10-06-2018, 06:59 PM
The S31 has developed a fault and a bad one at that! The instrument had been left on over a long period. When I returned to the workshop a rather strong smell of burning transformer was noticed and it was coming from the 'scope.
The cause of this disaster was two capacitors in the EHT circuit having gone short circuit, the 8mfd electrolytic C43 and the 0.1mfd paper dielectric C50. Resistor R111 was reduced to a conductive cinder and it's likely selenium stick rectifier MR1 will need replacing. The offending components supply the negative HT to the stability control in the timebase circuit.
The rectifiers MR1,2 & 3 along with capacitors C49 and C50 supply -1,300V to the cathode of the CRT.
The mains transformer has survived it's ordeal.
Geordie McBoyne.
The cause of this disaster was two capacitors in the EHT circuit having gone short circuit, the 8mfd electrolytic C43 and the 0.1mfd paper dielectric C50. Resistor R111 was reduced to a conductive cinder and it's likely selenium stick rectifier MR1 will need replacing. The offending components supply the negative HT to the stability control in the timebase circuit.
The rectifiers MR1,2 & 3 along with capacitors C49 and C50 supply -1,300V to the cathode of the CRT.
The mains transformer has survived it's ordeal.
Geordie McBoyne.
