Manley MIC EQ 500 COMBO - Manual (Page 10)

BASIC MAINTENANCE
CHANGING THE FUSE
As with most gear a fuse may need to be replaced. The symptom is "no power" and no LEDs lit even though
you have checked that it is plugged in correctly. The first thing to check is the fuse. Unplug the AC power before taking
a look at the fuse - Simply turning the EQ 500 "off" is not safe enough. A blown fuse will either look "blackened" or the
little wire inside will look broken. If you have a multi-meter you can check continuity of the fuse. A good fuse will look
very similar to the reading you get simply by shorting the test leads. Remember that the fuse is there to protect the unit
from big damage caused by small problems. Replacing the fuse with the wrong value could be disasterous and would
void the warranty. Use a 2 Amp Slo-Blo type or "MDL 2". If this fuse blows then there is very likely a problem that
requires a technician or return to Manley Labs for repairs.
CHANGING THE METER LAMP
The lamp behind the meter should last several years but it is incandescent and will eventually burn out. The
symtom is that everything works but the meter is dark. To replace the lamp is very easy. Unplug the power and let the
unit rest for at least 15 minutes to allow the capacitors to drain. You could get a shock if you poke around inside the unit
too soon after powering down. Remove the two phillips screws holding the top perforated panel in place. They are
located at the top of back panel. Slide the perforated top back at least half way. Behind the meter you will see a small
black printed circuit board with what looks like a fuse. This is the lamp. Replace it with the same type which is a 12 volt.
0.15 amp (150 mA) and the size is 1/4" X 1 1/4". If you have difficulty finding such a lamp - call us and we will mail
one to you for a small charge.
CHANGING A TUBE
Like lamps, tubes have a lifespan. Sometimes this is a few years and sometimes it is a few decades. 30 years
ago the average person could repair his TV or radio by removing the tubes and taking them down to the local drug store
where a tube tester was available. They could buy the tubes there and have an entertained family in less than an hour.
Almost as easy as changing a light bulb. Changing the tubes in this unit is easy and should not require a technician if you
can get the tubes (you can get them from us). The symtoms can be; loss of signal in one section, microphonics (tapping
on the unit causes too much noise in the speakers), hiss has increased or unusual distortion has become apparent. Follow
the instructions for changing the Meter Lamp to open the top of the unit. The two tubes involved with the MIC PRE are
located toward the side of the unit. The other two tubes are involved with the LINE AMP and EQ. A tube that has turned
white is a sign that air has leaked into the vacuum (as opposed to the vacuum leaking out). A tube that does not have a
slight glow when powered is a sign that it it is not functional. If you have waited at least 15 minutes - the tubes should be
cool. Gently wiggle out the tubes to pull them out. You do not want to damage the printed circuit board. Replace one or
all. Put the cover back on and test out the audio.
ADJUSTING THE METER GAIN
This unit has been factory aligned but should you need to re-adjust, follow these instructions. There is a trim pot
located in the unit mounted on a small printed circuit board mounted right on the LINE OUT XLR. You will need a
good "reference meter" to calibrate to. Plug it into the LINE OUT XLR. Put a 1Khz oscillator tone into the LINE IN.
Adjust the LINE GAIN for 0 VU (+4 dBm) (1.23 VAC) on the reference meter. Do not touch anything except the trim
pot and do not put pressure on the trim pot because the leads could break. Adjust the trim pot for 0 VU on the internal
meter. Done. Close it back up.
page 10
MIC
GAIN
MIC
TUBE
LINE
AMP
PASSIVE
EQ
TUBE
MIC
PREAMP
LINE
GAIN
MIC
IN
MIC
PRE
OUT
LINE
IN
LINE
OUT
BLOCK DIAGRAM OF MIC EQ-500 COMBO
5751
6414
MIC
PRE
5751 7044
METER TRIM
TUBE LOCATIONS
LINE AMP
LAMP