I have a W129 (93 300SL) which should be delivered tomorrow. The PO stated that the cluster died and he replaced it with one from a 140; since the mileage on the new cluster was ~30k miles below the old one, on advice here (as well as intuition), I asked for the original cluster instead.

I understand that the circuit board on these early (wheel odometer) clusters have a tendency to go bad and that the popular options are replace or send out for rebuild.

I have a chip programmer which will accommodate most programmable chips with the right pin adapter as well as a solder/ desolder station. The PO said the dealer told him there was a chip in the cluster that died from leaving the battery disconnected for a prolonged period.

Does anyone know the most common failure points on these circuit boards? I have already seen the post on replacing the capacitor (475Ω?) on the board and will do that automatically. I also plan to replace all the fuses and check the voltages at the connector pins, but there seem to be enough SL posts about dead clusters traceable to a bad circuit board to sound like a not-uncommon failure.

Do the members who have solved their own dead cluster issues find that it is mostly traceable to the capacitor, the solder joints, the traces, or is there a chip which can actually loose its programming?

"Mother board" chip failure was common on the 1990-94 SL's.

Haven't seen anyone try a repair themselves.

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I had mine (92 140) rebuilt and new bulbs installed, I had the issue of it flickering which was a common issue. It seems the electrolytic is in the voltage regulation circuit of the cluster, and a drop of voltage shuts down the regulator. They returned all the parts and bulbs which included some sort of power transistor, the much discussed capacitor, and a smaller transistor. I would replace the exterior temp bulb, since it is soldered in on the non digital version. I also have all the tools and skills to repair my own cluster but decided to have it done (Programma) is local and got it back the next day with a two year warranty $300. The 129 and 140 clusters are not interchangeable per
http://mbcluster.com/

MB DOC, its maybe $10 in parts and a can of beer to try it. What's my downside? We have some football games coming up. Soldering during halftime sounds like a match made in heaven.

Peter, thanks for the info, I would not have thought about the transistors. I will replace them just because they are cheap and I now know they have been know to fail. I suffer from the 'While you are in there' syndrome...... It may be a week longer for results since I may have to order the parts but with this weather and a convertible, I am in no hurry.

I will, of course, check the traces for breaks. Its dead. Its not like I can make it much worse. I will let you know whether this works or not.

Peter, since you mentioned that bulb, while I have the cluster out, I may as well refresh the illumination for the whole cluster. I can't help but wonder about LED replacements just from a MTBF standpoint. For other contributors, since there is usually a ton of bling on eBay, keep in mind, I just want replacement. I don't care about bling; no colors, strobes, or holographic hookers. Just functionally equivalent LED illumination. Anyone have any recommendations within those parameters?

If you look at the link it discusses various LED options, most the bulbs are rather unique when it comes to the socket/bulb holder.

There are a few out there. Here are just two. The trick is to determine the "functionally equivalent" part. There are also some suppliers which offer LED 'stacks' with side LEDs to provide a more balanced "throw". The problem I have is I have never burned out a replacement incandescent dash bulb. The second link has LEDs which are cost competitive with incandescents. Anything 2X that price is probably not cost efficient. Next is to determine how 'functionally equivalent' site two's bulbs are considering they only illuminate forward (light all comes out the end).

A small transistor commonly fails when the vehicle is improperly boosted or possibly charged incorrectly.
It is a BC640 which is a TO92 case. Looking at the circuit board with the component side facing you, it is at the very left side next to a heat sink mounted 8.5 volt regulator. Exact replacements are available from any of the electronic suppliers such as Digikey, Mouser, etc.

If you are replacing electrolytic capacitors, choose high quality and go for the 105 degree C versions (as opposed to the 85 degree).

Remember if you plan on sending the cluster to a repair center as a last resort, the last thing that they want to see is a circuit board that someone has made an attempt at fixing themselves.

Rick76,

Thank you. I knew I had seen, somewhere along the way, that failing to do xxxx could cause the cluster to blow when jumping a Mercedes. I can not remember what xxxx is and my searches the last few days have not turned up any evidence. At least you are aware of the same thing I was searching.

From talking to the PO, that is what I suspect happened to my latest acquisition. He mentioned 'jumping it off' at least once and I have always had an aversion to jump starting German cars (there is some different consequence for BMW, and I don't remember what; I may have seen the first reference 10 or 20 years ago).

In any event, concordant with Peter's report, I will replace the capacitor, the 'small transistor' (BC640), and the power transistor (which should be pretty obvious when i remove the cluster). Check for trace integrity, insure proper ground on re-installation, and I think we may be ready to go.

I am not sure I want to pull the cluster in 16° weather and I left everything on the street last night so I can get out tomorrow. I may try to find the picture I have seen posted of the rear of the cluster to get the part number for the power transistor.

I have re-capped several sat receivers with Mouser parts and have a pretty good confidence level with their offerings.