Problem with HP 25

[krazyk]

Just picked up a HP25 and after cleaning up the battery contacts and supplying 2.6volts of power and selecting RUN mode I am presented with a startup of
0 0.0. . . . . .

So basically the normal startup except the decimal point is displaced one digit to the right and is followed by an additional 6 decimal points making a total of 7

I believe the RAM is working and i can execute the basic + - multiplication and divide as I can enter all numbers on the keyboard after excercising the buttons EXCEPT 4 AND 5.

Would this imply a display chip anode/cathode problem or could the ACT chip still be partially faulty even though its delivering correct results on basic arithmetic?

Does the apparent total loss of 4 and 5 on the keyboard indicate anything specific?

Is there a series of key entries for these Woodstock units that help to deduce more?

When I select Prog mode it simply displays 00 which I assume is normal.

I havent pulled the unit apart yet to inspect the board closely but the unit is in excellent physical outside condition for a 45 year old calculator.

Anyway if anyboy has any ideas about what might be wrong it would be most helpful.

Thanks in advance.

[Geoff Quickfall]

On some occasions when the ACT is getting two inputs, for example, two key presses held down (engaged)at the same the display will be strange.

The fact that 4 and 5 key do not respond, combined with the display might, MIGHT indicate a short due to contamination or corrosion within the keyboard or the connections (pins).

Before analyzing anything. Undo the screws at the top. While pushing in on the battery contacts, pivot the calculator bottom shell away from the keyboard shell using the base a the pivot point.

Once apart, carefully separate the PCA and the LED boards from the keyboard PCA.

QUESTION: does your keyboard PCA have tiny through holes above each key? If so, then introduce a tiny amount of IPA (not the beer, isopropyl alcohol) and exercise the 4 and 5 key. If you have DeOxit in your cupboard then that is even better for the keys. Last resort on the keys is to introduce a single strand of copper wire to act as a swizzled stick.

Next, clean the through holes for the pins as well as the pins for both the LED block and PCA using a fiberglass pen or your choice of brush or eraser. Clean with the IPA or DeOxit.


Reassemble. If that does not cure the problem, then it is a logic fault on the board.




The upshot is, clean up the connections and PCA to remove the easy fault of poor connections, a dirty keyboard or contamination shorting or changing resistance between components.




You may have multiple faults so ensure good batteries and clean battery contacts. NEVER, NEVER use the wall wart (adapter) unless you can confirm the batteries are good and the battery to calculator contacts are 100% effective.

Rechargeable batteries may not leak contaminants BUT may outgas. This is not perceivable as visible contamination but has the same affect as liquid leakage.

[AndiGer]

You JUST see the battery low indication!

From the Owner's Manual (download at https://literature.hpcalc.org/items/654 if you don't have it):

Low Power
When you are operating from battery power in RUN mode, all
decimal points except the true one light to warn you that you
have a minimum of 1 minute of operating time left.
6 0.2. . . . .. 23 Low Power Display
^
True Decimal Point

Andi

[Geoff Quickfall]

Yes, low battery indication,

but many things can cause a low power indication. Including poor high resistance connections due to contamination.

So of course, the first thing as Andiger states, and my assumption ( oops) was use new batteries!

However, the 4 and 5 key suggests more than batteries are wrong. So disassembly would be required.

[Steve Simpkin]

How are you powering the calculator. The multi-decimal point low voltage indication can come on if the voltage source drops while under load.

For the issue with keys 4 and 5, there may be contamination under the contacts for those two keys. Most Woodstock and many other HP models have a small hole on the keyboard circuit board under each key. Many people have had some success with using some very thin stranded wire, spread out and inserted in the tiny hole in the PCB under a malfunctioning key. Put a drop of 99% isopropanol into the hole first then insert the wire bent at at angle and use this to brush around on unseen side to the PCB. You can try Deoxit too.
The following post by Geoff Quickfall has some example pictures that show the holes under the keys on several models. The rest of the three page thread is interesting reading too.

https://www.hpmuseum.org/forum/thread-59...l#pid52993

[krazyk]

Yep you guys were right......

I feel like such a NOOB on these Woodstock calcs.

I upped the voltage by changing one of the AA batteries and up came 0.00 so thankfully another HP25 has survived into the 21st century.

I have just gone out and purchased DeOxit in its industrial strength nail varnish style bottle and will apply 1 drop to each of the VIAs that are under each of the switches on the keyboard PCB.

Heres hoping after some keypressing that 4 and 5 come back to life. 1 an 2 are fairly intermittant as well so it needs it thats for sure.

I read about Pannamatiks Low Voltage Mod and am sorely tempted to just DO IT to this unit.

I am thinking though that you guys would suggest waiting to pick up a VOLTAGE failed ACT unit and do the mod to that. What would you guys do?

Anyway thanks for your help and will let you know if and when I get my buttons all working properly.

[AnnoyedOne]

(09-16-2024 05:07 AM)krazyk Wrote:  What would you guys do?

This is my opinion and mine alone. I'm sure some here would disagree.

I've looked at the Woodstock models and considered purchasing one. I didn't because

• Finding a half-way decent one is difficult. It may not even work or do so for long even if you find one.
• These are "collectible" models and sell for a lot of money (working or not).
• Replacing the ACT/batteries and performing other repairs is likely to be costly.
• One has to have the equipment and skills to make some of these repairs. And I have neither anymore.
  

For me too much for a calculator that would sit on a shelf 99.99% of the time. That said it may be worth it to you.

Instead I have (free) emulators on computers.

A1

[Maximilian Hohmann]

Hello!

(09-16-2024 05:07 AM)krazyk Wrote:  What would you guys do?

I am a big fan of the Woodstock calculators. In the other thread about the three favorite calculators I ranked the HP-25 among those three.

I like the small size, the LED display and the excellent keyboard (unless damaged or corroded). Over the years I have acquired quite a few of them. Only one each of the rare ones (27C and 29C) but multiple units of the common ones (mostly 21 and 25). Some are working perfectly, some have minor faults (like single missing display segments or single keys which do not respond well), some don't work at all.

If you like the extra features of the Panamatik low power module I would go for it. Waiting for another calculator with a failed ACT or display driver chip may take very long. And if you buy a non-working unit, you never know what fault it really has. I have a couple with severe battery leakage that caused different parts of the calculator to fail, e.g. the display or the keyboard. Both can not be repaired if they are in a really poor state.
When you install the Panamatik module, you will have to desolder the ACT and the display driver chips. You can keep these as spares in case you find a damaged calculator some time later. It does not even have to be the same model.

I installed a Panamatik low power module in one of my Woodstocks. It is a very smart device and you will find that the battery is almost always full when you use the calculator. And the memory does not get lost when you turn it off.

Regards
Max

[krazyk]

Woo Hoo

After carefully dissassembly, the blue green corrosion from the battery pack was easily visible on the keyboard assembly PCB. I then applied the DeOxit 100% RED solution to all of the large VIA holes under each button using the foam coated toothpick they supply in their kit. I then used a resistor lead with a small L shaped kink in one end and ran that around each of the VIAs to encourage the DeOxit to do its work and to mechanically scratch away the corrosion under the inacessible key bubbles.Be careful though and do not push too hard, just gentle abrasion.

It is obvious why 4 and 5 were the worst effected as they are the closest to the NiCad battery pack terminals. It had also attacked some of the RAM and ACT legs but that was easily rubbed away.

   

I waited for a few hours and then reassembled the HP 25 which is a little annoyingly difficult for the first time.

   

4 and 5 needed a LOT of excercising but eventually they started reacting to my enormous relief. I hope the Deoxit may continue to work over the next day or 2 as the 4 in particular needs a FIRM click to register.

This has been very satisfying and the build quality of this device is fantastic. They dont make them like they used to thats for sure. I can see why you guys love resurrecting as many of these 1970s HP units.

Hmmmmm....... now to find another unit....... :-)

[AndiGer]

And don't forget - as always - to mention:

If you find a charger don't run the woodstock calculators from the charger without a good battery pack installed that gives good contact to the terminals!

Best advice: Don't USE the charger at all!

Andi

[ctrclckws]

I do not have any of the Woodstock calculators, but I've seen so many of these "Be Careful" messages, that I wonder if there is any way to retrofit the devices?

Panamatik, maybe?

[AnnoyedOne]

(Yesterday 05:04 PM)ctrclckws Wrote:  ...wonder if there is any way to retrofit the devices?

From what I've read the ACT often fails. A Panamatik ACT/Teenix PCB replacement is usually the "fix".

The OP seems to desire a new lower-power ACT so...

A1

[Ren]

(Yesterday 04:15 PM)AndiGer Wrote:  Best advice: Don't USE the charger at all!

Andi

And if you do use a charger on a Woodstock, make sure it is putting out the right voltage!
12 volts is not good!
DAMHIKT! (don't ask me how I know that)

Hopefully, the Panamatik ACT will fix mine!
Ren