Manley MAHI MONOBLOCK AMPLIFIER - Manual (Page 9)

Here are some suggestions to try out in the event you encounter some of the symptoms below.
If you encounter some other symptoms, then maybe you have some other problems that we don't know about.
HUM: Forgot the words. Try a mains ground adapter if they are legal in your country. They are also called 3
pin to 2 pin adapters or “cheaters” and are available in hardware stores. There should be one ground in your
system and only one. If two or more pieces of gear have 3 pin AC mains cables, and they are grounded into the
wall, a ground loop can occur which will usually cause hum. Either the preamplifier OR the power amps, when
sharing an earth connection, are probably the best ground reference for your system, but not both or all of
them.
HISS: Stray snakes in the room. Plug a shorted RCA plug into the input. Did the hiss stop? If so, then the
source of the hiss is something upstream from the MAHI. If the noise level is the same, then the problem is in
the MAHI - probably a noisey 12AT7 or 6414. Try swapping (with the power off please) one tube at a time
across to the other channel to see if the hiss moves over there. If it did, then you found the troublemaker and
you can contact us and we will report him to the proper authorities and send you a tube. And maybe sell you
some spares for next time.
OUT O' BALANCE: Mom told you not to put anything smaller than your elbow in your ear. The two
speakers sound different. Make sure you have both amplifiers' MODE and FEEDBACK switches set to the
same positions. It may be the CD or source and the way it was recorded. First try a different source, or switch
the source to the mono mode if possible, and listen for any level shifts. Notice that each MAHI’s overall gain
is carefully checked at the factory, and should be within 0.25 dB (or better) of each other. Next try swapping
the inputs. Power down and swap left and right inputs. If it is the source, then the problem will “follow” the
swap. Return them to normal (L=L). Power down again and next try swapping the speaker connections by
putting the left speaker wire in the right terminals and right wires into the left terminals. If the problem
switched sides then one MAHI is suspect; if the problem stayed on the same side it is probably a damaged or
fatigued speaker or some crossover switch that got changed by The Cleaning Lady.
NO SOUND, NO PILOT LIGHT, TUBES DARK: Did you pay your Edison bill? Check the MAHI's AC
Mains fuse. Check AC power cord. Is the amp plugged into a working electrical outlet? (This has happened to
everyone at least once!).
NO SOUND, PILOT LIGHT ON, TUBES LIT: Forgot to lower needle onto record. Check speaker
connection and input connection (exchange with the other channel). Take a bias measurement. Do all bias test
points read zero volts? If so, the B+ fuse is blown. CAREFULLY INSPECT ALL OUTPUT TUBES BEFORE
REPLACING THE B+ FUSE because you probably blew one. That B+ FUSE info is on the next page, page
10. (See also “Replacing Tubes” on page 7 if you forgot already what a blown tube might look like).
ONE OUTPUT TUBE WILL NOT BIAS: It doesn't want to. Try to will it to comply. If the bias on ONE of
the tubes will not adjust at all or reads zero volts, and the tube filament is lit, try replacing replace that
particular tube. If the reading still is way off or reads zero, turn the amplifier off. Set your multi-meter to
“ohms” (the Omega sign) instead of “DC volts” (NOT the wavey line, that's AC volts!). Now measure the bias
test point resistance (that's what Ohms do) between the red test point and the ground test point. It should read
approximately 10 ohms. If it reads very high or not at all, then the 10-ohm cathode resistor connected to the
tube has become hurt by that tube not being nice to it. One function of this resistor is to act as the final safety
valve in case of a shorted (not nice) output tube, preventing damage to the rest of the amplifier should a short
occur. Replacing this resistor can be done by anyone with adequate soldering skills. We recommend
contacting our service department here at the factory for specific instructions on how to do that because we are
only giving you enough information in this owner's manual to almost be dangerous.
9
TROUBLESHOOTING