[Amps] Alpha fault 17

[k2cb at comcast.net]

Good points, Dick.  I seem to recall a similar thought when I first inspected the board. At first glance, I thought there was no issue there.  Only once I removed the coil and scraped away the foam did I see the damage (carbon) on the circuit board itself.   It seems to want to arc near the one end to the left of the amp, where there is a mounting screw close by, and the associated ground plane.    
I also had damage to the winding wire itself, about 1/4" from the board. The end of the wire near the board was brittle, and broke as I handled it. I was able to repair the winding lead without having to rewind the entire coil, but if it was any further into the torroid, I would have had to rewind the entire coil. 
  
While I don't recommend it, you could defeat the safety interlocks, ramp the amp up in rf power, and closely watch the area to see if it arcs when the fault occurs. 
  
A pen cap slid over the HV shorting terminal works well as a temporary defeat. 
  
Eric 
K2CB 
  

----- Original Message -----

From: "Dick Green WC1M" <wc1m73 at gmail.com> 
To: "K2CB" <k2cb at comcast.net>, "ve6jy 1" <ve6jy.1 at gmail.com> 
Cc: Amps at contesting.com 
Sent: Friday, December 9, 2016 12:48:08 PM 
Subject: RE: [Amps] Alpha fault 17 

Some additional points: 

- You may not be able to see evidence of arcing until you remove the choke. 
- You may need to replace (rewind) the coil. Just count the turns and use 
the same gauge/type of wire 
- When my choke coil started arcing, I didn't get fault 17. I got faults 8 
and 9 (and 1, I think). 
-  This was evidence that the arcing damaged one of the transmit PIN diodes, 
which I had to replace. 

Don't use the amp until you attend to the choke coil. You don't want to risk 
damage to the PIN diodes, which are expensive. 

73, Dick WC1M 
  
-----Original Message----- 
From: K2CB [mailto:k2cb at comcast.net] 
Sent: Friday, December 9, 2016 12:54 AM 
To: ve6jy.1 at gmail.com 
Cc: Amps at contesting.com 
Subject: Re: [Amps] Alpha fault 17 

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