Re: Tek 2235A re-cap


On Tue, 02 Apr 2013 15:02:28 -0000, "vdonisa" <>

It's me again... after doing a little bit more research (looking at other 2200 series oscilloscopes with fans) I came to the following conclusions:

- the case is designed so that the fan should be installed as an "exhaust" (outblow) fan; the air flow would be from the intake located on the left side near the middle of the CRT's length and gradually heat up until it flows along the hottest heat sink (the one between the 3 damaged caps) then gets exhausted through the rear vent

- installed like this it will also help with the power resistor located on the mainboard, under the CRT, near the intake - i saw some slight coloration of the PCB around it so I believe it heats up handsomely
Those resistors are the load resistors for the output of the CRT
vertical amplifier and they do run hot. They are a common failure
point in the 22xx series oscilloscopes that lack fans. I replaced a
set not too long ago and someone on the list here has also done so

Some of the 22xx series use 3 resistors in series on each side instead
of 2 which distributes the heat load somewhat.

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