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

[Ed Palmer]

The voltages are correct even with a half-fried transformer.  Sounds 
like typical HP overdesign.  :-)
Did you check for ripple or noise on the outputs?

I'm intrigued by the fact that the error message is pointing you towards 
the Outguard Controller, but the only apparent damage is to the Inguard 
Power Supply.  Could the error message be a red herring?  Could the 
actual damage be in the Inguard Section as shown in Fig. 28 (p. 70) of 
the Assembly Level Repair Manual?  This would at least be consistent 
with damage to the Inguard Power Supply.  But it seems odd that HP would 
have such a misleading error message.

Does the error change if the fiber links are disconnected?  Can you 
probe the optical receivers with a scope to see if there's data on the 
links?

Ed

Brooke Clarke wrote:
> Hi Ed:
>
> Yes, all the supply voltages are within spec, but the error message 
> stays the same.
>
> The Outguard supply visually looks OK and the voltages are centered in 
> the spec.
>
> Yes the transformer has seven wires feeding the outguard p.s.
>
> See: http://www.prc68.com/I/HP3458DVM.shtml#Bot
> You may need to <shift><reload page> to see it.
>
> Have Fun,
>
> Brooke Clarke
> http://www.prc68.com
>
> Ed Palmer wrote:
>> You're right.  Sorry.
>>
>> Brooke, now that you know the source of at least this problem, have 
>> you considered powering up the system by applying DC to the inputs of 
>> the regulators?  This would allow you to limit the current in case 
>> there's been some damage further in.
>>
>> Also, is the Outguard p.s. connected to the same transformer?  I 
>> would expect to see a similar circuit topology on both supplies.  Is 
>> there any heat damage on the Outguard p.s.?
>>
>> Ed
>>
>> J. Forster wrote:
>>> Look at the Ohms readings. It's not open, if the readings are right.
>>>
>>> -John
>>>
>>> =============
>>>
>>>
>>>  
>>>> Try putting a light load on the transformer when you measure the 
>>>> output
>>>> voltage (maybe 1K).  You may find that terminals 2-3 are open circuit
>>>> rather than short.  Maybe that's why CR10 survived - the transformer
>>>> blew first.
>>>>
>>>> Ed
>>>>
>>>> Brooke Clarke wrote:
>>>>   
>>>>> Hi John:
>>>>>
>>>>> It's hard to say.  With the A4 Inguard p.s. board removed when 
>>>>> powered
>>>>> up the fan comes on and the display lights up with the error message.
>>>>>
>>>>> So, measured on the primary side, there's 25 ma AC current going to
>>>>> the transformer then to the Outguard p.s. and fan.
>>>>>
>>>>> Have Fun,
>>>>>
>>>>> Brooke Clarke
>>>>> http://www.prc68.com
>>>>>
>>>>> J. Forster wrote:
>>>>>     
>>>>>> Looks like it. Does the transformer draw much current with the PCB
>>>>>> removed? If it has shorted turns, as it appears, it likely will. 
>>>>>> Does
>>>>>> it
>>>>>> get hot?
>>>>>>
>>>>>> -John
>>>>>>
>>>>>> =================
>>>>>>
>>>>>>
>>>>>>       
>>>>>>> Hi:
>>>>>>>
>>>>>>> I think the power transformer got cooked.  Have a look at the Vac
>>>>>>> and Ohms
>>>>>>> data:  http://www.prc68.com/I/HP3458DVM.shtml#T1
>>>>>>>
>>>>>>> Force a browser refresh to see the latest schematic.
>>>>>>>
>>>>>>> Have Fun,
>>>>>>>
>>>>>>> Brooke Clarke
>>>>>>> http://www.prc68.com
>>>>>>>           
>>>
>>
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