Update on Epoxy Potting Removal

Tony Duell ard at p850ug1.demon.co.uk
Sun Nov 28 14:11:37 CST 2010


> 
> Now that I have access to the main unit the plot thickens. All of the
> outputs of the potted brick go to full-wave bridge rectifiers in the main
> unit such that you get a plus and minus voltage reference to the CT ( center
> tap ). That big potted POS is nothing more than a big friggin transformer !

Right... That should make things a little simpler. But why so many 
secondary windings?

> The main output leads ( 1 2 and 3 ) have 28 VAC coming out of them. I put a
> Variac on the " transformer " and turned it up very slowly. At not much
> voltage it gets very HOT ( I suspect shorted windings or a whole shorted
> primary on the input side. The 28 VAC output figure came from estimating

Unforutnatel, if you have shorted turns in a winding, it will throw the 
voltages off. 

I asusme you can now identify the ends and taps of the windings, based on 
the rectifiers, etc, in the main unit. Can you make sensible estimates of 
the secondary votlages from that (e.g. if thres's a smoothing capacitor 
rated at 25V, the RMS ac input can't be more than 25/sqrt(2)). If there 
are 3 terminal regualtors, or simular, you can prsumably deduce a 
sensible input voltage for them.

-tony




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