I haven't looked at the block diagram to see how the Tune LEDs might be tied
in but I had this easy diagnostic that sounds like it could be affecting
your TUNE LEDS plus give you a fault 17. I found it in my archive from the
original Alpha site "AsktheHams". You should post your question on the
Yahoo groups Alpha 87A forum sometimes Glenn from Alpha monitors and
responds. See below.
73 es HH
Jerry NY2KW
**********************
The Fault 17 is a TUNE, or GAIN, fault. If it is happening on all bands, it
is possibly because of a failed diode (1N5711) in one of the wattmeters.
There are Input and Output wattmeters.
Here are some tests.
1) Connect PC to serial port with a modem program communicating with the
amplifier.
2) With the 87A in STANDBY, transmit through the amplifier with 100 w from
the radio to a dummy load (or antenna with low SWR).
3) On the PC, type EXT ON.
4) On the PC, type GPIO (radio still transmitting 100w). This command
reports Grid current, Plate current, Input power, and Output power each time
it is typed. It should be showing about 100w input and about 100w output. If
one of those is not reading correctly, that indicates the wattmeter diodes
are damaged.
***********************************
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Don Moman VE6JY
Sent: Friday, December 09, 2016 1:38 AM
To: Amps@Contesting. Com
Subject: Re: [Amps] Alpha fault 17
Many thanks for the tip, most appreciate it... however I opened the
shield cover as suggested - the black foam was there but looked pristine,
but I removed it anyway. No signs of any arcing at all. Powered it up and
it faults out as before. Drat. I'll leave it out and put something else
in there, so good PM for the future - if I get it to emit RF again!
That fault explanation doesn't address the TUNE bar graph not moving.
I did swap the tubes out, no difference - as I suspected.
Ignore my comment about the fan at startup - I was thinking of the $@%^&*
ICOM PW-1 that's also in my sick bay....
73 Don
VE6JY
On Fri, Dec 9, 2016 at 5:53 AM, K2CB <k2cb@comcast.net> wrote:
> Do a search of the 87A Yahoo group regarding the large L1 choke coil
> on the RF output wattmeter / pin diode / bypass relay module near the
> rear antenna jack. Don't quote me on the exact part designation, as I
> am not at my desk top at the moment, but it is the large green one on that
board.
>
> Remove the four screws and shield cover. You will see a large green
> wire wound choke coil. Alpha placed a piece of black foam between the
> coil and circuit board as an insulator.
>
> This material is breaking down over time, and causing the coil to arc
> over to the ground plane of the circuit board. It will get worse over
> time, and the fault 17 will occur with less and less rf output power as
time goes on.
>
> Remove the choke from the board, remove all the old foam pad, clean
> off any carbon on the circuit board from the arcing , and install a
> replacement piece of insulation material. I used some thin black
> plastic. Then reinstall the choke coil.
>
> If you must remove the entire circuit board, be especially careful
> with the pin diode mounting and associated insulators. They are
> somewhat fragile.
>
>
> If you like, I can send you some pictures I took of the last 87A I
> repaired with the same problem. The photos are on my desktop. I can
> send them tomorrow when I get back to my office.
>
> FYI - Credit is due to Brad from Alpha (or whatever their name is this
> year!) for originally suggesting this as a possible Fault 17 cause.
>
> Eric
> K2CB
>
>
>
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