September has been (and gone as I am writing this) a weird month on the repairs front line.
The X0XB0X wars are still on, the last one has what we suspect is a faulty 74HC174 latch for the DAC, it is strange to actually have a brand new good manufacturer chip in a socket to be faulty, but that would appear to be the case.
Alas, we cannot buy one anymore, or five, the most cost effective approach to buying a replacement is to buy twentyfive in a tube, most of which will sit in a tube somewhere and get lost over the years.
This last to be built or rebuilt X0X was also the oldest kit at a whole six months old, and the LED’s in it turned out to be standard low efficiency types instead of the high efficiency types used in the newer kits, so the forty 10k resistors for the LED’s in this one had to be replaced by 1k resistors, another block of time which we will never get back.
We got an old Crumar Trilogy in for restoration, it looked incredibly beat up and the front panel had lots of rust spots breaking through its black and grey paintwork. It also had two badly broken and badly repaired keys but as the client had told us previously about this, we had bought replacements from Senso at Vintage Planet,
www.vintageplanet.nl Vintage Planet stock a huge variety of parts for a large range of synths, and Senso constantly has feelers out for more synth related goodies from all corners of the world.
Back to the Trilogy, the new keys were installed and the keyboard contacts cleaned and the instrument fired up for first appraisal.
The first testing didn’t bode well, the Trilogy uses two Top Octave Generators (TOG’s) to generate all the tones for all the keys. This is standard technology for organs, but it also used in a variety of string machines including the ARP Omni and Moog Polymoog. The reason for the Trilogy having 2 TOG’s is down to the Polysynth functionality, each key can have 2 slightly detuned tones for that analogue fatness that is so desirable.
Unfortunately one of the TOG’s was lacking 7 out of 12 of its outputs, and this IC is obsolete, rare and expensive, if available it costs about €100 including shipping and duties. The high frequencies from the TOG’s are fed to a system of frequency divider chips which generate all the octaves down from the highest notes generated from the TOG. A number of these were also faulty, and at €10 a piece the potential costs were climbing.
To even begin to resurrect this instrument, the TOG and divider systems would have to be fixed at great cost, before the other issues of the machine could be addressed. And there were other issues, one of the Polysynth voices was generating white noise, and as the synth section is full of Curtis chips, this wasn’t going to be cheap either. The programmable synth preset section was also hosed. The only properly working part of this machine was the Chorus section.
This one went back to its owner with a “do not resuscitate” sticker on it.
It is unfortunate, but this one had been allowed to deteriorate so much that it became a basket case.