Author Topic: Broken Lightboard Tab - Kato SD40-2 (Part 17681L)  (Read 1293 times)

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StewRRFan

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Broken Lightboard Tab - Kato SD40-2 (Part 17681L)
« on: March 26, 2017, 07:56:43 PM »
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Need some help here.  Have an older SD40-2 where the forward tab (Left side - 17681L) has broken so the lightboard/decoder will not make contact.  Are there suggestions on how I can fix this or does someone have the left side of the mechanism in their parts box they would be willing to sell?

Thanks

Ross

jdcolombo

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Re: Broken Lightboard Tab - Kato SD40-2 (Part 17681L)
« Reply #1 on: March 26, 2017, 08:29:17 PM »
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Photo of problem area would be helpful.

Aren't there rear tabs as well?  Is the engine working via the rear tabs? 

If you are having electrical pickup problems because the left-front tab is gone, my suggestion would be to drill and tap a hole for a 1/8" 00-90 screw somewhere on the left side of the frame; cut a small strip of .010 or similar-thickness phosphor-bronze the width of the frame and about 1/4" long, drill a hole in the phosphor-bronze strip to clear the screw, then screw it to the frame with your 00-90 screw and then solder a 30 gauge or smaller wire from the phosphor bronze tab to the pickup pad on the board.  Pickup problems solved.

John C.

StewRRFan

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Re: Broken Lightboard Tab - Kato SD40-2 (Part 17681L)
« Reply #2 on: March 26, 2017, 08:40:06 PM »
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Photo attached.  There are rear tabs but no pickup.

jdcolombo

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Re: Broken Lightboard Tab - Kato SD40-2 (Part 17681L)
« Reply #3 on: March 26, 2017, 10:07:48 PM »
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Well, don't know why you aren't getting electrical pickup from the rear tabs.  I'd probably look into that first.  But my solution remains the same.  Get an 00-90 round-head screw (or really, any kind of head would do for this), tap drill, clearance drill, and tap.  You can get the tap and drills from Micro Trains, since they use 00-90 screws for couple body-mounting; I don't think they have a 1/8"-long screw, but you can get 1/4"  or 3/16" round-head 00-90's from a variety of places (you'll have to order a package of them, which usually means a dozen or so).

Pick a spot on the frame where the screw, thin piece of phosphor bronze and wire won't interfere with the shell, drill a tap hole, tap, screw, solder, done.  I might put the screw on the thick tabs sticking up in the center section of the frame, as long as that won't interfere with the shell fitting down on the mechanism; if that's not good, use the rear shelf and a longer wire.

John C.

jagged ben

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Re: Broken Lightboard Tab - Kato SD40-2 (Part 17681L)
« Reply #4 on: March 26, 2017, 10:23:08 PM »
+1
Fyi, that's a 'mid production' mechanism.  Not really an 'older' version, as it's the newest SD40-2 tooling.

MK

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Re: Broken Lightboard Tab - Kato SD40-2 (Part 17681L)
« Reply #5 on: March 27, 2017, 11:23:12 AM »
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To make John's idea even simpler, you can ditch the phosphorous bronze strip.  Instead, solder a thin wire to the pad of the decoder, strip the wire about 1/4" or so.  Wrap exposed wire around the 00-90 screw and tighten.  Just like attaching a wire lead to a terminal screw.

StewRRFan

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Re: Broken Lightboard Tab - Kato SD40-2 (Part 17681L)
« Reply #6 on: March 27, 2017, 11:27:47 AM »
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Thank you for the direction.  Does this still apply if I am keeping this DC?  Also, were would I attach the wire to the stock DC board?

peteski

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Re: Broken Lightboard Tab - Kato SD40-2 (Part 17681L)
« Reply #7 on: March 27, 2017, 02:38:32 PM »
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Thank you for the direction.  Does this still apply if I am keeping this DC?  Also, were would I attach the wire to the stock DC board?

Anywhere on the metal trace which was originally making contact with the broken tab.

Oh, and for John:  I looked at the design of that board and the rear tabs are only for locating and retaining  the board mechanically - there are no metal pads contacting the chassis. Kato apparently determined that singgle points of contact were sufficient.
« Last Edit: March 27, 2017, 02:40:59 PM by peteski »
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jdcolombo

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Re: Broken Lightboard Tab - Kato SD40-2 (Part 17681L)
« Reply #8 on: March 27, 2017, 04:00:24 PM »
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Oh, and for John:  I looked at the design of that board and the rear tabs are only for locating and retaining  the board mechanically - there are no metal pads contacting the chassis. Kato apparently determined that singgle points of contact were sufficient.

Ah.  That's an odd manufacturing choice (particularly given Kato's usual attention to electrical pickup issues), but at least I now I understand why it won't run!

John C.