Dangerous voltages are present in the EA-230. Repairs and biasing should not be attempted by those not familiar with servicing equipment containing high voltages.
Failure-prone parts, order to check: 10 K-2W resistor on power supply, 100K trim pots (can be intermittent, causing failure of output tube), 220K resistor connected to trim pot, 270K cathode resistor on 6SN7, Output tubes, 33 ohm cathode resistors on output tubes, 1N4148 diode grid to cathode on 6SN7, Main power supply capacitor (540uF at 450 V), 270K-2W resistor on plate of output tube, also takes out 1.5K cathode resistor on 12AT7 (V2). Failed 1N4148 diode can indicate arc-over in 6SN7. Burned 33 ohm cathode resistor can indicate failure of output tube or 6SN7 driver. Bias set-up: 100 mV measured between large metal area under each output tube and ground (speaker post). CAUTION-a long insulated probe must be used.
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