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1-8 of 8 messages
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Page 1 of 1
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Ft-726r tuning problem
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by K1MCN on August 27, 2004
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I have a ft-726r that the vfo dial dosn't work when the unit is cold. after it warms up for a while the tuning works fine.
I have isolated the problem to the control board. I have used freeze spray to locate an area that seems to cause the problem. I replaced several of the cmos IC's and did a lot of resoldering around the area but still when it's cold the unit dosn't tune. I am thinking that it must be a cap or possably a resistor in the area? I cann't really direct the freeze spray in a fine enough area to isolate a single component.
Is it possable that a cap or resistor could be cold sensitive? I have never run into this problem before.
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RE: Ft-726r tuning problem
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by KB1SXD on October 19, 2009
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I also have a FT-726R with the same sort of start up problem. I just purchased it at a local hamfest, but found problems as described below:
I've had SSB and FM contact on the radio with good reports, but it takes exactly three and a half minutes for the vfo to start working after start up. Then it's very stable. I was told that I was on frequency on SSB which agrees with my frequency counter readings on FM.. Watt meter / dummy load shows correct output.
I did find an additional problem that may be related to the 1st. The s-meter reads past +20 on any frequency on ssb or cw mode for the 1st half hour or so. After that it settles down and is fine. Durring this time the receiver acts like its receiving a dead key. This doesn't happen on FM. Durring the half hour the meter slowly works its way back to near 0 and the sensitivity improves as it goes. At the very first moments of power up on ssb its ok, but the meter slowly rises and static disappears in about 3 seconds.
I started to question the internal power supply voltage and tried connecting 13vdc to the rear dc input, but it did the same thing. The problems are the same on both the 2 meter and 70CM modules so I had ruled those out for now. I did take the cover off the vfo and gave it a good cleaning with contact cleaner, but that didn't help.
I really like this radio so I'm pretty serious about getting it working right. If anyone can steer me in the right direction, I would appreciate it.
Chris
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RE: Ft-726r tuning problem
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by WA4ZZW on October 22, 2009
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My 726R has been apart for over 6 months with this same problem. I replaced the IC's and the caps but no luck. I have looked at the scope traces and can see the weak voltages at the IC but the optical encoder pulses look OK. I'm still don't know what the problem is.
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RE: Ft-726r tuning problem
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by KB1SXD on October 22, 2009
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Hi WA4ZZW,
Just wondering.. Does your's also have the sideband / cw issue I described. Would be nice to know if that is also a symptom of the VFO issue. I gave that control board a kind of shot gun approach with re-touching all the solder joints to no avail. The one thing I did notice was that cooling spray to the Q05 (NEC D8255AC-5) programmable IC did seem to re-create the problem after warm up. Not sure if this is conclusive as the cooling spray might be enough to throw off a good IC anyway. Did you happen to replace that one? I've ordered one of those ic's and it hasn't arrived yet.
On the SSB / CW issue, I also noticed that turning the "tone" control counter clockwise makes the problem worse. Might be a clue as all the front end controls pass through that control board..
Good luck and I'll post again if I find any more clues / solutions..
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RE: Ft-726r tuning problem
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by WA4ZZW on October 22, 2009
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Hello,
The two problems are unrelated I think.
I once had the problem you are talking about.
The S meter goes to the peg till it warms up in SSB and CW. FM is OK.
This problem turned out to be it an AGC problem in the receiver board.
I change out many parts till I found a small cap across the AGC line
that was leaky. Take a hair dryer and heat up the receiver board which
is on the bottom of the radio. If it goes away you probably have the
same problem.
The AGC circuit is high impedance and it does not take too much to
pull it down.
I could measure the AGC voltage with a good meter and see this happening.
All I remember was that it was a small ceramic cap. When the meter
finally starting moving back down it would be OK in just a few minutes
seems like.
I still don't know about the VFO problem. The IC's are set up as
schmitt trigger. That's what the caps and resistor do.
It's like something is pulling the input voltage down on the IC's
until it warms up. I even though about some sort of leaky path in the
PCB board.
I need to get it back together so I can work on it's other problems.
6 meter module has very low output and I fear the PA module is bad. I
blew the the FET in the two meter module and the replacment does not
seem to work. 432 was working until I started on the VFO.
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RE: Ft-726r tuning problem
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by N1WBD on October 22, 2009
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Chris as you and I and several others have mentioned this topic these problems are being seen all over the place and reported on the Internet but we have'nt found the answer. I hope someone here can help. It's like finding a needle in a haystack. :-)I'll keep searching.
Bob
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RE: Ft-726r tuning problem
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by KE3WD on October 24, 2009
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Look for a hairline break in a PC trace around that circuitry.
Power off and ohmmeter may find it, helps a lot to have schematic in front of you and trace connects from point-to-point sometimes. Other times, under power and use voltmeter to look for a power or ground trace break.
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