[Amps] Alpha 87A Fault 20 Problems and General Questions

[Dave Haring]

When powering up, we get a Fault 20. After clearing with Stby/Operate, it
recurs from from time to time and switches the amp to Standby.
The unit has date code 9408, s/n 0614. Software is version UPX-X 108-G.

An internet search did not reveal that units with a Fault 20 normally
experienced high filament current, but pointed to possible high-resistance
contacts at connectors or aging monitoring circuitry and components such as
C27, and C28 as likely suspects.

Manual selection of bands and sub-bands worked properly when the amp was
not faulted. Changes were also successfuflly done using a terminal program.
When connected with a terminal program (https://putty.org/), we tried the
commands listed in the 2005 manual... but a few were returned as Syntax
Errors (perhaps the manual was more current than the software in the amp?),
and possibly needed additional parameters which were not documented. These
are the commands from the list which did not work or function as expected,
and no explanation or example was found in the manual:

DM# (“use with factory help”)
ENT

The HELP command listed many commands; the following were were ones not
listed in the manual:

ADS
ANTENNA
GPIO
AD
KEY

Here are the questions:
1. What’s recommended for our next steps to resolve this Fault 20 issue?
Start with Deoxit on the contacts in the Filament Sense line as suggested
by N8RR and respondents, and then follow up with possible capacitor
replacement if the problem continues?
2. Are the AlphaMax chips and associated software still available somewhere
for owner installation?
3. Are there more complete instructions available anywhere on the command
set, and any needed parameters to use them? Including the DM# command, and
how to use it? Why might some of them not work - no AlphaMax, or something
else?
4. Though hopefully not needed in the future, how is the Hard Fault lock
cleared? I can’t find anything online.
5. We’re uneasy using schematics that are probably a lot more recent than
this amplifier. Are older schematics available? I expect there are
differences...

thanks in advance,

Dave N3AC