If the bias voltage is OK, I would suspect a problem with one or both TX pin
diodes. This can be caused by arcing from L1 on the T/R board. There's a
rubber insulting pad under the inductor that disintegrates over time,
allowing the coil to arc to the PCB, a nearby screw, etc.
I would start by carefully examining L1 and the area around it for any sign
of arcing (black char, bare coil wire, etc.) If it's present, the coil
should be removed, the old rubber insulator cleaned away, a new rubber
insulator put down and the coil rewound. It's possible to do this without
removing the T/R board by clipping the coil leads and soldering the new coil
to them, but it's a little tricky.
If L1 has not been arcing, then it might be a breakdown of one or both TX
PIN diodes due to age, faulty part, etc.
In any case, since you're getting a reduction of receiver signals, I would
suspect that one or both TX PIN diodes will have to be replaced.
73, Dick WC1M
-----Original Message-----
From: George Fremin III <geoiii@kkn.net>
Sent: Monday, October 29, 2018 11:45 AM
To: amps@contesting.com
Subject: [Amps] Alpha 87a Fault 9
I have an Alpha 87a that is presenting the following symptoms.
When switching from standby to operate I get a reduction/loss of receiver
singals.
When the key line is grounded the amp faults with code 9.
The manual says this about fault 9:
"Transmit PIN diode forward current below minimum require value key down."
I have done a fair amount of searching on the web and I have not found
anyone describing a fault 9. K4RO had fault 8 witch is similar but it is on
"...key up." instead of down.
I have done some poking around with my volt meter.
The RX pin diodes seem to be checking OK as far as I can tell with them in
the curicut per the troubleshooting described here:
http://www.alpharfsystems.com/wp-content/uploads/2016/05/Alpha_87A_Receive_L
oss.pdf
I have also checked some of the voltages as described here:
http://www.k4ro.net/k4ro/Aplha-87A/TX-PIN-Diode-Replacement.pdf
I have not checked the TX pin diodes yet.
I will do that later today.
But would like to hear if anyone has any ideas about fault 9.
Thanks
--
George Fremin III - K5TR
geoiii@kkn.net
http://www.kkn.net/~k5tr
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