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Old 10th Jun 2019, 1:04 pm   #97
WaveyDipole
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Join Date: Mar 2013
Location: Leicester, UK
Posts: 2,505
Default Re: Hameg HM307-3 Cleaning and Repair

OldTechFan, sorry, yes, I am confusing things again. I am not very well at the moment so its probably tiredness on my part. I said collector when I meant emitter of T352. When I was looking at from your readings in #93 there is a difference between Pin 5 of the optocoupler (-873v) and the E of T352 (-866v) of 7v which shouldn't be there. You did mention earlier that the -867v line read -874v. In post #84 you also mentioned that all pins of T352 were at -875v, readings that seem reasonably consistent, but now we seem to have -866v at the emitter of T352. Similarly, you had previously reported the -900v line at -909v. I therefore wondered whether you had tweaked the -1kv line at some point between readings or whether the -1kv source was shifting. I suspect the latter due to warming but it does confuse the readings a little.

Getting back to the blanking circuit, yes, agreed T353 is not getting switched on and thanks for the clarification regarding manual trigger mode. I could see that Ext X will give full unblanked brightness, but wasn't sure how to get a steady blanked signal. All the readings so far seem to show an input voltage present, either 3.38v or 3.22v at the input to R363, or 1v at pin 4, which would be about right with the stated 3.2v input. But why is there a voltage present when Ext X is pushed in? I was therefore going to suggest lifting the input end of R363 and grounding it to get a 0v input and then measuring again.

Last edited by WaveyDipole; 10th Jun 2019 at 1:26 pm.
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