I was fixing many Kurzweil PC3LE’s with a blinking problem, which looks pretty much like this:
This fault is probably caused by long power cables, together with shit Molex connectors, at which voltage drop occurs. During power on, the boot loader stresses the power supply by turning ON all the LEDs. This causes voltage drop at the reset circuit U6 (MCP120T) located at the connector board (or U7 on older models). Therefore U6 performs reset, and the story begins again.
There is some service bulletin available to all Kurzweil’s authorised service centres, but the steps described there does not always work. I have applied the mods in about 20 cases, but the instruments were occasionally coming back with the same problem. You can download the service bulletin below.
It seems like the only ultimate solution is to remove the U6 entirely and put a low ESR 2G2/10V capacitor (or higher) into the U7 holes between 5V and GND (see the picture above). This may sound funny, but no instrument came back after this modification and no one has complained so far to any malfunction caused by missing reset circuit.
The only side effect I found is the OFF – ON cycle must take at least 2 seconds, otherwise the instrument wont boot up.
Jan 2020 Update: Before you remove the U6, always check the MOLEX connectors (Big white body with thick wires). The contact springs are usually tired and / or oxidized. Pull out the pins, clean them, stretch the springs and inset them back. If this does not help then proceed with U6 removal