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Hi,
The following has been sort of haunting me for a while:

When I switch on my 2445B, the fan starts running at a low speed and is barely
audible. After a while, it increases its speed to what I consider its maximum.
It is quite audible by then.

Hi Raymond,

I own a 2465A and 2467. At least with those models, there is only one fan speed as there is no thermostatic control. I do not think the fans are very noisy and the amount of air flow is not tremendous.

I suggest that you remove the rear plastic cover and measure the voltage from the feedthrough capacitor located in the upper left corner (when viewing the rear) to ground. Note that the fan receives DC power via that capacitor.

You should find this voltage is constant. If you agree that the voltage is constant, yet the fan speed varies, then the fan needs help (perhaps cleaning) or replacement.

Good luck,

Patrick Wong AK6C

--- In TekScopes@..., "raymonddompfrank" <r.domp.frank@> wrote:

Hi,
The following has been sort of haunting me for a while:

When I switch on my 2445B, the fan starts running at a low speed and is barely
audible. After a while, it increases its speed to what I consider its maximum.
It is quite audible by then.

Hello Bob and Patrick,
Of course, what I really should have asked is if I should be worried about the internal temperature because the fan seems to run at full speed all the time and still there's no obvious airflow (detectable outside), although there's no obstruction. I have measured the voltage at the red feedthrough capacitor as around 12VDC.
From your comments, I tend to conclude that there's no need to worry. While calibrating the 'scope a few weeks ago, I had an external fan blowing air over the hybrids in very low volume at a very low speed, hardly more than a draft. It was enough to keep all hybrids almost as cool as the environment, whereas e.g. U600 heats up to at least 50C (untouchable) in still air. So, together with your comments, I've answered my own question I guess.

Thanks again for your input!

Raymond

--- In TekScopes@..., "Patrick Wong" <patwong3@> wrote:

Hi Raymond,

I own a 2465A and 2467. At least with those models, there is only one fan speed as there is no thermostatic control. I do not think the fans are very noisy and the amount of air flow is not tremendous.

I suggest that you remove the rear plastic cover and measure the voltage from the feedthrough capacitor located in the upper left corner (when viewing the rear) to ground. Note that the fan receives DC power via that capacitor.

You should find this voltage is constant. If you agree that the voltage is constant, yet the fan speed varies, then the fan needs help (perhaps cleaning) or replacement.

Good luck,

Patrick Wong AK6C

--- In TekScopes@..., "raymonddompfrank" <r.domp.frank@> wrote:

Hi,
The following has been sort of haunting me for a while:

When I switch on my 2445B, the fan starts running at a low speed and is barely
audible. After a while, it increases its speed to what I consider its maximum.
It is quite audible by then.

Hello Bob and Patrick,
Of course, what I really should have asked is if I should be worried about the internal temperature because the fan seems to run at full speed all the time and still there's no obvious airflow (detectable outside), although there's no obstruction. I have measured the voltage at the red feedthrough capacitor as around 12VDC.
From your comments, I tend to conclude that there's no need to worry. While calibrating the 'scope a few weeks ago, I had an external fan blowing air over the hybrids in very low volume at a very low speed, hardly more than a draft. It was enough to keep all hybrids almost as cool as the environment, whereas e.g. U600 heats up to at least 50C (untouchable) in still air. So, together with your comments, I've answered my own question I guess.

Thanks again for your input!

Raymond

Hi Raymond,

To provide you with another reference: I measured the fan voltage on my 2465A from a cold start: 7.5V initially.

I ran the scope for 20-30 minutes, measuring low voltage power supply ripple. At the end of that process the fan voltage was 9V and the fan remained fairly quiet. My TDS 3032 fan makes more noise (if that means anything to you.)

I don't know if your scope is behaving normally or if mine is. I've run the scope for hours with the cabinet on, and no overheating is apparent so it seems that the fan is adequate.

I haven't measured the fan voltage on my 2467 but subjectively I would say that both fans are running at around the same speed and producing similar noise.

Perhaps the thermistor in your unit is changing its resistance at a faster rate given a certain temperature change. In any event, if your fan is running at full speed I suppose that can't hurt.

Patrick Wong AK6C

--- In TekScopes@..., "raymonddompfrank" <r.domp.frank@> wrote:

Hello Bob and Patrick,
Of course, what I really should have asked is if I should be worried about the internal temperature because the fan seems to run at full speed all the time and still there's no obvious airflow (detectable outside), although there's no obstruction. I have measured the voltage at the red feedthrough capacitor as around 12VDC.
From your comments, I tend to conclude that there's no need to worry. While calibrating the 'scope a few weeks ago, I had an external fan blowing air over the hybrids in very low volume at a very low speed, hardly more than a draft. It was enough to keep all hybrids almost as cool as the environment, whereas e.g. U600 heats up to at least 50C (untouchable) in still air. So, together with your comments, I've answered my own question I guess.

Thanks again for your input!

Raymond

Hi Patrick,
Thanks for this valuable extra information. Do you know where the thermistor is located (in your 2465A)?

Raymond

Hi Raymond,

RT1110 is located below T1060 on the A3 Inverter Board which is part of the low voltage power supply. This is probably the same for your unit and all other 24xx analog scopes since they all share a similar LV power supply.

Patrick Wong AK6C

--- In TekScopes@..., "raymonddompfrank" <r.domp.frank@> wrote:

Hi Patrick,
Thanks for this valuable extra information. Do you know where the thermistor is located (in your 2465A)?

Raymond