Charles, I just Googled Alpha 87A Fault 20 and this is what came up... seems
to be a reasonable approach unrelated to temperator other than a marginal
connection may become intermittent as heat expands the metal contactors of
the connection. Alpha does a pretty good job of explaining the faults and
the systems that alert them, I think.
Alpha 87A Fault 20 or 18Sat, 12/04/2010 - 21:03 - administrator
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.
Once you have completed this process, email the factory with your results
and for further instructions on possibly changing the filament current
limits in the amplifier EEPROM
Forums:
Alpha 87A Entries
a.. Log in or register to post comments
Thu, 12/09/2010 - 02:23 - mollyhFault 20 on the 87A
Note that although the formal resolution above also talks about a possible
tube problem - in my 10+ years working directly with Alpha amps I have yet
to see a Fault 20 that is caused by a bad tube. Cleaning the connectors as
described above will give you anywhere from 6 months to 2 or 3 years more
20-free operating. Eventually you will need to get the connectors
changed......
a.. Log in or register to post comments
73,
Dave
wa3gin
----- Original Message -----
From: "Charles Harpole" <k4vud@hotmail.com>
To: <amps@contesting.com>; "Alpha alpha-service"
<alpha-service@crosslinkinc.com>; "Alpha Amplifiers"
<service@alpharadioproducts.com>
Sent: Sunday, January 22, 2012 7:08 AM
Subject: [Amps] A intermittent 87a
>
> 1. Looking for ideas re an intermittent flakey Alpha 87a. SN 91480337
> with factory Alpha Max and set on 220VAC with line voltage consistently at
> 230VAC (not counting dips occasionally but not apparently relevant). The
> problem was same with earlier internal xformer tap set at 240VAC.
>
> 2. Amp has has all PIN diodes replaced seeking an answer to an earlier
> Fault 9, which has cleared up totally lately.
>
> 3. Shack air temp at 27C to 30C (86F), the amp goes to Fault 20 either
> immediately upon turn-on or up to measured 4 hours of continuous stand-by
> ON condition. Position of the STBY/OPR switch does not matter in this
> kind of test. Sometimes cycling the STBY/OPR switch resets the amp to
> normal and sometimes does not. When the reset works, the amp does
> function normally with 40-50 watts of drive into 1.9:1 SWR antenna. At
> times--with no discernable pattern--the amp goes to Fault 20 and will not
> respond to reset for hours.
>
> 4. CHANGED Shack air temp after 24hrs., then test............. 25C
> (77F). At this lower temp. the amp works normally and puts out the full
> rated output. The amp then usually waits 2 to 4 hours to go to Fault 20
> during normal use (xmit 1 to 3 minutes, stand by 3 to 5 minutes or more).
> A wait of 5-10 minutes, then reset via the STBY/OPR switch, is effective
> (works ok) about 70% of the time. The 30% of the time, all other
> variables are the same, including ambient temp. in the shack, but the amp
> will not reset.
>
> 5. In the latter case, turning the whole amp OFF, and back ON after a
> 5-10 minute wait gives full operation again in about 90% of cases, but
> does not produce consistent full operation because amp goes back to
> pattern noted in paragraph 4 above (that is, again at 25C).
>
> 6. Note that the LOWER shack temp. seems to be the only variable that
> occurs along with the Fault 20 failures. The amp has the factory added
> external fan, the internal blower puts out equal and good air volume, and
> none of the vents are obstructed.
>
> 7. Any help and advice short of sending it to factory will be very much
> appreciated. 73,
>
> Charles Harpole k4vud@hotmail.com
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|