[Amps] Alpha 87A Fault 17

[Charlie Young]

By the way, these opens were not in the plugs.  The problem was in the wires.  I reused the plugs in both cases, splicing the new wire into the old wire coming out of the plugs about 1 to 1.5 inches behind the plug.


________________________________
From: Amps <amps-bounces at contesting.com> on behalf of Charlie Young <weeksmgr at hotmail.com>
Sent: Tuesday, January 10, 2017 12:19 PM
To: amps at contesting.com
Subject: Re: [Amps] Alpha 87A Fault 17

The 1994 vintage Alpha 87A that I repaired for a friend was picked up by him on January 9.


The amplifier, when tested on my antennas, made 1.5KW output on every band using about 60 watts drive with no faults or problems of any kind.


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.


The second harness issue was an open wire between the TR output module and the tube deck compartment in the operate relay circuit. The input and output relays are in series, fed from a 34VDC driver on the microprocessor board.  The open wire was in the circuit between the negative side of the input relay coil and the positive side of the output relay coil, preventing the relays from closing.


The harness failures must be related to the blower change that my friend performed on his amplifier, but close inspection failed to reveal any wires that were pinched.   The AC input module, if one is not careful, could pinch the wire harness but these were clear.  The harness makes a 90 degree transition behind the AC module into the Output TR  module and below it, where the harness runs over to the tube deck enclosure.  The wires then make another 90 degree bend and enter the tube deck enclosure.


There is an opportunity for the blower housing to pinch the wire harness beneath the Output TR module, but these wires were in the clear.   At the opening where the wires enter the Output TR module, the sharp edges are bushed by plastic inserts, which were in place.  Where the wires enter the tube deck enclosure, the sharp edges of the opening are bushed by foam rubber pads, which were in place.


After failing to find any obvious problem with cut wires or harness pinching,  I consulted with the amplifier owner.  The options were to replace the open wires and hope for the best or to partially unravel the harness  and pull the affected wires, so we could observe what happened to them.


If the owner didn't pinch the wires during the blower installation, the problem could have been caused by simply moving the wires around. Both the Output TR module and the tube deck enclosure must be moved for the blower install.

In the end, the owner elected not to risk further damage to the wiring harness by partially unraveling it.


I would like to know exactly what happened to the wires in the harness but agreed with the owner we did risk additional problems by moving the wires around.  These are very stiff, stranded wires.


It is possible the wires were pinched at one time and this problem was corrected before I got the amp.



I will likely see this amp again, but hopefully the situation will remain stable as long as the harness is left alone.


73 Charlie N8RR





_______________________________________________
Amps mailing list
Amps at contesting.com
http://lists.contesting.com/mailman/listinfo/amps

Amps Reflector - Contesting.com Ham Radio Mailing Lists<http://lists.contesting.com/mailman/listinfo/amps>
lists.contesting.com
Welcome to the Amplifier mailing list! This list is intended for the exchange of information on HAM RADIO Amplifiers related topics ONLY. Our goal is to keep ...