The ACT repair Kit for your HP-25      Now GPS version available!

Now also supports HP-25C HP-27 HP-29C and HP-67 and IR Printer HP82240B!

After many years without possibility of repair, there is finally a replacement available for the famous PMOS ACT (Arithmetic and Control Timing) chip for all HP woodstock calculators.

Many ACT chips of the “Woodstock” series HP calculators were damaged while using its power supply without batteries, due to a design flaw of the original power switching unit.

In most cases of a non functioning woodstock calculator only the ACT Chip is defective, but power supply, ROM, RAM and display drivers are still  working. The new ‘chip’ takes over all signals on the board, communicates with the components and establishes a running display and keyboard matrix while emulating the arithmetic logic unit.

The new ACT supports HP-21 HP-22 HP-25 HP-25C HP-27 HP29C and HP-67* calculators!

It executes either the original ROM code from the on board ROM chips or internal ROM code. The RAM chips are no longer needed after the replacement, because the new ACT uses internal RAM.

If other components or the power supply on your board are defective, the replacement will not make your calculator work again. But most likely you will give your beloved calculator a new life and you will see  its beautiful LED numbers 0.00 light again.

There will be no visible difference in the behaviour to the original, except for additional features.

*HP-67E ACT doesn’t support card reader, instead it has 22*224 program steps and 186 registers in Continuous Memory

HP-25E Standard ACT Version

1.) Automatic Power Save

There will be an automatic Power Save Mode when there is no keyboard activity for a while. The display will show only a single moving decimal point, even while a program is running. The next key will show immediately the full display again and will be directly executed. If you just want to wake up the calculator and dont want to do any action, then use the f or g key followed by ENTER. This Power Save Option saves about 50 mA, a third of the total power consumption, and makes your battery less often empty.

2.) Show Logo and your serial number

Show the calculator Logo and the serial number of your calculator at power up.

3.) Continuous Memory

If you run your HP-25 calculator with the “new ACT”, you will automatically  own an HP-25C with “Continuous Memory”! Your program steps and registers are saved in Flash Memory. Even replacing the batteries will keep your data in “Continuous Memory” with modern technology.

4.) Internal and External ROM

You can decide to run the firmware from the original external ROM chips or from internal ROM which is faster and can be used when your external ROM is defective..

All new features can be individually switched on and off by keys at power up and will be saved in “Continuous Memory”.

The Standard ACT is not a separate version, but is part of the Extended ACT version described below.

HP-25E Extended ACT Version

The “Extended ACT Version” for the HP-25 calculator is the first upgrade ever made for this calculator. Additionally to the standard features there are many new features included.

1.) Stopwatch

There will be an 8-digit Stopwatch including a Chess Clock and two independent timers. It displays up to 99 hours with 1/100 of seconds resolution. Lap times can be stored and recalled and there is even a calibration procedure.

2.) Program collection

There will be more than 5000 program steps available in “Continuous Memory”, containing the complete HP-25 application collection, predefined constants and many free space for your own program library.

3.) Undo

You can “smart insert” and “smart delete” program steps and you have an Undo button.

4.) Auto Repeat

Some buttons have Autorepeat function and you will see many more improvements, which make your vintage HP-25 calculator a very special one.

Download the Quick Guide for having an idea of the new features.

Download the detailed English User Manual to have a complete reference.

Price 80,- Euro + 4,90 Euro international shipping (order by mailing to

HP-25E Ir, HP-29E Ir, HP-34E Ir, HP-67E Ir ACT version

This Infrared printing version of the ACT contains all “Extended ACT” features and allows you to print to the HP82240 Infrared printer.

1.) Printing your program collection

 You can print your programs with their mnemonics and program code.

2.) Tracing manual calculations

You can activate tracing your manual keyboard entries and calculations, which shows you the operators and their results as you are typing.

The Ir ACT contains an already mounted amplifier transistor to control an IR diode and the manual includes instructions how to fix the IR diode inside your HP-calculator.

The trace calculation print functionality is available for all models from HP-21 to HP-29C, but especially the programmable models HP-25 HP-29C can benefit from printing also its programs.

Each Ir ACT version is including Update Kit and Overlays


Price 139,- Euro + 4,90 Euro international shipping (order by mailing to

Update Kit and Overlays

The update Kit allows you to change the firmware of the ACT. Not only programming a new version but also the emulation of another calculator is possible. Imagine, you can convert your HP-21/HP-25 to one of the high end models HP-29E, HP-34E or even HP-67E.

It consists of an USB/TTL RS232 Converter and programming cable, which fits directly into the ACT circuit.

You will get also three vinyl overlays as shown below, which are available for HP-29E, HP-34E and HP-67E. The labels will fit perfectly for any woodstock calculator and the self adhesive vinyl is easy to apply, the fresh colors make your calculator look like new.



Price 30,- Euro + 4,90 shipping (order by mailing to

Each vinyl overlay can be ordered seperately 8,- Euro, or 18,- Euro per set + 2,- Euro shipping.

HP-25E GPS ACT Version

Do you want to be the privileged owner of the worldwide only red LED pocket calculator with integrated GPS Navigation? Then read more about the HP-25E GPS ACT version.

This ACT kit can be placed into your calculator by yourself. It uses a GPS (Global Positioning System) module with build in ceramic patch antenna, lightning fast TTFF (Time To First Fix), ultra high sensitivity (-165 dBm), low power consumption (20 mA) and ultra precise positioning under low receptive, high velocity conditions. Its battery backed RTC (Real Time Clock) gives you always the exact time even after you lost satellite contact.

You can activate or deactivate the GPS module, then you don’t have any additional power consumption, if you just want to use the calculator, and you still have the RTC time running.

All actual GPS data are fully integrated for calculating in your over 100 available HP-25 programs!

In GPS menu the HP-25E shows latitude, longitude, UTC (Universal Time Coordinated with atomic clock precision), altitude, speed (in knots or km/h), compass heading, DoHP and no of satellites.

Each kit contains the ACT extended version, the GPS module and a step up converter to supply the module. Connection cables are already attached for easy mounting (see manual for detailled description).

Price 175,- Euro + 4,90 shipping (order by mailing to


LED Module repair kit

This is a new replacement for the 7-segment LED display modules of any of the woodstock calculators from HP-21 to HP-29C. You can replace it without soldering, just by sticking it to the gold plated prongs of the display connector.

If a single or two LED segments of your original LED module are missing, this is normally beyond repair, because the very tiny bond wires have lost contact or the LED segments itself are corroded.

Now you can use this new LED module. Its digits are slightly smaller than the original and the impression of the digits gives it a different look, which is a beautiful new experience and you will have a complete new display again.

The display module uses three 4-digit bubble display components. These are not manufactured any more today but several thousands of them are still available on stock. We ordered a small amount of them to supply you with this new repair possibility for woodstock calculators.

All LED modules are fully assembled, tested and the bubble displays are preselected for having the same brightness.

Price 30,- Euro + 4,90 Euro international shipping (order by mailing to