Re: Help with (another) broken 7B92 please

Roger Evans

I am not sure I understand what is happening so these are no more than comments.

Have you set the P308/P309 jumper for 'non 79xx' mainframes?

If you set the trigger mode to normal then do the repeating hold off pulses stop?

The voltage on TP321 is suspiciously high. Apart from the 51R resistor R765 it is equal to the voltage across the gating tunnel diode CR750. Germanium tunnel diodes normally have a voltage drop of 50-100mV when armed and around 500mV when triggered. GaAs tunnel diodes go as high as 1.1V when triggered. The parts list says that CR740 and CR750 are Silicon diodes - I have never seen a Silicon tunnel diode, but a Google search says they do exist and would have an on state voltage drop around 700-800mV.



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