Repairing Yamaha THR10 Switch

The Yamaha THR10 is a fun little practice amp which sounds surprisingly good (and loud!) for its size. It weighs just a few pounds and can run on batteries, so it’s easy to toss in the car for a travel amp. Unfortunately, it is just as easily tossed out of the car, as I learned when my THR10 stage-dived from the car onto the pavement. Ouch! It survived mostly unscathed, except for the power switch. It still works, sort of… but it’s bent and hard to use. I’ve procrastinated on this because it’s not a trivial repair, but am finally getting around to it.

THR10 Broken Switch

Before I could order a replacement part, I needed to open it up and examine the current switch. First, I removed the three screws on the back and two screws on the front feet with a phillips screwdriver. Then I removed the 4 bolts on front with an allen wrench.

Remove 3 Screws On Back Remove 4 Bolts On Front Remove 2 Front Feet Screws

Then, I was able to separate the metal top/front from the black plastic back/side. It was a bit fidgety and required some wrangling to get the chassis open.

Open THR10 Chassis

In order to release the circuit board containing the power switch, there are two nuts which must be removed from the panel. I removed the nut on the power switch easily with a crescent wrench. There’s also a nut hiding under the AMP knob which was tricker to remove. The knob pulls up relatively easily, but the nut is recessed beneath the panel, so I had to use a pair of needle nose pliers instead of a wrench to get it loose.

Removing Nut And Washer On Switch Removing Amp Knob Removing Nut On Amp Knob

Next I removed the one screw holding the circuit board in place, and gently turned over the board to examine the switch.

Removing Circuit Board Screw Thr10 Power Switch Exposed Back Thr10 Power Switch Exposed Front

Fujisoku 8a SPDT Switch

The switch is labelled as a Fujisoku 8a1012. I found the datasheet at Nidec Copal (archived here), and referenced the naming table on page 3 to determine that the 8a1012 is a 1-pole On-On standard toggle with PC Straight terminals, rated for 6A at 125V.

I found this exact part for $4.09 at Digikey (part #563-1629-ND). With shipping the total was $7.28, which is a bit spendy for such a simple switch. I wasted some time searching around for a comparable cheaper part, referencing the lug spacing and power ratings from the datasheet, but in the end just decided to play it safe in order the part from Digikey.

The switch is held in place by a retainer U-shaped clip which is soldered to the board. So there are six lugs that need to be desoldered, labeled SW612 on the PCB. I used my Weller WES51 soldering station, and a solder vacuum like this one.

Circuit Board Sw612 Ready To Unsolder The Switch Switch Removed Old Switch Removed With Clip Assembly

Fast forward a week, and the new switch had arrived from Digikey looking like a perfect match.

Old And New Switch New Switch In Position Ready To Solder

I referred back to my pictures from before I removed the switch, to ensure I was orienting the switch properly, and soldered it in.

With new switch soldered in place, I did a quick play-test to make sure it was all good, before reassembly. Check!

Play Testing THR10 Before Reassembly

Time to put it all back together! I just reversed the original disassembly steps and referred back to my original pictures as necessary.

Mission accomplished!