Ramsey Electronics UAM4SYS Assembly And Instruction Manual page 27

Input Buffer, Headphone Amp, Loudness, and Tone/Volume/Balance
Circuits
Once the power supply is plugged in and the audio input source is turned
on you should be able to hear audio in the headphones (even with the
power, S1, switch off). If you cannot press and hold HEADPHONE
LEVEL UP switch until audio is heard.
Press the HEADPHONE LEVEL Down button to test for function.
Test the bass, treble, balance, and volume control for proper function.
Check the Loudness control for proper function. Verify the loudness LED
D3 illuminates.
Making a Headphone Test Jig
Remove the headphones from J20.
Connect an alligator clip lead to the sleeve of the headphone plug. The
second clip of this lead will be use to connect to ground of the circuit
board.
Connect one end of a second alligator clip lead to the tip of the headphone
plug. To the other clip connect the (-) lead of the extra 10uf electrolytic
capacitor. The positive end of the capacitor will be used as a test probe
for testing and troubleshooting.
Line Output Buffer
Connect the ground lead of your headphone test jig to the outside bracket of
J8. Touch the (+) lead of the electrolytic capacitor of the headphone test
jig to J8's center conductor. You should hear the right channel audio in
the left headphone speaker.
Leave the ground lead of the test jig in place. Touch the tip of the (+) lead of
the electrolytic capacitor of the headphone test jig to J1's center
conductor. You should hear the left channel audio in the left headphone
speaker.
Power Amp
Set the bass, treble, and balance controls to midrange
Set the volume control to minimum or fully counter-clockwise.
Verify the mute and loudness LED's are off.
Turn on power switch S1. The power LED, D4, should illuminate.
Slowly rotate the volume control. Listen for clean audio from the
speakers.
Press the MUTE switch. Verify the speaker audio mutes and the mute
UAM4SYS • 27