[Amps] 87a Fault 9

[Dick Green WC1M]

First, I¹d like to echo Paul¹s comments about the 87A. Like all equipment,
it needs maintenance from time to time. But I¹ve been able to keep mine
running for over 15 years. Alpha has always been extremely helpful and
effective at diagnosing and resolving problems.

Second, I recently had a bout with faults 8, 9 and 11. I think I posted a
writeup on this reflector about it not long ago. You can search for it on
the website.

My problem was a little different than yours in that it caused a sudden
failure of the amp on transmit, after which it wouldn¹t transmit without
producing one of the above fault codes. Eventually the amp wouldn¹t even
warm up without faulting. With Alpha¹s assistance, I found that one of the
transmit PIN diodes was blown. After replacing it, the amp worked OK until
it got to about 1500W, then it would fault again. I think it was fault 11 or
9, but I don¹t remember. Anyway, Alpha once again helped me troubleshoot,
which led to discovery that the insulator pad under L1 on the T/R board had
partly disintegrated over the years, allowing the inductor to arc to the
ground plane of the circuit board underneath. The repeated arcs had dug a
nice hole in the board. The arcs were undoubtedly responsible for the faults
related to PIN diode current, and ultimately killed one of the transmit PIN
diodes. Luckily, I found the root cause of the problem before blowing
another very expensive transmit PIN diode.

If you¹re know how to work inside amps, and are comfortable doing so, UNPLUG
THE AMP, remove the cover, and remove the small perforated cover over the
T/R compartment. Look for burned or charred areas on the T/R board,
especially near and under L1. Remember to replace both covers before you
plug the amp in again.

I repaired L1 myself by removing it, cleaning off the old insulating pad,
cleaning up the PCB, installing a new insulating pad (a piece of rubber
sound insulation mat), rewinding with the correct gauge magnet wire, and
reinstalling L1 with a layer of silicone between it and the insulating pad
for mechanical stability and more insulation. I was able to do all this
without removing the T/R board, which is a bit of a chore.

Of course, your problem might not be caused by L1. It could be caused by a
problem with the LV supply. Alpha has some troubleshooting steps you can
follow to try to isolate the cause, but since it sounds like it happens
intermittently, I would check for evidence of arcs at L1 first.

Hope this helps.

73, Dick WC1M


On 1/3/11 9:07 AM, "Paul Christensen" <w9ac at arrl.net> wrote:

>> > I have been plagued for years with my 87a giving Fault 9.  Been back to
>> > the clowns at Alpha several times for same problem.  The 87a may be
>> > Alpha's big mistake in their line.  Piece of junk.
> 
> I think that's a bit harsh, Chuck.  There are many 20 year-old, problem-free
> 87As performing very well on the bands every day.  There's a reason why it's
> faulting and it's a matter of uncovering the root problem.   It's easy to
> say that there's a design flaw when it's you that has the burden of
> isolating a persistent problem.
> 
> By now, you know the fault is relates to "transmit PIN diode forward current
> below minimum."  But, the problem may be indirectly related to something
> like the LV power supply or arcing on a wiring harness, for example.
> 
> I know that Alpha has the means to isolate these types of faults, including
> quick component and/or board substitutions.  Since it's been back to them
> several times, is it an intermittent fault, occurring only occasionally?
> 
> Paul, W9AC
> 
> 
> 
> 
>