Ramsey Electronics UAM4SYS Assembly And Instruction Manual page 34

[READING varies between 0 and 5.4VDC] Otherwise check for
opens, shorts and incorrect component installation, C26, R13
and R20 and connected circuit paths or U3 may be defective.
Problem:
Checks:
1. Measure the voltage on U3 pin 17, [READING = 5.4VDC] If
correct go to step 2, otherwise go to the "Improper operation of
bass, treble, balance, loudness and volume controls"
troubleshooting section.
2. Make sure the "LOUDNESS" control button toggles the loudness
LED on and off. If it does not go to "LOUDNESS AND MUTE
FUNCTION PROBLEMS" problem section. Otherwise go to
step 3
3. With the loudness LED off turn the volume control to mid position
and measure the voltage on U3 pin 7. [READING approx
5.4VDC] If not check for shorts, opens and correct component
installation for all circuit paths associated with U6 pins 1, 2, 3, 4.
Otherwise go to step 4.
4. Press the loudness control button to turn on the loudness LED,
adjust the volume control to mid position and measure the
voltage on U3 pin 7. [READING approx 3VDC +/- 0.2VDC] This
reading will change with the setting of the volume control. If this
is not correct then check for shorts, opens and correct
component installation for all circuit paths associated with U6
pins 1, 2, 3, 4. If this is correct then U3 or U6 may be defective.
LOUDNESS AND MUTE FUNCTION PROBLEMS
Problem:
The loudness and mute functions are controlled by two flip-flop circuits
that both work the same way. The flip-flops are both part of U5. The
following checks apply to both the loudness and mute functions. The
entries in "()" refer to the mute function components. Also refer to the
schematic diagram.
Checks:
1. Measure the voltage at U5 pins 1(15), 2(14), 5(11), 4(12) and 16.
[READING = +5VDC +/-0.02VDC] If good go to step 6.
Otherwise check all connections and components between
these pins and the +5 volt supply for open and short circuits and
correct installation.
2. While measuring the voltage at U5 pin 4(12) press the loudness
Loudness control only not functioning properly
Loudness and/or mute LED's and/or functions not working
UAM4SYS • 34