AM700 factory Power Supply Mod Docs?


I posted a while back about excessive LF noise in the A channel of my AM700 Audio Test Set.

Although I haven’t cured it yet, I have found an intermittent noise in the front end of Channel A and I am on the way to hopefully curing the problem.  I believe that the noise is coming from the clamp circuitry. As a side issue,  the switching power supply is apparently very close to not being able to turn on the +15 and – 15V rails due to startup inrush current tripping the Overcurrent detection circuitry of the Power supply.  I am hot on the trail of this problem as well, comparing the old CRT supply schematics (mine) and the newer Color LCD version power supply, which shows quite a few changes.


Close examination of my power supply, showed a TEK factory mod that disabled the current sensing comparators on the floating +/-22V.  The 0.1Ohm series current sensing resistors in that supply have been removed and replaced with 5 Amp solder-in pico Fuses.  The stickers covering up the resistor nomenclature convince me that this was a factory mod, not one done in the field.  Also, my unit is a factory refurbished unit.  The pdf service manual that I have has no mention of this mod, in which TEK decided to replace the onboard current sensing/shutdown with fuses to better float this supply which feeds the analog generator outputs.


Does anyone have any documentation on this modification to the AM700 supply?





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