Authenticity opinions

Philip Belben philip at axeside.co.uk
Sat Jun 5 12:52:24 CDT 2010


>> Since in this case the first test is an easy one to do (namely measuring 
>> the AC voltage from the transformer secondary winding), I wouldn't even 
>> think of not doing it.
> 
> Yes Tony... I have done all of that.  The secondary is dropping to nearly
> 6 VAC with only 5A load on the DC side of the bridge and 120VAC supplied
> to the primary.  The ripple on the DC side is in excess of 1V with that
> same 5A load.  I have swapped in alternative filter caps temporarily
> and see little improvement.  I checked the bridge for shorted diodes or
> excessive loss and it looks OK.

That sounds very low indeed.  I wouldn't expect a transformer secondary 
to drop below rated voltage with only half load on it!  Are you sure you 
haven't got a shorted turn somewhere?

I agree with Tony that you should do some more tests to see if there's 
something wrong with the transformer or rectifier.  For a start, look at 
the secondary voltages and current drawn from the supply with all the 
secondaries open circuit.  Excessive no-load current is a reasonable 
indicator of a shorted turn.

If you eventually do need to upgrade the power supply, could you fit 
just one switcher in the cabinet with that transformer?  Use it for the 
8V line, and keep the old PSU for the rest?

Philip




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