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11801 questions - funny fan noise and light


Ragnar S
 

Hi all,

I have some questions about a 11801;

- After it has been powered on for a while, 20 minutes or so, the fan starts to make interesting sounds, like if it is revving up one or a few times a second, only for a fraction of a second. Is this normal? Could it be a problem with the fan speed regulation, or maybe a mechanical problem with the fan itself?
Interestingly, if I remove the screws to the fan and just hold it in my hand it stops doing that, like if it had something to do with the resistance for the air it tries to move, or maybe a problem with how it is mounted. But I have not succeeded to make it do the sound by blocking the air path.

- There is a small neon (?) light in the power supply that can be seen through the fan or from the top when the lid is off, that flickers. Is it supposed to do that?

Thanks for any hints, and best regards,

Ragnar


Chuck Harris
 

My 11801C does that too. I believe it has a temperature regulated
fan, and the feedback loop is kicking the fan motor too hard when it
comes on, and then it takes a while for the motor to slow back down,
only to get kicked again: brrrumm, brrrumm, brrrumm, ...

Probably a bad capacitor somewhere.

-Chuck Harris

Ragnar S wrote:


Hi all,

I have some questions about a 11801;

- After it has been powered on for a while, 20 minutes or so, the fan starts to make interesting sounds, like if it is revving up one or a few times a second, only for a fraction of a second. Is this normal? Could it be a problem with the fan speed regulation, or maybe a mechanical problem with the fan itself?
Interestingly, if I remove the screws to the fan and just hold it in my hand it stops doing that, like if it had something to do with the resistance for the air it tries to move, or maybe a problem with how it is mounted. But I have not succeeded to make it do the sound by blocking the air path.

- There is a small neon (?) light in the power supply that can be seen through the fan or from the top when the lid is off, that flickers. Is it supposed to do that?

Thanks for any hints, and best regards,

Ragnar





Reginald Beardsley
 

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,
Reg


Chuck Harris
 

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,
Reg




Ragnar S
 

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 V.
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,

Ragnar

On 25 Jan 2020, at 16:01, Chuck Harris <cfharris@...> 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,
Reg




Gudjon Gudjonsson
 

Hi list

I bought a TM5000 and nearly started crying when I heard the noise :)
But I replaced the fan with a new 24V fan and the instrument is quiet
and lovely.
Plugged it directly to the 25V supply.

Has anyone replaced the 11801/CSA803 fan with a more quiet one?

Regards
Gudjon


Leo Bodnar
 

Quiter fan would mean that 11801 can be used more and for longer.
And this is exactly what I don't want!
Leo


 

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
To: TekScopes@groups.io
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
V.
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,

Ragnar

On 25 Jan 2020, at 16:01, Chuck Harris <cfharris@...> 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,
Reg



--
Dennis Tillman W7PF
TekScopes Moderator


Perdad
 

I have an CSA 803C and I also have this Fan-problem and the Light.

The Fan in my instrument works fine for about 2 minutes after turning it on and after that it starts beeing noisy.
I have now changed to a Noctua Fan (Noctua NFA12x25, PWM/FLX does not matter) which I really can recommend.
The air flow is good and it is wisper quiet to start with and gets a bit louder when the error hits the Fan so to say :o)

I have tried to remove the PSU but the cables are very short and entangled with the boards surrounding it and the
conectors are hard to reach, but I will try to give it a go some day.

Regards, Per