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[KE4YD]

While operating 12 meter phone my 8410 suddenly powered completely off. After turning the power switch off and back on the amp went thru its usual warm up process, after 3 minutes the amp was ready to place in the operate position, when trying to tune the amp there is no output and it goes in the fault mode. The HV led is maxed out and the IP led is 0. The gain also shows 0.
At the time it tripped out I was only running about 700 watts.
Any ideas where to look.
Thanks,
David  KE4YD

[KA4DPO]

Tube failure?

[AE0Q]

there is no output and it goes in the fault mode. The HV led is maxed out and the IP led is 0. The gain also shows 0.

David,

Unplug the amp, remove the cover and measure the resistance from two test points to chassis, they are on the right-rear edge of the top power supply board.  Measure TP1 to chassis, and TP4 to chassis.  They should each be about 5.7 ohms.  That is the cathode resistor, in series with the cathodes of the two tubes in parallel, going to the chassis.  There are 3 or 4 resistors in parallel, inside the tubedeck.

If a tube had an internal arc and shorted the HV, they may be open now.  That would cause the zero Ip reading when keying the amp.

Glenn AE0Q

[KE4YD]

Thanks for the replies guys, will check it out tomorrow when it's not so late.
At least this is a good place to start.
73,
David  KE4YD