repairing common woodstock problem - hp 22


I have an HP-22 which suffers from the common woodstock problem cited on the repairs page of the MoHPC.
(The calculator performs all basic stack and math functions, but the summation and memory operations produce spurious results.)
I would like to try to repair the machine as described in the pages, but I cannot identify all the chips on the mother board. Can anyone help?

Information I have: At the lower end of the board (between the battery connections and the keyboard connector), there are 4 ICs and space for another:

  • 8-pin: 1820-1983
  • 16-pin: 1820-1564
  • 22-pin: 1820-1523
  • 18-pin: 1818-0164
What are each of these chips - which is the ACT chip, and which is the ROM chip?

The board also suffers from some minor corrosion. What would be the best way to clean it?



  • 1820-1983: function unknown - my HP-22 does not have this or any other 8-pin chip, but I have seen the 1820-1983 in an HP-29C. Possibly part of the power supply or power-on reset circuit? The one I saw was made by AMD (not AMI!)
  • 1820-1564: RAM
  • 1820-1523: ACT
  • 1818-0164: ROM

You should also have two other chips near the display:

  • 1818-0163 ROM/anode driver (18 pin)
  • 1820-1382 cathode driver (20 pin)

In general, the 1818- prefix parts contain ROM (or have other customizable mask variations), so they are usually specific to a single calculator or very closely related calculators (e.g. -67 and -97). The 1818-0012 and 1818-0078 CTC chips were in theory mask-programmable for different word select digit timings, but in practice were used across the entire classic series.

The 1820- prefix parts are usually more general-purpose.

An exception is the 1818-1396 RAM chip used in the HP-85,
which AFAIK is an industry-standard 16K DRAM.


Your problem is most likely (99%) a bad RAM chip. Very minor chance that once you get the corrosion cleaned up it will work.

Try standing the circuit board up in a glass of vinegar for around 30 minutes (to the top of the battery contacts). Then brush it with a stiff toothbrush. Rinse very well with water. Shake ir dry. Then let it dry fully for 24 hours.



If you want to know about spare HP classic calculator ICs', try to found it on the next site:

A cross reference IC numbers are available.



They don't list calculator chips, and generally calculator chips don't cross-reference to anything since they were custom designed by or for HP.


Sorry but,

Did you see already such cross-reference list? For instance, inside my HP-67, the 1858-0050-1D display driver is a CA 3082 standard IC (coming from the well known RCA manufacturer). The 1858-0023 is a CA 3081; both 2x8 DIP encapsulated IC.

Maybe not all ICs have spare, but at least, 5% could be found out in a ordinary Radio Shack.




And those are just about the only ones. NONE of the ICs in an actual Woodstock calculator is standard, nor are any of the ICs in the Classic, Spice, or Voyager series. The 67 and the Topcat models are the only HP calculators I can think of made before the mid-1980s that contained any standard ICs at all, and they didn't have many even in those.

The HP-85 was AFAIK the first Corvallis division product to use industry standard RAM chips. The HP-75 was the first handheld to do so, and the HP-28S was the first handheld calculator to do so.

I've inspected the innards of every released model of HP handheld calculator and almost every desktop (including some unreleased ones). I've done a fair amount of reverse engineering of how the custom circuits work. I'm not just making this stuff up.

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