Cruise amp repair - PeachParts Mercedes-Benz Forum

lowriderdog37 · #1 01-17-2009, 10:34 AM

In the near future, the class I am in is going to be going through a section on circuit board repair. I was thinking about setting up a cruise amp repair service, or something. If you want to temporarily part with broken amps, I will 'try' to get up and running. I ask that you provide costs for shipping, and repair parts. You can throw in a donation if you want to.

If you want to donate, I won't say no either.

I provide no promises on getting anything working. I fixed mine a while back and had no problems. Just throwing that out there in case anybody would like it.

DeliveryValve · #2 01-17-2009, 10:42 AM

Sounds great! I am interested!

bgkast · #3 01-17-2009, 02:24 PM

I have the one in my SD that does not work, and a junkyard one that also does not work in the SD. The circuit board of the junkyard one looks fine, no burned patches or bad looking solder joints, but the cruise does not respond at all with either amp in place. Do you think both amps are bad, or do I have another problem?

I would be interested in sending my junkyard amp in if it is the problem. I just have the board, no metal case. It was too hard to get the bracket free at the junkyard.

jumbo · #4 01-17-2009, 03:29 PM

I would like mine done. Pm me.

Dionysius · #5 01-17-2009, 07:08 PM

I have found the what has caused these to fail in very large numbers is that the electrolytic Capacitor(s) have gone bad. The unit loses its 'memory' because of this.

I do not know which one however since I have no schematic. If you touch all of them with a hot iron they may 'rejuvenate' but the effect may also be temporary.

Talk to me if you want to explore further......This piece of engineering info will help you greatly.

If you can get me a schematic I will locate the problem to a single component. Talk to me. There are a million of these out there all failed with the same problem. Email me with your phone number and I will call you.

lowriderdog37 · #6 01-17-2009, 09:12 PM

Quote:

Originally Posted by bgkast

I have the one in my SD that does not work, and a junkyard one that also does not work in the SD. The circuit board of the junkyard one looks fine, no burned patches or bad looking solder joints, but the cruise does not respond at all with either amp in place. Do you think both amps are bad, or do I have another problem?

I would be interested in sending my junkyard amp in if it is the problem. I just have the board, no metal case. It was too hard to get the bracket free at the junkyard.

I don't know what exactly makes these go bad, the first one I fixed all I had to do was take the lacquer off, and it's worked fine ever since. Another, I had re soldered and it did just as dionysius explained...dying a few months later. I had also seen one that had a blown resister.

Quote:

Originally Posted by Dionysius

I have found the what has caused these to fail in very large numbers is that the electrolytic Capacitor(s) have gone bad. The unit loses its 'memory' because of this.

I do not know which one however since I have no schematic. If you touch all of them with a hot iron they may 'rejuvenate' but the effect may also be temporary.

Talk to me if you want to explore further......This piece of engineering info will help you greatly.

If you can get me a schematic I will locate the problem to a single component. Talk to me. There are a million of these out there all failed with the same problem. Email me with your phone number and I will call you.

I don't know where to get a schematic as of yet. I haven't seen any around. It would be helpful though. The cap failure makes sense in my head.

Does anybody know where to get a schematic? I may make one if I get really bored, but I don't see myself having that kind of time/patients. It's not a complicated design, just has one fatal flaw.

PM's replied to

I have several on their way to me, let me play with these and I'll take on more business. I'll let everybody know what I find...just give me some time. Like I said before, my experience with this kind of stuff is me playing. I will be starting actual training on this within a few weeks.

Dionysius · #7 01-17-2009, 09:46 PM

I am so disenchanted that VDO (I think they designed the board) will not let us have a schematic. I appealed to our German friends on this web to see if they could help.

Making your own schematic is possible since it is not a complex board but you do need to be patient and you have to be able to identify each part or at least it would be nice to be able to do so.

If you make or get me a schematic I will answer every question you have plus tell you how to fix all of the units.

The setpoint parameter is speed represented as a voltage and this is memorized using the charge on a capacitor. If the capacitor leaks then you lose the setpoint. That is why you can still operate the manual speed up/down controls but no auto control is possible. This is what I have found.

lowriderdog37 · #8 01-18-2009, 05:31 PM

huh?

shertex · #9 01-18-2009, 07:00 PM

Something to keep in mind: sometimes the reason an amp goes bad is because of a bad actuator (it draws too much current). I had a bad amp (blown transistor at output stage), had it rebuilt, and it went bad within a few weeks...now I/we strongly suspect a bad actuator. So for now, I'm going without. Make sure you get the actuator tested before only replacing the amp.

Lots of info at http://gdl-online.com/begin.html.

lowriderdog37 · #10 01-18-2009, 08:07 PM

Shertex, there is really not reason to repair an amp that you aren't sure is messed up. I was planning on hooking up and testing amps in my car (which works fine) before repairing anyways. But you are very right.

Dionysius, I got to thinking about this, if the capacitors are the shortfall, why shouldn't we just replace them all? Or better yet, if if just one is consistently failing, could it be because of something else? I haven't looked at one for a while, but most if not all of the capacitors are identical thought the amp, so if only 1 is failing, it could be because of something else making it fail.

shertex · #11 01-18-2009, 08:32 PM

Quote:

Originally Posted by lowriderdog37

Shertex, there is really not reason to repair an amp that you aren't sure is messed up.

I was certain that it was messed up, based on the symptoms. What I didn't realize initially was that a bad actuator could cause the amp to fail.

daw_two · #12 01-18-2009, 08:35 PM

Count me in as part of this project.

Dionysius · #13 01-19-2009, 01:15 PM

Quote:

Originally Posted by lowriderdog37

Dionysius, I got to thinking about this, if the capacitors are the shortfall, why shouldn't we just replace them all? Or better yet, if if just one is consistently failing, could it be because of something else? I haven't looked at one for a while, but most if not all of the capacitors are identical thought the amp, so if only 1 is failing, it could be because of something else making it fail.

Electrolytic capacitors will fail with age - they are prone to a leakage failure mode effect. When people claim they 'fixed' the board by soldering every land what they have really done is just touched the electrolytic lands with a hot iron and rejuvenated them with heat shock but this is a temporary fix IMHO. These caps were manufactured circa 30 years ago in a process inferior to what we would have today. You may find that not all have failed but my posit is the heavy hitter one which serves as the 'memory' in this ancient analog design is the one that is giving the major symptom. This circuit can be restored to its original and very fine original functionality. I admire you for looking at this and I will help where I can. The other caps act as filters (I am having to make assumptions here since I have no schematic) and their failure or partial failure could cause hunting and weird secondary effects. Note that these caps are polarity sensitive. And yes, you should replace all of the electrolytics. The other components are probably ok.

WD8CDH · #14 01-19-2009, 01:38 PM

Quote:

Originally Posted by Dionysius

The setpoint parameter is speed represented as a voltage and this is memorized using the charge on a capacitor. If the capacitor leaks then you lose the setpoint. That is why you can still operate the manual speed up/down controls but no auto control is possible. This is what I have found.

On the later CC amps, the ones with the electronic accuator (like my '85 300D), the setpoint parameter is stored digitally, not with a capacitor.

Dionysius · #15 01-19-2009, 02:11 PM

Quote:

Originally Posted by WD8CDH

On the later CC amps, the ones with the electronic accuator (like my '85 300D), the setpoint parameter is stored digitally, not with a capacitor.

If that is the case we have more than one version of board out there. Do the digital boards fail with same frequency and, if so, what are the failure modes and symptoms??
Is there a schematic for the digital boards?? Where in the name of the Almighty are VDO when we need them. Please give us some schematics. We are all being held hostage. Anyone going to Germany soon?? Can the moderators such as Brian Carlton render any assist here in locating schematics??