So, back when people started building synthesizer modules, they were extremely possessive of their circuit designs. In order to keep their circuits a secret, Tonus, the ARP company, put them in epoxy.
I bought these epoxy modules back in 1972 before I picked up the 2600.
Here’s a voltage controlled low-pass filter, an oscillator, a sample and hold, a noise generator and a waveshaper card. Well, as J was getting close to wrapping up the restoration, he found that one of the sealed oscillator modules wasn’t working right and needed repair.
Rather than have him breathe the fumes of acetone to dissolve all that epoxy, I bought a new 4027-1 replacement from Discrete Synthesizers. I was a little surprised at how skinny it is compared to my original 4017 VCO.
With a little rearrangement of modules, the new one worked out and all my VCO’s track perfectly.
As it turns out, I have no reason to keep these old modules, if you’d like to make me an offer.