Inside

There are 3 modifications someone previously did.  Aside from maybe the LFO speed select, I'm not a fan of the others and plan on undoing them.

A quick look inside also shows why the EG leds don't work: they are unsoldered.  Not sure if that is because someone wanted that, or if they did so just to remove the board and didn't reconnect.  Hopefully an easy fix.

Modification 1

This is labeled on the inside of the case as "LFO", and just looks to switch in a resistor on the LFO Speed pot between the wiper/output and the +15 rail.  Unless there is another part to the mod, this wouldn't increase the maximum frequency, just give finer control at the high side.  Will want to look more when the board is pulled.

Modification 2

This is labeled on the inside of the case "Noise to VCF2".  This cuts the trace from the output of PVR 20, the noise pot in Mixer 1.  When the switch is in the down position, that output is instead connecting the output of Mixer 2.  When the switch is in the upper position, the outputs of Mixer 1 and Mixer 2 are combined.

This is a strange mod which doesn't make a lot of sense.  I wonder if it was done wrong.  For instance if the two white wires on the switch were reversed, it would be a more logical function of just changing which mixer the noise pot is connected to.  Definitely want to remove this mod.

Modification 3

This is labeled "Filters - Series" on the inside of the case.  A jumper on the top side is cut to implement this in addition to the switch.  In the down position, it should restore that jumper.  In the up position, it takes the output of PSW32, which is the output of VCF 2, and feeds it to  the input of VCF 1. The input to VCA 2 is left open.

This doesn't seem to align with my prior testing, so after reverting it I'll need to do testing again to see if something else is wrong.