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Old 19th Nov 2020, 3:29 pm   #1
Skylark UK
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Default Trio TS120V Not showing 21MHz Display

My first post!

I have a Trio TS120V which, until today, had been boxed, in my loft since I last used it in 1986.

Very pleased that it burst into life, albeit I've not used it to transmit as yet.

The display did not show frequency when the band selector switch was rotated to 21, 28, 28.5, 29 and 29.5MHz. After working the switch for a while and rotating the main tuning control wheel, the higher frequency bands now work. The 21 MHz band still isn't showing a frequency but it does show two dots.

I'd be very grateful if anyone had any ideas?

Thanks in advance

G4PYH


(I also have a Trio 830S and it's next to come out of hibernation )
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Old 19th Nov 2020, 4:22 pm   #2
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Default Re: Trio TS120V Not showing 21MHz Display

Welcome to the forum! Try easy things first,in view of your previous action with the rig, I would try cleaning all the switches with De-Oxit.Not cheap but superb.
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Old 19th Nov 2020, 7:45 pm   #3
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Default Re: Trio TS120V Not showing 21MHz Display

That sounds like PLL unlocked.
Since the 21 MHz band has a VCO of it's own maybe the problem is there although the band switch does provide BCD information to the PLL for configration purposes.

I suppose the right course of action is check that the switch is providing the correct BCD after you have "worked" it a bit. If it is then better suspect PLL Q2 the 21MHz VCO and associated components.

The TS120S service manual is not hard to find online (was it mods.dk I forget?) but the quality of what I have is not great. TS120V was same in most respects except different PA I believe. Good luck from a TS130V owner. I like 'em.
(BTW there is a display fault which loses odd segments in some digits. Bad diodes associated with multiplexing the decimal points was to blame for me.)

Last edited by Jon_G4MDC; 19th Nov 2020 at 8:01 pm.
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Old 20th Nov 2020, 1:34 pm   #4
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Default Re: Trio TS120V Not showing 21MHz Display

Thank you, both.
I’ve ordered contact spray and I’ll keep my fingers crossed.
I’ve also downloaded a TS120S service manual.
With only very basic test equipment, is it realistically possible to fault trace PLL unlock on 21MHz setting?
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Old 21st Nov 2020, 11:10 am   #5
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Default Re: Trio TS120V Not showing 21MHz Display

In most cases it should only need an ordinary multimeter.
A High Z DVM is preferred but an Avo 8 would also serve.

You would need to measure the data lines from the band switch for the correct BCD code. These will be logic levels in all probability maybe 5V or 10V. If these are correct then there is nothing wrong with the switch.

After that you would measure the PLL tuning Voltage which will in all probability be stuck at high or low Voltage depending on what is wrong.

The 21MHz oscillator tunes between 29.83 and 30.33 MHz. Another receiver capable of tuning that range might be useful but not essential.

[Edit] I have just spotted that there is another feed from the band switch to the PLL Board. The +Ve supply to the oscillators themselves is switched appearing at J17. If that is missing for the 21MHz Band it would be an obvious source of your problem.
Also while we're here J15 is where the band selecting BCD appears. I have added a screenshot of how it should be for 21MHz. The levels are TTL so 5V.
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Last edited by Jon_G4MDC; 21st Nov 2020 at 11:35 am.
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Old 22nd Nov 2020, 10:51 am   #6
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Default Re: Trio TS120V Not showing 21MHz Display

Thanks, Jon,

Very helpful. The switch cleaner hasn't arrived so I haven't as yet removed the covers. I'll report back in due course!

In keeping with forum "rules", I've added an Avatar of the head of this household
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Old 22nd Nov 2020, 12:17 pm   #7
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Default Re: Trio TS120V Not showing 21MHz Display

With a PLL, looking at the tuning voltage can give a lot of clues. Most use a phase/frequency detector and the tuning voltage will ram itself against one endstop if the loop unlocks. You do heed a high-Z voltmeter or a scope to look at it without too much disturbance.

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Old 22nd Nov 2020, 3:10 pm   #8
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Default Re: Trio TS120V Not showing 21MHz Display

An interesting development!

Still waiting for the delivery of the switch cleaner, I decided to check the transmitter output stages so I connected an SWR meter and dummy load. Very pleased to report that all seems well using both mic and key.

When I first switched it on, 3 days after it was last powered, the 4 28MHz frequencies all showed no frequency, just the two dots on the display. Fairly vigorous rotating of the tuning knob and the frequency re-appeared. Still nothing on 21MHz.

I left the set with power on for about an hour (lunchtime). After lunch, I selected 21MHz and rotated the frequency knob and lo and behold .......guess what appeared on the frequency display.

Subsequently selecting any other band, now all working, then returning to 21MHz, no frequency in the display. Rotate the tuning knob and it re-appears.

Does this make sense to anyone? Any pointers to a fix?

Many thanks
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Old 22nd Nov 2020, 3:43 pm   #9
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Default Re: Trio TS120V Not showing 21MHz Display

Not quite following you....is this purely related to the bandswitch?

Or is it (as I think it may be) that you switch to the 21MHz then tune around with the VFO (main tuning) and suddenly display appears? If that is the case the PLL Voltage Controlled Oscillator has probably drifted somewhat and you are "catching it" by tuning into the range where it can lock.

It needs to be set so it will lock reliably across the range. Lets be clear exactly what it is doing first.
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Old 22nd Nov 2020, 4:38 pm   #10
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Default Re: Trio TS120V Not showing 21MHz Display

Yes, Jon, just as you describe.

When I first powered the set after it being 30+ years in the loft, the display did not appear on any of the 5 band switches, 21MHz and higher, just two dots.

The other, 3.5 to 14MHz frequencies worked fine.

After working the selector switch and rotating the VFO, the 28MHz and higher frequencies started to appear. I did notice that the VFO position was fairly consistently reading 28,200 as the display burst into life. This happened after about 30 minutes of my messing around.

However, this method did not work for 21MHz, hence my OP.

Today, I wanted to see if the set was transmitting so I powered it up again. The higher frequencies didn't show again but the 28+ suddenly reappeared after just a few minutes by rotating the VFO. Again, the set burst into life with the VFO around the 200 position (range from 0 to 500).

21MHz still dead.

I left the set switched on for over an hour. When I returned to it, I selected 21MHz and rotated the VFO and the display finally appeared and was reading around 21,200 MHz.

So from your post, it does indeed sound like the PLL Voltage Controlled Oscillator requires resetting to lock reliably across all frequency ranges.

How is this done? Basic equipment and faltering knowledge I'm a retired mechanical engineer with a career in automotive supply chain so please be gentle.

Really appreciate the help and guidance, thank you
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Old 22nd Nov 2020, 5:06 pm   #11
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Default Re: Trio TS120V Not showing 21MHz Display

Just dirty contacts if you are lucky.The only other thing is dodgy capacitors ,if indeed they appertain to that band only.
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Old 22nd Nov 2020, 6:00 pm   #12
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Default Re: Trio TS120V Not showing 21MHz Display

Thanks for the futher explanation. It is definitely worth taking the Voltages from the Bandswitch and making they are all in order before starting to tweak with VCOs.

If the Voltages are all correct then it would seem that the VCOs might have simply aged away from the correct setting. I would have thought that unusual but it's not impossible. That would make them more willing to work at one end of a range than the other.

The 28-29.5MHz ranges all use one VCO so I would have expected that the "middle" ranges 28.5/29 should be probably OK and the issue would be on either the 28 or the 29.5 range but not on both. If it misbehaves on several ranges and then more often at the LF end than the HF then I start to wonder about the 8MHz VFO level but let's not jump the gun on guesswork. Does either of these behaviours match what you see please?

You mentioned in an earlier post having basic test equipment. What exactly do you have - in particular for measuring DC Voltages up to say 20V?

PS I like the head of the household.
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Old 22nd Nov 2020, 9:30 pm   #13
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Default Re: Trio TS120V Not showing 21MHz Display

There is a post on this problem, the probable cause and the likely solution on the MODS DK site at this link, uploaded to MODS DK by ZS2ACP:

https://www.mods.dk/view.php?Article...o-RX-all-bands

(It isn't appropriate of course for me to copy and paste the information on this forum).

Hope that might help.

Good luck with it.
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Old 23rd Nov 2020, 10:01 am   #14
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Default Re: Trio TS120V Not showing 21MHz Display

Interesting David & thanks. A pity that mods.dk only allows 1 article/day unless you subscribe. There were a few other similar contributions that it would have been good to read but now they will have to wait for tomorrow!

I'm surprised he thinks the VCO transistors fail..that's not impossible of course but I would have thought quite unlikely. I would be looking for some other reason - like Coils with "Q killer" wax that a higher gain transistor might still be able to make oscillate but I suppose if the transistor test method was good then so be it..
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Old 23rd Nov 2020, 12:30 pm   #15
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Default Re: Trio TS120V Not showing 21MHz Display

Around this time, the Japanese 'big three' were using ceramic trimmer capacitors in their VCOs which rotted apart where some of their usual brown locking stuff was slarted around VCO circuits to combat microphony.

The same trimmers in general circuitry survived, it was the anti-vibration guck which did them in.

If it's this, you need tweezers and infinite patience to pick the damned stuff off the board to be able to replace the capacitors, then you have to adjust them.

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Old 23rd Nov 2020, 5:38 pm   #16
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Default Re: Trio TS120V Not showing 21MHz Display

Thanks to you all for helpful suggestions.

Removing the covers, the insides looked clean and dust free.

Switch cleaner does not appear to have solved the issue.

With a mid-price digital meter, spec says 10Mohm, the voltage at pin 21 on J17 on the PLL board read 8.94v. The BCD code when switched to 21MHz correctly read pins A=1,B=1,C=1 and D=0. The voltage was 4.88v

Not sure if it was too liberal a spray with contact cleaner, my inability to put the covers back on correctly or simply that it's had its day but the set now has a new fault.

As soon as it's turned "on", selector switch to "Rec", not "Send", a relay clicks and the meter goes FSD. But it's not putting power out and no longer receives.

The mic PTT and mic gain control are still able to put power through to the dummy load. When the mic PTT is pressed, the meter needle goes back to rest and the ALC responds normally to speech. Release the mic PTT and the meter goes FSD again after a relay clicks in. Seems to be a VOX issue.

I looked at the MODS DK link, thank you. The article didn't disclose the symptoms and/or what led him to look at the car unit so it's unclear to me. That said, there's a guy clearly breaking down a TS120V on ebay and has the car unit for sale at £24 + postage.

Would appreciate any further advice but I think my nextis to search a local repairer

I'm reluctant to give up on the unit and, because it's 12v, I'd like to use it Maritime Mobile sometime next season.
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Old 23rd Nov 2020, 7:55 pm   #17
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Default Re: Trio TS120V Not showing 21MHz Display

No, don't give up on it.

I think I have had this latest problem you describe on my TS130V and it was down to some issue with the VOX. Can it be that one of the 3 VOX adjust knobs on top was moved when removing/replacing the covers?

That would explain it going to TX but can it explain the S meter behaviour? Sorry but I forget.

I think we can help you resolve the problem with the lock/display so I really wouldn't advise buying any boards or going off to a repairer yet. Unknown boards could be as bad or worse than what you have after all!

You have the right Voltages from the band switch so that is a good start. Find the VOX issue and hopefully get back to where you were and we can get started on what is really wrong. Good Luck!
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Old 5th Jul 2021, 9:26 pm   #18
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Default Trio TS120V Not showing 21MHz Display

Mods,
Is it possible to re-open the historic thread with the above title from last November 19th posted by Skylark?

I took on this repair for David.
I have an update.


I checked the inputs to the PLL board:
PSUs - OK
10MHz - OK
500KHz - OK
BCD signals at J15 to IC Q16 74LS163 - All OK, noted 7MHz and 14 MHz setting give the same code
Checked the switched feeds at J17, all OK
Checked Q2, seemed OK with reasonable gain above 100, swapped it with Q5 from the 3.5MHz (working band) and the problem did not move with the transistor
Checked C12 - low ESR good capacitance
Bias resistors OK
so I believe this stage to be working OK

TP1 was showing a low signal when the 21MHz band was malfunctioning
The PLL sprang back into life when the VFO frequency was increased as originally advised by David.
Setting it at the threshold point between functioning and not functioning I was able to determine temperature sensitivity (using freezer spray and also hot air gun) around D15 and Q16 (2SC460)
slight heat on D15 got it working until it cooled again (seconds later) Freezing stopped it working for a while. So I surmised the reduced forward voltage due to heating was helping to increasing the signal level, hinting at a possible cause due to low signal level.
Changing D15 had no effect
Q14, Q10, Q11 (2SC460) all measured low gain ~30 these were replaced by BC182L. This seems to have fixed the PLL, it is working reliably on all bands even when chilled.

Note: the removed low gain transistors have the black oxidation on the leads. I have seen transistors before that have failed with this oxide present. Some remain working with the oxide I know but is there a causal link here...

Regarding the other reported problem with the RF meter...
It is behaving as follows:
RF gain at maximum, meter shows minimum deflection
RF gain at minimum, meter shows maximum deflection.
Same behaviour on all bands

Can anybody please comment on the above meter behaviour if you know this set

Thanks
Chris
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Old 5th Jul 2021, 11:13 pm   #19
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Default Re: Trio TS120V Not showing 21MHz Display

Photos: Schematic extract of PLL and PCB

Green highlights show areas initially under suspicion that eventually proved to be OK.

Red highlights show failed components that have been replaced.

Yellow highlights show marginal, possibly still OK parts that were replaced b new for good measure.

I might decide to change all the 2SC460B transistors for good measure since at least 3 have already failed.

BC182L seems to work fine but is there a better substitute for the 2SC460B?
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Old 6th Jul 2021, 1:46 am   #20
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Default Re: Trio TS120V Not showing 21MHz Display

Quote:
Regarding the other reported problem with the RF meter...
It is behaving as follows:
RF gain at maximum, meter shows minimum deflection
RF gain at minimum, meter shows maximum deflection.
This is the normal action on many HF receivers that have an RF gain control and AGC.

Think about it - what does the AGC do? In order to keep the audio output more or less constant, the AGC voltage reduces the gain of the IF (and sometimes the RF) amplifier on strong signal and with a weak signal turns the gain up high.

What does the "S" meter do? It indicates the approximate level of the incoming signal by measuring the voltage on the AGC line, so with weak signals it reads low and strong signals it reads high.

What does the RF gain control do? It adds a voltage to the AGC line thereby reducing the gain of the IF amp AND it moves the "S" meter - clockwise reduces the added voltage and increases the gain so the "S" meter reads lower and you hear the gain increase by the noise level coming up.

Some radios will have a switch on the RF gain control that turns the AGC on when fully anticlockwise and as soon as the switch has operated, the only variable gain is via the control - others just swamp the AGC voltage but allow the signal-produced AGC to still override the RF gain voltage.

Hope I haven't made this too complicated.
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