Philips PM 3214 Oscilloscope Repair Notes

Display Dim, Long Warmup before trace is visible, Squeals

Recap the power supply, using good-quality electrolytic capacitors. This has given mine another 22+ years of life, so far.

Sweep Speeds from .5 msec and slower Don’t Work: they repeat .5µsec – .5msec

Found a bad solder joint on V1212, preventing it from switching C1206 3.3 µF capacitor (? this is from memory and cryptic notes from January 1987).

No/Insufficient/Intermittent Intensity Control

Of course there can be many reasons for this set of symptoms. If the more common sorts of failures (component problems in the Intensity and related circuits) have been eliminated, knowing about the odd failure i eventually discovered and remedied may prove useful.

After spending all sorts of time carefully testing and troubleshooting, and eliminating all the usual suspects, i was left with anomalies such as all circuits and components appearing to work correctly, yet no intensity control and occasionally weird voltages at the CRT terminals. Cutting to the conclusion of weeks of troubleshooting, i discovered that the rubber gasket holding the CRT neck had become conductive! Indeed, removing the gasket and reassembling everything with temporary, or no, CRT neck support showed consistent normal operation.

It was easy to see the physical change in the rubber (shinier), and in some places measure finite resistance with a typical 10 MΩ input impedance DVM.

In the process of troubleshooting, i discovered some faint arcing between one or more socket contacts and the now-conductive rubber gasket. This could most easily (or only?) be seen looking at the socket from the side^*, in a dark room, with the unit started up “cold”. The arc was small and continuously arcing (not pulsing) when it was happening. Whether this arcing was the cause of, result of, increasing, or unrelated to, the rubber gasket becoming conductive i do not know. On my PM 3214, the arcing seemed to settle down when the unit was warmed up.

With parts for this model not easy to find in 2005 (when this work was undertaken), the solution i chose was to remove the conductive rubber layer, exposing non-conductive rubber underneath. I do not know how long this repair will last… as i type this in 2008, the repair continues to “hold”.

Hopefully the successful resolution of my weeks of troubleshooting and puzzlement will save someone else similar efforts and lost time, and keep a decent analog oscilloscope productive and out of e-waste!