A few month ago I recognized that my Yamaha THR 10C had a problem with the effects knob. It was not able to disable the Chorus effect anymore in the Knob’s zero position. Switching off/on the amp as well resetting to factory settings did not improve the situation. The only working workaround was to connect the amp to the computer and deactivate the Chorus effect using THR’s computer program “THR Editor” and then save the settings in the user memory. Somehow this solution did not satisfy me for long.
I searched the internet for solutions to solve this issue. Unfortunately I did not find anything on this specific issue. This is the main reason for me to write this instruction. I hope it will help others who encounter the same or a similar issues.
How could I solve the problem?
My initial idea was that most probably the resistance of the potentiometer of the effects knob may have changed (increased) over lifetime and therefore YAMAHAs microcontroller/DSP was not able to detect the “deactivation” voltage level any more. (voltage level on micorcontroller input to high). So I decided to start the repair by changing the potentiometer and to see if this could solve the problem.
In the end it did solve the problem and I have to say that the repair itself was not difficult and was done in about 30 minutes as the amp can be disassembled very easily and it was not a problem to lay open the potentiometer PCB.
Before finally opening up the amp I did check out the instruction “Reparing Yamaha THR10 Switch” http://www.planetz.com/repairing-yamaha-thr10-swi... lays out detailed how to open and disassemble the amp.
What are the work steps?
- I ordered a new potentiometer (YAMAHA THR 10 spare part potentiometer)
- Website where I ordered the spare part: https://artaudioparts.com/rotary-pot-gain-master-...
- Opened up and disassembled the amp until I was able to lay the potentiometer PCB open
- Desoldered the defect potentiometer
- Resoldered the new potentiomenter
- Reassembled the amp
- Test and Done
Step 1: Remove Housing Screws
Start to remove the 3 screws on the back of the amp and the two screws at the front feet of the amp.
Step 2: Remove the Bolts
Remove the 4 bolts on front with an allen wrench
Step 3: Separate the Metal Top/front From the Black Plastic Back/side
Separate the metal top/front from the black plastic back/side and then
Disconnect the 3 connectors connecting the metal top/front with the black plastic back/side. You can put the black plastic back/side beside and continue with the next stop with the top/front part.
Step 4: Remove the Knobs
Remove the knob heads from the knobs and remove the nuts and washers. You do not need to remove the knob and net nut from the AMP selector knob (as seen in the phote) because its located on a different PCB which can stay inside.
Step 5: Disassemble Main PCB
Unscrew the two screws of the main PCB and disconnect the two connectors.
Step 6: Disassemble Potentiometer PCB
Unscrew the one screw holding the potentiometer PCB and then remove the PCB. Now locate and mark the broken potentiometer. I used a simple marker for it.
Step 7: Desolder Broken Potentiometer
Start with desolering the potentiometer using a soldering iron and a solder sucker (desoldering pump) . Take out the broken potentiometer and replace it with the spare part.
Step 8: Solder New Potentiometer
Insert the new potentiometer (spare part) and solder it. Check for solid connection and possible short circuits.
Step 9: Reassemble
Now, basically the work is done and you can start to reassemble all the parts (PCBs, screws connectors) in the reversed order like we did disassemble all the parts.
After the reassembling is finished power up the amp and test it. If everything was executed correctly the amp should work again and the problem should be solved. In my case, the problem was solved.