Re: Challenging 2465 PS repair


Ozan
 

On Thu, May 20, 2021 at 06:45 PM, - wrote:


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.
--
Each resistor is 25W capable so even one would be sufficient in terms of power handling. Reading it again they may wanted to say one 2-ohm from J303 to ground and one 2-ohm from J232 to ground.
Ozan



On Thu, May 20, 2021 at 5:42 PM Ozan <ozan_g@erdogan.us> wrote:



My weird mind has a question: the service manual says to use 2 pcs of 2
ohm
resistors to load the 5VD output, however, the manual does not say
whether
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,
Ozan





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