Fisher 400 -right channel cuts out-

[orangeit]

I came across a fisher 400 with original tubes in fine cosmetic condition. First i thought i had the balls to attempt a restoration my self, ordered the kit off ebay and once i realized i was in over my head i had a local tech install the fisher doc resto-pack kit into the receiver. This repair shop mostly works on guitar amps so i hope that wasnt a mistake going there.

Months after the overhaul the problem started. The right channel will make a pop sound and then cut out. It can happen either 30 minutes later, or an hour later, or i could go 5 hours straight with NO problems. So its kind of random. But it feels like half the time it happens with in 45 minutes. It doesnt matter what source im using. The unit sounds good otherwise!

I dont know where to look for the issue, is there any advise anyone may have for me?

 

[gadget73]

Sounds like dirty / loose connections somewhere. Maybe pull the tubes one at a time, clean the pins and sockets to see if that sorts it out.

 

[orangeit]

Well, i flushed all the tube sockets with deoxit, been listening for 6 hrs without the right channel cutting out. If that fixes it, thanks!

The channel would cut out at random followed by the audible "pop". To get sound from that channel again, all i had to do was turn the unit off for a few minutes. That made me think something inside was over heating and giving out. I really dont know though.

 

[larryderouin]

Agree with Gadget. Dirty sockets and or contacts. The contact points in the sockets and pins get hot from dirt (resistance to current flow) and go open by expanding slightly. When they cool down they contract and you get contact again. I get this in my 400 and 800c occasionally, and it's just dust and dirt floating around in the air that gets in the sockets and switches/pots. While you're in there in cleaning mode, do ALL of the SWITCHES, and POTS. DeOxit D-5, then follow up with Faderlube F-5. Re-tensioning the socket pins will also help.

 

[sgmlaw]

Don't forget to clean the pins on every find.

Isopropyl, deoxit, whatever floats your boat.

Kevin Deal used to recommend polishing them with high grit sandpaper, but I don't agree with that.

Dirty old tube pins are an increasing problem nowadays. Even the rarest old Mullard sounds lousy when it has to fight through a film of crud.

Unlike pots and switches, tube contacts get no exercise to keep them clean.

So even with daily runners, an occasional partial pull and reinsertion, once a year, can work wonders.