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Author Topic: Kenwood TS-940S  (Read 1764 times)
N8HQV
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Posts: 8




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« on: March 09, 2008, 09:18:49 PM »

I am having a problem with my TS-940S rig.  When I turn it on, it will operate about 5-10 minutes.  The audio drops out and the display shows decimal points (dead).  I then turn off the rig and reset the microprocessor by holding in the A=B button and turn the power back on.  It will work again for about 5-10 minutes and the whole thing starts all over again.
Any ideas before I send it out for repairs?
Thanks
Mark
W4EET
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N6AJR
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Posts: 9910




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« Reply #1 on: March 09, 2008, 11:03:21 PM »

does that have an on board battery to hold memory, they get weird when the battery dies
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K7UNZ
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Posts: 691




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« Reply #2 on: March 10, 2008, 06:41:23 AM »

I can't really answer with a solution to the problem Mark, but I can tell you that it's a common problem in the '940S.

In fact, a friend brought over his a couple of months ago and said "here....it's yours if you want it!"

Was showing all the indications for a dead memory battery, but after replacement it was still the same thing.

Another odd thing....the user manual states there are "two" batteries in the rig, but I've only been able to fine one (hi)!

At least this one runs fine after the "A=B" trick at start-up.  In fact, left it running (RX) for three days and it was still spot-on with WWV.  Unfortunately, it's a pain bringing it up from scratch every time you want to use it.

Looked thru many, many pages on the internet concerning this problem, and some had been corrected by the usual solutions, and some stated that even Kenwood didn't know what the problem is.

I'd suggest the easiest things would be to make sure all the screws are snug and connectors are seated.  But there also seems to be a problem with dry solder joints.

Good luck!

73, Jim/k7unz


 

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WQ3T
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Posts: 209




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« Reply #3 on: March 10, 2008, 07:01:21 AM »

Virtually every TS-940S(AT) either HAD, HAS, or WILL HAVE problems with the PLL/VCO circuitry. This is evidenced by distortion on receive and/or transmit, "all dots" on the display (which temporarily go away when the dial is spun), or intermittant transmit output. If you have a TS-940S(AT) that exhibits any of these problems either full time or intermittantly, your rig needs the FULL MONTE treatment!

http://www.ham.dmz.ro/kenwood/ts-940s-pll-unlock.php
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N3OX
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Posts: 8847


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« Reply #4 on: March 10, 2008, 07:18:05 AM »

"In fact, left it running (RX) for three days and it was still spot-on with WWV.

This happened with my TS-440 (very common problem with some hygroscopic rubber in one of the VCO circuits ; absorbed water vapor detunes the VCO and makes the PLL unlock)

Leaving it on all the time worked for me.

Haven't worried about it for a while because I got a new radio but in the case of the TS-440 it's possibly a relatively easy fix.  In fact, scraping out most of the rubber from the relevant VCO seemed to work OK.  

I think maybe scraping out the rubber and resetting the VCO to the proper test point voltage is probably better and maybe I'll try that.

I have no idea if the problem is the same in the TS-940.  I know there's an *alternative* problem in the TS-440 that involves cold solder joints but the VCO5 problem seems to be the one in my rig, maybe something similar in yours.

73,
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
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