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 Post subject: Ac Calibration on a B&K 290 multimeter
PostPosted: Jul Sat 28, 2012 1:33 am 
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Joined: Sep Sat 22, 2007 6:07 pm
Posts: 48
Location: NE Pa.
Hi
I cant seem get the AC calibrated, I checked meter deflection and its right on. The ohms and DC + and - calibrate fine. Any Ideas on what it might be or where to start looking? I have the original probe and set it to direct.

Thanks


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 Post subject: Re: Ac Calibration on a B&K 290 multimeter
PostPosted: Jul Sat 28, 2012 1:37 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 12369
Location: Albuquerque, NM 87123
Germanium diodes may be bad.

Looking at the schematic it would seem there are a couple of capacitors in the circuit; one is a tantalum.


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 Post subject: Re: Ac Calibration on a B&K 290 multimeter
PostPosted: Jul Sat 28, 2012 1:57 am 
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Joined: Sep Sat 22, 2007 6:07 pm
Posts: 48
Location: NE Pa.
Johnnysan wrote:
Germanium diodes may be bad.

Looking at the schematic it would seem there are a couple of capacitors in the circuit; one is a tantalum.


Thanks for the help, are those diodes still available if you know?
Thanks


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 Post subject: Re: Ac Calibration on a B&K 290 multimeter
PostPosted: Jul Sat 28, 2012 2:08 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 12369
Location: Albuquerque, NM 87123
I would replace all the capacitors first.


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 Post subject: Re: Ac Calibration on a B&K 290 multimeter
PostPosted: Jul Sat 28, 2012 2:12 am 
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Joined: Sep Sat 22, 2007 6:07 pm
Posts: 48
Location: NE Pa.
will do thanks


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 Post subject: Re: Ac Calibration on a B&K 290 multimeter
PostPosted: Jul Sat 28, 2012 4:48 pm 
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Joined: Sep Sat 22, 2007 6:07 pm
Posts: 48
Location: NE Pa.
I replaced the three electrolitics and the two tant caps, they seemed to be fine but I replaced them anyway. Still having the problem calibrating AC, I noticed that in AC mode at full scale the needle drifts back and forth slightly which makes it impossible to set it correctly. Ohms, DC + and - calibrate fine.

I guess there is a typo in the calibration procedure, it says " set range switch to the 50mv posistion, apply exactly a 0.5v RMS sine wave (60Hz) to input terminals and adjust cal pot R39 for a .5 indication on the meter 0 to .5 Volts/Ma scale. I guess they meant 500mv not 50mv.

thanks for the help


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 Post subject: Re: Ac Calibration on a B&K 290 multimeter
PostPosted: Jul Sat 28, 2012 6:39 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 12369
Location: Albuquerque, NM 87123
Could be the germanium diodes; they cross to NTE110A. I don't think that FET is bad, as it would probably affect DC and maybe ohms readings.

Might be some bad connections also.


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 Post subject: Re: Ac Calibration on a B&K 290 multimeter
PostPosted: Jul Sat 28, 2012 6:50 pm 
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Joined: Sep Sat 22, 2007 6:07 pm
Posts: 48
Location: NE Pa.
ok I will check around and get those parts.

thanks again


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