Casio RZ-1 Power Supply Repair

This article discusses PSU diagnosis/troubleshooting and covers general power supply operation for the Casio RZ-1. This section of the RZ-1 has voltage that can damage property and injure or kill living creatures.


From the wall outlet, AC voltage goes into the RZ-1 3-prong IEC socket. From the IEC socket, the white wire goes directly to the PSU board while the red wire goes to the Power Switch. When the power switch is turned on, the red wire connects to the blue wire which connects to the PSU board.

AC voltage between blue and white on the PSU board should therefore be equal to the AC mains voltage. If no voltage is present between blue and white then a bad power cord or power switch is likely.

Upon entry to the PSU PCB, AC voltage passes through the first fuse (250V, 0.5A) and exits the PSU PCB on the orange and black wires. Again, the AC voltage on orange and black should be the same as mains voltage. If there is no voltage between orange and black then fuse 1 is highly suspect, but the EMI/RFI powerline filter (PLA8021C) is also a candidate.

The black wire leaves the PSU and goes directly to the transformer primary input. The orange wire goes to a selector which should correspond to the mains voltage of the region in which the RZ-1 is being used. The region voltage selector (ESE-371) is used in other Casio units of the same era, such as the CZ-1, FZ-1, FZ-20M, VZ-1, VZ-10M, and Hohner HS-2/E.

The operating voltage can be changed from the underside of the unit by pressing and turning the selector with a flathead screwdriver. This should only be done with the unit off, and only when operating the unit where it would otherwise be necessary to use an external step-up or step-down transformer!

The ESE371 switch does nothing more than connect the orange wire to one of four possible transformer primary inputs. Orange connects to either yellow, blue, white, or red dependent upon whether 100V, 120V, 220V, or 240V has been selected, respectively. This essentially sets the corresponding step-down ratio for each region’s mains voltage, so that the secondary output of the transformer remains constant.

The transformer is a TAMRADIO (Tamura) TE-194-1M1 marked for operation at 110/240VAC input and 9.5/14VAC output. The secondary wires are green and purple, and they connect back to the PSU board where the AC output voltage of the transformer can be measured. If proper voltage is measured at approximately 13VAC between green and purple then the transformer is operating correctly.

Green passes through the second fuse (125V, 2A) and then goes to one side of the 4-pin bridge rectifier (S2VB10) while purple goes to the other side of S2VB10.

The bridge rectifier takes the two AC inputs (green/purple) and outputs positive DC voltage on a single pin, with the remaining pin connected to DC ground.

Both AC (input) and DC (output) voltages are clearly marked and easily measured at S2VB10 on the top-side of the PSU. DC output is the upper-left corner (+), DC ground is the bottom-right corner (-), and both bottom-left and upper-right are the two AC inputs.

If no AC voltage is measurable between the inputs of the bridge rectifier then fuse 2 is suspect.

If no DC voltage is found at the output of S2VB10 but AC is between both of its inputs then the bridge rectifier is suspect. The measured DC voltage should be above 10V.

After being rectified, the newly created DC voltage is smoothed by the large electrolytic capacitor (16V, 4700u) to remove any remaining AC ripple. If high ripple is found on any DC line, this capacitor is suspect.

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