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Author Topic: Kenwood Repair.. TM-255A will not Transmit  (Read 9407 times)
W6TGE
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Posts: 154




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« on: December 17, 2012, 04:43:06 PM »

Does anyone know of a good Kenwood repair facility? Kenwood wants $75/hr with no idea of how long to allow. I guess Hamrepair has GREAT reviews so I should call Cal.

First, does anyone know if there is an easy fix?

I bought this rig new in 1995 and after 6 months we moved. It has been packed in its original box for all this time. So here is what happened when I tried it out last week!

1. It would not power on. I looked and there was info about adding a cap across C6 for the reset circuit. I did not do this yet, but as the TIP said, when the rig is cold, it will power up. So, I put it in the garage for an hour or so and yes it did power up OK.

2. OK, next I tried to transmit and it would not. I tried 144.2 SSB and 146.27 FM and I can listen but no transmit. The offsets were correct.

Is it possible that once the mod in 1, above, is done, it will work or does 1 have nothing to do with 2?

Thank you forr any help.

Dave W6TGE
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KA5IPF
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« Reply #1 on: December 17, 2012, 05:52:34 PM »

Define "Does not tx" No power out or not going into tx mode? Once the radio is up and running 1 will not affect 2.

Clif
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W6TGE
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« Reply #2 on: December 17, 2012, 06:09:05 PM »

When I push PTT on the mic, it has NO power out. I can hear a relay click. This is in SSB mode on 144.2 or in FM mode in 145.27. I tried a watt meter but also went to simplex and listened with another rig. It is not transmitting. I first noticed it when the repeater did not come up and then noticed that even on SSB the S meter lcd's did not move.

Receive is fine.
« Last Edit: December 17, 2012, 06:44:06 PM by W6TGE » Logged
WN2C
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« Reply #3 on: December 17, 2012, 08:51:54 PM »

Do you know what the final is in this radio?  I remember a power module used in some FM rigs during the mid to late 90' would go bad.  If they were taken out of the radio and opened, one could see the traces in the module.  Well, one of the traces would lift when it got hot and stop producing power.  Not sure if this is the same type of power module in the 255.  I think it was the SAV-17 module.

de wn2c  Rick
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KA4POL
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« Reply #4 on: December 17, 2012, 10:11:57 PM »

When you switch to transmit, does the TX indicator come on? Keep in mind, transmitting in SSB always requires some modulation for power output. So just being in transmit would not give any indication of power, unless the rig has a defect that is.
It may be as easy as wrong adjustments, but it could also be some part inside being the problem. So first check out the controls. If the rig has been sitting without use for such a long time there might be corrosion in some connectors inside or a bad capacitor. I doubt the final has a problem from just not being used.
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W6TGE
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« Reply #5 on: December 18, 2012, 11:25:39 AM »

Thanks all: I can check the power module type. There is no output even on FM and in SSB there is no modulation when I speak into the mic. The Signal strength LCD's are supposed to move when in XMT and speaking and they are not. Even if it were a bad Mic, I should hear a carrier on FM with a different rig listening. It does go into TX mode...at least the on air light thinks so.

As far as bad contacts goes it has been packed in a spare bedroom and NOT in a basement or garage.

I will get the CAP today and I think that C6 is in the small panel that I can detach. I believe there are a few small screws that I can take off and expose the back and find the C6/IC5 area.
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KE3WD
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« Reply #6 on: December 18, 2012, 05:45:59 PM »


As far as bad contacts goes it has been packed in a spare bedroom and NOT in a basement or garage.


That has diddly to do with controls and switches drying out from not being operated. 

You still could be just suffering from Ye Olde Dirty Switches.



73
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W6TGE
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« Reply #7 on: December 18, 2012, 07:11:02 PM »


As far as bad contacts goes it has been packed in a spare bedroom and NOT in a basement or garage.


That has diddly to do with controls and switches drying out from not being operated. 

You still could be just suffering from Ye Olde Dirty Switches.



73

OK, but first I need to put that cap across C6. Easy to take control panel off and now I need to solder the 10mfd cap across it. Hardest part is seeing it!

Then I will see what is going on.
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W6TGE
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« Reply #8 on: December 20, 2012, 02:59:33 PM »

Well, the cap fix was easy. I used a Radio Shack 10 mfd Tant cap across C6 in the control haad.

Now I need to see why it will not transmit!
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W6TGE
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« Reply #9 on: December 27, 2012, 04:10:31 PM »

When I push PTT on the mic, it has NO power out. I can hear a relay click. This is in SSB mode on 144.2 or in FM mode in 145.27. I tried a watt meter but also went to simplex and listened with another rig. It is not transmitting. I first noticed it when the repeater did not come up and then noticed that even on SSB the S meter lcd's did not move.

Receive is fine.

Clif, did you ever get my reply here? I did add the cap across C6 in the control head and it powers on OK now. Still no transmit on any mode, however.
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W9GB
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« Reply #10 on: December 27, 2012, 04:18:02 PM »

Kenwood TM-255A/E SERVICE MANUAL
Opening an Amateur Radio for DIY Repairs without the Service Manual is a Fool's Journey.
http://www.radiomanual.info/schemi/TM255_serv.pdf

Kenwood TM-255A/455A –
Partial reset with the power off press the A/B key, and turn the radio on.
Full reset press the MR key, and turn the radio on.

Here is photo of C6 repair you performed , Don Taylor, DL2KCE
http://home.scarlet.be/depreg/Mat_HAM/KENWOOD/Start%20Problem%20KENWOOD%20TM255_455.pdf

Lithium coin cell battery (located on control board) -- still good?
PAGE 44 in Service Manual
Kenwood part number: "W09-0599-05" Lithium Coin cell, 3 V, 210 mA. $6.00
IN STOCK at Kenwood Parts
http://www.kenwoodparts.com/parts/search.php
« Last Edit: December 27, 2012, 04:43:26 PM by W9GB » Logged
W6TGE
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« Reply #11 on: December 27, 2012, 08:41:27 PM »

Thank you. Yes, I do have that manual. Also, for some reason the battery is still good. Yes, that is the fix I did. I got a 10mfd 16v tant at Radio Shack and put it across C6.

The rig just will not transmit. All else is OK. In fact I listened to a SSB net Monday night. Not sure why xmt stopped after being in the box for almost 18 years!
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KA5IPF
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« Reply #12 on: December 28, 2012, 10:30:11 AM »

Start on the Tx/Rx unit A/5 CN2 and make sure you have all the voltages as shown in the SM. Especially TXB (transmit bias). If good there go to the Tx/Rx C/5 final unit and check the voltages on CN605, especially TXB and DB. That should give an idea of what is going on. If all those are correct time for a 'scope and looking around at signal levels.

Clif
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W6TGE
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Posts: 154




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« Reply #13 on: December 28, 2012, 02:04:06 PM »

Thank you Clif:
One thing I don't like is that when I opened the rigs covers I can smell "something". Not bad like something burned, but more like something got hot. This was not there before I tried to transmit. I wonder if I should have done a reset before I did anything else? I know it should not have mattered, but after I tried to transmit, it would only receive in FM. In SSB it would go silent. After a reset, all was OK again...except for transmit! I did want to look inside the cover where the finals were but the 6 screws were tight. I may try again to see if anything in there looks/smells bad!
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K1HC
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« Reply #14 on: January 01, 2013, 08:44:44 AM »

If you are still asking for recomendations on repair facilities, I would recommend N1EQ who fixed my TM-255A.  Just check out the Eham comments on him.  He has also worked on other gear for me successfully.  Very prompt too.

73,

Dick, K1HC
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