JCM900 fuse keeps blowing (newbie)

[j-loe]

Hi all,

I'm new to posting on this forum and am looking for some help.

I'm having an issue with a JCM900 whereby when I power it up the fuse blows. I've also been told it 'may have had a cup of tea spilt on it recently' (musicians eh). Assuming this is a power amp issue, visually the components all look fine, and the Resistors all measure good.

Any ideas what could be causing this?

Could this be being caused by a dodgy transformer?
The valves all look fine but is it worth testing with new ones just incase? (luckily I have some sitting about)

Massive thanks in advance

J

[Alex R]

Definitely test the power tubes. That's usually the cause of blowing fuses.

[rf7]

Pull all of the tubes and clean up any spills with Anhydrous alcohol. Then power up the amp, with the tubes still removed, and see if the fuse blows. If it blows, it may be your power transformer. See http://www.geofex.com/ampdbug/ampdebug.htm for how to go further with this. Report back with your results.

[Mars Amp Repair]

It would be a huge leap to go from cleaning the spill from the tube sockets to a bad power transformer. If the fuses blew, they would have protected the power transformer & it is most likely good.
The circuit boards should be removed & inspected for 'tea' residue & should be completely removed before moving on. The afforementioned alcohol should do the trick...most likely it's the sugar in the tea causing the issue.
Did the fuses blow immediately after the spill or did the amp run for a while once it dried out? I have had liquid spills that work for a while until the residue begins to draw current between 2 conductors on the pcb or 2 pins of a tube socket & then starts to burn.
glen