AKAI VX600 MATRIX SYNTHESIZER
VX backlight, old one and new LCD version bought in 2018
unfortunately this does not cure the high pitched whine noise on many VX600's
It's actually the yellow pulse transformer (2e16-1001-01) making the noise, not the display. I may desolder it as the new LCD doesn't use it.
Actually to removed the high pitched noise after LCD replacement, simply remove the inductor L2. Thanks to Andre Theelen for this tip!
It takes about 15 minutes for the synth to stabilise before doing a VCO tuning calibration. I looked at this on a DVM and found the voltage sits at .22v then rises up to 2.5v over a period of 9 minutes. Why this happens is unclear. I have found that if the auto calibration doesn't complete, or takes an eternity you my need to check the DAC voltage. It should be 2.5v DC. Procedure is in the service manual. If your VX600 sounds bad this is possibly the reason.
If you cannot set the DAC voltage at 2.5v, check the SSM2300 multiplexer IC's. These are roughly equivalent to 4051's but differ in that they have S&H and internal capacitors I believe. This means you can't do a direct swap in the Akai. I discovered a bad SSM by removing them all, plus all the voice cards. I monitored the DAC voltage with a meter and inserted the SSM's one by one, turning the synth off of course whilst doing it. I notice one IC caused a voltage drop and this turned out to be a bad IC.
Some pictures of the insides:
Voice Cards x6. Voices play from bottom to top, when first powered on. The synth calibrates top down.
Below the voice cards. Opamps and multiplexers
If servicing, watch you don't bend the 2 regulators in the middle of the image too much as they can just break off as must have happend previously on my synth. The heat sink is not supported
There was some UV damage to the side panels. I'm not a fan of nicotine yellow so I must try and restore these.
In 2018 I bought a EWI3020m synth module and the 3020 wind instrument on eBay. The main reason I purchased these is not become an electronic KennyG, but to get replacements for the CEM3374 and 78 chips for my VX. The EWI module has 1 of each. The EWI modules is essentially a single voice, similar to the VX. The module is pretty cool in it's own right and the wind instrument may turn out to be fun
The synth can have 6 separate outputs. I believe back in the day the VW-X6 DIN/PHONO cable was available. It possible to make your own using a 13 pin cable similar to those found on old Atari ST monitors, Digikey part number CP-1013-ND. The pinout for the VOICE OUT connector is shown below.