Servicing a Novachord

"Servicing the Novachord need not be unusually difficult. If adequate tools, correct replacement parts, and a logical, methodical approach used, the large majority of repairs may be made easily and quickly, with the assurance that the instrument will give excellent service. On the other hand, a hit or miss procedure is sure to result in loss of time, needless replacement of parts, and unnecessary repeat calls."   --  Novachord service manual

OVERVIEW

Any Novachord at this point in time is going to require a large amount of repair or total restoration.  Restoring a Novachord is a monumental task.  That said, it is also a very fun long term project.  A lot is involved -- lots of parts, lots of time, lots of money, patience, patience, and more patience.  Many have started the project of restoring one but few have finished!

An oscilloscope, capacitance tester, multimeter, soldering gun or iron, and the usual hand tools are required.  Parts I used included poly capacitors, metal film resistors, terminal strips, wire, screw terminals, and a handful of electrolytic capacitors for the power supply.  It all depends on how far you want to go with it.
THE GENERAL PROCEDURE

The first thing I did was take a lot of digital pictures of every wire, screw and component.  This gave me a great reference in case I forgot how something went together.  Make a backup copy of them while you're at it!

It all starts with having good power.  When I first powered the Novachord up, there was an 80 volt ripple in the output of the power supply.  The power supply circuit is very unusual, and is worth a close study.  I replaced all the resistors and capacitors in the power supply except the large high wattage resistors.  Because the old oil filled cap was so much larger than modern caps, I installed a solder lug strip to mount the new ones on.

The next step I took was to test the power amplifier.  The easiest thing to do is plug a Hammond organ into it.  Mine happened to work without any type of hum, so I left it alone for now.  It would be a good idea to replace the power supply filter capacitors, the coupling caps, and the resistors.
 

There are also some DC filter capacitors mounted in the preamp module.  It is very important to replace these because they contain cancer causing PCBs!  They often leak brown-black stuff out of them.  I wore rubber gloves when I removed them and I made sure all the gunk was removed from the chassis.  Again, solder lug strips are a great way to mount new capacitors.

Carefully inspect the AC and DC power supply wiring.  It would not hurt to replace it with something more modern.  After that, I fired my Novachord up on a variac to see what was going on.  Verify that the power supply is generating the proper voltages and that there is not an excessive amount of ripple.

Play the top most octave and see if the oscillators are working.  If they are, you're lucky, and you have a great starting point for the project.  On my Novachord all 12 oscillators were working because some work had been done on it probably 20 years before I got a hold of it.  I tuned the oscillators to a Hammond organ and found that roughly half to three quarters of the keys play, the vibrato works, and all the front panel controls work properly.  If the oscillators are not working, I would start by replacing all the resistors and then replacing the caps using a "guess and check method" of reading the pan number on the caps and testing new caps to find one within the permissible range.  It may take two or three caps in parallel to accomplish this.

It would also be advisable before going too much further to replace the capacitors and resistors in the keyboard assembly because they handle 270 volts.  These control the attack and decay of the notes.  I found the best way to do this was to mount 5 lug terminal strips in there because modern components don't have long enough leads to go across the existing solder terminals.  This also may be a good time to address the method of connecting the keyboard to the generator.  Springs were originally used, which are usually corroded, stretched, missing, not to mention downright hazardous considering that 270 volts goes across them!  I chose to use screw terminals because I don't plan on moving the Novachord much, and they were the most economical way to achieve a solid connection.  Other options would be Amp or Molex connectors.

From here there are two basic approaches to the rest of the project.  You can choose to disassemble everything and replace all the capacitors in the generator according to the pan chart, or you can only replace what is broken.  Full rebuilding is a long and expensive process, but can assure a much longer service life.  The best way to attack the Novachord is a "top to bottom" approach of starting with the oscillators and working down through the dividers.  Replace all the old resistors with new ones, and replace troublesome capacitors with new ones.  I would recommend rebuilding one note at a time, from top to bottom.  That way you get a feel for the dividing process and can easier troubleshoot the bottom octave, which is the most difficult to get working because of the cumulative effect of the higher octaves being out of calibration by very small amounts.