开云体育

hi Guys

Am spending the first few days of the newly instigated UK national lockdown calibrating several 500 series scopes – a 545B and a 547.

In each case there is an intriguing point where the manual, as part of the A and B timebase trigger level centering calibration asks you to:

for A Time Base Cal- ground the junction of R19 & R20 – both 545B (Change instructions) and 549 (manual)

for B Time Base Cal – ground the junction of R69 & R70 - both 545B (manual) and 549 (manual)

Now here is the issue. Finding and connecting to the required junctions can be/is hazardous particularly for those of us who have something of the shaky hand syndrome and a well developed sense of self preservation when working with high voltages in cramped spaces.

But wait: there appears to be a simple solution in every case. With the timebase trigger switch in the *Auto* position there is a direct path between those resistor junctions and chassis – the schematic says so and a simple continuity test with the scope off confirms it. Interestingly my version of the 545B manual uses this method in the manual, before changes brought in by the change information.

So am I missing something here? Does the suggested 'jumper lead' provide magic continuity properties? Is there some hidden feature not shown on the circuit diagram?

Any ideas why the obviously easy way is not followed, indeed is specifically disavowed it the case of the 545B change information.

Thanks in advance