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On Sun, 10/8/17, knener@... [hp_agilent_equipment] <hp_agilent_equipment@...> wrote:

Subject: RE: [hp_agilent_equipment] HP AN/USM 281A Oscilliscope needs repair (San Antonio TX)
To: hp_agilent_equipment@...
Date: Sunday, October 8, 2017, 12:44 PM


?









The resistors in the deflection amplifier output
stages (in this case the horizontal deflection amplifier)
have an annoying tendency to drift much higher in value and
eventually fail open. This is also an issue with the HP853A,
I have repaired three or four of these with essentially the
same failure. You can check the resistors easily with an
ohmmeter - if you measure higher resistance than the value
shown in the schematic, then the resistor has failed.
Suitable replacements are available from DigiKey or Mouser
at low cost. If you find a failed resistor of a specific
type, then change all of the resistors of that type in the
deflection amplifier output stage (even the "good"
ones). I have repaired at least one unit where all of the
deflection amplifier output stage resistors were
open-circuit on both the horizontal and vertical
amplifiers.









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