[Amps] Alpha 87A Fault 17

[Jim Brown]

Hi Charlie,

40 years ago, my job was field service of audio and video systems, many 
of them large and spread out. Experience taught me that the first thing 
to look for was a short to ground, which nearly always accompanied cable 
damage, and which nearly always accompanied work by some building trade 
in the area of the wiring. At Wrigley Field, I was often able to quickly 
find damage to loudspeaker wiring by asking where building trades had 
recently been working. The same techniques applied to low level wiring 
(like mics and control lines).

There are other reasons for Fault 17, and I've encountered them with a 
newly acquired 87A that seems to be in excellent shape. One is a memory 
tuning that doesn't come close to matching the load, and the amp 
instantly faults to 17. This can be tricky to solve, but I've done it at 
least once by copying a memory setting from a nearby band segment to the 
band segment in question.

Another cause seems to  have been bad data in RAM -- killing power and 
restarting eliminated the fault.

Based on my limited experience, I would recommend exhausting these 
possibilities before opening up the amp.  I'm not criticizing your 
troubleshooting, which is certainly excellent, but rather to caution 
others not to unnecessarily open a can of worms.

73, Jim K9YC

On Tue,1/10/2017 10:19 AM, Charlie Young wrote:
> Besides correcting a few issues following a blower change, the main problems preventing the Alpha from working were in the wiring harness.  The first issue was an open wire on the Rbias monitor circuit which resulted in a hard fault 1 when the operate switch was pushed.  This wire runs from the TR output module over to the microprocessor board.   Not only was this wire open, one side of the wire was at chassis potential.