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Author Topic: Kenwood TS-440S now Working: Certain Bands Have Momentary Dots  (Read 246 times)

WA4ZYN

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Kenwood TS-440S now Working: Certain Bands Have Momentary Dots
« on: November 14, 2022, 11:48:13 AM »

Hello again.  I had a previous thread regarding my “dotty” Kenwood TS-440S.  I tried all suggestions and known “fixes” for that.  Eventually, I found working PLL and RF boards, and installed them.  That brought the 440 back to life with good receive and full output power.  I then found a working encoder and installed it, thus fixing the “lagging” and skipping tuning action.  There is just one lingering “issue”:  On power-up on certain bands, dots flash momentarily before locking on the frequency display.  It’s very quick, quicker than anything I have to measure with, but it is concerning that it might mean eventual failure again. 

I went through all the VCO’s yesterday, making sure voltages were correct in each.  At the suggestion of a friend that it sounded like it was a VCO1 issue, I picked out the residual brown goop there and while in the neighborhood, I replaced the 5 electrolytic caps in VCO1, in case it was a slowly-charging capacitor. After all that, the problem still exists.  I will pull out my oscilloscope next, but in the meantime I’m open to hearing from anyone who might have seen this issue before. 

Thanks in advance for any and all suggestions.

73,

Francis WA4ZYN
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WA4ZYN

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Re: Kenwood TS-440S now Working: Certain Bands Have Momentary Dots
« Reply #1 on: November 14, 2022, 11:54:18 AM »

I’m attaching the link to a YouTube video showing what the 440 does on power-up on certain bands.

https://www.youtube.com/watch?v=qqK2mk3n7cc
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KB1GMX

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Re: Kenwood TS-440S now Working: Certain Bands Have Momentary Dots
« Reply #2 on: November 15, 2022, 08:45:11 AM »

If the VCOs are incorrectly adjusted lock up will be spotty.

The goop has toe be scrubbed out, period. It contaminates
over time and messes with the VCOs (detuning) and is the
primary cause of Dots.

In the end you didn't fix it, you just put in a board with the
same problem and cause only not as bad... Yet.

I know, I have a TS440S/AT and did the full treatment
including parts with rotted legs from the goop.


Allison
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WA4ZYN

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Re: Kenwood TS-440S now Working: Certain Bands Have Momentary Dots
« Reply #3 on: November 16, 2022, 06:58:35 AM »

Well, sure, it’s not totally “fixed.”  I had tried all the on-line “fixes” for the dots. With the previous PLL board, since VCO5 would not adjust to function,  I had totally stripped VCO5, thoroughly cleaned the board, rebuilt VCO5 with new components, reflowed solder for entire board, and it still didn’t help.  Yes, at that point I gave up and put in a working PLL board.  For the RF board I stripped out VCO1, thoroughly cleaned the board, then rebuilt with new components.  Then reflowed solder on entire board. The replacement PLL board got rid of continuous dots.  “Repaired” RF board “worked”, but then I had practically no RF output on transmit. I then decided to bite the bullet and replace the RF board too.  Now I just have dots on start-up on some bands, but full RF output.  Yesterday I made some adjustments on VCO1, which got rid of dots on all bands, for a while.  Now I have a problem with VCO1-1, which I think is bad solder.  I can adjust T21 to it’s “proper” voltage, and all dots go away, but then, after a while, the voltage there drops and dots come back 22-30MHz. 

So, yes, I “cheated” a bit by replacing entire board, and bought myself another set of problems.  I am still learning how to repair radios.  In the meantime, I am learning quite a bit, and I believe I will eventually save this old 440 from the junk pile.  That’s worth a lot to me.

I plan to re-solder all components in VCO1-1 today.  If that doesn’t help, I will totally rebuild that section.  The other VCO’s in VCO1 adjusted yesterday to function properly, after I removed some residual gunk. 

Thanks for your help and suggestions.
73,
Francis WA4ZYN
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KD6VXI

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Re: Kenwood TS-440S now Working: Certain Bands Have Momentary Dots
« Reply #4 on: November 16, 2022, 11:36:14 AM »

Download the service manual.

Do a full alignment.  Complete.

If that doesn't fix it, you have a good problem.

I love the TS440.  It took me 3 times to fix the dots on mine. 

I HATE Sonybond.

--Shane
WP2ASS / ex KD6VXI
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W2NAP

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I AM THE VOICE OF THE VOICELESS!
https://www.w2nap.com User & Service manuals and more.

WA4ZYN

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Re: Kenwood TS-440S now Working: Certain Bands Have Momentary Dots
« Reply #6 on: December 06, 2022, 05:03:26 PM »

Tnx for the suggestion and the link.  I have the service manual, which has been invaluable.  I swapped in another RF board that has a totally-rebuilt VCO1, and all dots go away.  So, I am now rebuilding VCO1 on this board.  I had hoped to avoid going that far, and had feared it might be in the IC17 circuit on the PLL board.  The board with the known good VCO1 showed me IC17 is functioning.

73,
Francis WA4ZYN

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WA4ZYN

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Re: Kenwood TS-440S now Working: Certain Bands Have Momentary Dots
« Reply #7 on: January 19, 2023, 10:06:50 AM »

Update 1/19/2023:  Well, I got rid of all dots by replacing the RF board with one I had worked on previously.  On that board, I had rebuilt VCO1 successfully.  The only problem left is no transmit output power.  Ugh.  I just posted about that on another of my TS-440 threads:  DRIVE from RF board measures at 90mV, and no output from PA.  Gonna measure all voltages and trace signal on the PA board to find where signal drops out, but I think DRIVE level should be more than that.

Tnx es 73!
Francis WA4ZYN
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WA4ZYN

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Re: Kenwood TS-440S now Working: Certain Bands Have Momentary Dots
« Reply #8 on: January 22, 2023, 05:55:28 AM »

Further update 1/22/23:  I know that my 440 has low drive output from the RF board, but I wanted to verify that the PA board was functional.  I “experimented”, and drove it with the appropriate level of RF from my signal generator.  Still no RF output.  I then pulled the PA board and discovered a blown trace in the 14V line going to Q1 (predriver) and Q6 (driver bias).  That would definitely explain no output despite appropriate drive.  So, another thing to repair in this 440. 

Tnx for reading.
73,
Francis WA4ZYN
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WA4ZYN

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Re: Kenwood TS-440S now Working, MOSTLY
« Reply #9 on: January 26, 2023, 06:48:02 AM »

Well, this 440 continues to be the “gift that keeps on giving”.  I finally gave up on the malfunctioning RF board and replaced it with a working one.  Result:  NO dots, and good DRIVE output on transmit. BUT, still no power out.  I pulled the PA board back out again, after having repaired and wired around the blown trace. What I discovered was C25 (electrolytic) had a hole blown in the side, and one of the final transistors is shorted base-collector.  Oh, boy.  I have ordered replacement finals, and will check the rest of the board for shorts and other issues before risking new 2SC2879’s.  I went ahead and replaced all five electrolytic caps on the board “just in case.” 

I may be an idiot for putting so much into this old rig, but I don’t want it trashed or parted out.  I want it to have a second chance.  And, I’m chalking it up to a learning experience for diagnosis and repair. Maybe when I get a little better at this sort of thing, I will actually figure out what is wrong with the RF board that I removed.

Tnx for reading.
73,
Francis WA4ZYN
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