The 7904A has a screen protect - anti burn circuit. Mine functions exactly
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the same as well. The service manual calls this out though I forget which
page it is on.
On Mon, Jan 6, 2020, 10:33 AM Tom Bowers <pvhengineering@...> wrote:
I have a 7904A and it works exactly as you describe. I consider that
normal, nothing to worry about. Just a minor annoyance.
On Mon, Jan 6, 2020 at 8:29 AM Alberto, IZ2EWV <iz2ewv@...> wrote:
Hello dear friends,if
I own three beautiful oscilloscopes from the series 7000: a 7904A, a 7104
and - the most recent arrival - a 7854.
Some of them had common issues, after powering on (failure at the RC
snubber and the AC line filter - which I replaced with new components and
everything come back to normality.
I ask you about a behavior that is common to the 7904A and the 7854: at
power on, the traces and the readouts are bright, but after some minutes
they dim: to restore the brightness it’s a matter of little correction on
the related controls.
By the way, I ask you if it is a normal situation (e.g. “normal” at the
time that the equipment was younger, by memory of somebody of yours) or
it is a sign of aging of some component in the main power supply or inthe
HV power supply. In this latter option, I ask you advice to let me get
closer to the problem (I have the service manuals).
Tnx es 73 de Alberto, IZ2EWV