Since the kit is discontinued, for the adventurous who knows their way around a soldering iron here’s a very quick explanation on how to achieve the same result as what the kit does, only not as clean/self-contained.

Note: The mod is NOT compatible with the ESQ-1.


The information and methods described herein are provided “AS-IS” WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED. Use the concepts, examples and information at your own risk. There may be errors and inaccuracies, that could be damaging to your devices. Proceed with caution, and although it is highly unlikely that accidents will happen because of following advice or procedures described in this document, the author does not take any responsibility for any damage claimed to be caused by doing so.


For details about the operation of this mod, see here and the original recipe.



(Click to enlarge)





Cut traces

  • EPROM socket pin 20 (/CS) to U18 pin 12 or 11 (depending on chosen socket, LO or HI) (I wanted to minimise the number of upwardly bent pins, but alternatively one can lift EPROM pin 22)

Chip added

  • One extra 74LS74 or 74HCT74 piggy-backed on top of the existing one. Don’t use the HC variant.


Pin number for each chip between parentheses:

  • CSRB (U21 6) to extra 7474 2Clk (11) - YELLOW
  • CA3 (U21 10) to extra 7474 2D (12) - ORANGE
  • extra 7474 2Q (9) to EPROM A17 (30) - BROWN
  • extra 7474 pins 1, 2, 3, 4, 7, 8, 13, 14 soldered to same pins on original 7474 (U12)
  • extra 7474 pins 5, 6, 9 unconnected (lift up / cut out)
  • SA15 (U19 19) to EPROMs A15 (3) - GREEN
  • DOC BS (U21 40) to EPROMs A16 (2) - NAVY BLUE
  • E (U21 5) to EPROM /CS (22 if lifted, or socket 20) - CLEAR BLUE
  • EPROMs /P and Vcc (31, 32) to Vcc - RED
  • EPROMs Vpp (1) to GND - WHITE

Note: the proposed soldering points in the pictures above are chosen to avoid as much as possible soldering anything directly to the original ICs (especially the fragile DOC). Specifically the only original chip that is soldered to is U12, as it provides a convenient resting place for the extra 7474. This also makes it easy(er) to cleanly revert the mod should the need arise.


  • EPROM type: 2Mbit 27C020
  • Source: original SQ80 waveroms are available from Rainer’s website
  • Flashing order for the original SQ80 waveroms (512kbit each): 1/3/2/4 (concatenated)

Final notes

I tried to get Vcc as close as possible from its original location to benefit from existing decoupling capacitors (instead of burdening the 373). It also looks cleaner I think.Also the first half of the 7474 can’t be used as easily, as original’s 1/S and 1/R signals aren’t tied to Vcc as are the other half’s. This also matches the prototype’s pictures.