512/Repairs

Capacitors

All the electrolytic capacitors in the unit need attention due to age of the instrument. They may be dry or leaking DC. You may want to test and replace them if required.

There are also Bumble Bee capacitors (aka "black beauty" capacitors) used in the instrument which will be leaking DC and need replacement.

The HV power supply module also contains capacitors, do test/replace them as well if required.

Power Supply

Out of tolerance precision resistors in the power supply can cause the stacked rails (+250 V and/or +450 V) not to regulate or fail to adjust with the main −150 V adjustment. Check precision divider resistors R216, R217, R208 and R209.

Potentiometers

Many of the control pots and switches may need cleaning. Special note on R56 - Vertical position potentiometer - which supplies cathode bias to the driver stage in vertical amplifier. If this pot is noisy or not working, it can cut the bias and bring down driver section, resulting in no vertical deflection.