Sorry, the confusion is mine.
Quote:
Originally Posted by WME_bill
As I suggested a long time ago, stop the timebase operating to measure voltages.
The trace will then be blanked. Then switch to External X and the trace will change to full brightness. That should be self evident.
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I was trying to follow WME_bills excellent idea and had wrongly assumed that there was an X-Y mode position on the timebase dial that stops the timebase and then we needed measurements with the Hor Ext in the out and the in position. However, I can see from the pictures and the manual that the Hor Ext switch serves this purpose.
Ok, so we have current at the input of the LED in the optocoupler. The light sensitive transistor appears to be turned on because it is pulling E towards to -867v line. However, T353 is turned off and the circuit is still in the blanked state. Your measurements show the base of T353 at -899v when it should be pulled up to -877v. You already tried substituting T353, so is R362 o/c?
BTW, maybe its the effect of warm up by you show -873v on pin 5 and then -866v at the collector of T352, but both are on the same -867v line?