Rick,
Fault 17 means abnormally high or low gain. The CPU measures the power in
and power out. If the ratio is out of normal specs, the fault is generated.
This can be caused by a number of things, including high input SWR or
excessive drive.
The answers to a couple of questions might help diagnose the cause:
1. Does the fault occur on every band, certain bands or only one band?
2. What kind of transceiver are you using?
If the fault does not occur on every band, my guess would be a bad input
wafer on the band switch. I used to get fault 17 every now and then on 10m
and thought it had something to do with the antenna, RFI, etc. Sometimes it
happened a lot, other times not. It seemed if I pulled back on the drive it
would happen less. I lived with this problem for 10 years. Then last year I
started getting the fault every time I transmitted on 10m. There are no caps
in the output network on 10m, so I suspected the bandswitch or input
network.
When I first got the 87A, I had a problem with high input SWR on 15m, and a
tech at Alpha talked me through a procedure for determining if the
bandswitch was properly registered on that band. This involved patching the
firmware to land the switch slightly ahead or behind of the factory setting.
This solved the problem. When the constant fault 17 on 10m occurred, I tried
the switch alignment procedure on 10m, but it didn't fix the problem. (It's
possible when you sent the amp in they adjusted the bandswitch parameters.)
Alpha said the fault could be caused by a weak finger on one of the
bandswitch wafers, which can be remedied by gently bending the finger with a
pair of dental pics (not for the faint of heart.) None of the fingers
appeared to be weak, but I adjusted the fingers for 10m. I also cleaned the
pads and underside of the fingers with tuner cleaner. Still had the problem.
Inspection of the schematic revealed that 10m and 12m use the same output
path. So, I manually rotated the bandswitch to the 12m position and
transmitted on 10m (NOTE: THIS REQUIRES DISABLING THE INTERLOCKS -- DO NOT
DO THIS UNLESS YOU HAVE EXPERTISE WORKING AROUND HIGH VOLTAGE -- LETHAL
VOLTAGES ARE PRESENT.) After I rotated the bandswitch manually, no fault 17!
Using the bandswitch adjustment procedure I learned from the tech at Alpha,
I was able to patch the firmware to position the switch in the 12m position
when 10m is detected. That allowed me to use the amp on 10m, though I
couldn't quite push it to maximum power.
This ruled out a problem with the output network and output wafers on the
bandswitch, and pretty-much implicated the input network. I inspected and
cleaned the input wafer, looked for band components on the input board, etc.
I couldn't find anything (the wafer and board are in a small compartment
behind a panel underneath the amp.) Finally, I gambled $75 and sent for a
new input board, which comes with the wafer already mounted. It was
relatively simple to replace (requires soldering and desoldering skills.) Lo
and behold, the problem went away. My guess is that the input wafer was bad
from the start and progressively got worse. It's not a high-quality part.
If the fault occurs on every band, I would suspect the rig. Certain brands
(like ICOM 781, Kenwood 940/950) put out a leading-edge spike that can be as
high as 250W (yes, from a 150W rig.) You would expect this to cause an
"excessive drive" fault, but the 87A firmware checks for abnormal gain
*before* it checks for excessive drive and thus returns a fault 17. Dick
Ehrhorn confirmed that "bug" here on the AMPS reflector years ago. You might
be able to deal with this by adjusting the rig's ALC. Otherwise, you may
have to switch rigs. When I got rid of my 950SDX, the problem went away
(except the fault 17 on 10m.)
Hope this is helpful.
73, Dick WC1M
> -----Original Message-----
> From: Rick Boulis [mailto:n4hu@mindspring.com]
> Sent: Sunday, February 12, 2006 1:24 PM
> To: amps@contesting.com
> Subject: [Amps] Alpha 87A
>
> I have a 87A that I bought new in 2000. It has low hours and
> until yesterday hadn't been turned on in 2 1/2 years. Now it
> showing fault #17 when keyed into antenna or dummy load. Any
> output around 100W or more causes the fault.
>
> Its seems to me that shortly after I recieved the amp that I
> had the same problem. I removed the transformer to lighten
> the weight and returned the unit. The factory repaired the
> problem with no exlplaination and no charge.
>
> Can someone make a suggestion? Is there a repair facility?
>
> Thanks
>
> Rick
> N4HU
>
>
> Rick Boulis
> n4hu@mindspring.com
> EarthLink Revolves Around You.
>
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