Author Topic: HP 8657B Cooling Fan Intermittent  (Read 1230 times)

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Offline BjwTopic starter

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HP 8657B Cooling Fan Intermittent
« on: June 21, 2018, 04:45:44 am »
Anyone have any history with the fan turning on at power up and then shutting off after 5 to 10 seconds ??  I believe the fan runs continuously and not temperature controlled.

Thanks,

Brad
 

Offline RFDUK

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Re: HP 8657B Cooling Fan Intermittent
« Reply #1 on: June 21, 2018, 07:59:26 am »
Hello Brad, I've had a couple here for about 15 years, one in regular use. To confirm the fan is on continuously, I've never noticed it off after hours of use and it isn't that quiet. Great generators for low level setting accuracy and low leakage.

Some signal generator fan drivers are complex, don't know if this is one of them. Example is the iconic HP 8640A & B, zero non harmonic spurious except for AC line, low phase noise and lockable. Wonderful things.

The full service 8657B manual pdf is available on line. Regards, Martyn.
Weak signal comms specialist. Very low noise amplifier & precision calibrated noise source manufacturer. Embedded antenna design services. http://www.g8fek.com  http://www.rfdesignuk.com
 

Offline BjwTopic starter

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Re: HP 8657B Cooling Fan Intermittent
« Reply #2 on: June 22, 2018, 12:13:46 am »
Thanks Martyn,

Got the manual and will start with the power supply to see whats going on.   Thanks for the comments !!

73 de Brad
 

Offline BjwTopic starter

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Re: HP 8657B Cooling Fan Intermittent
« Reply #3 on: June 23, 2018, 08:05:49 pm »
So (DUH !!) of course it ended up being the fan ....I have never in my life had a fan failure like this.  Now to go find a replacement Matsushita or alternate drop-in replacement.

Update: Matsushita ?? This can't be the original fan....internal board had some surface mount components.....from 1994 ?? 

73 de Brad
 

Offline BjwTopic starter

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Re: HP 8657B Cooling Fan Intermittent
« Reply #4 on: July 02, 2018, 03:48:49 pm »
Fan Update:

Replaced the fan with an ebay "new old stock" same model Matsushita.  Works fine now.  But while checking the power supply rails I did find the unregulated +/- 15Vdc was running at about 30V......back to the bench.

Brad
 


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