[volt-nuts] HP3468A

gbusg gbusg at comcast.net
Sun Aug 28 08:02:15 UTC 2011

Neil's suggestion (to check the power supplies) is a good one.

Make sure the +5V, -15V and +15V rails are correct - and use an oscilloscope 
to check for excessive ripple.

You didn't mention if you have the rechargable battery option (opt. 001), 
but if so, that adds to the number of possible problems.

I definitely would replace the 3 volt lithium cell (BT551) ASAP.

Also make sure that the front panel "Reset" button isn't stuck in the 
pushed-in position.

If you're lucky, doing all the above will lead to a cure. If not, then it 
sounds like some other fault is still causing the "RESET" line (at U501) to 
keep cycling. It doesn't sound like you're getting through the turn-on 
self-tests far enough to see possible further error codes (e.g., Calibration 
RAM error, or RAM error, or ROM error, or A/D converter error).

Let us know how you come-out on it.


----- Original Message ----- 
From: "Bob Smither" <smither at c-c-i.com>
To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
Sent: Saturday, August 27, 2011 9:48 PM
Subject: [volt-nuts] HP3468A

Dear All,

Not sure where else to ask this question - I am hoping that a fellow
volt-nut has experience with the 3468A.

I have an EBay special, known bad when I got it, HP3468A.  When powered
on it simply cycles through what looks like a test (all / most elements
of the lcd display turn on) and an Overload indication.

I have followed the repair manual as far as I can, but since the unit
never stabilizes - the processor is continually interrupted and the
cycle repeats - I have not really found anything.

The 3468A uses a 3 volt battery backed up RAM.  The 3 volt lithium cell
reads ~ 1.5 volts so clearly the RAM contents are gone.

Could there be something in the RAM that when not present forces the
processor to reset?

If it is possible that the missing RAM information is causing the
continuous run / rest cycle, any idea how I could I restore the RAM

Thanks for any pointers!

Best regards,
Bob Smither, Ph.D.                                 smither at c-c-i.com
The Three Great Lies:
1.  Your check is in the mail.
2.  I'll respect you in the morning.
3.  We're from the government and we are here to help you.


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