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Nife Sima Nife Sima is offline
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Default Tek 7141 graticule backlight - no voltage on connector

On 20.02.2020 15:51, wrote:
First, the obvious, stupid stuff... (been there, done that):

a) Are there any internal fuses? Often, there will be board-mounted fuses and/or fusible links to protect sub-assemblies not immediately visible. If you have a schematic (you DO have a schematic??), look for one of these symbos:

https://qph.fs.quoracdn.net/main-qim...40b083cc4e4f-c

Maybe there are? The part of backplane is under the CRT tube so I'll
have to find a way to remove it accessing from the bottom side. The
backplane's on the bottom, CRT on the right and a card cage on the left.
I don't have a schematic. More on that later.
b) Corroded and/or broken trace in the voltage path. Follow the voltage for the lamps back to the source and look for anything that could cause a discontinuity.

I will check that, however the traces are just under the power switch
rod that goes all along the side to the mains switch. There seems to be
no way of removing the backplane from the bottom side. Looks like I can
only access it from the top, having to remove the CRT and the cards.

I was able to find where 2 of the 4 pins go on the backplane with
continuity check mode.
c) Are you sure you are using/measuring to the correct 'ground' for those lamps? In some few cases, the lamps are part of the active circuit, such that voltage must be measured across the correct points, not to the common ground.

Yes, I've measured DCV relative to chassis ground and voltages between
each of the pins. None of these were higher than 0.3 ~ 0.4 V, which is odd.
Again, I have no schematic, I am just enumerating the stupid-before-doing-surgery-diagnostics-as-general-practice. Please let us know.

Peter Wieck
Melrose Park, PA


For the record as I already responded to a different person - my bad -
the model is actually 1741. And it's not 1741A as these are completely
different, newer devices. There are service manuals for the -A version
but i think these aren't the manuals we are looking for. I wasn't able
to find schematics for the non-A version.

/Nife