[ETO_Alpha] ALpha 87A Fault Code

[Glenn AE0Q]

On 3/15/06, N2TU <N2TU at adelphia.net> wrote:
> All,
>
> I have an 87A...which has just begun giving a fault code 20...."filament
> current grater than 3.5 amp. Possible shorted filament"...


Hello Lou,

  We have found that reseating the connectors on circuit boards may stop
the erroneous filament current readings.

  Stand the 87A on the right-hand side and remove the plate under the
tube-deck.  Unplug and carefully reconnect the plugs inside the tube
deck.  Also reseat the orange connector on the LVPS (Low Voltage Power
Supply) directly in front of the power transformer, and just above the
bottom orange connector that is on one of the transformer cables. Use
Caig DeOxit contact cleaner (available at Radio Shack) on those
connectors to ensure a better contact.

  Reseat the two large red connectors on the top edge of the control
board.  They are accessable through the slot in the top-right side of
the front sub-chassis (behind the LED bargraph displays).

  The Fault 20 may indicate a bad tube or a metering resistor that has
aged and changed value.  With a computer connected to the 87A serial
port you can use the following commands to see what the filament current
is (they are always followed by the ENTER key):

  Type  EXT ON (ENTER) ,  this puts the amp in the 'factory mode' and
will let it accept the next command.

  Type  ADS FIL (ENTER)  numerous times and record the readings.  This
will give you the filament current.  It will read some filament current
even when the 87A is turned off, this is normal and is not a 'real'
number because the tubes are turned off.
  The fault limit is 4.0 amps.

  When you are done testing, type  EXT OFF  to turn off the 'factory
mode' so that no wrong commands will accidentally be written to the
microprocessor.

Glenn AE0Q
Alpha Radio Products