Male Mini-DIN Soldering Issue

I agree about using a VERY hot iron; I started with a 40 W one, as time was to lonng, jumped to 60 and finally to 150W, You are right, this job needs at least 4 hands, so I held the plastic isolator with the pins on it on a vice. I did tin the wires,,,, but not the terminals.... (that might have been my mistake). Thanks for the idea, I´ll try it out tomorrow!

If a 25 Watt doesn't do the job, you'll need to clean the contacts first and get a fine point soldering iron. Go also for the thin 50/50 lead- tin solder with flux inside. You should warm up the pin ends to about 200 a 250 degrees Celsius and then add the tin, pointing it against the tip of the iron, that has contact with the pin, Just let a small amount of the tin melt to the point and use that to make a better heat contact with the pin. You should add tin solder to the pin, otherwise you risk a "cold" solder point. You might be working easier fixing the plug to have more play with you fingers. I always did it in the hand, but I probably soldered hundreds of them. Let your iron warm up first and work with a lot of light. If you have dropped solder that connect 2 pin, you clean your tip an collect some on it or use a stranded string of fine copper or tinned wire to suck it up when you heat it with your iron. A fine tip and clean carbon free tip is what you need.

EUREKA! Based on trial and error + your tips, I finally got a decent job done: the aid of a "primer" (contacts cleaning acid) and a better solderer (220V / 60W) was the clue to it. First, I dipped both the nude end of the cable and the back of the pins in the primer for some sec´s. To prevent movement, I constrained the DIN socket in a bench vise. With the aid of a magnifying glass with light each part to be soldered was heated up in sequence, to place a drop tin on each. Then I slightly pressed the tip of the cable against the corresponding terminal and heated both parts wit the tip of the iron. parts got properly soldered when tin acquired a silvery shine. Thanks to you all

Since the job is already done, it's probably too late to remind you not to use acid flux. But, it is not too late to suggest that you flush the connections with lots of water. Your acid flux will, over time, make the wires go away. Good luck.

I have not yet met the hobbyist who likes to solder DIN connectors.

My GA to Just and the previous to this about using acid flux in electrica soldering. Also too late, as I always do to used heat shrink tubing over each connection. Makes a big difference in longevity of any given connection.