Surfmaster PI Pro coax bad

[bklein]

I discovered the PI Pro I am restoring from saltwater damage has a bad coax cable, starting at the box and leading down I don't know how far yet. Water got in at the waterproof feedthrough due to flexing I guess. The copper coax shield is seriously corroded to the point it is open circuit. Is there a watertight inline connector you would recommend or is it time to make this a "water resistant" machine and just replace the coax using a heatshrink coated splice? Or I suppose I could just put a coax connector on the box as well... (who sells a (salt)watertight one?)

Barry

[Carl-NC]

Usually the SMPI cables are long enough that you can trim off a foot or so and still have enough. Option 2 is to splice it; there are waterproof in-line splice housings that are used for underground cable repair. Option 3 is to call White's and see if Service has a spare SMPI loop in the junker bin they will send you for free.

- Carl

[bklein]

Yeah, I stripped back about a foot and a half. Turns out there was a tiny nick in the insulation and that fed water up the shield braid to the control box. I think there likely is enough left to work. But now I discovered that its missing the center shaft rod! I suspect the previous owner shortened it for underwater use. That, or it's in my garage somewhere and I misplaced it....


Barry

[bklein]

Awww crap. That still did not work. I was fooled into believing the connection to the coil was good. Today I thought I'd spend some time teaking trimpots and discovered the coax remains open. So I unscrewed the plastic connection at the coil and a bunch of water came out. I would think this means the whole insides are compromised(?). What next at this point? I'm thinking the housing is seriously glued together, right? Should I try drilling an access hole on the bottom side to see/fix the coax connection? I could always later glue a scuff cover over the bottom...

[bklein]

I decided to go ahead and drill a hole. I found two wires hanging in the air - one was the coil, the other the shield I'm thinking. The center coax wire was still a good connection.
I put it all together and now it works - sort of. I'm thinking it should work better than it does. A quarter or a gold ring has about 5-7 inch detect range in air. I think my Surfmaster PI_950 detects better. The PI Pro has a bit different circuit than the 950 (has a gain and tuner control and the PI_950 has a Pulse Delay and Tuner knobs). Anyway, I've attached a scope photo showing the coil signal (190V peak) and the 4093-pin 10 - showing the adjustment range of the timing trimpot. Does this look right? (8-20uS after TX release)

[bklein]

I'm guessing my issue now is the water contamination of the coil housing interior. But how do I confirm that instrumentally? How do I prove by instrumentation my coil is faulty? Would it be a resonant frequency test? The flyback voltage of 190V seems quite a bit higher than the 130V I get on the PI_950 coil. Is that just due to the mosfet used or is the coil that different? (I'll find out fairly soon as I plan to try it) The inductance is 233uH and resistance .9 ohms (seems a bit low..).

Barry

[homefire]

Just do a Ohm test on it.

Shorted?

That high of a Flyback would tell me No.

Put it in your oven at 100f for four hours and it will dry out .

Worst come to Worst, Build a new one.

[bklein]

Just do a Ohm test on it.

Shorted?

That high of a Flyback would tell me No.

Put it in your oven at 100f for four hours and it will dry out .

Worst come to Worst, Build a new one.

I stated the inductance and resistance measurements earlier - I think they're in the right ballpark...
I will be making my own coils regardless. Just was planning on this being a valid reference sample - likely end up buying a new one.

[hobbes_lives]

The inductance should be 230uH and the resistance 1.37 ohms, as stated here...

http://www.geotech1.com/cgi-bin/page...oils/index.dat

I've confirmed these values in my own tests.

[bklein]

I am still confused with the PI Pro. It has this behavior where it tends to take a set and work and then I put everything back together and it doesn't. I even went to the extremes of swapping coils between my PI diver-950 zero buoyancy coil and the PI Pro coil. The PI worked on my bench with either coil. The PI Pro though seemed to have a lock in our out behavior depending on the timing trimpot setting that was worse with the original coil than the 950 one. The problem I am having is that when I put the damn thing together it doesn't work on anything but iron. Sure this could be a wiring issue or the like. Or maybe the feedline is the culprit. Let me explain:
I have a B&K 975A LCR meter. Here is what it measures for the coils, measured at the box end of the feedline:
SurfDiver950(Surf PI):
1.37 ohm resistance
178uH
SurfPIPro:
1.35 ohm
224uh
Interesting that the 950 has less inductance - works great though.
So maybe capacitance?
So I tried the technique where you use one detector to send an impulse signal to the test coil and you measure the frequency of the ring response. Problem here is the period of the ringing response is not constant. So do you used the first ring period (which has a lot of DC bias differential) or a later one? (sorry I don't have a photo of it)
Regardless, the Pro gets frequencies - depending on where I take the time periods - of 505/538/536Khz and the SurfPI gets 555/588 Khz. So I guess it is worth trying a new feedline, or see if White's may have a used replacement like Carl suggested...

As soon as I get my garage cleaned out better I can look at this in more detail as well as just go ahead and make a replacement coil to test on both (and 2 surfmaster longboards I have just populated).

One other naive question I have to ask... wiring polarity of the coil feedline. I did see a slight difference in behavior on my bench dependant on the polarity of the feedline connection. As some guys here don't seem to get expected results I wonder if the coil wiring polarity could explain it? My bench is so noisy I can't really say for sure so I thought I'd just ask.

Barry

[bklein]

Please see attached diagram of a ringing signal.
Is the frequency we should use A-C, B-D, or ?

[Alexismex]

No ringing signal at all like A

[mikebg]

Please see attached diagram of a ringing signal.
Is the frequency we should use A-C, B-D, or ?

Bklein, For better accuracy of the measurement, points are used in which the swing crosses the zero line. Note that the transition of zero line should be in the same direction as shown.

[bklein]

Thanks. As you can see from the example, the first half of the ring is longer duration than the 2nd half - and the periods get shorter with time. So would the most accurate reading be if you were to take the first half cycle and double it for T? Or is this just nitpicking and all we want is ballpark anyway?