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Kenwood TS440S Too high voltage in VCO 5 (7.8v versus 5v)

You know what, I'm an idiot. You can skip all the audio stuff and just poke the varactor watching the test point. If the PLL is getting both signals and solder joints are good and doesn't respond to that, its probably toast. Hearing the 5kHz signals is just for fun really. Sorry for rambling, I just thought it was cool spying on the internal workings without a drill bit.
 
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Thanks Brandon, I am just slow with it. Re: VCO 4 (radio on 27mhz rx) If I probe D3 it changes audio and drops the TP1 voltage down a bit (7.8v to 7.6v) . TP slowly rises on startup to nearly 7.8v after 5 minutes and sits there pegged out.

I just decided to check all voltages as shown in schematic. I can see IC1 (MN6147C) is not getting any voltage on pin 8 and 16 (orange):

vcco 4 test point voltages.jpg


I'm confident I have the skills to to replace that IC, I have a solder sucker.

Trying to work out if I can somehow test the IC - was going to start probing a good one vs IC1 to make any comparisons in diode/resistance checks between pins.

Maybe I need to bite the bullet and swap the IC's around from VCO 4/5 like your saying. IF I did that - would that mean I would get SSB RX but loose FM RX if IC1 was faulty? I'm just thinking out loud - I'm not into FM anyway. For me its really just SSB. I can also buy a replacement IC for $27AU.

And thankyou as always for your time. I feel like a broken record thanking you all the time but you deserve it.
 
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Not having 2v on pin 16 makes me think that PLL is shot. There is no other source of DC except from inside the IC, so I think it is a safe bet saying the IC is gone.

edit to add if C15 were bad, the reading would not be zero, it would be the emitter voltage, so that cap has to be good.
 
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Posting this here is probably a total waste of forum space, but I can't stop wondering what would happen if you ohm'd out pin 16 to ground with the radio off. Is it a short, or some kohm value? .17vRMS signal into an inverter is going to need bias. Maybe, if you are lucky, it was just the internal bias resistor that gave out. Could it be possible to use an external resistor to pull that pin back up to 2v?

It's probably not worth the time, but I know I would be curious enough. Nothing to lose there but time.
 
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brandon7861 said:
what would happen if you ohm'd out pin 16 to ground with the radio off. Is it a short, or some kohm value?
Click to expand...
Reading open with no resistance to ground no matter what ohms range I try.

brandon7861 said:
It's probably not worth the time, but I know I would be curious enough. Nothing to lose there but time.
Click to expand...
I'm always willing to give it a try!

Are you saying tap a voltage source from the radio and bias to supply 2v with a resistor and then supply that to pin 16?

Getting excited - I feel like there may be a chance of getting it working. I found the IC now for $17AU. Was going to do a one off solder joint side check (again) on VCO 4 and IC1 traces before I order it.
 
I wish there was a better datasheet for that chip. Most of it is chinese and there is very little information about the inner workings.
No reading at all is not what I expected for something that supposedly has 2v dc on it with no external source. I expected a divider of some sort. Being it is a CMOS chip, maybe those resistors are megohm range and your meter can't see them. IDK.

Looking at the PLL datasheet again, I see it shows a minimum input of 1v pk-pk, which is odd given the manual/schematic has .17Vrms noted on that signal line.
1763690074142.png

1763690123157.png

If you did want to try sticking 2v into that pin while it is on, you could take 3 resistors, a 47k, 33k, and 100k, solder all three together on one side, then take the 47k leg to pin 18 4.8v supply, the 33k to pin 1 ground (the two pins on the end of the IC), and the 100k to pin 16. This would put 2v on that pin.

Ask anyone else here and they would rightfully say that this is a waste of time, its just something I would try out of curiosity/desperation. Chip swap is the best option if you want to save yourself the headache.
 
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Thanks, Just trying to scrounge up the resistors to try that with what I have on hand. Today I ordered the replacement chip (mn6147c) so in a weeks time I'll put that in.
 
lf you already have a PLL coming, may as well just wait. The odds of that resistor trick working are about the same as mc. d's new monopoly game being legit.
 
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Well Brandon , I think its working!!! Looks like that may been the RX problem. I will verify tomorrow with a second radio and report back. I just installed the new PLL into IC1 (mn6147c from aliexpress) and the 3khz sweep thingy is gone on startup and it has proper volume and no weird noises. Sounding like it should be - stable. Intermittent dot problem gone as well. PLL was $AU20 inc postage so it was worth it to get it up and running.

I have a feeling the ATU unit is not working (no motor noise) and I'm not sure of its TX state either but I'll start looking into that shortly.

Without your help there was no chance of me isolating that chip. Thanks again Brandon. Thanks Tech 5 for your help as well. :)
 
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Cool! That's great to hear! Hopefully everything else is working ok with the other VCO's now, such as RIT and FM. Hopefully it is just a alignment away from being back on the air.
 
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Unfortunately I think I spoke too soon. Today I've been testing with second radio. The second radio was really hard to hear - very low in static/signal on the ts440 regardless of RF Gain position or if I had a screwdriver in antenna socket.

At the same time it was blowing the doors off my old Navaho CB even with RF gain turned down.

I cant hear RIT changing tone either but IF shift does. I havent tested FM yet. I'll go back to checking all VCO TP voltages and see where I'm at. ie Try to align whatever TPs are stable or ballpark and hopefully identify a problem area. Will also check the rest of the PLL IC's pinout voltages on the PLL Board.
 
Just to clarify, you did hear the second radio, just really quiet? Or did it not come through at all? If you heard it, even quietly, thats a really good sign.

Let's see if the PLL is legit, getting its data, and doing what it should be doing.

Using your FM receiver again, see if the 91MHz is there. As mentioned in post 73, it should be 91.3 in USB/CW, and 90.7 in LSB.

If the 91MHz is there, try going back to manual wide on the filter and see if your second radio comes through better.
 
brandon7861 said:
Just to clarify, you did hear the second radio, just really quiet? Or did it not come through at all? If you heard it, even quietly, thats a really good sign.
Click to expand...
Turns out I did not hear it at all on supposed frequency and what I could hear was actual bleed though my laptop speakers nearby. Sorry for the bum steer.

Putting headphones on for the ts440s receive today, I found its doing similar to before, in that a 27.405 LSB transmission is actually being heard muffled/scratchy at 27.500 onwards, probably about 27.505, ie 100khz high.
brandon7861 said:
Using your FM receiver again, see if the 91MHz is there. As mentioned in post 73, it should be 91.3 in USB/CW, and 90.7 in LSB.
Click to expand...
Looks like IC1 is oscillating, I get the quiet noise for those frequencies. I've also have correct voltages now on pin 8 and 16 that were missing before. Attached a pic of the new IC1 with old ic below it:

20251204_144751.jpg


VCO 4 TP1 is now stable at 4.3v (should be 6.4v). It was drifting before IC1 replacement. I haven't tried adjusting any of it yet.

I can see a VCO 3 problem as well and I think IC4 and IC9 could be faulty as well.

To be continued shortly...just wanted to commit this post in case I have power outage while I'm having lunch.
 
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At least the replacement PLL made a positive change, so we were not wrong about that much. I am starting to think this thing saw a nearby (not direct) lightning strike that could have been just enough to kill the sensitive gates.

With the other VCO acting up, it too is probably toast. Chances are, anything CMOS could be damaged. Might be time to make a list of everything CMOS and check them out one by one. At least the micro is sending the correct data and clock signals, so that much survived.

I think we should go straight for the CMOS stuff and, rather than attempting to get one block at a time working, we should try to make a list of everything that we can identify as bad. If we end up hitting one bad chip after another buying them one at a time, part shipping could exceed the radio's value.
 
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brandon7861 said:
At least the replacement PLL made a positive change, so we were not wrong about that much.
Click to expand...
Agreed, 100%. Definitely was a step in the right direction.

brandon7861 said:
I am starting to think this thing saw a nearby (not direct) lightning strike that could have been just enough to kill the sensitive gates.
Click to expand...
I would not be surprised and I think that's a great theory because when I first got this radio it had a lot of surface rust and the bottom stand was removed and it looked like it had been bolted under a shelf (top cover had extra holes from bolts etc).....and my first thought looks like it come out of yacht around salt water or something.....

Looks like IC4 (another mn6147c) is missing voltage from pin 16 as well and its associated VCO 3 TP is drifting on startup like our VCO 4 before replacement from 3.6v to 7.7v in a couple of minutes. But then randomly that same TP tests at 0.7v. Delayed replying because I'm trying to find a consistent result. I think its the only TP that drifts now on PLL Board.

IC9 may be ok - still trying to work it out - has a bit of rust on pins throwing out readings. I just want to check every reading 10 times over before I blame that one.

brandon7861 said:
I think we should go straight for the CMOS stuff
Click to expand...
As a beginner are you saying checking all IC's? I dont even understand what your saying at this point :( I remember you saying your washington was TTL? <-I dont even know what that means. I'm on top of things!! :)

brandon7861 said:
If we end up hitting one bad chip after another buying them one at a time, part shipping could exceed the radio's value.
Click to expand...

Yeah, I hear you. Thats a worry for sure. If its only another IC or two I probably would attempt to fix but yeah I agree it could get out of control. I guess I'll try my best to test the other IC's on PLL Board at this stage.
 

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