MKS70 Board Removal

Internal View

The MKS70 is jam packed with wiring and boards, dismantling the unit can seem daunting especially the first stage of removing the Module Boards when upgrading ROMs or removing the Power Supply Board to fix dry joints or tapping off power for a new replacement VFD display.

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Before You Begin

Pitfalls

There are pitfalls to watch out for:

  • Weak brass standoffs that snap easily.
  • Weak Hot and Cold mains connections to transformer & switch.
  • Cables that look very similar between top and bottom module boards.

Static Electricity

AntiStatic

When handling boards, ICs can be damaged by static electricity. Many are irreplaceable without removing one from another instrument. It is essential that ESD precautions are taken when handling these circuit boards and ground the metalwork of the instrument to earth during disassembly & reassembly.

Earthing can be achieved by connecting an audio out to a mixer or another instrument that is connected to mains earth, or simply using a piece of wire from metalwork to a nearby pipe or radiator.

When storing PCBs use anti-static packaging.

ROM Upgrade Only

If just upgrading ROMS it may be possible to do it by just hinging the boards out, however take great care and beware of the following:

  • Fouling components on the module boards against the sides of the casework.
  • Stressing and snapping the spacers between the module boards.

It is easier just to simply remove the Boards by unscrewing the fixings at the hinges.

Reassembly

Reassembly is simply in reverse order whilst observing the additional notes where applicable.

Unplug & Remove Top Module Board

This is identified with voice ROM marked “C”. First unplug the cables. The left hand “control cable” near the ROM and CPU doesn’t have the black wire installed at position 1.

Next remove the screws with a suitable screwdriver bit. Many Roland synths I have looked at have had chewed screw heads because the wrong type of screwdriver has been used, this unit in the pictures is no exception.

Screws for the hinges can be easily replaced with M3 pan “cross” head. If replacing the screws it isn’t advised to use slotted ones because otherwise the risk of a screwdriver flying off and damaging circuit traces when tightening is very likely.

The Module PCBs have many integrated circuits that cannot be replaced easily because they are simply not available anymore. It is a great idea to use anti-static measures to prevent damage.

Place the module board on some anti-static surface like the blue mat in the pictures. There are easily available anti-static products like “pink bubble wrap” or “metalised bags” like in pictures below.

Unplug & Remove Bottom Module Board

This is identified with voice ROM marked “B”. First unplug the cables. The left hand “control cable” near the ROM and CPU has a black wire installed at position 1 to indicate which board it is to the assigner.

Next step is to remove the brass spacers. These are very fragile in a sense that the shafts are unable to take much torque or side loading, often these break when re-tightened or removed.

The best way to remove these is by hand.

Note that when putting back, only finger tighten and do not use any “loctite” on the thread. They wont come out because the clips and PCBs hold everything together and so they don’t need to be tight. I have seen many of these simply broken causing poor earthing or boards that wobble when the unit is transported.

Remove the module board and place on an anti-static surface or bag.

The picture below shows what it will look like with the module boards removed. This is “factory spec” wiring arrangement. Note this page showing how to rearrange the wiring to reduce noise: Roland MKS70 Noise Reduction

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Power Supply Board Removal

Leaving the module board spacers in place and being careful not to knock and break them, remove the 4 bolts holding the heat-sink plate with a 7mm socket.

 

Note the white nylon spacers in the picture below, they are normally attached to the module board black fixing clips, in this case they have remained stuck to the spacer, so have been left in place.

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Finally unplug the cables and remove the screws holding the PCB in place.

Optional Step: Complete Removal

If the Power Supply Board needs to be completely removed then the best way to remove the wires properly is to cut them as close to the tag terminal as possible.

When reconnecting, strip the wire back about 3mm, tin the wire with solder and attach to the tag after melting the joint. There is little point in looping the wire through the tag again, solder is enough to hold it in place. It is a good idea to apply flux to drive out impurities if the old solder is not removed from the tag.

Experts will remove the solder from the tag, remove stray wire, strip and re-loop the wire through the tag before soldering. This is ok but accessibility when the PCB is reinstalled is difficult.

Remove the Power Supply Board

Carefully pull the board clear avoiding pulling on the white and black mains wires shown in the pictures below. The mains connections to switch and transformer tags can be weak and break easily because the interface between the wire and the solder joints is brittle due to the type of mains cable used.

If the board is not being completely removed and transformer wires are still attached, then pull partially clear and tilt to gain access to the other side. This would typically be done to correct solder joint issues or change the electrolytic capacitors.

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For a method of wire reattachment, see the page SuperJX Power Supply Rebuild.

 

Copyright © 2017 Super Synth Projects, Guy Wilkinson

 

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