One of the most common mistakes made when trying to troubleshoot a synchronous timing control system is to try to fix the whole thing at once. It’s entirely possible that one component caused a series of other components to fail, or entirely possible that a lightning strike has damaged a lot of the organ. But it’s just electronics - and they function in a predictable manner. The hints on this page are designed to get the technician ‘thinking in the right direction’ by listing some best practices we have found.
Break it down!
If the entire instrument isn’t working and a few quick chip changes on the master oscillator didn’t do the trick, there is something wrong that is affecting the instrument globally (probably affecting clock or sync). With an oscilloscope, you can likely see the affected waveforms. Any kind of capacitance, inductance, or extra load on these pins will result in timing misalignments between the various signals. A two channel oscilloscope is quite helpful to find these (or a differential probe between them).
A good rule of thumb to follow is that if you don’t have it working again after an hour of throwing parts at the master oscillator, it’s time to dive deeper:
Look at the power rail with an oscilloscope. Verify a solid DC power voltage.
Disconnect all clocks and syncs from the oscillator. Once its completely isolated, verify proper signal outputs from the one single board.
Pick a single rank that will be made to play and identify the needed components to make it play (may be stop input board, stop output board, rank combiner, keyboard input board, and maybe etc.).
Bypassing any special processing that may be present, run a jumper wire straight from the master oscillator to these identified boards. The goal will be to get one single rank to play. Prior to energizing the system again, it may be beneficial to remove fuses from all disconnected ranks to ensure they do not “grand cipher” with a lack of clock/sync.
Once the organ has been minimized to a handful of circuit boards, the data can be followed from the keyboard all the way to the rank combiner. It shouldn’t take too long to find where the data gets scrambled or lost.
Experience indicates that things fail en mass in Ztronics systems. If you find a combiner with defective 4086 chips, be prepared to change every 4086 chip in the organ, but don’t do it until the cause is determined to be no longer present.
