Instruction manual

UAM4SYS • 31
and output jacks J1 and J8 for shorts, opens and proper placement
of C17, C30, R32 and R33.
Problem: No audio from any output
Check: 1.First, make sure you have an audio signal applied to both left and
right channel inputs. If you still don’t hear any audio remove any
jumpers installed on H1 and H2 and check for audio on the
headphone and speaker outputs. If you still don’t have any audio
on the speaker and headphone outputs go to the “No audio from
only the line output jacks J1 and J8” problem section. Otherwise
go to step 2
2. Make sure ALL of the power supplies are operating properly.
See the “POWER SUPPLY PROBLEMS” section if you have any
doubts. If correct go to step 3.
3. Use the headphone test jig to check for signal on pins 1 and 7 of
U1. If signal is present go to step 4. Otherwise check for shorted
connections in the entire signal path between these pins and pin 1
on H1 and H2 and also pins 2 and 19 on U3. Also check that C4
and C9 are installed correctly.
4. Measure the voltage on U1 pins 3 and 5. [READING = +5VDC
+/-0.02 VDC] If good go to step 5. If the reading is not correct
check for component placement and shorts on the connections
around R1, R11, R14 and R23.
5. If you still don’t have any audio outputs there may be a problem
between the input jacks, J2, J3 and J4 and the input buffer
amplifiers U1:A and U1:B. Unfortunately the headphone test jig will
probably not work to test signals in this area. The best thing to do if
you don’t have any other test equipment is to check all the
components and connections between the input jacks and input
buffers.
BASS/TREBLE/BALANCE/LOUDNESS/VOLUME CONTORLS
Problem: Improper operation of ALL controls (bass, treble, balance, loudness
and volume)
Checks:
1. Turn all controls fully counter clockwise and measure the voltage
on U3 pin 17. [READING = 5.4VDC] If the voltage is correct
check the entire circuit path for open circuits from U3 pin 17 to
all connections on both the main board and front panel board.
This is the only ‘signal’ that is common to all these functions. If
the voltage is not correct go to step 2.
2. Check the entire circuit path for short circuits from U3 pin 17 on