Manley ELECTRO-OPTICAL LIMITER - 1994 - 1997 MANELOP020-318 - Manual (Page 9)

TROUBLE-SHOOTING
There are a number of possible symptoms of something not quite right, some may be interfacing, others we will touch
on as well. The preceding page shows that all the inputs and outputs of the Electro-Optical Limiter are unbalanced. No need
to panic. We have sold hundreds of these units and less than 1% ever had a problem with hum or interfacing to balanced
consoles or other gear. However if you suspect a problem the following paragraphs should help.
NO POWER, NO INDICATORS, NADA - Probably something to do with AC power. Is it plugged in? Check the fuseon
the back panel. A blown fuse often looks blackened inside or the little wire inside looks broken. A very blackened fuse is a
big hint that a short occured. Try replacing the fuse with a good one of the same value and size. If it blows too then prepare
to send the unit back to the dealer or factory for repair. The fuse is a protection device and it should blow if there is a problem.
If the unit works with a new fuse, fine. Check the MAINS VOLTAGE SELECTOR if one is fitted. Some of our models are
able to have them and some don't. It should be set correctly for your mains voltage.
LIGHTS BUT NO SOUND - First try plugging the in and out cables into some other piece of gear to verify that your wires
are OK. Assuming that it was OK into the other unit it probably is still a wiring thing. The XLRs are transformer balanced
(isolated / floating) that require the LOW or negative part of the signal on PIN 3 to be connected even into unbalanced inputs.
With unbalanced sends or returns are used with the Limiter balanced inputs/outputs then PIN 3 and GROUND should be
connected together. The Limiter's unbalanced inputs and outputs kill the balanced XLR signals to provide a transformerless
audio path. Once again, when using a balanced to unbalanced (or vice versa) don't forget to have PIN 3 connected to the
SLEEVE of the 1/4" plug.
LEVELS SEEM TO BE WRONG, NO BOTTOM - Several possible scenarios. Manley uses the professional standard of
+4 dBm = Zero VU = 1.23 volts AC RMS. A lot of semi-pro gear uses the hi-fi reference of -10 dBm = Zero VU. This is a
14 dB difference that will certainly look goofy and may tend to distort. Often there are switches on the semi-pro gear to choose
the pro reference level. We do not provide that kind of switch because of inevitable compromises in the signal path. If the
loss looks close to 6 dB and it sounds thin then one half of the signal is lost. The cause is probably wiring again. One of the
two signal carrying wires (the third is ground / shield on pin 1) is not happening. Check the cables carefully because
occasionally a cable gets modified to work with a certain unit and it seems to work but its wrong in other situations. If only
one side of the Limiter exhibits this problem, it may be a problem in the Limiter. See the next item.
ONE SIDE WORKS FINE BUT THE OTHER SIDE IS DEAD - Let's assume this is not wiring. We are pretty sure it is
the Limiter. If it were solid state you would generally send it back for repair. Being a tube unit, you can probably find the
problem and fix it in a few minutes. Not too many years ago, people could "fix" their own stuff by taking a bag of tubes down
to the corner and checking said tubes on a tube tester. These are practically extinct but no prob'. Most Manley gear is two
channel meaning you can swap tubes to determine the bad boy. Do two at a time just watching that they are the same number.
Be careful - there are some high voltages inside the chassis and tubes can get pretty warm but if you can replace a light bulb
you should be able to cruise through this. Before you remove a tube, just take a look at them powered up. They should glow
a bit and they should be warm. If one is not, you have already found the problem. The tube's filament (heater) is burnt out
or broken like a dead light bulb. The other big visual symptom is a tube that has turned milky white - that indicates air has
gotten into the tube or we joke "the vacuum leaked out". Either way replace the tube. They are not hard to find - even Radio
Shack carries a fair tube stock and Manley can ship you a tested one. Back to swapping - before you pull a tube, pull the power
out, let the unit sit and cool and discharge for a minute or two, then swap, then power, then check. Gentle with those tubes,
don't bend the pins by trying to insert them not quite right. A little rocking of them as you pull them out or put them in helps.
When the problem follows the tube you found the problem - a bad tube. No soldering, no meters, one screwdriver - easy.
HUM - Let's assume it knows the words. Once again - several possibilities - several cures. Most likely it is a ground loop.
If you are using the 1/4" unbalanced inputs, try the transformer XLRs. Balanced inputs can reject hum fromground loops,
but it would be good to break the loop. The two most common procedures are: try a 3 pin to 2 pin AC adapter (about a dollar
at the hardware store) which is better than messing up the power cable by bending the ground pin until it breaks off. Method
two - cutting the shield on one side of the cable. This is usually done at every female XLR to "break" all loops. You may
get a loop simply from the rack. All the other gear in the rack is "dumping" ground noise onto the rack rails. Try removing
the Limiter from the rack so that it is not touching any metal. You may have cured a non-loop hum. Some gear radiates a
magnetic field and some gear (especially if it has transformers) might receive that hum. A little distance was all it took. A
cool method of reducing all sorts of hum and noise is to use the new 60-0-60 balanced AC power transformers available from
Equi=Tech and Furman. It costs more but works best. Hum might be because of the unbalanced input but this hints at ground
loops and questionable wiring.
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