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12 TROUBLESHOOTING - If something goes wrong
12.1 No power
• When you switch on a DX-2, it takes about 3 - 5 seconds for the lights on the front panel display to come on. This is due to the
"soft start" circuit. If nothing happens after turning the power on, switch off at the front panel, then check the following:
• make sure the power outlet has power
• make sure the power plug is fully pushed in into the power outlet.
If it is still not working, unplug the power cord from the mains, then remove the fuses from the fuse holders on the rear panel of DX-2
and check them with an ohmmeter.
• If a fuse is blown, replace it with a fuse of the same type and try again.
• If the fuse blows again, or if the fuses were not blown in the first place, contact your supplier.
12.2 Fan goes to high speed
This could happen especially during tuning, or when the ambient temperature is high. It could also happen when the ventilation is
restricted, for example by blocking the openings at the back, sides or on the top of the amplifier. In normal operation, with correct
tuning, the DX-2 should be able to handle the maximum power with the fan still running at low speed. Usually driving the amplifier
with high power and bad tuning can make the fan to go high speed. When this happens, the tube temperature is nominally 120° Celsius.
This offers a margin of 30°C before a temperature cut-off occurs, and way below the tube rating, of 200°C. That means you can
continue to operate the amplifier with the fan at high speed, but the best is to let it idle until the fan drops back to low speed. This
usually takes less than one minute.
12.3 Fan not working
As soon as you switch the power on, you should notice two things about your DX-2: the display should indicate about 2500V of plate
voltage, and you should be able to hear the fan running. The amplifier is not supposed to be powered without the fan, even in idling
mode. If the fan does not operate when you power up, or if it stops while using the amplifier, switch the mains power off immediately
and contact your supplier.
12.4 If the FAULT light turns on
The FAULT (red) light turns on in two situations:
• Over-current in the plate circuit
This could happen due to a flash-over in the tube, or as a result of a momentary high plate current during tuning. This completely
disables the amplifier for about 2 minutes. The same timer is activated as when the amplifier is switched on, causing the READY light
to turn off. If the OPR/STBY switch on the front panel is put on STBY, the FAULT will turn off, but the READY will be also off.
When the READY comes on again, the FAULT will disappear (if the amplifier was left in OPR), and the DX-2 is ready to operate
again.
• Over-temperature cut-off. See below.
12.5 Over-temperature cut-off
This would normally happen after a change of the fan to high speed. The operation of the amplifier is disabled, but the timer is not
activated. The FAULT light turns on.. When the tube cools down, the FAULT turns off and the operation can resume. This type of
fault should never happen. DX-2 has a very efficient air cooling system. When the ventilation is not restricted, in normal ambient
conditions, when properly tuned, a DX-2 can operate at full power for extended periods of time, with the fan not even going to high
speed. The temperature cut-off happens when the tube reaches 150º Celsius, with ample safety margin to the specified limit of 200ºC
for the GU84B tube.
12.6 Over-current cut-off
If the plate current exceeds even for a brief time a pre-set safe limit, an over-current detector will activate the power up timer, disabling
the amplifier for about 2 minutes. During this time the READY light is off, and the FAULT light is on, if the amplifier is left in OPR
mode, as explained under 12.4, "If the FAULT light turns on".
12.7 Ig2 blinks fast - No plate voltage
If the high voltage is lost due to a fault in the amplifier, the screen current tends to reach very high values. This is an unlikely situation,
but if did happen, this would normally guarantee a tube failure in unprotected amplifiers that do not have a current limiting circuit. The
screen current limiting in DX-2 is so efficient, that the tube is fully protected even in such a situation and test bench DX-2's have been
extensively run with no plate voltage and maximum screen voltage, with no effect on the tube. If this loss of high voltage should
happen to your DX-2, the Ig2 display will have the red LEDs flashing, due to the screen current exceeding the pre-set limit, with no
input power applied to the amplifier, while switched to OPR.
In such a case, it is possible that the high voltage is still shown on the display, but it does not reach the tube. In any case, this is a major
fault. Put the amplifier on STBY and the flashing will stop. Then switch the power off and contact your supplier.
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