549/Repairs

Trace compressed on right side

549 scopes from the Portland factory contain one black Aerovox 0.5 µF / 400 V capacitor (C335) in the horizontal amplifier (in the middle of the upper chassis) which is often deteriorated (leaky). When this is the case, the trace is compressed on the right side. To confirm, temporarily disconnect this capacitor and power on the scope with intensity control at CCW, and after initial warm-up of a minute increase the intensity to test if the problem disappears.

This capacitor is part of the beam steering arrangement during power-up to avoid screen burn. A −150 V power-on pulse is coupled to the R/C340 network in V343A's grid via this capacitor to move the beam to the left and off the screen during initial power up. The beam returns to screen after R/C340 discharges.

The leaky capacitor can be replaced with a modern 0.47 µF / 630 V (or higher) capacitor.

This problem does not appear to occur in Dutch-made 549s.

compressing trace on right side
Bad capacitor in horizontal amplifier schematic
Location of bad capacitor in horizontal amplifier
Location of bad capacitor in horizontal amplifier

Excessive brightness

Symptom: Excessive brightness, intensity control inoperable
Noted: R862 getting hot
Root cause: Cathode choke (L862) hairline fracture of magnet wire

No vertical amplification

Caused by V514 side delay line short circuit. In the drawing you can see the resistive values measured without the transistors for the working model and for the non-working one. In the photo you can also see how the delay line has been replaced, being impossible to find it on the market. Surely the calibration will have to be done again but the instrument is usable.

Connection side v514
Connections side L554 553
Temporary/Provisional connections
Schematics