Re: 485 No Trace - some progress, question


Robert Simpson
 

Funny, as I was thinking about this while falling asleep, the thought of a stuck front panel switch came to mind, like being in single trace mode or something. It will take me some serious manual reading to figure out the switch/signal circuit effects.
Bob

--- In TekScopes@yahoogroups.com, David wrote:

I suppose that is good news since U1560 would probably be difficult to
replace. On the other hand, that just moves the problem into the
inscrutable oscilloscope logic.

I would take a close look at the horizontal and vertical mode switches
because they are subject to mechanical failure and those pullup
resistors. Those are easy to check.

Sometimes a pushbutton switch can conduct a static discharge into the
circuits and damage them so I would check any logic ICs directly
connected to them like U1530, U1535, and U1580.

On Thu, 31 Jan 2013 05:39:01 -0000, "Robert"
wrote:

Quick test: I tried IC U1560 in the working scope and got a trace, so it looks like some input is keeping it in blanking mode. On to more circuit analysis and tracing.

Bob

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