The Fault 20 topic was just discussed on the Yahoo Alpha 87a Group a few days
ago. John Stanford KF6I (www.islandamplifiers.com) provided a detailed
explanation and schematic as to why this tends to occur with aging connectors
adding a bit of resistance (50mOhms ach) enough to increase the voltage drop by
0.3V acrossing the sensing resistor (via opamp) so the microprocessor) sees
>4A when 3A is the warmed up filament current. Yes cleaning the connectors
J3-3 and J7-7 with Deoxit is the usual solution.
The only publicly available schematics is what has been on line for many years.
There have been many updates on the 87a over its manufactured lifespan but I
have not seeen anyone discuss the differences except in the voltage supply
circuits.
Attached is instruction to clear Fault 99
I believe your ROM version 108 is the last before the 1.00 AT Alphamax. The
last owner of Alpha (I lose track) had them in stock.. you can also check with
Brad:
K0HM Electronic Repair
Brad Focken
6288 Gunshot Pass Dr.
Colorado Springs, Colorado 80917
Phone: 719-629-7045
Phone: 303-579-5173
Website: www.k0hm.net
73 Jerry NY2KW (ex-K1JOS)
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Dave Haring
Sent: Saturday, February 9, 2019 3:24 PM
To: Amplifiers <amps@contesting.com>
Subject: [Amps] Alpha 87A Fault 20 Problems and General Questions
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
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