[volt-nuts] FET HP3456A

[Tom Miller]

Borrow Q108 (or any of the like devices) to test your hypothesis. It is just 
used as a low leakage protection diode. You can replace Q108 with almost any 
n-ch fet.

Tom

----- Original Message ----- 
From: "Tony Greene" <tonygreen924 at inbox.com>
To: <volt-nuts at febo.com>
Sent: Tuesday, April 01, 2014 10:13 PM
Subject: [volt-nuts] FET HP3456A


>I have been troubleshooting a HP3456A voltmeter.
>
> Its giving a stange fault, but I beleive I have nailed it down.  The unit 
> is reading +10.00000 volts input at +9.99661 volts.  If you reverse the 
> input, it reads correct at -10.00000 volts. All other ranges read correct 
> on either polarity.
>
> What I need is a source for the FET  A20 Q109 or a suitable substitute. 
> Its HP part number 1855-0298, it was made originally by USA mfg 02883 - 
> Siliconix, Inc, Santa Clara, CA.  It crosses to NSN 5961-01-135-1324.  And 
> Vishay has bought them and the part number is now obselete.
>
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