Repair of Impedance switches

[tdogzthmn]

My assembled SEX amp which was assembled by a friend received some damage during shipment, notably I found several of the impedance switches had been broken off when the wood base popped apart allowing the amp to drop through.  I tired to crudely reattach all the switches to the boards and tested the amp.  Both tubes do light up quickly and I did get a signal through the right channel but it was pretty poor.  With headphones the signal is faintly audible.  I did not see any other obvious damage or loose connections, making me think the boards and their offsets keep the rest of the circuitry from physically hitting anything.

I was able to quickly order new switches to which I intend to resolder to the boards.  Best case I can easily replace the broken switches and get the amp functioning properly.  If anyone can think of something I should test or inspect while I wait for the replacement parts please let me know.

I'm hoping to have this beast up and running so I can show it off at the Bay Area Head-Fi meetup early next month!

[tdogzthmn]

Any tips on how one might desolder the switches from the PCB?  I was trying to apply heat and pressure to the solderpad of the switch to push it back through the hole.  I dont want to damage the boards themselves but its proving difficult to remove my broken switches.

Thanks!

[Paul Birkeland]

I'd get one of the little hand held suckers that can suck the solder out of the holes.

The better suckers will have a big spring in them, not the rubber bulb.

[tdogzthmn]

I replace all the switches on the PCBs and reattached all the leads to the boards.  Fired it up and put both switches on "LO" and plugged in headphones and got music.  I still have a few issues which I will try to sort out later.

I notice a slight channel imbalance where the right channel is slightly louder than the left. 


Going through the ML MH and HI settings I dont get signal or only get signal on the Left channel through headphones.

I did get sound through both speakers on ML with the Balance switch on.

Either way I will need to spend more time checking and resoldering the switch connections.  I am glad the my problems seem to be isolated to the Impedance switches and that I can get decent sound out of the amp for the meantime. 

[Jim R.]

Tom,

That is some difficult stuff to do correctly and not damage anything.  I suspect that in the long run you'll want to replace the pc boards and switches, but hopefully you won't have to resort to that.

Good luck,

Jim

[tdogzthmn]

Here are images of the underside for both boards.  Looks like there is enough solder on each of the connections for contact to be made. 

[Grainger49]

The board and solder joints look perfect.  Unless the switches are damaged you look good to go.

[tdogzthmn]

I did find one or two points that did not have a good solder connection and re-did them. 

I get great sound on the ML and MH settings, the HI and LO settings still have issues but I am content with the performance of the amp for now. 

On a side note I have notice that the when I have the switch set to unbalanced, channel separation is much greater with the speakers.  On balanced mode I get a smaller soundstage and a bit more bass but right now the unbalanced mode sounds better with my Orcas.