A quick Google check of relay (NEC) UB2-4 5NU, shows that it's a 4.5VDC relay.
You'd only have a diode across the coil if it was an AC relay, so I gave you the wrong
advice to check.
I see from your other post, you're trying to get a schematic of your board, which is the
best thing you can do to troubleshoot your problem.
(Try not to post questions about this problem on several different category topic headers,
or the Moderators are going to correct you. They try to keep all the questions about
one problem together, it helps with a more complete understanding of your problem)
If you successfully obtain a schematic, it will be a lot easier to isolate your problem.
The first thing to check, would be to make sure the board itself is the issue.
Are you pretty sure the signal or signals being input to your board are correct?
The second most commom problem to look for, would be a problem with the power
supply to your board. You may be picking-up AC line frequency, causing your buzzing
sound.
Are there any markings on the board itself, test point voltage values?
If there are, it would be helpful to check them, and see if the voltages on the board
are correct. That's a good place to start.
(An example is your NEC relay. When tripped, you should read about 4.5VDC on
the coil)