at all.

When I got my HP-97 the battery did not hold any charge so when connected to the charger the calculator would disply just gibberish. Afeter I installed a fresh battery pack the calculator operated normally again.

It seems the battery plays a part even down to basic calculator operation, but probably not damaging like the Woodstocks. I would imagine it behaves as a large capacitor, when charging is taking place, to smooth out the raw rectified AC.

Maybe the large resistor on the CPU board gets a bit warm when the battery is missing or faulty as it absorbs this excess voltage and the circuits cannot work properly due to the rather large ripple on the supply.

cheers

Tony

Paul Dale · 03-18-2020, 01:24 PM

My understanding was that the battery controlled the voltage for the printer.
The charger was sufficient by itself, but the battery helped enough to make it work.

As an aside, I've had no problems with a 67 on the chargers (albeit without loading a magnetic card).

Pauli

hewlpac · 03-18-2020, 02:23 PM

Made that mistake once. Destroyed the plastic gear immediately on trying to print... Can replace but very hard to find the part.... Calculator could still function but printing impossible....

Dave

teenix · 03-18-2020, 08:14 PM

(03-18-2020 01:24 PM)Paul Dale Wrote: My understanding was that the battery controlled the voltage for the printer.
The charger was sufficient by itself, but the battery helped enough to make it work.

As an aside, I've had no problems with a 67 on the chargers (albeit without loading a magnetic card).

Pauli

The battery directly supplies all the heavy currents for printer motor and heads, card reader motor and LED display. Each sub system has its own regulator to maintain consistent operation. The printer heads are the hungriest drawing at times a few amps, hence the large batteries. The charger won't be able to provide this amount of current.

With the high cost of replacement batteries, I was thinking of adding a second power connection to accept an external 5VDC 3A wall wart for the 97 replacement CPU. These are quite cheap but obviously not portable in this mode.

cheers

Tony

AndiGer · 03-20-2020, 05:11 PM

As I remembered I read that running the HP-97 from the power supply it may not be damaged but will not work correctly - especially no printing and no card reader operation - I found a (very) old thread where this is confirmed. Even mentioned in the service manual on page 2-5:
https://www.hpmuseum.org/cgi-sys/cgiwrap...?read=6200

Also the damaged idler gear of the printer is mentioned there if you try to print without battery installed. BTW: Currently I have a hand full replacement gears (made from brass) on hand.

teenix · 03-20-2020, 09:58 PM

(03-20-2020 05:11 PM)AndiGer Wrote: Also the damaged idler gear of the printer is mentioned there if you try to print without battery installed. BTW: Currently I have a hand full replacement gears (made from brass) on hand.

Are idler gears available?

I'm working on emulating the PIK chip and printer interface and would like to avoid using the original idler gear during testing.

cheers

Tony

Paul Berger (Canada) · 04-02-2020, 03:22 PM

(03-20-2020 09:58 PM)teenix Wrote:
(03-20-2020 05:11 PM)AndiGer Wrote: Also the damaged idler gear of the printer is mentioned there if you try to print without battery installed. BTW: Currently I have a hand full replacement gears (made from brass) on hand.

Are idler gears available?

I'm working on emulating the PIK chip and printer interface and would like to avoid using the original idler gear during testing.

cheers

Tony

If you have been unable to obtain a gear I have a couple spares.

Is your emulated PIK chip going to be a drop in replacement for the PIK? I have a 97 with a broken PIK.

Paul.

isanchez · (This post was last modified: 04-02-2020 04:13 PM by isanchez.)

(03-18-2020 08:14 PM)teenix Wrote:
(03-18-2020 01:24 PM)Paul Dale Wrote: My understanding was that the battery controlled the voltage for the printer.
The charger was sufficient by itself, but the battery helped enough to make it work.

As an aside, I've had no problems with a 67 on the chargers (albeit without loading a magnetic card).

Pauli

The battery directly supplies all the heavy currents for printer motor and heads, card reader motor and LED display. Each sub system has its own regulator to maintain consistent operation. The printer heads are the hungriest drawing at times a few amps, hence the large batteries. The charger won't be able to provide this amount of current.

With the high cost of replacement batteries, I was thinking of adding a second power connection to accept an external 5VDC 3A wall wart for the 97 replacement CPU. These are quite cheap but obviously not portable in this mode.

cheers

Tony

Hi, I have done it. I have implemented a Barrel type (discreet) female connector. With this, I operate the HP97 without batteries inserted, just with a Barrel-USB plugged to a mobile charger (2A). It works really great! It moves the printer & card reader flawlessly. I have done this in three or four HP97. It works also fine with the HP41 series printers...same issue: connector, USB cable, Mobile wall charger...

I enclose a picture of how does it look like...also a brief manual I made for people that requested it from me...I hope it helps...

Hans-Peter · 04-03-2020, 04:39 AM

I will try this sort of panel mount micro usb plug:
https://www.ebay.ch/itm/1Pc-Micro-USB-2-...w0WNuShuqw

teenix · (This post was last modified: 04-03-2020 04:54 AM by teenix.)

(04-03-2020 04:39 AM)Hans-Peter Wrote: I will try this sort of panel mount micro usb plug:
https://www.ebay.ch/itm/1Pc-Micro-USB-2-...w0WNuShuqw

When the printer is working, 4 or more print heads may be operating. The duty cycle is "probably" on average about 50%, plus the motor current, so a few amps may need to be available by a power supply.

The plug looks like it is not designed to carry that sort of current. An inline DC plug/socket like the ones that plug into a laptop should do better.

I've tried the regulated 5VDC 3A wall wart I mentioned earlier and it copes easily.

One problem with this setup - The battery should not be in place, and this type of supply should not be used to charge it.

cheers

Tony

aurelio · (This post was last modified: 04-18-2020 08:11 PM by aurelio.)

(03-18-2020 11:31 AM)teenix Wrote:
(03-18-2020 08:02 AM)Moggul Wrote: Mine did not like it at all.

When I got my HP-97 the battery did not hold any charge so when connected to the charger the calculator would disply just gibberish. Afeter I installed a fresh battery pack the calculator operated normally again.

It seems the battery plays a part even down to basic calculator operation, but probably not damaging like the Woodstocks. I would imagine it behaves as a large capacitor, when charging is taking place, to smooth out the raw rectified AC.

I met years ago a 97 which was equipped with capacitors in place of the battery pack, it works regularly if connected to the main.....

Edit. I found the capacitor pack I was talking about.... Smile

aurelio · 04-18-2020, 08:12 PM

here attached a pic

teenix · 04-18-2020, 11:59 PM

(04-18-2020 08:12 PM)aurelio Wrote: here attached a pic

One problem with that setup is the voltage applied to the calculator will be the RMS value of the AC transformer output minus diode drops from the rectifier bridge, not the intended 5V from the battery. Depending on the transformer used, it is possible that the overvoltage circuit is working to a degree to trim excess voltage back to avoid circuit damage. If the transformer is a low current type like the charger, then it probably wont reliably supply power for the printer and maybe the card reader.

cheers

Tony