Korg Forums

68bassman · Joined: 12 Feb 2023 Posts: 5 Location: Alabama, USA

Hello:

I recently pulled the jack board (KLM-1937) out of my N364 to solder a connection on an output socket. After reinstalling the board into the synth and making all connections, the synth will not power up. When I engage the power switch, I get no power, but I hear a faint high pitched squeal coming from the area of the power supply board (KLM-1944). Is it possible that I connected something incorrectly, or that the power supply failed at this exact moment? Is there a way to test the power supply with a multimeter?

Thanks all,

Todd

68bassman · Joined: 12 Feb 2023 Posts: 5 Location: Alabama, USA

Hey All,

Does anyone have some tips on testing this power supply? I have checked/replaced the fuse, but no change. I'm still hearing a faint, high-pitched "squeal" coming from the power supply pcb area.

Thanks again,

Todd

voip · Platinum Member Joined: 27 Nov 2014 Posts: 3773

A squeal could be produced by a switched mode PSU that is unloaded, because of a disconnect somewhere, but it could equally be produced by a fault in the PSU itself.

A multimeter could be used to probe the output voltages, but care is needed, as there are high voltages present - up to 350Volts DC. There are several output voltages, and also at least four different connectors carrying the supply output, including 71V A.C.

The two 5-pin connectors next to each other with red wires coming from them might be the place to start. Pin allocations are:
Pin V
1 -12V dc
2 analogue ground (0V)
3 +12V
4 digital ground
5 +5V digital supply

If the correct voltages are present there, check the other ends of the red leads, at the boards that they connect to, to ensure the boards are getting their supply OK .

.

68bassman · Joined: 12 Feb 2023 Posts: 5 Location: Alabama, USA

Thank you for that information. I assume I touch one multimeter lead to the pin. What do I touch the other lead (ground) to? The chassis or something else?

Thanks again

voip · Platinum Member Joined: 27 Nov 2014 Posts: 3773

Circuit voltage measurement is normally with respect to the relevant ground. So, for the + and - 12V measurements, use pin 3 as the reference for the multimeter's black lead probe, which should be connected to the COM socket on the multimeter. For the +5V digital supply, use the digital ground as the reference.

It might be better to take the keyboard to a keyboard tech, since the presence of several hundred volts in parts of the circuit, does carry with it the risk of potentially lethal consequences.

.