Re: Challenging 2465 PS repair


Tek probably specified two 2 Ohm resistors instead of one 4 ohm resistor
since they would allow twice as much heat dissipation. Yes, you could
probably use a larger wattage resistor but the one larger resistor might
have cost more than two small ones. Or two small resistors was what they
had on hand when they developed the procedure so that's what they wrote
into the instructions. I've seen similar *unnecessary* requirements
written into thousands of TE requirements for military systems. Things like
very high precision HP power supplies being used to simulate an ordinary
battery simply because that was the type PS that the contractor had in
stock in their tool crib when they were developing the test procedure.

On Thu, May 20, 2021 at 5:42 PM Ozan <> wrote:

My weird mind has a question: the service manual says to use 2 pcs of 2
resistors to load the 5VD output, however, the manual does not say
they should be in series or parallel?
I put them in parallel, because if they needed something like 4 Ohm,
they just
would have used a 3.9 Ohm resistor.
Hi Leo,
In 2465 schematic 5VD has a 5A fuse so 2//2=1ohm would be too small (too
much current for the supply). Interestingly 2467B has a similar PSU and
the load instructions say: "TEST LOAD. Connect a 2-ohm, 25 watt resistor
(Tektronix part number 308-0205-00) from the +5 VD pins of J303 and J232
(on the Inverter Board) to ground.". Almost the same instructions as 2465
but "a 2-ohm" instead of "two 2-ohm".

A single 2-ohm might be intended if this is a typo; however, it is better
to start with two 2-ohms in series to be safe,

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