Noise Abatement

[itsmoked]

Hi all!

I have been called in on a product that is having some difficulty that needs a solution.

Essentially it is an OT-Shelf video camera/display screen that gets bought, disassembled, and reassembled into a different form factor.

Well the fly-in-the-ointment is the original camera head (size is about 1/2 a walnut) was plugged directly onto the main board with a tiny ~20pin connector. the new geometry results in the camera head having to be about 6" away. The 'uninformed solution' was to "just put a cable in". A ribbon cable resulted in nasty video artifacts that rendered the unit useless.

The next attempt was to run individual wires, twenty of them. This was marginally better as with all those itty bitty wires ungrouped the system works well. As soon as you gather those wires into a bundle things go sour. The display which is fed from data received over these wires and subsequently processed into what the LCD displays starts showing horizontal lines of non-sense spread over the video image. As you squeeze the wire-bundle together this gets much worse - as you spread it out it gets much better to the point that all the defects disappear. Of course the assembled product needs them mostly bundled.

I know what I'm going to do to try to solve this but I would really like your informed input and hunches before I join battle with this thing. Note: there are no schematics or even any information available for the ICs used. I'm flying totally blind on this.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Skogsgurra]

Logbook,

I guess that I am too old to learn new views on things. But I shall give it a try.

For the time being, I still think that it is much better to have the return in the shield than in a nearby unshielded conductor.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

macgyvers2000; My joints are much poorer. Some may even be cold joints. I used AQUA washable solder which has crappy cleaning ability. Also we are talking about really tiny stuff. I used 3/4" of 0.015" solder to solder all 72 wires and 72 connector pins.

14 of the lines stab into the bottom of the board and are blind soldered from the side the wires enter from, as the other side is not accessible. I did not know that the wires would blind up against wires in the socket that were exposed on the bottom of the socket. My cable wouldn't work and so after checking I saw this was a possibility. I went back and heated these leads and backed them out about 0.010". The cable then worked. THEY ON THE OTHER HAND knew about this and so have put a piece of Capton tape under the connector to prevent this problem. So actually that is another difference between our two cables.

Lengths are very close to the same. +/- 1/8"

I cannot cause the problem with my cable by any manipulation of [my] cable. My leads do all spring straight out of the little boards and theirs all swoop to the middle of the little boards about 3/8-1/2" above it and are subsequently constrained by the clear epoxy.

Keep in mind the little boards are about 1/3 the size of a postage stamp.

Maybe they washed the board and residue has contaminated the Capton tape tying, socket connectors on one side and blind leads on the other, together via high resistance tracks.


You guys trying to hijack this thread.. Have at it! Honestly, I do not mind a bit. Especially since it is related.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[MikeHalloran]

Washing may indeed be the problem.

Kapton is known to break down (to carbon) when exposed to water, which is why USAF doesn't/can't wash it's F-16s (with Kapton insulated harnesses).

I am not kidding. Look it up.







Mike Halloran
Pembroke Pines, FL, USA

 

[itsmoked]

Oh my gawd!! Very nice info there!! Thanks!! I will run down that possibility. Not sure they wash them but they were very clean. Suspiciously clean!

Thanks Mike.

I thought Capton looked wrong.. Kapton!

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[MacGyverS2000]

I'm going to have to disagree with Mike on this one. Kapton can absorb a high quantity of water and change its dielectric properties (bad for impedance controlled flex cables), but water does not make it turn to carbon (in fact, water is a typical byproduct of Kapton creation). Electrical arcing can, however, and it's a self-propogating process... once some turns to carbon, it can continue along the entire bundle, allowing current to flow on the outside of the bundle.

Still, washing may be an issue... if high quantities of flux and other junk gets trapped in the Kapton, you may have a high-resistance electrical path there. Worth checking out.

Keith, can you get a hold of any of their boards (showing the problem) without the potting? Check the resistance of their cabling and see if it's high. I'm going to assume there's no change in cable layout between theirs and yours, but if that assumption is false, we're talking a noise issue. Are the connectors different?

Dan - Owner

http://www.Hi-TecDesigns.com

 

[logbook]

skogs,

>For the time being, I still think that it is much better to have the return in the shield than in a nearby unshielded conductor.

I don't disagree. The mutual inductance between innner and outer conductors is one of the key properties that makes a coax cable good above 1kHz or so.