MD41-524 troubleshooting

[SantosDumont]

My MD41-524 annunciator has been giving me issues lately, it has been giving an intermittent signal to my HSI. Today I did some troubleshooting laying underneath the panel and when I wiggled the connectors on the back of the MD41 I was able to reproduce the intermittent signal.  I’m not sure if the issue is the connectors on the MD41 unit or the cable coming into it. 

What’s the easiest way to troubleshoot further?  Do I need to find another MD41-524?

[N201MKTurbo]

It is most likely In the cable and connector not the unit itself. The wires coming out of the connector can move with vibration and over the years can fracture internally, usually at the interface between the stranded wire and the solder. The point where the solder stops wicking up the wire is a high stress point and usually inside the insulation and/or heat shrink tubing. When the wire fractures at the high stress point it is held in place by the heat shrink so it looks fine but is broken inside. This causes the wire to make an intermittent connection as it is physically moved by vibration or wiggling the cable.

[carusoam]

A picture of the device, in case somebody didn't know what you were referring to...

Best regards,

-a-

[SantosDumont]

I’m not convinced it’s the cable. I played with it some more today and took the 524 out of the panel to clean the contacts and I could hear parts sliding around inside. I figured it was broke and out of warranty anyway so I took it apart and a screw and nut came out that were sliding around in there. I also examined the cable ends and I couldn’t find anything that seemed loose or un-soldered. Put it back together, plugged the cables in and it seemed to work while vibrating the cable.  

Then I put it back in the panel and vibrating the cable did nothing... so it seemed like it was working.  So I went to zip tie the cable to the frame and I found if I pushed the connector slightly so it moved the MD41-524 connector it would lose signal.  My thoughts are that those screws that came out were securing the boards inside the MD41 somehow and they are shorting each other when the plane vibrates them  

I found a MD41-534 on eBay which is the vertical mount version but should work for troubleshooting. 

Edited January 3, 2018 by SantosDumont