I have a 67 with what has been described as a classic ACT failure, it reads all 0's across the display.

My question, is it true ANY ACT chip, from any year Woodstock except the 27 will work? I just tried a 1820-1396 from a 25 to replace 1820-1596 and now just the card reader runs when turned on.

I think the ACT was good, but maybe I'll try another.

Adam,
the spare part is ok, but what do you see in the display when you switch on the calculator? If nothing appear you have some trouble with the switch of the reader, maybe the motor control switch is touching the keyboard PCB.

HTH

Ignazio

The display is blank. I'll break down the unit further to make sure the leaf contacts are not touching.

While it is *typically* the ACT, don't assume that is the only cause with the 67 - as anything corrupting the data bus could do that. You can leave the card reader board disconnected while troubleshooting.

What I found was that you can usually go down in function level... i.e. a 67 ACT works in a 25 but I have seen inconsistencies going the other way as you did. FWIW, the 21 ACT is unique and will not work up model at all as it lacks the I/O signal.

Eric Smith might have some more detail as he has cataloged most the processors by part number.

Thanks Randy.

I used Eric's list to start my swap search. I thought I heard of the upward compatibility issue that's why I asked. What is a little confusing to me is that I am very sure I pulled the -1396 chip from a nasty 25 I have. But Eric's list only shows it to be used in the 21.

What are telltale signs of a corruption on the data bus? Ripple?

My list only shows which models each chip has been observed in. That doesn't mean that there weren't other combinations. However, there certainly are some differences between the various ACT part numbers, so I wouldn't expect them to all be interchangeable.