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Author Topic: Kenwood TM-733A Duobander with no output on 2 Meters (VHF)  (Read 5981 times)
KA4POL
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Posts: 1907




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« Reply #15 on: March 07, 2013, 09:38:09 PM »

My fault, I did not check the connector that actually leads to the UHF board. However, if Q232 is not working there should be a problem for both modules. What might be worth checking is the connecting cable from UHF to VHF board then.
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WA4ZYN
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Posts: 39




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« Reply #16 on: March 08, 2013, 07:47:29 AM »

Thanks for checking that out.  I've been confused about the Q232 issue.  There seem to be no problems with UHF.  Which cable connects UHF to VHF?  Is it that ribbon cable toward the front of the radio? 

Thanks again!
73,
Francis
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WA4ZYN
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Posts: 39




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« Reply #17 on: March 08, 2013, 09:51:19 AM »

As an addendum to the problems with this 733, I just tried it out on 440.  I had assumed it was working (and it certainly has output power), but was just told by a friend that I broke the squelch on the local  440 repeater, but had no audio.  I am wondering now if this little rig is even salvageable. . .

Thanks again, everyone.

Francis
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KA4POL
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Posts: 1907




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« Reply #18 on: March 08, 2013, 10:45:23 AM »

The audio would be a second battle to fight.
Looking at the service manual, which is only a bad copy, I could not find any connector. I see the markings FB and DB on the drawings. Could both PCBs sit on top of each other and the connection is like a bolt? It must be close to the terminals FB and DB.
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KA5IPF
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« Reply #19 on: March 08, 2013, 03:00:31 PM »

Bingo, there is a brass pin going between the 2 boards. FB and DB are tied together

The 2A is total dc current drawn by the radio. If the current is around 8-10A then the switching diode is open. If the current is low the module is no good. The FB and DB voltages are correct.

Clif
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WA4ZYN
Member

Posts: 39




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« Reply #20 on: March 09, 2013, 07:28:36 AM »

I had mentioned that I found out I had no audio on my 440 output, even though it puts out full power on 440.  Yesterday I tried listening on another radio while transmitting, and my friend was right.  Whenever I key the PTT, I hear a signal, but the audio is just very loud static.  I took that microphone and connected it to my TM-G707, and got great signal/audio reports.  So, it's not the microphone as I had hoped!  A microphone would have been a relatively "cheap fix." 

I'm gonna have to rethink this 733.  It may not be fixable.  I hate that.  Does anyone have an immediate idea of what could cause this lack of audio problem?

Thanks to any and all.
Francis
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WA4ZYN
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Posts: 39




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« Reply #21 on: March 09, 2013, 07:40:49 AM »

Another question:  in trying to dissassemble the 733, I have found that I cannot remove the VHF circuit board.  I have removed all screws, but it still doesn't budge.  Are those two large solder points just in front of the PA module connecting this board to the UHF board? 
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KA4POL
Member

Posts: 1907




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« Reply #22 on: March 09, 2013, 07:51:52 AM »

Those are the ones for FB and DB voltages and they must connect.
The audio goes through IC 411. An oscilloscope would be helpful to see if there is any unwanted change. Also check the inside connection of the microphone connector for good ground etc.
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W6AOA
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Posts: 35




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« Reply #23 on: March 11, 2013, 07:25:48 PM »

Francis,
I have  Kenwood TM-731A which is very similar and the 70cm amp module went out on mine. I tried to open the case of the amp mod, but just prying it apart from all the adhesive ruined it. Try removing the VHF module and jumping the input to the output with a small wire. If all else is well you prob get about .6 watts at the antenna.  The 70cm amp I finally did find was about $90 the the supplier only had one..   Most of those who have them want to sell minumums (10 or more). Be sure not to transmit without the proper dummy load or antenna connected.  Good luck hope this helped..
Ed  W6AOA Pensacola..
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WA4ZYN
Member

Posts: 39




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« Reply #24 on: March 12, 2013, 06:42:40 PM »

Thanks.  That is a great idea.  I will try it next time I pull the 733 out.  I hit a wall (kept myself from hitting the wall with the 733!), and put it all in ziplock bags to deal with another day.  BUT, next time I pull the critter out, I'll try your idea. 

I had no problems opening the module up, and DID find some cracks, but had NO luck repairing cracks.  I see places where I can find replacment power modules, used and/or new.  One is in China (on eBay)--the Icom equivalent of the S-AV17:  the SC-1091 (80 bucks new from RfParts).  They want $45, which I think is a bargain.  If I had the budget right now, I'd go for it.

I have full output on 440, but found I had no audio.  Darn.  Tore into the front end, and found an IC which was missing one pin because of corrosion.  That happens to be an IC that is an audio amp for the microphone.  I figure that's my culprit.  That IC is an NJM4558E, and believe me, that one is a trip to find!  It's officially "obsolete."  I have found, like you, many who have it in stock.  Ha!  I keep finding the IC's for anywhere from $0.50 to $13.99 each, for a minimum of ONE HUNDRED!  Gee.

Ain't it fun? 
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KA4POL
Member

Posts: 1907




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« Reply #25 on: March 13, 2013, 12:06:24 AM »

If I had the budget right now, I'd go for it.

I keep finding the IC's for anywhere from $0.50 to $13.99 each, for a minimum of ONE HUNDRED! 

Time to start a business  Grin
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WA4ZYN
Member

Posts: 39




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« Reply #26 on: March 13, 2013, 06:11:19 PM »

Ha!  I'll think about it.  Hey, are there 99 other hams out there looking for a NJM4558E or a Toshiba S-AV17?  Maybe we could work something out. . .

73, all.
Francis
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WA4ZYN
Member

Posts: 39




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« Reply #27 on: March 17, 2013, 07:53:56 PM »

Well, I have gone through the 733 some more.  I was unsuccessful repairing either the PA module or the bad IC.  I don't have the cash to replace these components, so I have decided to put it up for sale on eBay as a "parts radio."  Thanks so much, everyone, for the suggestions and encouragement.  I had hoped that the radio's problem would be something simple like a broken trace or a bad solder. 

73,
Francis
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