[Test-Equipment] need some help

[Howard Weeks]

I have one that blew smoke when I first plugged it in.

Investigation revealed that it was one or both of the AC bypass caps 
across the AC line.  Plugged it back in and turned it on.  Worked fine
and has continued to do so for years.  Didn't replace the caps.

Howard K5JCP

On 10/19/2013 8:05 PM, Brian Harris wrote:
> I have an HP4261A LCR Meter however I have no manual for it.
>
> It seems to work correctly in that, when I measured a precision 1000 Ohm resistor, the display agreed exactly with the resistor value and, when I measured a 0.047uF silver mica capacitor, it read 0.0484uF.  The problem came when I tried to measure a 2.5mH RF choke.  While it read 2.4mH, it continually showed 'out of range'.  I manipulated the controls trying to get the out of range indication to disappear but it didn't.  After about five minutes the 1/2 Amp slow blow fuse blew and there was more than a wisp of smoke that came out near the front of the panel.  I pulled the cover off quickly in an attempt to see where the smoke was coming from but by the time I got it open I couldn't tell.  I pulled all the boards out of it including the display board and switch panel board but could find nothing that looked like it was hot except a white ceramic integrated circuit on the first board behind the board that drives the display board.  The metal lid which
>   seals the ceramic packaged chip looked like it had gotten hot but then it could just be oxidizaton.  After spending 30 years in the semiconductor industry I would think if this chip got hot enough to discolor the metal it probably would be toast however, when I replaced the fuse and turned the meter on again (without having the RF choke attached), there was no more smoke and the new fuse didn't blow although I didn't leave the meter on more than a minute or so.  Note:  I didn't try to measure any other components.  When the fuse blew the controls were in the positions below:
>
> 1V drive
> L
> Auto
> 1 KHz
> DC Bias 0V
>
> Also, the DC bias jumpers were connected to the measurement terminals.  I don't know if these are supposed to be connected for measuring an inductor but since I had the DC bias at 0V I didn't figure it would make any difference.  If anyone can shed some light on my problem please do.  I need to try to find an electronic copy of the user and service manuals.
>
> Thank you,
>
> Brian Harris, WA5UEK
> cell 214-763-5977
> email cosmophone at yahoo.com
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