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at its best and will take several months of regular
use before it is fully 'run in'.
Upgrading Valves!
Quality valves should sound better and have a
better service. The valves supplied with selected
models are the result of careful comparison with
other makes. But beware of paying a premium for
"New Old Stock" valves where you may be paying
for rarity value and not performance. Icon Audio
normally keep a range of upgrade valves in stock.
1. Amplifier Dead
Check the 5 (or 10amp for 115 V) amp mains fuse in the
IEC socket at the back of the amplifier. To gain access,
remove the mains lead. The fuse is in a small plastic
drawer, which forms part of the socket assembly. To
open insert a flat blade screwdriver or similar and prise
open. The fuse in use is the innermost the outer is a
spare. Should the replacement fuse also blow there is a
fault you should disconnect from the mains and seek
qualified help or Icon Audio. Replacements should be 5
Amp 'anti-surge'.
The fuse in the wall plug should be a 3 or 5 amp fuse,
although unlikely to fail, this should be checked if the
amplifier fuse is OK.
There is also a HT fuse inside the amplifier. This
would not normally blow unless there is a valve fault
or an overload condition. This should be checked by
your dealer, or only
Disconnect amplifier from the mains power and wait
20 minutes before removing bottom plate. If the HT
fuse has blown, there are replacements inside.
Replace bottom cover afterwards and check bias
immediately after switching on.
2. No sound
Have you selected the right input? Is the "Tape Monitor"
switch up? Are all the connections OK? Is everything
switched on? Are the speakers connected?
Distorted sound.
Could be your source, the speakers or the amplifier,
check all wiring, and try swapping things around to
eliminate or prove which component if the problem.
Left or right amplifier? If both probably the source unit.
Try another source. If one amplifier is distorted check the
bias. No bias reading means either a fuse blown or a
faulty valve. Distorted sound at higher volumes may be
because one of the output 845 valves is not working.
This could be due a faulty 845 or one of the 845 internal
fuses blowing. A symptom of this would be no 220mv
bias voltage at the test point. Also the valve would not be
as hot as the others. Refer to an engineer or to Icon
Audio. Spare internal fuses are secured inside the
chassis. Replacements are available free of charge from
Icon Audio.
3. Hum Problems
If you experience hum, try disconnecting the input, if it
clears it is external to the MB845 and further advice
should be sought from your dealer or see below. By
elimination find out which unit is
Interconnects should be well screened.
If hum persists with no input this is probably the hum
adjustment.
4. How to adjust the hum adjustment:
Ideally use a AC millivolt meter connected to the 8 Ohm
speaker terminals (together with loudspeaker) with a
*See engineers notes at rear
5 Trouble Shooting
if you
feel
competent.
causing this.
Cabinet Care
To remove dust we suggest gentle brushing of the
polished stainless steel cabinet with a soft
paintbrush. Other marks can usually be removed
with a damp cloth. The Perspex valve cover may
need a gentle wipe with soapy water and drying
with a duster. Never use anything wet on the
amplifier, and always clean with the power
disconnected.
shorted input, or no input connected. Adjust hum
adjustment for minimum hum (about 1mv AC).
OR Adjust by ear:
This is easier with one person listening another
adjusting, rotate adjustment backwards and forwards
for minimum hum (like tuning in a radio)
This will normally be necessary after changing 845
valves. Or after the amplifier has been in use for
some time. Check and adjust (if necessary) bias first.
5. External hum causes;
Identify which input is causing hum. Connect one
input at a time. A common cause is a 'hum loop'
caused by having too many earths, and may be
identified by unplugging each input source from the
mains. One remedy for this is to use an interconnect
which only has the screen connected at one end.
Other causes of low-level hum can be from adjacent
equipment, so experiment with moving equipment
around to see if this makes the hum better or worse.
Never disconnect a mains earth. They are for your
protection!
6. Strange noises coming from speakers
Turn volume to minimum on unused input, if the
noise disappears, the fault is with the source or the
connection. If noise persists, the problem is with
amplifier.
If a whole output valve glows red (other than the
heater), often accompanied by a hum through the
speakers, switch off immediately, and refer to Icon
Audio or a service engineer, as this could be valve
failure.
7. Service: Should you suspect a problem, you could
return the unit to your dealer or Icon Audio for a
periodic service or return the valves for testing free of
charge. You should carefully remove the valves (the
845s should be held by the base when removing, to
prevent damage) numbering them with a marker from
left to right as you do so in order that that may be
replaced in the same position. They should be well
packed in cardboard & foam or similar, and returned
to Icon Audio for testing. (Valves are very rugged if
packed properly).
Mains Supply
This amplifier is hard wired to work on 230/240v ac.
The transformer may be re-configured for 110/120v
ac by a qualified engineer. See engineers notes or
contact Icon Audio for more information.
This manual is provided for guidance only, and is not
intended as a comprehensive service manual. In
case of problems you should refer to your dealer or
directly to Icon Audio.
Page 7
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