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Author Topic: TH-D7A Blown Final. Worth Fixing?  (Read 3899 times)
KJ4KLM
Member

Posts: 19




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« Reply #15 on: November 15, 2011, 08:56:20 AM »

Its definitely worth fixing, but not by a third party. I'm sure someone who is handy with a soldering iron will take it off your hands. I doubt the total for the repair would be over $75 parts, but it's the labor that's expensive. Don't throw it in the recycling bin yet ;-)

So VE2DC,  I am passable with a soldering iron, but have no knowledge of the parts etc, I am no electrical engineer, and have no real testing equipment other than a good multi meter. If  you think that qualifies me to attempt this I am game to try.  I can't really wreck this much further and if I do, it was free. 

First, I really don't know what parts to replace.  I have downloaded the Service manual on this radio and (as you would expect) there was no part labeled "VHF Final" .  So can you or anyone tell me what parts I am looking for?  KA5IPF said the part was $46.  Thus I assume he must know what "The Part" is I need to try to fix this?  Someone else suggested that some of the other parts feeding "the final" might be bad which may have led to the the final being blown.  What are these parts which might have led to this and how do I test them?

Any elmers have some help on these questions before I jump into trying to fix it myself?

Lee
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KD4LLA
Member

Posts: 450




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« Reply #16 on: November 15, 2011, 10:45:17 AM »

"Someone gave me a TH-D7a"  Pretty much sums up the value right there...  If it were an easy fix, the other person would have kept it.

Mike
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N4NYY
Member

Posts: 4742




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« Reply #17 on: November 15, 2011, 10:57:22 AM »

Quote
So VE2DC,  I am passable with a soldering iron, but have no knowledge of the parts etc, I am no electrical engineer, and have no real testing equipment other than a good multi meter. If  you think that qualifies me to attempt this I am game to try.  I can't really wreck this much further and if I do, it was free.

There is more to it than just changing the final. As someone mention, there may be other failures. Then you may need a transmitter alignment. Then you may be working with SMD. And HT radios are packed like 100 lb of crap in a 5 lb bag.
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AD6KA
Member

Posts: 2232




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« Reply #18 on: November 15, 2011, 11:28:01 AM »

My Vote: Not worth fixing.

$43.00 for the PA may SEEM reasonable, but it's
NOT just a matter of replacing the PA.

SOMETHING caused that PA to blow, and it may
very well still be lurking in the rig.....


It may prove handy as a VHF/UHF receiver for testing
other radios. Or leaving on desk to monitor local repeaters
while you're futzing with other projects, etc.
73, Ken  AD6KA

PS: I agree with OM who posted that the
the fact it was "given" to you is a big clue.
Probably that ham is experienced to know
what the end charges will be.

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AK7V
Member

Posts: 249




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« Reply #19 on: November 15, 2011, 12:58:11 PM »

The radio was free.  Spend the ~$45 on the part and give it a shot.  If you fail at fixing it, you've likely got a $45 receiver.  If you succeed, you've got a $45 RX/TX, and a big confidence boost with regard to your soldering/electronic skills.
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N4NYY
Member

Posts: 4742




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« Reply #20 on: November 15, 2011, 01:05:20 PM »

Quote
The radio was free.  Spend the ~$45 on the part and give it a shot.  If you fail at fixing it, you've likely got a $45 receiver.  If you succeed, you've got a $45 RX/TX, and a big confidence boost with regard to your soldering/electronic skills.

Why would he want a $45 receiver when he already had a $0 receiver? Put the $45 toward a FT-60 or something. It is a better investment.
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AD6KA
Member

Posts: 2232




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« Reply #21 on: November 15, 2011, 06:22:22 PM »

Quote
I am passable with a soldering iron, but have no
knowledge of the parts etc,

Warm up that soldering iron and put the $45
towards an "SW+ Series" kit rig ($60) or a
"Rock Mite Series" kit rig ($29) from Dave Benson
at Small Wonder Labs.
   Grin

http://smallwonderlabs.com/

You'll not only have fun assembling it, you can
get on HF. Conditions keep getting better!
Much more fun than VHF/UHF FM, IMHO.
(uh oh, here come flames)
I'd get the SW+ for 20m or 30m,
but 40m CW can be a blast too.

73, Ken  AD6KA

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KJ7YY
Member

Posts: 13




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« Reply #22 on: November 22, 2011, 04:29:28 PM »

I like the "Small Wonders" idea as I am building a Retro-75 right now.  However, what you got to lose by tearing into the free radio?  Maybe the giver really doesn't know what is wrong.  Could be a simple loose connection or some such thing.  Never assume anything.  The worst you can do is break a radio that doesn't work now.  Good luck.
John
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AD6KA
Member

Posts: 2232




Ignore
« Reply #23 on: November 22, 2011, 07:34:08 PM »

Just for the hell of it, have you tried a Full Reset
of the radio?
A rest wont fix a "Blown Final"
but how was it determined for sure it was blown?
And what do you have to lose anyway?

With the power off press the F key, and turn the radio on.

Reset appears in the screen, now press up or down on the jog
cursor to select either VFO or FULL Reset, now press OK.

Now press up or down, and select Yes or No now press OK.

GL ES 73, Ken  AD6KA
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KC5CQW
Member

Posts: 98




Ignore
« Reply #24 on: November 27, 2011, 06:59:10 PM »

Worthless, just box it up and send it to me.
That way you'll never have to worry about it.
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KA5IPF
Member

Posts: 980


WWW

Ignore
« Reply #25 on: November 28, 2011, 08:13:58 AM »

First go to www.mods.dk and download the service manual. In the rf section board layout you will see the VHF and UHF Final module. The VHF Module is a M67798LRA (www.kenwoodparts.com). If you have a DVM you can check it. The end closest to the antenna is the output. The 2 middle pins are power. The last pin is the input. Call the input #1 and then check pins 2 and 3 for voltage when keyed. Pin 2 2.5v, pin 3 11v. If that's ok you need to find out if you have drive. I have in the past just touched a DMM to Pin 1 and if it went stupid there was RF there. Didn't hurt the meter. The output might but if it's the module there won't be anything there. Your call. DMM's are $4.95 at Harbor Freight for the throw-aways.

Replacing the module is easy just don't forget the heat sink compound. It probably didn't have any and that's why it failed.

N4NNY, that's why the power is turned down to 6w with 13.8 in. To not stress the module.

The main problem is heat dissipation, not battery life.

Clif Holland
www.avvid.com
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