Odometer/speedometer question, 85 380SE. - PeachParts Mercedes-Benz Forum

Clemson88 · #1 02-02-2018, 10:00 AM

From memory the odo on my SD was a bit different than this. I just removed the screws that held the plastic cover/cap on at the end of the gear housing, replace the gears and put everything back together. It still works well.

I need to repair this SE odo so I can use it in the diesel conversion if I want to have an accurate speedometer/odo. It appear that the small circuit board is hard fastened to the clear plastic cover.

Does desoldering this board appear to be the proper way to replace those gears?

Rick76 · #2 02-03-2018, 12:03 PM

I can't give you specifics on the 126 cluster as I don't have one in my collection but make sure you change that redish electrolytic capacitor while you have it apart.

For unsoldering that board, de-soldering wick works well without investing much in equipment.

Clemson88 · #3 02-03-2018, 12:25 PM

Quote:

Originally Posted by Rick76

I can't give you specifics on the 126 cluster as I don't have one in my collection but make sure you change that redish electrolytic capacitor while you have it apart.

For unsoldering that board, de-soldering wick works well without investing much in equipment.

This?

Diseasel300 · #4 02-03-2018, 12:33 PM

Yes that capacitor, including any other "can" type caps you find on the board. They're notorious for failing and causing weird issues.

As far as that circuit card, if it doesn't unclip or come off easily, desolder it to remove the cover. When you're resoldering it in place, touch up any other iffy looking solder joints at the same time.

Clemson88 · #5 02-03-2018, 12:45 PM

Quote:

Originally Posted by Diseasel300

Yes that capacitor, including any other "can" type caps you find on the board. They're notorious for failing and causing weird issues.

As far as that circuit card, if it doesn't unclip or come off easily, desolder it to remove the cover. When you're resoldering it in place, touch up any other iffy looking solder joints at the same time.

As far as touchup am I to just melt the solder on those pins to make sure they have good conduction and holding power or should I remove and replace the solder?

Those are excellent point of restoration to make this assembly long lived and dependable. I just bought a 3 in 1 Zeny soldering station. I've wanted a decent station for years and couldn't justify the spending until now.

I have two cruse control amps to repair too but I'm not looking for work.
Thank you for the advise.

Rick76 · #6 02-03-2018, 12:58 PM

There is no need to remove the old solder but you will need to add a bit of fresh electronics grade rosin core solder to the joint. Just reheating is not adequate for a good joint.

Clemson88 · #7 02-03-2018, 01:10 PM

Thanks, Rick76. It's obvious I'm a novice at this. I've spent some time on youtube and absorbed a number of tricks of the trade but in my 65 years of life I've never been too proud to take advise and appreciate the time of those who are willing to help.

Well, maybe a decade or two between 15 and 30.

Diseasel300 · #8 02-03-2018, 01:53 PM

Quote:

Originally Posted by Rick76

There is no need to remove the old solder but you will need to add a bit of fresh electronics grade rosin core solder to the joint. Just reheating is not adequate for a good joint.

Adding to this advice, if you have a really NASTY looking joint, use some solder wick and remove the old solder, preheat the pad and pin well with the iron, then flow in some fresh solder. My go-to solder alloy is a 63/37 with No-Clean flux from Kester. The higher tin content makes it a harder joint than 60/40 and it tends to wick better. After soldering, clean the flux residue with some denatured alcohol and a toothbrush.

Clemson88 · #9 02-03-2018, 02:33 PM

Quote:

Originally Posted by Diseasel300

Adding to this advice, if you have a really NASTY looking joint, use some solder wick and remove the old solder, preheat the pad and pin well with the iron, then flow in some fresh solder. My go-to solder alloy is a 63/37 with No-Clean flux from Kester. The higher tin content makes it a harder joint than 60/40 and it tends to wick better. After soldering, clean the flux residue with some denatured alcohol and a toothbrush.

I think I can do that. I got a short strip of wick with the station.

Clemson88 · #10 02-04-2018, 03:59 PM

Just wondering if the circled end is positive or if there's another designation on the underside of the capacitor. There seems to be nothing on the other side of the board which indicates how the replacements go.

Diseasel300 · #11 02-04-2018, 04:28 PM

The stripe on the opposite end to your circle indicates the negative side. Typically Electrolytic capacitors mark the negative end, tantalum capacitors mark the positive.

Clemson88 · #12 02-04-2018, 04:31 PM

Thanks. I know asking question about stuff that others think is common knowledge removes all doubt to my ignorance but putting a capacitor in backward would be much worse.

Thank you, sir.

Diseasel300 · #13 02-04-2018, 04:35 PM

If a forum isn't for asking questions and receiving answers, what is its purpose?

Clemson88 · #14 02-05-2018, 10:23 AM

Quote:

Originally Posted by Diseasel300

If a forum isn't for asking questions and receiving answers, what is its purpose?

I had studied the DYI thread intensely, took notes which included identifying the polarity of those old capacitors by the stripe on the negative end but didn't review them. The moment I read your response I remember my note including that bit of information.

I'm so fearful of messing something up I need someone to hold my hand through the first experiment and I thank you again for your patients.

I removed the old capacitors and installed the three new ones I bought from mouser's website. My solder work looks pitiful, like something a kindergardener would do. I mean no insult to kindergardners.

I intend to experiment with a variety of solder tips, heat ranges and such until I get the hang of this. I'm not about to put anything in my car that lacks first quality workmanship.

I guess I'll watch a few more youtube videos and try this again. If you happen to know of a tutorial on this type work I'd appreciate you sharing it.

Thanks again, Gentlemen.

Rick76 · #15 02-05-2018, 11:36 AM

For someone starting out it helps to get an old piece of electronics to practice on. Lots of old vcr's, radios etc being dropped off at e-waste sites.
Too much heat and you can lift copper traces and damage components. Too little and you get a poor quality joint that can cause intermittents. Just takes practice.
Also some boards such as the cruise modules have a lacquer conformal coating that has to be removed or you get contaminated joints.