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[DPRG] Frequency Counter Question

Subject: [DPRG] Frequency Counter Question
From: Earl Bollinger earlwbollinger at comcast.net
Date: Sat Oct 4 19:08:00 CDT 2003

Normally I'd agree, but they've effectively eliminated anyone from ever
being able to repair the thing when it does fail. Then if I send it to
HP and they even agree to look at it, they'd probably exchange it for a
newer one and want me to cough up a $1,000 or so for the new one. I
don't think anyone ever fixes anything anymore except us little guys.

I sure wish I had my old milli-ohm meter tool. At least it would get me
down to about where the offending short is maybe. Humm that's a project
idea.
I'll start a new thread for that. :)

But then that probably wouldn't do me any good either, as the part has a
secret HP part number on it, and I doubt anyone would know how to get a
replacement nowadays. I tried the burn out test to see what happens, and
it sank 2 amps and nothing got hot, swelled up, or smoked, most
impressive.
Anyway, I substituted a $20 5v switcher supply and it has less ripple
than that piece of junk analog original did. But then that probably
implies the original was going bad for a while then.



-----Original Message-----
>From: dprglist-admin at dprg.org [mailto:dprglist-admin at dprg.org] On Behalf
Of Chuck McManis
Sent: Saturday, October 04, 2003 4:06 PM
To: DPRG
Subject: RE: [DPRG] Frequency Counter Question

Glad to hear you got it working!

At 10:21 AM 10/4/2003, Earl Bollinger wrote:
>I think the HP engineer who came up with that weird supply should have
>been shot. All they needed was a transformer, rectifier, some filter
>caps and a voltage regulator, what's with the extra 5 IC's, several
>transistors, big inductor, ferite beads, diodes, and zeners, choke
>coils, 30 or so resistors and caps? It doesn't even have the battery
>option installed either, that's a bunch more parts to add.

Typically the supply in DMM's and Frequency counters have to be very 
careful about not introducing any ripple into the power bus. The reason 
being the obvious one that various input and measurement circuits depend
on 
the power being what it is supposed to be. At low input voltages a 
frequency counter can read 60 hz if there is cross coupling between the
AC 
line through power supply.

All that being said, the HP guys are particularly over-the-top fanatics 
when it comes to such things! The HP supply I got for testing H-bridges 
specs something less than 10mv ripple at full load (1KW!) But it also
means 
that these things often work for a long time because changes in
tolerances 
of their components are often compensated in other ways.

--Chuck


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