Yamaha THR repair – THR5

Yamaha THR Repair

I thought I ought to document this Yamaha THR repair whilst I could still find the photos!

The amp had fallen from a height and the DC power input socket was damaged. Simple enough job, or it should be! Yamaha supply a an external converter to convert the mains supply into useable DC, but they use a non standard DC plug. (Note: some call it a mains socket, but it isn’t fortunately! 🙂 )

The photos show: Yamaha’s little class D amp, my PCB/ DC socket modification top side, the Yamaha SoC and RAM, the marking for the case modification, the PCB modification reverse side and the second layer of boards.

Yamaha THR repair

Yamaha THR repair

Yamaha THR repair


Yamaha THR repair

Yamaha THR repair

Yamaha THR repair
These are cool little solid state modelling amps. Sadly, for such an otherwise great company Yamaha aren’t very good at supplying spares so I was forced to fit a different socket and slightly modify the THR case to make it fit.

If you need a Yamaha THR repair, please contact me.

Here’s a video:

AV Receiver repair – Yamaha RX-V450

AV receiver repair

This AV receiver repair, a Yamaha RX-V450, was completed on a fast turnaround for a local radio producer who needed it in time for a show. It’s got 6x85W channels and more inputs and outputs than you can shake a stick at.

Although I’m well versed in solid state electronics, this is the first AV receiver I’ve worked on, because most of my work is on musical instrument amplifiers.

The fault was with the power supply and is a known design flaw with the otherwise reliable unit. Over time, power surges can damage a 600V capacitor that resides in the soft start circuit. This might sound surprising when UK mains is 230V, but audio equipment should be designed to cope with 1kV or 4.5x the rated mains voltage to withstand surges. I replaced the device with a 760V capacitor, which was the biggest part that would fit in the available space. I added epoxy glue to prevent the larger part becoming a vibration risk. AV receiver repair

The amp was dropped off on the tuesday and the repair completed by the thursday. Just one hours work, with a short break for 24h turnaround on the new part.
The repair was completed within the first hour and returned quickly to the customer, who then brought me two other AV receiver repairs! He’d not been having much luck with them!

If you have an AV receiver repair, please let me know and I’ll see if I can help.

Bass preamp repair – Yamaha RBX JP4

This recent bass preamp repair was for a friend, bass player for professional party band the soul thieves. The preamp came from one of his backup instruments.

Identifying the circuit was a bit of puzzle due to conflicting information on the web. The bass preamp has bass and treble controls, a blend for the pickups, a master volume, two trimmers for gain, a mid frequency select knob and a mystery mid switch.Yamaha bass preamp repair, notch with bass and treble at max

The model later became the John Pattitucci signature model. Certain other builds have piezoelectric inputs.

The repair was relatively simple – the unit was producing no sound on either pickup which turned out to be a loose connection between the two board layout. It’s worth noting that later units were a single board design.Yamaha bass preamp repair, bass and treble responseYamaha bass preamp repair, notch with bass and treble at minimum response

The graphs of the response show the range of bass and treble control as well as the performance of the mid frequency control with bass Andy treble at max and minimum.

If you have a bass preamp repair, please get in touch and I’ll get it sorted for you.