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 and Black beauty bumble bee capacitors used in the instrument which will be leaking DC and needs replacement. HV power supply module also contain 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 and/or +450) - not to regulate or may fail to adjust with the main -150V 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.