CWS Diagram

[87SharkS4]

Took out my non functioning Central Warning System box out of my 87 and found a burnt resistor. I'd like to replace it but i cannot tell what the specs of it are (resistance/watts)

Does anyone have a diagram/parts list for the CWS? it would be grest help and save me from buying a new unit for a 25cents resistor.

Thanks

[Outbackgeorgia]

I would look for a reason the resistor failed. They are a passive component, very reliable, unless too much current is drawn, for example. Replacing it is just like replacing a fuse without knowing why it failed.
Good luck in finding a diagram! I have searched with no success so far.
Dave

[Danglerb]

Maybe post some picts and somebody with a good one can compare them.

Wiring diagrams might show the external connections, which might hint at a value.

Guessing on failure that it could be from a bad ground where the current is flowing via some shared back path through another circuit to ground.

[harborman]

I wonder if you can read any color codes on the resistor? Resistors can change value with age and of course fail for other reasons as mentioned above.

[87SharkS4]

Thanks for the help. I'm an aircraft avionics technician by trade and quite familiar with repairing electronics. The resistor most likely failed because it's 27 years old. It has not color bars or part number. The circuit board is not marked at all so without some diagram is a guessing game.

Cheers

[harborman]

Originally Posted by 87SharkS4

Thanks for the help. I'm an aircraft avionics technician by trade and quite familiar with repairing electronics. The resistor most likely failed because it's 27 years old. It has not color bars or part number. The circuit board is not marked at all so without some diagram is a guessing game.

Cheers

Sounds like you know enough to fix it if you get a schematic. I was able to get the warning light computer quite cheap used. Maybe look for a used one. I think I paid $49.

[Danglerb]

It must be a fairly simple circuit, trace it out, very likely similar function elements of the circuit will use the same value. Also likely its a standard value, so shotgun and try a few, or use a pot and measure the setting that works.

[toreboee]

87SharkS4

I assume you resolved the problem? I'm also trying to find the correct replacement resistor for my CWS but can't find a diagram anywhare. Can you or anyone else please post a picture showing the color bands of the burnt one in my picture? As you can see its impossible to determine the colors. I'll post photos of the rest of the board for others to use as refference later on today. One should be able to find most of values based on the color codes, am i right? Hope someone can help me and that this could be usefull. Sorry if its done before, I couldn't find a picture with high enough resolution.
Thanks!

[toreboee]

An overview of the location in case it was difficult to see in the first photo.

[harborman]

It looks like that capacitor might be bad. Is it leaking on the circuit board? That might be the cause of the burnt resistor.

[harborman]

Ok, I remembered I kept my old warning system unit with all the other things I replaced.

It appears that resistor has the color code of orange, orange, red, silver. So it's 3,300 Ohms at 10% and looks to be 1/2 watt. Now I tired to see the value of the electrolytic capacitor next to it and it has the numbers 100/10 on top. So possibly is 100 MF @ 10 volts. The one next to it looks to be the same from what I can tell. Hope this helps. Always good to keep the old parts!

[harborman]

One more thing. Our boards look about the same but mine is from 1986, so there may be some changes. In looking at the placement of the caps, diode, resistor and the three terminal transistor under the heat sink, this might be some kind of regulator circuit. Just guessing. Old electrolytic's tend to short out or become defective with age. The one in your picture seems to be leaking, can't really tell for sure. Something black which is under the cap on mine as well, but looks OK here. Looks to be the bottom of the capacitor.

[toreboee]

Thanks harborman, thats great info! I tried VDO directly, however they would not give me any info since it was Porsche purpose made and they did not have the rights.

Glad you held on to that old part:-)

I'm new to dealing with the electronic components and appreciate all the help I can get. There was another identical100/10 capacitor on the oposite side with no sign of leakage. I bet you are right about the first one leaking. Attached two photos for comparison.




Here are more photos of the internals in case anyone is looking for the color codes.
It was hard to get all angles with the phone camera so I may have missed a few.

[harborman]

You need to pull that cap and get a replacement or two. You might get them on Ebay or a company called Digikey. Note polarity when removing. You can test the cap with an Ohm meter. Hopefully no other components were damaged. Unfortunately Radio Shack is no longer. Or.... you can do as I did, find a good used CWS. If any of those IC's are blown it might be impossible to fix.

[toreboee]

Thanks for the input. I ordered a few new Capacitors and as close a Resistor I could find. 5% tollerance instead of 10%. Otherwise it is 1/2 watt and 3,3Kohm. Hope its close enough.
Hope the IC's are OK.
If it doesn't work I'll buy a replacement as you suggest.

[harborman]

Originally Posted by toreboee

Thanks for the input. I ordered a few new Capacitors and as close a Resistor I could find. 5% tollerance instead of 10%. Otherwise it is 1/2 watt and 3,3Kohm. Hope its close enough.
Hope the IC's are OK.
If it doesn't work I'll buy a replacement as you suggest.

OK on the new parts, maybe worth a try as components are cheap. The tolerance just means the value is + or - , so 5% is better but not critical since it was a 10%. Hard to say if any other damage was done. Good luck on the repair and let us know.