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Old 25th Mar 2020, 11:01 pm   #1
sentinel040
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Default Kenwood TK-359 VCO adjustment.

I hope these ex-PMR radios are old enough to come within the forum limits.

I have a couple of these, one I have had on 70cms for the best part of a decade and more recently another fell into my lap. The latest victim to enter the collection of tantalising tat has recently surfaced to the top of the pile file and it seems to work OK on the original frequencies, I say OK, the VCO locks up and it heard the sig gen on the bench.

However, there is always one of those it seems, when I reprogramme this more recent addition the VCO is out of lock. The two radios are the same variant, and whilst not strictly covering 70, the first one does so without any apparent bother, although it was on 70 when I first obtained it. I have spent some time trawling around the murkier corners of the internet trying to unearth a manual and full set-up procedures, but with a frustrating lack of success. I have found some limited information on the TK-250, which frustratingly gives some VCO tuning voltages and refers to Pin 3 of connector CN501, but does not give any indication where that is actually situated. That is also assuming that the information for the TK-250 is applicable to the TK-359. Perhaps I should have stuck to Pye Cambridges after all.

Consequently I come cap in hand to the great repository of knowledge to see if anyone can help, OK I admit I am creeping, but when needs must the devil drives!

Regards and best wishes,

Ian G8KSZ.
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Old 26th Mar 2020, 9:29 am   #2
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Default Re: Kenwood TK-359 VCO adjustment.

Quote:
Originally Posted by sentinel040 View Post
Consequently I come cap in hand to the great repository of knowledge to see if anyone can help, OK I admit I am creeping, but when needs must the devil drives!
Lummee, how do you follow that?

I don't know those sets at all, but I assume they have a straight-forward single-loop PLL synthesiser, done with dividers and PSD on a chip?

Often the PSD drives a 'charge pump' which applies width modulated pulses of current to a passive CR network to ground. The filtered DC component of the voltage biases the varactor diode in the VCO.

If these guesses are reasonable, then the tuning voltage is a very good point to look to see how a loop is performing. The synthesiser will hold a VCO on pretty much exactly the right frequency right up to the point where VCO tuning errors mean that the varactor bias reaches the limits of the voltage that the charge pump can supply.

These phase detectors, implemented as a few flip-flops and gates are phase-frequency detectors, so if they can't get phase lock, they at least steer the tuning voltage as far as it can go in the right direction. By monitoring the tuning voltage and doing some finger poking in the RF parts of the VCO, and setting the full range of frequencies the synth can do, you can get an idea of how much voltage swing the charge pump can really give.

Varactor diodes go nasty and lose Q at their low voltage end, but in radios with limited supply voltages available, then there may be no other option than to let it go low at one end. Low is less than 1v of bias. At the high end they might be able to get within 0.7v of the power supply rail voltage feeding the synth chip.

Once you've guessed these voltages, tune the synth across its range and see how well the tuning voltage fits between the goal posts. Seeing it hit an end stop as the thing loses lock gives you a confirmed kill of one of the limits! A bit of twiddling will be needed if it starts getting too close at either end.

It's likely that the same synth runs on the channel freq on transmit, mut offset by the IF freq for receive. If you're lucky the designer put in a switched capacitor in the VCO to help with the tuning range needed for this offset. You still need to check tuning voltage across the full band in both transmit and receive modes.

If you can ID the synth chip, then a data sheet and applications note can give a lot of help in the absence of a manual for the radio.

All finest guesswork. Contents liable to settle!

David
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Old 26th Mar 2020, 6:21 pm   #3
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Default Re: Kenwood TK-359 VCO adjustment.

David;

Well, having given my remaining pair of brain cells time to settle and folded my tongue back out of my cheek.....

The first hurdle at which I fall is that the TK-250 manual, or part thereof, that I have found and may or may not be similar to the TK-359 (the 200 series seem to be VHF and the 300 series UHF equivalents), does not give a layout or a complete circuit. It provides simplified extracts from specific part of the radio that tantalise but do not really help. Also, the internal layout and screening means that I cannot see what is what anyway. I suspect this last point is why the manual gives a measuring point on a connector - because you cannot easily get at much else. Its just where is it!

Regards

Ian G8KSZ

PS - By the way, if you ever need a signalling system designing for your monorail let me know.
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Old 26th Mar 2020, 9:30 pm   #4
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Default Re: Kenwood TK-359 VCO adjustment.

That's usually an indication that there might have been a full service manual for that radio. Kenwood wouldn't have wanted a lack of good info slowing down their own repair technicians doing warranty work that came out of Kenwood's pockets

Signalling system? I thought I only needed the german lady with the very very piercing voice to shout orders at people "Svitch on der nuclear reactah!"

David
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Old 28th Mar 2020, 2:53 pm   #5
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Default Re: Kenwood TK-359 VCO adjustment.

David,

Thank you, the problem is despite looking, including on slightly dubious potentially virus riddden websites, I have not found a full manual. Usually I manage to find some suitable documentation, or manage to find my own way through it, but this is one of those times that I cannot and a manual eludes me.

(I still think your monorail would need some form of signalling, or control and command in modern parlance. Otherwise, when a some hero or other throws a spanner in the works and said german lady and associated cat have to use the monorail to head to the escape pod, you need to also be able to let goons come the otherway as well! )

Regards

Ian
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Old 28th Mar 2020, 6:29 pm   #6
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Default Re: Kenwood TK-359 VCO adjustment.

Yeah, I guess that's it put on hold until some info turns up.

Did it get flogged under any other model numbers in other markets? There might be something in the UK under Trio. You might be able to track down someone who was at Lowe's in Matlock. It's got to be out there somewhere.

Yup, I'd have to take the cat with me to the escape pod - I'd get lynched on this forum otherwise The shouty lady and the goons are needed to slow the hero down while cat and I make good our escape.

One cat at the stables I named "Geronimo' because he'd leap straight into the middle of anything going on. Some people nearby had a pet ram that used to wander round. So there I am doing some rather heavy welding on the tractor and a shaggy sheep comes to rub against me while I've got tens of kW of flame on the go... sheep lack survival instincts.
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Old 30th Mar 2020, 3:55 pm   #7
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Default Re: Kenwood TK-359 VCO adjustment.

David,

Hmm, Inshallah, methinks.

I have continued to trawl around and the net is empty, I did find a reference to a manual that had been on sale in the states for the TK-250 and it seems to be the one I have downloaded, only my download is minus the circuit diagram and layout pages shown in the example pics of the one for sale. Although the internal layout of the TK-250 and TK-359 are slightly different I have discovered over the weekend. So there is probably a specific TK-359 one anyway.

The irony is some time ago when I read, out of then pure interest, about setting the VCO on these, I am sure it was a post by someone from this forum, posting elsewhere, but I just cannot remember now.

As you say it is probably time to place it back in the pile file and see what else I can find to play with. There are plenty of options of other radios to wreck!

I agree with sheep and survival instincts, I keep my traction engine on a sheep / cattle farm. Some years ago I had sheep run down a field en masse, struggle through a fence then stand on the railway track in front of me, not the best of moves.

Take care and thanks.

Ian (G8KSZ)
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Old 31st Mar 2020, 8:47 am   #8
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Default Re: Kenwood TK-359 VCO adjustment.

A suggestion for you Ian, many on here have dealt with similar sets before and if you posted a picture of the internals front and back there is a fair chance the VCO trimmers could be identified from them.

You would probably have to sort which is TX and RX by experiment.
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Old 4th Apr 2020, 1:33 pm   #9
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Default Re: Kenwood TK-359 VCO adjustment.

John et al;

Thank you for your comments and sorry for the delay, being away from home caring it has taken me a while to find a digital camera on which I could select a low enough resolution.

The problem is not so much finding the trimmers/cores, I think I have worked out where they are, they are the pair grouped together towards the centre of the chassis in the attached images. The problem is finding the relevent test point to measure the associated voltages. I have tried to see if I can get it lock by merrily twiddling them, gently and slowly; after making a careful of note where I started! But no luck on that approach, not that I really expected it to be a success.

Regards and best wishes

Ian (G8KSZ)
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Old 4th Apr 2020, 1:58 pm   #10
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Default Re: Kenwood TK-359 VCO adjustment.

That looks like microprocessor, power supplies, audio sort of board.

The other one, seen through the hole in the casting may be a better candidate.

David
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Old 4th Apr 2020, 3:38 pm   #11
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Default Re: Kenwood TK-359 VCO adjustment.

Yes can clearly see 2pole and 3 pole helical resonator filters.
In Pye sets that used to be a 2pole between Ant & RFamp then 3 between RF Amp and Mixer. The slugs in these were a polythene type material as seen here.

I think the other 3 adjustments are more likely what you are looking for except I'm not sure what it is lurking down the holes in the casting. Are all 3 the same?
Trimmer capacitors or potentiometers I wonder. It doesn't look like inductor cores...

2 capacitors and 1 pot might be good. 2x VCO adjustments and TX peak deviation maybe.

Do you have an RTL-SDR dongle? (the ones that were used for Digital TV but which can also tune VHF / UHF)
Makes a good poor mans spectrum analyser even if you can only span max of about 1MHz.

One of these with a bit of wire for antenna, placed near the chassis, would enable you to find the VCO quite easily and
then you can watch what happens as you tweak. You will see it pull to a fixed frequency when you hit lock. This way you might get away
without having a testpoint to measure tuning line Voltage.

(Later added: A further thought, the fact that the dielectric trimmers for what I called a 2pole filter are some way apart might mean that actually they are the VCO adjustments. Then they could be single resonators 1 TX 1 RX maybe... On reflection I think you already concluded this. )

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Old 6th Apr 2020, 10:43 pm   #12
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Default Re: Kenwood TK-359 VCO adjustment.

Thank you both.

Sorry for the slow response, acting as a carer and so sometimes between that and work I have limited time to myself.

Yes the RF deck will be the one beneath the screen, the control board being hung out of the way, I try to disturb those flimsy connectors as little as possible. The idea being to give a general view of the inside of the radio, it being slightly different to the TK-250 layout. As I mentioned, probably not very well as I knew what I was talking about , I believe the VCO adjustment to be the two cores towards the centre of the image, rather than the radio. Looking at the RF deck with a torch and a small hand magnifier, I wish I was in the workshop/office back home in Staffs rather than using the dining table down here, I can now see the following next to small lands on the pcb, These are marked as - PE, CK (clock?) and DT located next to the ribbon cable going to the control(?) pcb and LO, SV and RF doted around the board. I wonder if any of those are the VCO adjustment measuring points, or is that too much to hope?

Unfortunately I do not have a TV dongle, or much kit at all, down here in London.

I have attached a few more images I took this evening, I am getting this radio well trained, it almost comes apart when I whistle. They are specifically of the RF side, the block being the PA I assume. The image suffixed '48 is from the screen side (I tried to remove that but it did not want to move) and is what I assume to be the VCO cores (which probably means they are not...). The image suffixed '45 is a general view and '50 a closer view of the area, just to the left of the connector, that tallies with where the cores shown in '48 are. That is probably as clear as mud.

Regards

Ian (G8KSZ)
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Old 6th Apr 2020, 11:06 pm   #13
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Default Re: Kenwood TK-359 VCO adjustment.

Peeping through the hole looks to be a mini helical filter like Toko used to make. If so it would appear to be a rather good receiver with a band-specific RF filter rather than one of those infinitely wide and overloadable general coverage ones. The mixer and synth shouldn't be far away, so one of those trimmers may be what you need.... but which one?

How hard is it to get the board out?

David
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Old 7th Apr 2020, 7:27 am   #14
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Default Re: Kenwood TK-359 VCO adjustment.

David;

The RF board is multi-point soldered into the outer frame, amongst other things, not quite mission impossible, but..... There are three screws going through it into the screening die casting shown in image '48. One screw has to be removed to take the outer "tinplate" screen off to gain access to the print side of the RF board, removing the other two results in no movement. I wonder if there is/are others coming into the screening die casting from through the front panel? If so getting to those would be, shall be say, "interesting".

As you say a proper receiver, in fact all in all, a proper job. All that's needed now is to find that pesky test point; which is why I tried to remove the die cast screen to see what is below; but, considering matters, it would (or at least should) have to be easy to "get at" for initial setting and / or subsequent re-alignment. Well in theory anyway.

73

Ian
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Old 7th Apr 2020, 7:46 am   #15
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Default Re: Kenwood TK-359 VCO adjustment.

Ian,

I know nothing about these but would any of these sets be similar?

Andrew
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Old 7th Apr 2020, 10:56 am   #16
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Default Re: Kenwood TK-359 VCO adjustment.

Aye, you not only need to find theright trimmer, you also need to find the tuning voltage test point. The two things are needed together, so as they've done peep-holes for the twiddlers, the tuning voltage has to be proddable without pulling the board.

It looks like you definitely need service info to go further without risk.

David
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Old 7th Apr 2020, 11:04 am   #17
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Default Re: Kenwood TK-359 VCO adjustment.

That oval window with the SMD Caps in it is there for a reason. Maybe tune Voltage is measurable there? Worth a prod with a meter.
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Old 9th Apr 2020, 6:58 am   #18
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Default Re: Kenwood TK-359 VCO adjustment.

Thank you all;

Andrew, thank you, but I have already trawled through those in vain hope!

Jon, I wondered too, but there appears no reason for the shape of the holes, or no reason my eyesight and brain could come up with; but I might just have a second look.

David, I learnt many years ago that to some extent, and in my case at least, that experience gained is proportional to items ruined, so I do intend to place this on the back burner. I tend to be a bit tenacious so it will not be a case of giving in, rather watching and waiting.

When, not if, I find a solution (pays to be positive) I will let people know, so its easler for the next person.

Thanks again.

Regards

Ian
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