Hi:
I've traced enough of the circuit to know the Zener diodes that blew act as
input protection for the A4 power supply. This unit had a sticker saying
"Strapped for 220 VAC" when I received it. I changed it to 120 VAC.
BUT, if the prior owner plugged it into 220 VAC while it was strapped for 120
VAC this is exactly what you would expect to happen. For partial board layout
and partial schematic see:
http://www.prc68.com/I/HP3458DVM.shtml#A4
Note that the line fuse for 220 VAC is 0.5 Amp and for 120 VAC is 1.5 Amp. The
Zener diodes are rated for 5 Watts so a drop of 40 volts can only support 125
ma. and the line fuse would be 1.5 Amp so offers no protection. Best to put a
fuse at the input to the board as a way to protect A4 from this mistake.
Could probably run it without the Zener diodes, but will replace them prior to
powering it up.
Have Fun,
Brooke Clarke
http://www.prc68.com
Brooke Clarke wrote:
Hi:
I've started a web page for the HP 3458A and it's problem with more info
at:
http://www.prc68.com/I/HP3458DVM.shtml
Have Fun,
Brooke Clarke
http://www.prc68.com
Brooke Clarke wrote:
Hi Greg:
I tried both Blue then Error and Blue and Error and could not get
anything, i.e. the display just showed ISOLATOR DTACK
Have Fun,
Brooke Clarke
http://www.prc68.com
Greg Burnett wrote:
Brooke:
...Correction to my last post... If I remember correctly, you would
hit "key shift blue" + "Clear" to clear out each error message in
order to read the next error message (if any). You keep clearing the
error messages until there are none left. Be sure to use the left &
right arrows to scroll through a given error message's complete text
line.
Poul-Henning's suggestion (about the optical cables on the bottom
side) is worth trying. If I remember correctly, the box will still
function (except for Ext. Trigger Input and VM Complete Output) if
the rear optical cables are disconnected. However you will get an
isolator error if the front optical cables are disconnected. But I'm
not sure if it will be your error 201 or 200 (Isolator does not
respond).
Let us know what you find.
Greg
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