'85 w123 push button climate control??? - PeachParts Mercedes-Benz Forum

85 DSEL · #1 10-27-2006, 05:35 AM

Can someone tell me what to look for regarding the condition of the solder on the board? Mine is apart and ready to be 'fixed' but not sure if there's any solder issues with mine!

I cleaned the temp wheel and its contacts and put it back together, replaced a couple of the tiny bulbs and managed to break the other two that WERE actually working as I pulled, wiggled, & tugged on the bulbs that illuminate the push buttons! I still need to dig out the bulbs from the little sockets yet.

Any good source for new push buttons?

Any help will be greatly appreciated.

mplafleur · #2 10-27-2006, 02:31 PM

My bulbs were the same. The problem was that they were the replacement bulbs I installed a year ago. They are much hotter than the OEMs and they melted in place. I picked up some frosted bulbs some time ago that are much cooler. I will be looking for those again.

As for the solder, look for hot spots on the board: discolored board material, or solder that doesn't look clean. The solder may have brownish junk around it that shows that the flux has come to the surface. Look at the terminals or leads of the relays, etc and see if it looks like the solder does not flowup on to and up the lead. If it looks like you can see a dark line around the lead, then the solder may have reflowed and you could have a cold solder joint, where the solder does not actually contact with the intended lead or at least a high resistance contact is made.

To resolder these, first heat up the lead and surrounding solder and remove the solder with solder wick or a solder sucker. Then you can resolder the connection with new solder. Do not resolder the connections by just heating up the old solder, or just by adding solder. Remove the old stuff first. You will see a bigg difference between connections that have seen reheated and those that have been cleaned and resoldered.

Jeremy5848 · #3 10-27-2006, 04:44 PM

Although M. LaFleur's method is superior, I resoldered my board the lazy way, by reheating each joint and adding a little fresh solder. Actually, what that does is to add a little fresh flux so that the solder will flow around and adhere to all of the components. I resoldered each joint whether it looked good or bad. The most important joints are where the little side boards attach. As a design failure, the problem is that solder is supposed to be like glue -- it holds things together but there should be metal to metal contact between the components. In printed-circuid board work that doesn't always happen. If the solder joint fails you get an open (or intermittent) circuit.

On my board there were also some burned traces, perhaps due to a failed auxiliary water pump. (If the pump freezes, it will draw too much current and fry things in the ACC. The fix is to add a 1 or 2 Amp fuse in line with the pump's power lead.) The burned traces had been poorly repaired so I took it all apart and soldered in new wires to replace the burned traces. Once that and the resoldering was done, my system came back to life.

Jeremy

85 DSEL · #4 10-27-2006, 08:00 PM

Thanks for the replies!

While I tend to try to do things the "right" way I'm so inclined to go out and buy a solder wick! However, in real-time I am most likely to do as Jeremy suggests - seems to have worked for him! I know, I know - give it a while and it will be broken again!

Soldering. I'm pretty durn good at it...on my copper pipes at home!

I went out to Radio Shack and purchased a 25w iron and some real tiny "High-Tech Silver-Bearing solder". Do I actually touch my iron gently to the leads sticking out of the board to heat it first then touch the solder to the iron and let a small drop settle in around the lead?

A "trace" I assume is a silver "path" that goes all over the board?

There is some brownish discoloration on part of the board that I think has been referred to so I'll attempt to redo those. Thanks again for your help and support! You guys are great...