Miata Mailing List: October 1995, Message #24
sponsored by



     


   From: Sean Timm 
Subject: REPOST: Radio & Humidity
   Date: Mon, 2 Oct 1995 00:47:27 -0400

For the person who requested the info, and for others who missed it the 
first time...

On Thu, 21 Sep 1995 MazdaClub@aol.com wrote:

> Miata Radio On/Off Switch Fix
> 
> Jeff Anderson from the Capital Chapter - Mazda Sportscar Club of Washington
> forwards the following as a proposed solution to the Miata Radio On/Off
> Switch problem.  Jeff's narrative is as follows:
> 
> "If your stock AM/FM Miata radio does not always turn-on I've found a simple
> no-cost fix that almost anyone can do.  This common problem is widely
> reported on the Internet and other places.  As Miatas age the problem often
> occurs in high humidity conditions and may occur when the car has not been
> used for several days.  It's far more difficult to do the simple task of
> removing the radio from the dash than it is to perform this "fix". 
> 
> Once the radio is removed, or at least pulled out from the dash far enough to
> expose the plugs on the rear of the radio, pull out the round black plastic
> plug with the finger-hold black plastic loop.  After you remove the plug look
> down inside of it and you'll see four metal pins.  This plug is called SHORT
> PLUG on page T-119 of the 1991 workshop manual.  
> 
> Next you'll need a piece of un-insulated solid wire to make a jumper
> connection into the black socket on the back of the radio between pins #5 and
> 11.  Match the wire's gauge (wire diameter) to the metal pin size in the
> black plastic plug you removed -- it's about 20 gauge.  Bend the jumper wire
> in a "U" shape with sharp 90 degree angles.  The bottom width of the "U"
> should match the spacing between socket pins #5 and 11 -- 0.22 inch.  The
> sides of the "U" forming the pin connections should each be about 0.3 inch
> long.  
> 
> Press the U-shape jumper wire you made all the way down into pins #5 and 11
> of the radio's socket and replace the SHORT PLUG -- you've fixed the "on
> switch" radio problem.  
> 
> Note that the pin numbers are labeled on the radio's socket but you may need
> a magnifying glass and good light to see them.  Looking at the radio, top-up,
> from the back, Pin #5 (ground) is the socket hole on the far right, center
> row.  Pin #11 is on the bottom row, second from the left.  The workshop
> manual says pin #11 is "NC" (no connection).  However, inside the radio it's
> not.
> 
> If you need instructions on how to remove the radio, see DASHBOARD AND
> CONSOLE Removal in a Miata Workshop Manual -- pages S-52 to S-54 in the 1991
> manual.  One hint, don't be discouraged when removing the Center Louvers --
> the pull string (rope may work better) you loop through may need to be pulled
> VERY hard the first time the louvers are removed.  Don't forget, you must
> know your anti-theft code before disconnecting the battery or radio.
> 
> I found through disassembly of the radio and lengthy experimentation that the
> radio's turn-on problem results when a minuscule amount of moisture forms
> between the bottom of the SHORT PLUG socket and the printed circuit board
> that it is mounted on.  When any detectable amount of condensation forms on
> the printed circuit board a conductive path is produced between pin #11 and
> other nearby positive voltage sources.  The circuit associated with the
> unused pin #11 is a very high impedance one that if allowed to go positive
> prevents the radio's turn on.  This type of printed circuit board problem
> generally becomes worse over time due to the greater conductivity of water
> when it is mixed with dust.  The "fix" jumper ties pin #11 to 5 (ground) and
> prevents pin #11 from going positive.  I recognize that this may not be the
> most professional repair of the radio's design problem, but it is one that
> anyone can do for free (not counting the cost of less than an inch of wire).
>  
> 
> I don't know if this "fix" solution will work with installations that have
> the CD player -- I don't have the CD.  The SHORT PLUG is used to substitute
> for the CD player's plug.  With the CD player plugged-in the added fix-jumper
> will likely interfere with the CD player's additional plug connections.  Pin
> #11 may be used (independent of what the book says) for turning the radio off
> when the CD player is used.  In this case a 10K ohm resistor from pin #11 to
> ground may be a solution." 
> 
> Sincerely,
> Dave Nugent
> 
> 
> 

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
	  Sean C. Timm		   sct2m@fermi.clas.virginia.edu
                URL: http://fermi.clas.virginia.edu/~sct2m
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-