This modification should be applied to all Pro-150 controllers with serial numbers 0198 or higher and lower than 0550. On 0550 and later controllers the capacitor is not fitted. On serial numbers 0198 and lower an additional modification must be made also.
Remove capacitor C1. Position shown below. This is 1µ0 63v electrolytic capacitor. Unsolder it (needs a lot of heat as the board is double sided) or cut the body as close to the circuit board as possible, and remove the remaining bits.
C1 is a capacitor in the power supply. At power up, it is discharged through a transistor. If this transistor is particularly high gain, the resulting discharge current can damage the transistor – and a nasty chain reaction can then occur.
The transistor concerned is particularly vulnerable at 48v.
As the capacitor is not needed, it should be removed.