The VP330 is an interesting synthesizer, from sound as well as construction point of view. This is a one of the early production models with the large rocker switches on the frontpanel and a chorus (‘ensemble’ ) section using SAD BBD chips. This one has been on my workbench multiple times, since it is so full of components it would in my opinion not be economically justified to replace all components at once, so it makes sense to replace only parts which fail.
The rocker switches had bad contacts so I had to take them apart for cleaning. For this it was necessary to unsolder them, pry them open and clean the contacts. This is fiddly but it can eventually be done.
After that I moved to the vocoder section, which didn’t work anymore. After measuring the test points I concluded that the CMOS switches which act as VCA’s in this circuit. (by PWM modulating the filtered carrier signals and LP-filtering afterwards)
On a sidenote, the people at Roland did an interesting design here since in most vocoder circuits OTA VCA’s are used for the amplitude modulation of the carrier signals. This must have had a positive impact on the production cost.
This time, the Vocoder compressor/expander circuit has failed, the loss of expander control totally mutes the vocoder. Two opamps in the vocoder signal input circuitry were dead.
Here another picture gallery of the VP330: