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eHam Forums => Elmers => Topic started by: KJ4KLM on November 13, 2011, 10:42:38 AM



Title: TH-D7A Blown Final. Worth Fixing?
Post by: KJ4KLM on November 13, 2011, 10:42:38 AM
Someone gave me a TH-D7a yesterday.  The antenna needs replacing, but in addition they told me that the VHF Band A final is blown.  I haven't tested it yet, but assuming this is the problem, does anyone know what repair cost might be for this?  I am trying to determine if this is worth fixing.

Lee
KJ4KLM


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: KA5IPF on November 13, 2011, 06:28:30 PM
The final itself is $42.60 from Kenwood. Figure from there.

Clif


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: K1CJS on November 14, 2011, 05:18:57 AM
Don't forget to figure in the possibility of damage/strain to components in the final stage.  Sometimes replacing just the blown finals will bring the rig back to life, but sometimes that won't, and just results in blowing the new finals.


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: N4NYY on November 14, 2011, 06:30:56 AM
Is that a 5W final? Why so expensive?

If that is the case, I would nuke it.


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: KA5IPF on November 14, 2011, 09:59:31 AM
Can you build one for that?


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: KJ4KLM on November 14, 2011, 11:33:38 AM
Is that a 5W final? Why so expensive?

If that is the case, I would nuke it.

Actually I think that is a 6W final per the docs on the unit.

Lee


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: KJ4KLM on November 14, 2011, 11:44:31 AM
Don't forget to figure in the possibility of damage/strain to components in the final stage.  Sometimes replacing just the blown finals will bring the rig back to life, but sometimes that won't, and just results in blowing the new finals.

Yes that is my worry.  The Kenwood service center tells me they charge $75/hr. labor.  Plus parts and shipping. With the mentioned price of the Final and any other parts they find which might be bad. this could easily get to $150 in no time.. I can buy one of these old guys used for that much.  Unless anyone has any other ideas, I am thinking of sending the unit to the service center just to get an estimate.  If it is over 100 I will just tell them to ship it back and I will have a backup UHF HT for emergencies.

Lee


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: N4NYY on November 14, 2011, 12:44:56 PM
Lee. Sell it as Parts/Repair on ebay, and put the money toward a new one. You are likely looking at a $200 repair, when you factor labor and parts.


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: AC5UP on November 14, 2011, 01:09:16 PM
...or you could stop right where you are and think: " Hey, how cool is this? Just got a free scanning receiver to listen to NOAA and the local repeaters...! "

I'm assuming the radio has wideband receive. If not, paint it hammertone green and give it to...............................


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: N4NYY on November 14, 2011, 01:14:15 PM
Quote
...or you could stop right where you are and think: " Hey, how cool is this? Just got a free scanning receiver to listen to NOAA and the local repeaters...! "

I'm assuming the radio has wideband receive. If not, paint it hammertone green and give it to...............................

My FT-60 has weather, and it has no mods. The green hammertone is a good idea, though.


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: KA5IPF on November 14, 2011, 03:14:06 PM
Actually the data sheet shows 20mw in, 12vdc, and just over 16w out.


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: N4NYY on November 14, 2011, 03:19:25 PM
16W ? You are kidding, right? That battery must last 2 minutes.


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: KJ4KLM on November 14, 2011, 04:06:49 PM
Lee. Sell it as Parts/Repair on ebay, and put the money toward a new one. You are likely looking at a $200 repair, when you factor labor and parts.

N4NNY What do you think it is worth selling it for parts? it has three batteries and the Charger and a Prime speaker mike.

I do like the idea of just using it as a scanning receiver, though.

Lee


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: N4NYY on November 14, 2011, 04:38:29 PM
Lee,

If you want to use it as a receiver and it receives well, I like that idea, too. I only suggested selling it for parts if you have a repair cost of like $150-200. Otherwise, keep it.

You may be able to sell the batteries and mic, though. Keep enough batteries to use one while another is charging. My FT-60 came in useful as a receiver during Hurricane Irene. Tornado warnings and all !


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: VE2DC on November 15, 2011, 05:55:10 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 ;-)


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: KJ4KLM 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


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: KD4LLA 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


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: N4NYY 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.


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: AD6KA 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.



Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: AK7V 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.


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: N4NYY 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.


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: AD6KA 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.
   ;D

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



Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: KJ7YY 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


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: AD6KA 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


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: KC5CQW 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.


Title: RE: TH-D7A Blown Final. Worth Fixing?
Post by: KA5IPF 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