Re: 11801 questions - funny fan noise and light


Hi Ragnar,
Maybe Tek switched to these kinds of fans to make their instrument more
energy efficient.
With the heightened interest in being ecologically responsible many
companies, like Tektronix for example, have made a concerted effort to make
their equipment more efficient. Every watt used by any electronic device
ultimately ends up as heat that other machines (like fans and air
conditioners) have to remove. The engineers designing new equipment know the
savings that will come from every wasted watt they can eliminate result in a
savings of several watts. Temperature sensing fans save power by not running
at all until needed and then only running as fast and as long as necessary
to remove the heat from the instrument.

Dennis Tillman W7PF

-----Original Message-----
From: Ragnar S
Sent: Sunday, January 26, 2020 9:20 AM
Subject: Re: [TekScopes] 11801 questions - funny fan noise and light

Thank you gentlemen for your replies!
So it is unclear if it is supposed to do this, but it is at least not
unheard of.

I checked the voltages on the feed wires to the fan relative chassis ground.
From start, the positive wire has about +6.3 V and the negative about +0.7
When the fan revving occurs, the negative wire goes to about -6 V for about
35 ms, making a total voltage over the fan of about 12 V. For some reason
the pulses come irregularly, around 1 or a few times per second.

My current hypotheses is that the intention is to regulate the speed of the
fan, but I would be surprised if this actually is how it was designed to
work. It is somewhat annoying. :-)

Are there any schematics on these boxes to be found?

Also - the neon (?) light in the power supply, right behind the fan, that
starts to flicker as soon as it has power (also in standby mode) - do you
guys have that too?

Thanks for you help and best regards,


On 25 Jan 2020, at 16:01, Chuck Harris <> wrote:

Mine is normal until after the scope has been turned on for about 30
minutes, and then it starts going "Brummm..... Brummm..."

I suspect a capacitor failure, as it is annoying, and would have
caused notice if it were a "normal" condition.

Annoying, though it may be, I can't see how it would cause any harm...
unless it presages a total failure.

What it isn't is a bearing failure, or lack of lubrication. My fan
spins for what seems like half a minute after power is turned off.

-Chuck Harris

Reginald Beardsley via Groups.Io wrote:
I don't recall mine ever doing that. I'm very sensitive to noise as I
investigate anything I can't identify, so I think I would have noticed it.

A fan on one of my HP Z400 workstations was doing that. I shut it down
to reduce the heat in the room and when I tried to boot it the fan was dead.
I've not had time to correct it yet.

Good luck,

Dennis Tillman W7PF
TekScopes Moderator

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