Shortcuts for CC amp re-soldering? - PeachParts Mercedes-Benz Forum

Maroon 300D · #1 10-30-2006, 11:55 AM

I just re-soldered my cruise control amp over the weekend. I did every point on the board except the ones for the long rectangular boxes that looked a little different from the rest. I figured those were the microchips that the guy who wrote the DIY on here said he didn't re-do. I decided to follow his lead.

I think it worked; I re-installed it and the cruise works. I don't know if it's totally fixed for sure, though, as the problem was that it wouldn't hold speed when it was cold out, almost always at night. I tested it in the evening.
Kind of chilly, but not enough to know for sure.

Anyway, it took a little while to re-solder all those points. I began to wonder if certain points are usually the culprit on these boards, and if I was fixing things that didn't need fixing. Does anyone have an answer to that? Are there shortcuts for this project that people undertaking it should know about?

Kynetx · #2 10-30-2006, 02:45 PM

I read that that joints for the connector are the usual culprits. I tried just doing those and had no luck.

Maroon 300D · #3 10-30-2006, 02:50 PM

Quote:

Originally Posted by Kynetx

I read that that joints for the connector are the usual culprits. I tried just doing those and had no luck.

Would those be the joints all the way toward the end of the circuit board where the pin connector is? The one that faces down when the unit is in the car?

I was thinking that those were the probable culprits. It's interesting that it didn't help you, though.

Kynetx · #4 10-31-2006, 11:28 AM

Yeah, those are the ones. To be perfectly honest, I just re-heated the solder and then read after the fact that the joint needs to be de-soldered first and then resoldered. I'm bringing some solder wick home today to redo it.

barry123400 · #5 10-31-2006, 03:35 PM

Somewhere there is a list of modest priced parts to change out on the board if your problem is not gone. I supect they are dried out capacitors mostly. Might be in the archives. Since you are bringing home solder wick from work you could probably cope with the changes. These are known failure items and as I mentioned really cheap if you have a good source. I have always wondered if the heat going up the component leg has reactivated some old part or if it is indeed just poor solder connections. I guess it could be the result of a poor wave soldering bath at time of production leaving a lot of marginal connections as well. It only takes one cold type joint to upset the apple cart. I wish there were schematics around for various mercedes modules. I suspect they would be very easy to troubleshoot with extension harnesses. They just want too much to recondition them. I repaired an idle control unit last night that had a rebuilt sticker on it from years ago. 1985 126 380se. There was some evidence I re repaired the original failure mode again. No active shorts but just a voltage divider network gone open. Almost like the original resistor sizes were not quite robust enough to go the distance. Will submit it to an active test in the next couple of days but should be okay. This module is pretty expensive new for what it is.

Maroon 300D · #6 10-31-2006, 03:39 PM

Quote:

Originally Posted by Kynetx

Yeah, those are the ones. To be perfectly honest, I just re-heated the solder and then read after the fact that the joint needs to be de-soldered first and then resoldered. I'm bringing some solder wick home today to redo it.

I'd never read that. I just re-heated my joints and in a few cases I added a little solder.

I think my problem is solved (knock on wood). My wife was driving the car last night and the cruise was working fine. Previously I would have expected it to not work fine in that situation.

barry123400 · #7 10-31-2006, 03:58 PM

Just re doing the joints seems to reactivate at least perhaps 50 percent of them back to good operational status. For how long no one seems to report. They may stay up for years for all I know. After resoldering a lot of people have reported improvemnts but still perhaps a residual problem left over. While others have reported no change. A few cases have located and changed the driver transistors out with more rugged improved conventional units. I expect most the problems on mercedes modules do not involve the intergrated circuit chips. I also supect the rebuilders change out all the usual known common failing items, the shotgun approach. This approach is not confined to mercedes modules. A vast amount of failure items are common faults in production run equipment. Thats how we used to make money years ago. Most the time you zeroed on to the known failure item like clockwork if you were familiar with what you were working on. Somewhere I read the list of parts that should be changed out automatically when servicing this unit. Again they are relatively cheap I believe. In otherwords if resoldering does not repair it you can go further if you wish and can deal with the other items at reasonable cost if you have the aptitude or a friend that has some electronic ability.

Maroon 300D · #8 10-31-2006, 04:10 PM

Quote:

Originally Posted by barry123400

Just re doing the joints seems to reactivate at least perhaps 50 percent of them. For how long no one seems to report. They may stay up for years for all I know. After resoldering a lot of people have reported improvemnts but still perhaps a residual problem left over. While others have reported no change. A few cases have located and changed the shorted or open driver transistors out with more rugged improved conventional units. I expect most the problems on mercedes modules do not involve the intergrated circuit chips. I supect the rebuilders change out all the usual known common failing items, the shotgun approach. Then resolder the board and check it. Somewhere I read the list of parts that should be changed out automatically when servicing this unit. Again they are relatively cheap I believe.

I imagine most of those parts would be a couple of bucks at Radio Shack, although I guess other suppliers have better quality electronic parts.

I figured it was just the solder with my unit. My basis for thinking that was the fact that re-soldering my CCU worked, and my cruise problems only occurred when it was cold. I figured that probably indicated a solder problem. I am certainly no expert on electronics, however.

I'll keep an eye on how my unit works and if it goes out again after a while, I'll report back so there's a record of it on here.

Thanks for the info., Barry. As usual you have a lot to contribute!

barry123400 · #9 10-31-2006, 04:44 PM

I do not wish to sound or imply being critical. For the ones like yours that come back to life by resoldering I really think that is great. I would live with that result willingly myself. My thrust is for the ones that do not and the guy gives up in disgust. Or lives with partial cruise control function. Not perhaps realising there is a second approach. But to be fair and keep it cost effective you would have to have access to an electronic parts outlet to get fair prices. Radio shack would be too expensive in my opinion. The list of parts is long. Perhaps a dozen or so. One known problem was that a certain type of capacitor was used in production that had an unusual high failure rate on these modules. Also some of the earlier transistors were garbage to put it mildly. I have seen many transistor junctions that were heat sensitive for example. I imagine the termination of the lead in the internal construction of the transistor was not really good in design or manufacture. . External heat running up the lead may restore the connection for a period of time in some cases. . This is why I am a little curious how long an average resolder job lasts. If of fairly short duration say six months then we know where to look next for example. If it lasts for years it was probably just a bad solder connection. Your problem was thermal for example and you are right it could be a poor solder or called in the trade cold joint that opened up when it shrank with lower temperatures. Perfectly understandable.

Kynetx · #10 11-01-2006, 11:33 AM

I would not be surprised in the least to heat that the capacitors have dried out. That's a pretty common failure mode for older electronics. If I do a re-solder and that doesn't do the trick I might replace the caps. I think we can be pretty sure that the resistors and ICs are still in good shape. The transistors usually fail with a visual indication, don't they?