05-28-2007 Ver 0.1

Equipment:

Astron DC Power Supply
35 Amp
Legacy 'Linear' model series

Model Number:

RS-35A and RS-35M

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Complaint:

1. LM723 Regulators 'blow' or performance becomes degraded after some period of use

   Solution: Extend device life by limiting the maxiumum current output from the LM723 IC by placing a 100 Ohm R in series with it's output pin

   One of the symptoms seen when the LM723/uA723 becomes troublesome is voltage 'sag' at moderate current levels of only 7 to 10 Amps; Replacement of the LM723 solves the problem. It is surmised that high start-up currents (at power supply turn-on into various high-capacitance loads) may be injurious to the LM723 and repeated on/off cycling weakens the output circuitry in the LM723.

   Recommended: Add a swipe of WD-40 to the pins before inserting the 14-pin DIP packaged 723 back into it's socket. A compound qualified to MIL-L-87177A Grade B sold by Lektro-Tech as Super Corr B (MIL-L-87177A) is also quite suitable. See also the references section below for more discussion/papers on corrosion inhibiting compounds suitable for use in and on electronic systems.

2. No bleed-off of unreg DC filter caps

   Solution: Add bleed-off resistor across main unreg filter caps.

   Additionlly an LED was added inside the power supply and provides an indication if unreg DC voltage is present (this is a simple, permanent aid for troubleshooting).

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Identify the power supply; View of circuit board in power supply with cover removed:

The added LED can be seen pointing up just outside the right edge of the printed wiring board.

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Schematic excerpt showing mod - locate Reference Designator Q2 and note the indicated insertion of a 100 Ohm resistor:

Note: The indicated location on the schematic may not be the precise location of the part on the actual printed wiring board.

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Picture showing the added 100 Ohm resistor and the foil cut - the left end of the resistor is connected to the pin 10 pad on the LM723's foil:

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Another picture showing the added 100 Ohm resistor and the foil cut -

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Schematic excerpt showing bleedoff resistors and LED and series 3.9 kOhm resistor:

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Added LED and 3.9 kOhm resistor - The anode end of the LED is soldered directly to the (+) foil and there is black heat shrink tubing on the other lead to the 3.9 K resistor to (-).

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Added LED and 3.9 kOhm resistor - Anode soldered directly to (+) foil and the 3.9 K resistor to (-).

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LED mounted to PWB inside power supply is visible through vent-slot 2nd from right on rear of top cover:

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Block Diagram

N/A

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Electronic Schematic Diagram

Available on the web

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LM723 Regulator

N/A

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Testing

N/A

Tests

...

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References/Link summary:

• BELL LAB’S CORROSION PREVENTIVE COMPOUND (MIL-L-87177A GRADE B) (pdf file size: 8 MB)

    BELL LAB’S CORROSION PREVENTIVE COMPOUND (CPC) (MIL-L-87177A GRADE B)
  
    - ELECTRONIC EQUIPMENT FAILURES PLAGUED BELL SYSTEM AT BOTH 
      AREAS PERCEIVED OK ENVIRONMENTALLY AND KNOWN CORROSIVE, i.e.
  
      o SNOWCAT TO MONTANA MICROWAVE TOWERS,
      o FREQUENT FAILURES AT COSTAL ENVIRONS EVEN WITH GOLD/GOLD CONTACTS;
  
    - CHEM ENG INVENTED A CORROSION PREVENTIVE COMPOUND (CPC) TO 
      IMPROVE RELIABILITY;
  
    - AIR FORCE MATERIALS LAB (NOW AFRL) WROTE MIL-L-87177 TO DESCRIBE 
      THE BELL LABS CPC.
  
     ...
  
    - THE RELIABILITY OF EVERY U.S. WEAPON SYSTEM THAT USES 
      ELECTRONIC PARTS MAY BE INCREASED BY USING THIS CORROSION 
      INHIBITING LUBE IN THEIR CONNECTOR SETS
  
    - MANY OTHER USES FOR THIS CPC COULD BE BENEFICIAL
  
    - COST IS SHOWN AS PRIMARY BENEFIT BUT EFFECTIVENESS & SAFETY 
      FOR OUR TROOPS IS EVEN MORE IMPORTANT
  

• EFFECTS OF CORROSION INHIBITIVE LUBRICANTS ON ELECTRONICS RELIABILITY

  Abstract - All electrical connectors corrode – even high quality gold plated connecting surfaces are not immune from the laws of physics.

  Thin and often invisible insulating films can form on the surfaces of electrical connectors. Such corrosive films are produced by the reactions of natural environments with the elements used in the manufacture of commercial and military electrical connectors. Such films may represent a significant source of faults such as Cannot Duplicate (CND) and Retest OK (RETOK) faults.

  USAF studies for the last twenty years have shown that application of certain corrosion inhibitive lubricants (CILs) or corrosion preventative compounds (CPCs) can substantially impact CND and RETOK rates thus improving avionics reliability. This paper addresses prior research and current operational and depot level application of CIL/CPCs in the Department of Defense (DoD).

• "Corrosion Control Even With Gold Connectors; corrosion preventive compounds (CPC)

  Discussion on Collins Listserve about corrosion.

• MIL-L-87177 Lubricant Bulletproofs Connectors Against Chemical and Fretting Corrosion (Warning: pdf file size = 161.9 MB)

  Abstract - Electrical connectors corrode. Even our best SA and MC connectors finished with 50 to 100 microinches of gold over 50 to 100 microinches of nickel corrode. This work started because some, but not all, lots of connectors held in KC [Kennedy space Center] stores for a decade had been destroyed by pore corrosion (chemical corrosion).

  We have identified a MIL-L-87177 lubricant that absolutely stops chemical corrosion on SA connectors, even in the most severe environments.

  For commercial connectors which typically have thinner plating thicknesses, not only does the lubricant significantly retard effects of chemical corrosion, but also it greatly prolongs the fretting life.

  This report highlights the initial development history and use of the lubricant at Bell Labs and AT&T, and the Battelle studies and the USAF experience that lead to its deployment to stop dangerous connector corrosion on the F-16.

  We report the Sandia, HFM&T and Battelle development work, connector qualification, and material compatibility studies that demonstrate its usefulness and safety on JTA and WR systems. We will be applying MIL-L-87177 Connector Lubricant to all new connectors that go into KC stores.

  We recommend that it be applied to connectors on newly built cables and equipment as well as material that recycles through manufacturing locations from the field.

• Stationary Lubricants Increase Connector Reliability

• Polyphenyl Ethers: Lubrication In Extreme Environments

  Table from EFFECTS OF CORROSION INHIBITIVE LUBRICANTS ON ELECTRONICS RELIABILITY above: