The line mixer I use in the shack to combine audio from the PC and the transceivers, has developed a nasty 60 cycle hum. It’s time for an SM10 Power Supply Board Swap.
![SM10 POWER BOARD](http://k6hr.com/wp-content/uploads/2022/04/20220427_213641-1024x1365-1-768x1024.jpg)
This is the suspect board. Can you see the problem already?
![SM10 POWER BOARD](http://k6hr.com/wp-content/uploads/2022/04/20220427_213704-1024x768.jpg)
The problem is a bit easier to see from this angle. Do you see it yet?
![SM10 POWER BOARD](http://k6hr.com/wp-content/uploads/2022/04/20220427_215005-768x1024.jpg)
There you have it. Those filter caps are bulging big time! These failed capacitors are the reason we have developed the annoying hum.
![SM10 POWER BOARD](http://k6hr.com/wp-content/uploads/2022/04/20220427_215011-1024x1365-1-768x1024.jpg)
Here are the same two caps on the replacement board. Notice how the tops are nice and flat! The vents are not open or stressed.
![SM10 POWER BOARD](http://k6hr.com/wp-content/uploads/2022/04/20220427_215016-1024x1365-1-768x1024.jpg)
Side by side comparison.
An easy fix! I’m now HUM-FREE
The SM10 power supply board swap did the trick!
I will order (2) 1000uf 35v and (2) 220uf 25v replacement caps, and partially recap the original board for use later on when the replacement fails!
From the manufacturer:
The SM10 features ten channels with 1/4″ stereo line inputs and a balance control for each channel. Two channels include XLR mic inputs. This allows you to blend the relative levels of stereo inputs to your liking. In addition, each channel includes a switch for +4 dBu or -10 dBV line level input.
For output, the SM10 provides electronically balanced main stereo XLR and 1/4″ line outputs. The SM10 provides versatile signal routing via Main Mix, Mix B, Monitor and EFX bus outputs, as well as low noise and discrete microphone pre-amplifiers with 48-volt phantom power.
Two auxiliary sends can also be used to route signals to external effects, or create a separate mix for on-stage monitors. The SM10 features front panel headphone and monitor outputs with dedicated level controls. The mix may be audited with the SM10’s 6-segment LED meter and a flexible meter/headphone source control.