[time-nuts] HP 3458A ISOLATOR DTACK err @ pwr up

Brooke Clarke brooke at pacific.net
Thu Jul 30 00:08:38 UTC 2009


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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>>>>
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>>
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