First time attempting CRT service - Conrac Industrial Monitor

[JohnCT]

Originally Posted by vintage.digi

I can see an orange glowing in the back of the tube.

Most consumer grade CRT displays use a secondary winding off the flyback to produce filament. If the filament was lit, there was at least high voltage. Some later high end units used a separate high voltage transformer and horiz output transformer instead of a flyback, and sourced the tube filament elsewhere. I suspect the Conrac uses something more advanced than a flyback to provide horiz scan, HV, and filament. This monitor may use a DC filament sourced from the power supply or even its own dedicated source.

Do you have a schematic for this unit?

Originally Posted by vintage.digi

At some point, I heard an extremely high-pitched whine come out of the unit, which I was probably almost too old to hear.

As we get older, our audio response drops considerably below 15Khz, and many units used double that rate. In addition, most switch mode supplies run over 30K, so we don't hear them like we did.

So, I suspect if you heard a high pitched whine, it could have been a load on the power supply or sweep. Since these circuits are current monitored and lower the frequency to reduce current, a load will often manifest itself as a squeal that's dropped into our hearing range.

Quick checks are to look at any high power transistors for shorts from Collector to Emitter. These transistors can be the metal TO-3 or big plastic transistors mounted on heatsinks. Any shorted transistor will shut the power supply down.

John