Changing supply voltage on *older* gpib-120a

[mormegil27]

I am attempting to use a GPIB-120A isolator that is was originally manufactured in the USA, but in Australia.  The USA uses 120V, Australia 240V.  There is an article here:

http://digital.ni.com/public.nsf/allkb/BF9B3AE63FF21F95862575B50080DCEB

on how to easily switch the fuse between the 120V and 240V settings.  The problem is that the fuse box on the model that I have does not look like the one in how-to page, I suspect my model must be older - it says on the back next to the serial number that it is Rev-B1.  My GPIB-120A does not have a 240V fuse bracket on one side of the fuse box, and 120V on the other side as it shows in the how-to page.  It is a smaller fuse box with only a single bracket, and it does not specify which voltage range to use.  

What I want to know is whether I can simply switch the fuse from a US fuse (250mA) to an Australian fuse (200mA) and not destroy the GPIB-120A.  

Thanks.

[GerdW]

Hi mormegil27,

I wouldn't connect a device made for 120V supply to a 240V supply - most probably it will just burn...

Use a transformer...

[mormegil27]

Yeah, I suspected it wasn't as simple as the help page suggested.  I opened the unit and inside there is a red sitch on the power connection circuit that switches between 115V and 230V, and this switch is before the wires that go to the internal transformer.  However, I still want to double check there is nothing else I need to switch.

[mormegil27]

So I'm going to call NI in the USA in the morning their time.  In addition, I've noticed that the red wire that is obviously the mains wire coming from the circuit where the power line goes in (and where the fuse is) to the transformer has been positioned in a rather bad place.  It runs up over the top of the transformer, and is quite close to the top of the outer shield cover.  It appears that the top of the insulation of this wire has been rubbed thin - and suspect that a short to the chasy would be a bad thing.  Have any models of the GPIB-120A been recalled?  I have the following units:

P/N: 181555-01 Rev B1

S/N: 02490

P/N: 181555D-01

S/N: AAE711

P/N: 181555-01 Rev B3

S/N: A3599F

P/N: 181555-01 Rev B4

S/N: A4775F

[sth]

The wire shouldn't rub against the case.  Especially a power lead.  But unless the unit sees a lot of vibration it seems odd that the insulation would wear.  IIRC the 220V you have is balanced and does not have a neutral lead?  That would make a short to the case bad in all circumstances.

Switching the power input should do the trick.  Since the unit just needs to convert to DC there isn't much else but a different primary winding on the transfromer to skip half the turns.  Fortunately most units today have a universal power supply that does not even need to switch windings.