Waldo928

Circuit board before


Circuit board after with new capacitors and resistor.

I've been wanting to update this thread for a while with my experience repairing my CWS. I want to give a shout out to brian928 with helping me track down the proper parts.

Here's the backstory: I had a bad CWS out of a friend's car (an '87 S4) that was completely TU. No lights, no nothing. I had swapped into my car with a good CWS (an '86 S, same part numbers on the boxes) and nothing came on. So I opened up the bad one to see if I could find out what was wrong. I found the same burned resistor as toreboee. Since I couldn't tell what the proper resistor value was because the stripes were burned off, I decided to open up my good CWS. That is the first picture I listed above. The value came out to 3.32 ohms. Then the capacitors had their values listed on top of them. I replaced them with ones of the same capacitance, but higher voltage on brian928's suggestion. I used a 100mf/50V (originally 100/16) for the large one and a 100mf/35V (originally 100/10) for the smaller one. There were 4 capacitors on my board so I replaced them all. I was able to find all the parts at Mouser.com (no affiliation). They cost me about $2.50. The resistors were 10 cents each with a minimum purchase of 10 of them. The shipping cost was more than the parts. I bought extras just in case.
I pulled all the capacitors and the burned resistor, put it all back together, and voila, everything worked perfectly. The second photo is of the new capacitors and resistor installed. So then I decided to do the same to my still functioning CWS to avert future problems and it still works without problems.


On a related note, seems like Porsche must have gotten a great deal on these electrolytic caps because they used them all over the place. I had repaired my odometer a couple years ago with a new gear when that failed, but it stopped working again about 6 months ago. Thinking the new gear had gone bad I pulled the speedo apart again, but the gear was still in good shape and the speedometer needle was moving so I suspected an electrical problem in the circuit board that controls the odometer stepper motor or the stepper motor itself. I tested the motor with a 12v battery and it worked fine. So I decided to replace the two caps on the little circuit board. Again, got the parts from Mouser for a couple bucks. Soldered them in and I am back in business.

So I hope this gives other folks out there some courage to try to fix their own boxes. All it takes is a couple bucks in parts, a soldering iron, and some patience. If you fail there are always professionals out there that you can send your parts to for a professional repair.

murray928

Just reviving this thread as I have the exact same problem. My igniton on start up sequence of warning lights lasts for just a fraction of a second. Im curious if you managed to resolve the malfunction and how..
I have just removed the CWS bulb controller and am looking for clues as to what to look out for.

brian928

Hi John,
This sounds like the CWS has failed. I believe my '87 symptoms were similar - all would blink then go off. It appears that the main failure is a capacitor that goes bad. Look at toreboee's photo posted on 09-04 -2017. The arrow is pointing to an over heated (burnt) resistor. But look at the capacitor just to the right of the arrow. This is what failed. There are some numbers on these capacitors, such as 100/10 FRAKO P 5. The 100/10 part means 100mF 10V. The mF number is the important part. Going above 10V is better (my replacement may be 35V). Also, get the highest temperature rated one. There are 4 or five on the two CWS boards, so replace all these. I am lucky that I have an old fashion electronics store nearby so parts were less than $2.00US.

Let us know how it turns out.
The 409-04-2017, 06:01 AM-2017, 06:01 AM09-04-2017, 06:01 AM 09-09-04-2017, 06:01 AM04-2017, 06:01 AM

M. Requin

IIRC this wasn't it, but just by coincidence I am removing the CWS controller today to chase some instrument faults that all seem to have the CWS in common. I'll check my notes and let you know what I found with the warning light problem in my post you referred to.

OK,, found my old thread: https://rennlist.com/forums/928-foru...st-solved.html - hope this helps!

murray928

Hi Brian,
Thanks for that post but thanks to great assistance from a new friend/928 owner in Dublin Ireland (Gazfish), I have been able to rule out a malfunction in the CWS bulb controller. He offered to check it out for me and plugged it into his 928 and hey presto all warning bulbs stayed on until engine startup.
He advised further to check for voltage on pin 1 of 14 pin connector and assuming that ok to ground pin M13 or L23. on the CE panel.
My mechanic did as advised but still have the problem.
Gazfish has advised again that my mechanic should turn on ignition to accessory position and then ground pin 12 on the black connector of the bulb controller.
If the voltage light then illuminates on the battery gauge, he reckons that would signify a problem with the alternator itself.
Car going back to mechanic on wednesday so that should be a quick test perhaps suggesting a problem with the voltage regulator.

I'll post the outcome afterwards. Many thanls also to all who have offered advice ion this and on other posts re Dash Pod Upgrade ncluding to Martin Requin.

Outcome:
Grounded pin 12 on black connector of the bulb controller and the voltage warning light illuminated.
I have ordered a new voltage regulator as the alternator had been charging properly in every other respect other than performing the warning light sequence. Hopefully that will cure the problem completely. Will post result when fitted.