As mentioned earlier in this thread, when I first received my DRO's one of them had a loose connector where the cable plugs in, so I took it apart to fix it. The reason the connector was loose was because of cold solder joints. The solder did not wick up onto the connector pins nor the housing. This is caused by a lack of wetting action where oxides on the metal surfaces of the components to be soldered are eliminated by the solder flux so the solder can form a molecular bond with the metal. Solder only flows where the metal has been wetted. I had to hand file the housing surface somewhat to get the solder to take, but I digress.
While nosing around the PCB I noticed they did not send the PCB through a cleaning cycle to get rid of the dross (flux residue). Over time, this dross can contaminate the solder joint and cause it to fail. That is one reason why the better manufacturers run their assembled PCB's through a washing cycle after they go through the wave solder machine. But I'm still digressing. :big:
I also found a few spots where the solder did not wick up onto some of the components as it should have. The solder, when heated thoroughly, should flow up onto the legs of the components and make a volcano-shaped fillet as it does so. If it looks like a blob instead of a volcano shape, it has been cold soldered (the wetting action did not take place) and will prematurely fail. I went around the entire PCB and touched each solder pad with a fairly thin soldering iron tip (PTA7, 700 degree).
You can do the same with most any electronic soldering iron (not the gun type). I don't know if that is the cause of your malfunction but it is certainly worth the effort to rule out that being the cause of this or future intermittent behavior.
-Trout
