1969 Chris Craft Roamer 46 Refit: Dialing in the CAPAC Anti-Corrosion System

When I recommissioned the CAPAC impressed current anti-corrosion system, I hoped that the controller survived the decades the boat spent on Purgatory Row in a southern Maryland boatyard. The circuit board was dusty from the refit, but none of the components showed signs of having let the smoke out. So having safely made the transit from Deale to my new home port marina, I was anxious to power up the CAPAC and see how it performs.

Initial CAPAC power up shows 5.5 on the meter

According to the meter and Engelhard Model 10A12D CAPAC manual, 5 is “unprotected” for aluminum and 7 to 7.5 is “protected.” So 5.5 is only slightly protected. I turned the set-point adjustment potentiometer (on the left under the meter) fully clockwise, which should be the maximum. But the needle didn’t budge.

The manual does say that it can take up to six weeks for the impressed current protective film to fully develop, so I made sure to keep an eye on that meter whenever I visited the boat.

Next day, the needle was just over 6!

Two days later, the needle was at 7!

My aluminum hull is “protected”!

Three days later, something changed

I checked all of the electrical connections and found nothing wrong. But then I noticed that a thunderstorm had moved the boat around enough that one of my shore power cords had dipped into the water.

Could a new shore power cord lose electrons in the brackish water?

I adjusted the cord so it won’t end up in the water again, but the CAPAC meter is all over the place. It’s dropped as low as 5 and risen all the way up to 7.5. But the set-point rheostat has very little effect on the needle.

I dug into the CAPAC manual, and it says that for this condition, test the anode and reference cell by putting a jumper between pin 2 and 3, which puts +12vdc to the anode.

Major component wiring diagram

Jumper from 2-3

CAPAC meter pegs at the top of the scale, as it should

The manual says if it passes this test, there’s a defect in the controller.

The schematic isn’t terribly complex

I’m no electronics expert, but at least I can see the individual circuit lines and see what each component is. So I decided to identify each component and look for trouble spots.

Everything looks fine…except for one thing

My blog host always resizes photos. Right-click the image and save if you want to see it full-size on a computer screen.

This 2 watt resister shows signs of letting some smoke out

That’s R13 in the schematic. The “Theory of Operation” section of the manual (pp. 23-24) says anode current flows through that resistor and on through two transistors before going to the anode. But I don’t know how to read the schematic. There’s -12v on one side of the resistor and 13.37v on the side with the transistors. I used jumpers to attach another known-good 2w 220 ohm resister across R13’s terminals, bypassing R13 if it’s internally lost continuity, but nothing changed.

The circuits around the scorched resistor look fine

So next I took voltage readings at every spot I could easily access, noting the results on the schematic.

But what does it all mean?

After removing the jumper from 2-3, the meter slowly dropped to 6.5

So…my CAPAC meter tells me the anode, reference cell, and meter are working properly. Turning the set-point adjustment potentiometer has no apparent effect on operation, near as I can tell. And none of the components appear visually to have failed, though R13 does show it’s gotten warm.

If anybody has any ideas, please let me know in the comments!

Next up in our 1969 Chris Craft Roamer 46 Refit: Remaking the Salon Settee III