Hi Ed:
I've fixed the schematic.
Yes, I plan to check the transformer and A4 board prior to connecting back to
the rest of the DVM.
Have Fun,
Brooke Clarke
http://www.prc68.com
Ed Palmer wrote:
Hi Brooke,
Three thoughts:
1. If CR11 or CR12 blew open, the LM317 and LM337 might have been
damaged. Are your +18 & -18 supplies okay? By the way, I think you've
got them reversed on the schematic. The LM317 should be connected to
CR01 and CR02.
2. On the web page you mentioned that CR10 survived. Does that mean
that CR09 blew open? If so, did your +5 take a hit? That could be the
cause of all your problems.
3. If it was strapped for 110 and plugged into 220, how much current
would the transformer itself draw due to the overvoltage? Would that
pop the fuse all by itself? I've never tried such a thing ( and have no
intentions of trying it!).
Ed
Brooke Clarke wrote:
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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