244B internal temperature

Bob Koller #78435 The fan control circuit in all these model variations have a thermistor to vary the fan speed as the internal temperature increases. The outgoing airflow is mainly directed out the right rear corner, when viewed from the front of the instrument. Air flow on all the 24x5x instruments is critical, or certain hybrids will overheat to destruction. The TDS420 and related scopes do not have temperature control, while the 465 series does, but the fan is indeed quieter. The 7904 does not have a fan, but the 7904A does. toggle quoted message Show quoted text From: raymonddompfrank To: TekScopes@... Sent: Saturday, July 21, 2012 2:00 PM Subject: [TekScopes] 244B internal temperature ? 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. At the same time, I detect no air flow. Using a piece of tissue as an airflow detector I can't "prove" there's any air flow, apart from the fan's location at the back. Inside the 'scope, nothing is impeding the air flow. This seems independent of ambient temperature, which varies between 18C and 25C. The fact that I can't detect an airflow as such does't give me much concern, since often it's just a little "moving air" that's enough but i'd like to know if this is normal behaviour. Can anyone of you confirm that it is normal for these 'scopes' (24x5y's) fans to be running at or close to maximum speed under normal operating conditions? FYI, I'd like to add that I'm sure it's not noisy bearings or anything like that. AAMOF, my TDS420 is even noisier, having a much larger fan as well. My 465B isn't anywhere near as noisy, let alone my 7904 (which has no fan). I'd appreciate to hear about anybody else's experiences. Raymond
raymonddompfrank #78446 Hello Bob, Thanks for your reply. Now, there's a strange thing: Within 2 minutes after creating this topic, I realized that i wrote "244B" in the title where it should have been "2445B". Since isn't possible to change the title line, I deleted the topic and created a new "Fan noise in 2445B". I received confirmation that it had been deleted but apparently it hadn't. I will continue using "Fan noise in 2445B" if you don't mind. Kind regards, Raymond toggle quoted message Show quoted text --- In TekScopes@..., Bob Koller <testtech@...> wrote: The fan control circuit in all these model variations have a thermistor to vary the fan speed as the internal temperature increases. The outgoing airflow is mainly directed out the right rear corner, when viewed from the front of the instrument. Air flow on all the 24x5x instruments is critical, or certain hybrids will overheat to destruction. The TDS420 and related scopes do not have temperature control, while the 465 series does, but the fan is indeed quieter. The 7904 does not have a fan, but the 7904A does. ________________________________ From: raymonddompfrank <r.domp.frank@...> To: TekScopes@... Sent: Saturday, July 21, 2012 2:00 PM Subject: [TekScopes] 244B internal temperature ?? 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. At the same time, I detect no air flow. Using a piece of tissue as an airflow detector I can't "prove" there's any air flow, apart from the fan's location at the back. Inside the 'scope, nothing is impeding the air flow. This seems independent of ambient temperature, which varies between 18C and 25C. The fact that I can't detect an airflow as such does't give me much concern, since often it's just a little "moving air" that's enough but i'd like to know if this is normal behaviour. Can anyone of you confirm that it is normal for these 'scopes' (24x5y's) fans to be running at or close to maximum speed under normal operating conditions? FYI, I'd like to add that I'm sure it's not noisy bearings or anything like that. AAMOF, my TDS420 is even noisier, having a much larger fan as well. My 465B isn't anywhere near as noisy, let alone my 7904 (which has no fan). I'd appreciate to hear about anybody else's experiences. Raymond

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244B internal temperature