E3500 Power/Cooling Module Fuse?

We have an E3500 that is, of course, long past EOL. However, we still
use it as a test box. Recently, it developed a failue of one of the
Power/Cooling Modules. We were able to replace it with another PCM
from a bone yard E3500 (which the current one is on its way to
becoming, it would seem).

The properly functioning PCMs display a solid green power indicator
LED, and a non-lit amber service indicator LED. In the malfunctioning
PCM, both LEDs were entirely off. The E3500 Reference Manual states
that that condition (Off/Off for Power and Service LEDs) means, "No AC
input".

Now, when we move the defective PCM around in the various slots, it
always has unlit LEDs, and the other two PCMs always have a properly
lit green LED, and an unlit amber LED. In other words, there is AC
available at all three of the PCM positions in the chassis. Hence,
the AC must be interrupted in the module, someplace.

That situation might hint at the possibility of a blown fuse. If so,
we wonder if the PCM might be "brought back to life" by the mere
replacement of a fuse.

A brief inspection of what is visible by removing the sheet metal
shrouding of the PCM does not reveal an obvious or accessible fuse.

Is anyone familiar with this old hardware, and able to say whether the
PCMs in the E3500 have a fuse that might be replacable?

Alternatively, might anyone have an opinion on the significance of 2
dark LEDs (= "No AC input"?

Thank you for any comments.

DG

 

Replying to own post...

Answer is, Yes. There is a 250V 10A fuse. It is neither readily visible, not easily accessible. obviously not intended to be field replaceable.

I wonder why.

But, can be done, if one is determined and persistent, and can get fingers in to remove a molex connector that contributes to fuse hiding.

 

If the internal fuse on any switch mode psu has blown, it's usually a sign
that either the input rectifier has shorted diodes, a reservoir cap has gone
short, or the switcher transistors have blown. The internal fuse is usually
rated higher than the normal line fuse and is a point of last resort,
protection
wise, though they do sometimes open due to switchon surge after many years.
If the pattern of use is regular power on / off, then this may be the case.

If you are a dab hand with soldering iron, try replacing the fuse.
Nothing to
lose other than the fuse and it may possibly fix the problem. Make sure you
use an anti surge, slow blow variety, not the fast blow...

Regards,

Chris

 

fuses only protect switching power supplies from making smoke or starting
a fire. If they blow their fuse, they're already destroyed. In a sense,
the fuse isn't protecting the power supply, the fuse is protecting
everything else from the power supply.