Mains input configuration and transformer tapping is explained here. It is focused on the MKS70 but has the same principles and components in the JX10.
- Conversion to different mains voltages by altering transformer tapping & fuse rating.
- Change the 2 pin mains input plug to 3 pin that includes earth for safe use in UK.
Note that it is good practice to set the transformer tapping to the correct voltage, the picture below shows the PCB becoming dark around the 5V regulator transistor (on left), this is because the Power supply runs hot. This PCB was taken out of a European spec MKS70 that had been run on a UK 240V supply with the 220V tapping for many years. Despite people commenting that it is ok, it isn’t. This is because if the PSU IC stops regulating properly, a common fault, the voice boards will receive a voltage of 20V that isn’t survivable for the rest of the instrument.
SuperSynthProjects take no responsibility for modifications undertaken by people following this guide and please note that you follow this guide at your own risk. There is danger of death if not modified to the required standard for the country of use. If you are modifying the mains input configuration, you must take responsibility for your modification and it is recommended to get the instrument PAT tested when complete. Please refer to the relevant Roland service notes for exact details of what is technically required.
Transformer Tapping Change
The picture below shows the layout inside a European MKS70 configured for 220 VAC.
When purchased on eBay, this had been in use in UK for many years on 240 VAC supply without the correct earthed 3 pin mains inlet. The incorrect tapping would increase the level of heating in the Power Supply because it is a linear regulated design.
Looking closely at the transformer terminals, the insulating sleeve had become dislodged on the 220 VAC terminal.
The wire was cut, stripped and moved to the terminal marked “240V”. Take care as the wire is internally tinned and can fracture easily if the wire is “nicked” when removing the insulation with wire strippers.
If it is being converted to USA 110 VAC then the 117V terminal would be used (and 100V for Japan). Note that the fuse on the power input filter board must be changed to “Slow Blow” 1.25 Amps for 100V or 117V tappings.
Solder the terminal and ensure the sleeve is put back in place. The wiring will be hard and not pliable, use a heat gun or hairdryer to warm it and place it close as possible to the top of the transformer.
Top view showing the wire in place and sleeve covering the terminal. The sleeve is important because it reduces the possibility of the “hot” connection touching the case lid as it is very close to the top of the transformer.
It is recommended to check the “cold” connection (white wire) and make good if suspect or has become a “dry” solder joint.
Fuse Ratings & Earthing
The fuse on the MKS70 mains input filter board is shown in the picture below.
Fuse Rating: Glass 20mm
- 220 VAC & 240 VAC use fuse type CEE T315mA (Slow Acting 0.315 Amps)
- 100 VAC & 117 VAC use fuse type SB1.25A (Slow Acting 1.25 Amps)
For the JX10 the same rules apply but the fuse and filter is located on the Power Supply Board instead as shown in the picture below for a UK specification JX10.
For 240 VAC UK specification, the MKS70 or JX10 MUST be earthed for basic electrical safety. The rules for Europe and USA in 1980’s were different in that the instrument could be classed as “double insulated” under the regulations in those countries, hence the symbol on the rear plate for 100 / 110 or 220 VAC instrumnets.
In the picture above for JX10, it is earthed and recognisable by the green wires that ensure a bond between the top panel, the base and the power supply board itself.
Conversion To UK 240 VAC
The sequence of pictures below show the conversion of a European 220 VAC double insulated arrangement to a 240 VAC UK specification.
Same information applies if a 3 pin IEC is wanted in any other country/voltage.
This involves replacing the 2 pin panel plug with a 3 pin IEC version that includes earth. The one chosen that fits without having to file the hole in the casing is:
- Schurter 6100.3200 – Power Entry Connector, Plug, 250 V, 10 A, Panel Mount
- Farnell part number: 2080464
- RS Stock No. 539-2039
The wiring and heatshrink tubing was prepared in advance to make for easy attachment later.
A 4mm bolt with shake proof washer and shake proof nut are used to ensure a low resistance bond to the earth wire and prevent it coming loose. The shake proof washer “digs” into the surface coating of the metalwork to ensure good contact.
A secure and low resistance bond is essential for electrical safety in the UK
Reason is that fault current through the earth bond during a short circuit condition can be between 30 and 150 Amps for a 13 Amp fused plug.
The heatshrink sleeving is shrunk into position using a hot air gun.
Note that in the picture below, the “Cold” or “neutral” terminal has been attached differently, this is because the tag had fractured and fallen away. This was another reason for intermittent operation on this MKS70!
To reattach it, the wire was pushed into the hole and bent at a right angle before being soldered in place securely.
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Super Synth Projects, Guy Wilkinson