When Improvements in Technology Don't Help
Unfortunately, the Pipe Driver Board (PDB-5A) which we have used successfully for over 20 years has become obsolete. Or rather, the driver chips on the board are obsolete; expensive and very difficult to obtain. Each chip is now $20, this will make service and repair of these older boards more difficult and expensive, you may find under certain conditions, it will make more sense to replace the PDB-5A with the new PDB-7.
We tried to make the PDB-7 a straight swap for the PDB-5A, it's the same size and same polarity. The PDB-7 has the advantage that it is also a high power board, so no more stacking chips if the bottom octave of a unit chest is only 20 ohms.
We did run into one barrier that prevents the PDB-7 from being a perfect swap to the PDB-5A, and it has to do with improvements in technology not always being helpful. Improvements in technology mean the IC's on the PDB-7 are more sensitive than the old chips, unfortunately in our application, more sensitive translates into more susceptible to noise interference. The old chips could handle a bit of noise on the cable running from the Pipe Control Computer (PCC) to the driver board, they weren't sensitive enough to notice the noise, the new chips do.
This means all systems that use the PDB-7 will need an RS-422 connection between the computer and driver. The PCC-1E/RS only comes with four, so most installations will also require the use of one or more Line Driver Boards (LDB). The LDB basically duplicates the end of the PCC, which has the RS-422, on a stand alone circuit. You will wire the Data, Clock, and four Strobe lines to the LDB. The LDB should be mounted right above the PCC, so the cable is as short as possible, 6 inches if possible. There are four outputs from the LDB which are wired pin for pin to the RS-422 inputs of the PDB-7s. You may use a shield on this cable if you wish and we would tend to recommend it if there is a significant distance between the LDB and PDB. The shield is attached at the PDB end of the cable.
As the cable between the LDB and PDB is now on an RS-422 connection, the previous limitation that we had, that the cable between the PCC and PDB be under 6 feet, no longer applies. This is the same type of signal we use to run data from the console computer to the pipe computer, and that can be over 100 feet long.
For more information on RS-422, I recommend reading the blog posting "Data Over Distances"