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Author Topic: Ham-IV Sanity Check Request  (Read 1644 times)
WA2OLZ
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Posts: 61




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« on: May 26, 2012, 01:21:22 PM »

I've spent the past few days on and off re-lubing my 1984 era Ham-IV rotator. It worked fine when last used over ten years ago, maybe more. The rotator has never been outdoors so it's in pretty darn good shape.

The problem I now have is with the direction indicating meter display. It is OK from leftmost south, past north (center scale) to about 40 degrees. There it stops. After a lot of circuit tracing and troubleshooting I am pretty sure the issue is with the meter itself. Strange, I know, but there it is. I pulled the meter from the board and placed my DVM where the meter normally mounts. I see a full smooth progression from about 12.6VDC down to 0, coincident with the rotation of the rotor head. I have also measured the directional pot in the head and it is all correct throughout the range. I did clean up the connections while I was in there.

What I am asking is for your opinion - is my diagnosis correct? Part two (extra credit question) how much $ and where to get a replacement meter? It may be cheaper to buy a used control box if the meter is too expensive.

73/
Jack
WA2OLZ
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W4IOW
Member

Posts: 34




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« Reply #1 on: May 26, 2012, 05:44:41 PM »

Have you taken the rotor top off and rotated the copper direction indicator with your finger while connected to the meter? You will be able to observe the movement of the needle on the meter as you move the copper indicator. The contact between the copper pointer contact and/or the rheostat may be poor and need a bit of cleaning.

BEWARE there are many ball bearings in the rotor. They are held in a nylon keeper, but still may drop put when you remove the top. Opening the rotor over a can or bucket will alleviate a lot of searching and swearing.

Good luck,
Ray
W4IOW
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WA2OLZ
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Posts: 61




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« Reply #2 on: May 26, 2012, 05:54:00 PM »

Thanks, Ray. Yes, I have had the rotor apart not once but three times. I'm getting pretty good at it now! The pot in there is good. I cleaned it and the copper contact and it is A-OK. I can measure the resistance at the rotor and the controller and it's right on the money. That would have been my bet also. In fact, it was. Disconnecting the controller meter and replacing it with my digital volt meter works fine, so the only thing I can think of is the meter bought he farm.
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W4IOW
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Posts: 34




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« Reply #3 on: May 26, 2012, 06:28:21 PM »

Well I haven't been in the controller so I am little help there. I think you're on the right track. Good luck!
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K1ZJH
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Posts: 884




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« Reply #4 on: May 26, 2012, 07:32:52 PM »

Is there a calibration pot in the Ham IV box?

It seems unlikely that the meter would be bad, but I suppose it is possible. I suspect they used
the same meter movement for most of the series, maybe going back to the TR-44?  You could
try one of the rotor repair shops to see if they have good, used meters in stock. I'd verify the
meter is really bad before going through that expense.

I assume you are reading about 500 ohms across the pot winding, and 250 ohms from the
arm of the pot (ground return) to either side of the outside legs at center of the rotation?

Peter
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AA4PB
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Posts: 12639




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« Reply #5 on: May 26, 2012, 07:38:07 PM »

One of the rotor repair companies like http://www.rotor-doc.com can probably supply a meter. This might also be a good time to locate one of the digital displays designed to replace the original analog meter.

If your DVM operates smoothly then I'd say it must be the meter itself that is defective. It probably has a bad bearing inside the meter but make sure that it isn't just a bent needle rubbing on the scale.
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W4OP
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Posts: 388


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« Reply #6 on: May 26, 2012, 08:26:04 PM »

Have you put the meter on a bench supply with a current limiting pot and run it through out it's range? Simle test.

Dale W4OP
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WA2OLZ
Member

Posts: 61




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« Reply #7 on: May 27, 2012, 05:31:28 AM »

Thanks for all of the replies. I appreciate the input.

K1ZJH: I also doubt the meter only because I've never sen one fail, but using my DVM in ins place works so that's what led me there. The pot does read the proper 500 Ohms and the wiper to each end 250 Ohms at center, tracking from zero to 500 through the rotation.

AA4PB: I found a reasonably priced meter on the Hy-Gain website, much less than the listed prices at the repair shops. I also sent Norm an email asking for a price but it's a holiday weekend so no reply yet. Thanks for the comment about a possible bad bearing. That seems to make sense for a few reasons. The control box was sitting undisturbed for 10 or more years in the basement. That alone can't be good for tiny bearings! I didn't mention in the first email that I need sometime 'flick' the meter with my fingernail as it sticks. That's strike two. I did manage to remove the clear plastic cover and very gently move the needle full scale. It's so delicate I doubt I would feel a bad/flat/dry bearing anyway.
I have seen pictures of the digital displays, but never one in person. That's a possibility but I imagine the price is far more than a replacement meter, even at fire sale prices.

W4OP: True confessions time: I have been out of the hobby for so many years I no longer have a test bench! That's silly, but the way it is. I'd likely spend more on getting the test stand set up than a replacement meter. Yours is a very logical thought, however.

Thanks again to all. I'll wait until Tuesday after the holiday to see if any deals pop up on a control box and, if not, go ahead and get the meter from Hy-Gain.

73/
Jack
WA2OLZ
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AA4PB
Member

Posts: 12639




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« Reply #8 on: May 27, 2012, 05:43:32 AM »

Jack, since you've got to get a new meter anyway, I'd probably take your meter apart and see if it could be repaired. Nothing to loose.

You may find some meters for sale on e-bay or ham sites. Some years ago people were replacing the meters with digital displays which left a number of unused meters available.
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K1ZJH
Member

Posts: 884




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« Reply #9 on: May 28, 2012, 03:01:43 PM »

Make sure the filter caps in the DC supply for the meter section haven't dried out. That's only other thing
I can think off--the DC supply has issues.

Pete
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KD0UN
Member

Posts: 55




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« Reply #10 on: May 29, 2012, 06:05:09 PM »

Better bet. Just pick up a control unit on eBay.  They are listed all the time.
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