Re: Woodstock parts compatiability? Message #3 Posted by Randy on 27 Mar 2012, 8:24 a.m., in response to message #2 by Ignazio Cara (Italy)
In addition to the 27, the ACT from a 21 is not compatible as it does not support the I/O bus.
FWIW, 29C troubleshooting is straight-forward. Google "HP Calculator Chips" and use Eric's great list to identify the five rom and ram devices. Remove them. Leave the one 8 pin next to the ACT, it is power up reset device. Power it up. If you get a 0.00 display, the ACT is okay, basic math should work. If not, check for oscillations at the tank circuit, pins 13/14. If it is dead there, the ACT is dead.
If the ACT is okay, re-install the roms and ram one at a time and test after each addition. Start with the 8 pin devices, finish with the 14 pin rams.
The purpose of the procedure is to isolate the data bus as any defective device will load the bus and cause the ACT to hang.
While the ACT is a common failure, so are the roms in the 29C. The combo rom/ram is especially fragile.
Edited: 27 Mar 2012, 8:38 a.m.
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