Ask the Right Questions - Part 4
Organist calls, tells you that when they turn on the Swell Diapason and press a key, nothing happens. The organist is able to tell you that the display for the Crescendo shoe is working, and Pedal stops play, therefore, you know that at least you have a 'Yes' to both 'Is it plugged in ?" and 'Is it turned on?'. You also have at least some of the answers to 'What exactly happen?'. What you don't yet know however is; where exactly is the problem.
4) Where is the problem?
Sometimes the challenge is figuring out exactly where the problem is. In Part 1 I gave an example of a Gamba that wasn't working, lets assume the diagnostics have told you that the console computer knows you have turned on the drawknob and are pressing the keys, and other ranks are working, so you know the PCC is working. This still doesn't tell you were the problem is, just that it isn't in one of those locations. The problem could be that the data isn't coming out of the PCC, it is not going into the Gamba's Pipe Driver Board (PDB), the outputs from the pipe driver are not working, or it's a problem with the magnets.
The best way to do this is to start swapping things. For example, if you have PDB -5A boards and Driver #5 has a Gamba 1-61 and Driver #6 has a Principal 1-61 try swapping the connectors on the Pipe Control Computer (JP-5 and JP-6), does the problem stay with the Gamba or did it move? Try swapping the other end of the cable, remember, the problem might not be with the boards, it could be with the cable connecting the boards. Don't just look to see if the Gamba started to work, also look to see if the Principal stopped working, there can be more than 1 problem.
Close up view of the Pipe Control Computer, showing the 3 pin headers that the Pipe Driver Boards (PDB) are plugged into. Each header contains strobe, data, and clock.
In our grey boxes the Switch Input Boards (SIB-4) are all identical, as are the output boards (OUT-N or OUT-P). The only difference that may exist in your system between output board will be the jumper, or if it is positive or negative drive. You can open the lid and swap these board around easily. I say easily but really these board are in there rather tight and I usually need a small screwdriver to get some leverage to pull them out, we don't want them falling out by accident.
Inside view of Console Control Unit showing Switch Input Boards and Output Driver Boards in slots.
If you find that a specific board is a problem, many of the I.C.'s we use are mounted in sockets, rather than surface mounted, and we send some spare part chips with every job. You can swap chips with new ones, or if you don't have the necessary chip in your spare parts, it is sometimes possible to swap a chip from another board. Just make sure that what you take from the other board isn't going to cause you other problems, and don't do this with the power on. Swapping chips like this to confirm exactly which chip is the problem can save you money, it is a whole lot cheaper for us to ship you 2 chips, than for a whole board to come back to the shop.
Last article next, "Is there a pattern?"