[sdiy] How to find a short-circuit? (Vox organ problem)

[Antti Pitkämäki]

Hi,

A while ago I won a Vox Continental 2 combo organ from Ebay. It doesn't 
work, and the problem is this:

When the organ is turned on, the power lamp is lit but no sound, not even 
noise or anything, comes out. When I checked the organ with an oscilloscope, 
I couldn't see any signal in there, and when I measured the output voltages 
of the supply, they were very low, so I suspected that the power supply is 
not working and the power supply capacitors especially are not working. A 
friend of mine, who has fixed vintage tube amps and other stuff, checked the 
power supply for me. He said the power supply is fine, and he is suspecting 
that there's a short circuit in the organ, which is a reason why there 
seemingly is only a very small voltage instead of the needed supply voltage 
on the cards. He said that it might be some cap one some card which has 
become a short-circuit and is causing the problem. He said that he might try 
to do the following to each card of the organ: Taking it out, and supplying 
it with the correct voltages, to see which card is short-circuiting. If he 
can't find it, I will have to continue since we only agreed that he checks 
the power supply and puts new caps there. In theory, I could replace all 
caps of the organ that possibly could cause something like this. However: 
there must be more experienced people than me on this kind of a problem. So, 
if anybody could recommend a good way to trouble-shoot a problem like this, 
I'd love to hear it! In other words: what is the best way to try to find a 
short-circuit that is making the power supply output voltages drop?

Thanks in advance,
Antti P.

_________________________________________________________________
Express yourself instantly with MSN Messenger! Download today it's FREE! 
http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/