NRG PLL Pro III - will not lock

[BriansBrain]

Afternoon all
l have been running the NRG at 1.5W as the Exciter for the 150W Linear flawlessly for over a year now

NRG Pro3 PLL 1-4w Exciter - Completed - S.JPG

Turned on this morning the Green Lock Led did not come on
Unlock Red Led on all the time.
RF output stage is working fine tried out-of-lock bypass with J2.

Tried VC1 to see if I could re-lock = no.

VC1 will tune it to a frequency but very critical tuning.
I the DIL switches have no effect on the frequency.
Suspect the PLL circuit not producing.

NRG Pro3 PLL 1-4w Exciter - S.jpg

Any help would be appreciated... what do I look for next

.

[jvok]

First thing I'd do is check the 13.8v supply is close to 13.8v, and the 5v supply is actually 5v. Also check on IC1 pin 16 you should get around 7.5v

Next check IC1 pin 15 on a scope/frequency counter. You should get a 6.25khz square wave. If not somethings wrong with IC1 or the xtal circuit.

If that all works try and get it tuned as close as possible manually then check IC2 pin 11. You should get a roughly 6.25khz square wave there too. It won't be bang on because your tuning by hand but should be close. If not you have a problem with IC2, IC4, IC5, dip switches or maybe TR5.

If everything else checks out then your problem is IC3 or the circuits around TR1 or maybe the varactor.

[BriansBrain]

First thing I'd do is check the 13.8v supply is close to 13.8v, and the 5v supply is actually 5v. Also check on IC1 pin 16 you should get around 7.5v

Next check IC1 pin 15 on a scope/frequency counter. You should get a 6.25khz square wave. If not somethings wrong with IC1 or the xtal circuit.

If that all works try and get it tuned as close as possible manually then check IC2 pin 11. You should get a roughly 6.25khz square wave there too. It won't be bang on because your tuning by hand but should be close. If not you have a problem with IC2, IC4, IC5, dip switches or maybe TR5.

If everything else checks out then your problem is IC3 or the circuits around TR1 or maybe the varactor.

Useful info = Thanks
13.8v, = OK
5v = OK
IC1 pin 16 = 7.339V
Next check IC1 pin 15 on a scope - You should get a 6.25khz square wave = NO

[jvok]

Ok check for bad solder joints around IC1, R48, C60, C61 and the xtal. If no bad joints its probably one of those parts thats bad. My money would be on the ic or the xtal but could be any of them.

If you have to replace IC1 make sure its either a CD4060 or a HEF4060. You can't fit a 74HC4060 without making other mods

[BriansBrain]

Ok check for bad solder joints around IC1, R48, C60, C61 and the xtal. If no bad joints its probably one of those parts thats bad. My money would be on the ic or the xtal but could be any of them.

If you have to replace IC1 make sure its either a CD4060 or a HEF4060. You can't fit a 74HC4060 without making other mods

All joints checked = Same
I have ordered a HCF4060BE like the original

Thanks for your help

[LeeCavanagh]

I have the same issue on one board, I replaced ic4 (not ic1, but only because previously when it worked ic4 was getting hot, but stopped doing so, now after changing it still doesn’t get hot and does not lock, I had considered changing the other small pll ic’s but holding off
I still get output from the vco and the two rf transistors

One thing came to mind, I could have sworn it used to have a small wire going to ic4 but I don’t see that in pictures of the same board (potentially could have been someone’s FIX but I don’t see any bad tracks).

Anyway thanks for those helping in this thread.

[Albert H]

If the board has been dropped or banged, the crystal might have died (they're quite fragile). I always mount the crystal with slightly longer legs, so that it's slightly above the board, and its legs can go some way to absorbing physical shocks.

[Krakatoa]

I never had a 4060 or a crystal fail, but it all could be possible.
My suggestion here is to check if pin 12 on the 4060 is making contact to ground because it is the Reset pin. The schematic is missing a connection from pin 8 to GND also. A simple check with a multimeter for continuity between pins 8 and 12 in the IC itself will confirm that. Also it is worth checking for shorts to GND in all the parts that conform the crystal oscillator, just in case there is a microscopic solder slump making a short on the PCB.

[BriansBrain]

If the board has been dropped or banged, the crystal might have died (they're quite fragile). I always mount the crystal with slightly longer legs, so that it's slightly above the board, and its legs can go some way to absorbing physical shocks.

In my case the board in it's case had not been moved in over a year so

Question, what is the crystal in that board of mine ?
I can't read it even with my #6 glasses on
Because I might get a spare

[BriansBrain]

I never had a 4060 or a crystal fail, but it all could be possible.
My suggestion here is to check if pin 12 on the 4060 is making contact to ground because it is the Reset pin. The schematic is missing a connection from pin 8 to GND also. A simple check with a multimeter for continuity between pins 8 and 12 in the IC itself will confirm that.

Pin 12 on the 4060 is making contact to ground = 100% yes
+ Pin 8 to GND = 100% yes

Also it is worth checking for shorts to GND in all the parts that conform the crystal oscillator, just in case there is a microscopic solder slump making a short on the PCB.

OK.... but in my case it has been in the same position on the TX shelf working perfectly for over one year
Turned on one morning and the Green Lock Led did not come on

.

[jvok]

Question, what is the crystal in that board of mine ?
I can't read it even with my #6 glasses on
Because I might get a spare

Original manual with parts listing is here: http://www.gareth.net.nz/nrgdocs/Pro3_pll_1-4w.pdf

Its a 6.4mhz xtal. Manual doesn't say the load capacitance but looking at the circuit it should be around 30pf.

I can't actually find 30pf 6.4mhz xtals anywhere, only 20pf ones like this: https://www.mouser.co.uk/ProductDetail/ ... 1KKw%3D%3D

If you fit that xtal youll need to change C60 to around 18pf otherwise the frequency will be wrong or it might not even work at all

[BriansBrain]

Original manual with parts listing is here: http://www.gareth.net.nz/nrgdocs/Pro3_pll_1-4w.pdf

Its a 6.4mhz xtal. Manual doesn't say the load capacitance but looking at the circuit it should be around 30pf.

I can't actually find 30pf 6.4mhz xtals anywhere, only 20pf ones like this: https://www.mouser.co.uk/ProductDetail/ ... 1KKw%3D%3D

If you fit that xtal youll need to change C60 to around 18pf otherwise the frequency will be wrong or it might not even work at all

Big thanks for all the info

[mpx]

It could be the purple trimmer that adjusts the PLL voltage. Sometimes they fail randomly.

[BriansBrain]

It could be the purple trimmer that adjusts the PLL voltage. Sometimes they fail randomly.

The only trimmer on the board is VR1 which is the audio input gain control.
Why would that stop the PLL locking ?

NRG Audio input.JPG

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[radium98]

Vr1 is not purple violet .it is just a 10k trumpet to adjust audio level. The purple one is the variable capacitor 20 / 40pf that may fail .but is not necessary that this is the problem .I suggest you to check all the bc non and pnp .then get all the ic and change one by one .the easy way even the variable capacitor wich all cost nearly nothing except that 4056hct that cost a lot.

[radium98]

Same pcb

[jvok]

The fact theres no 6.25khz reference oscillator proves the problem is with the circuit around IC1/the xtal. Get that working before you try anything else.

Don't play with the VCO trimmers yet. If you can tune to frequency manually then we know the VCO is working fine

[BriansBrain]

The fact theres no 6.25khz reference oscillator proves the problem is with the circuit around IC1/the xtal. Get that working before you try anything else.

Exactly that's what I am doing waiting for replacement for IC1

Don't play with the VCO trimmers yet. If you can tune to frequency manually then we know the VCO is working fine

Yes I can tune to frequency manually
Again.... thanks for all your help

[LeeCavanagh]

Can someone explain why one of my boards has the green pll light on permanently, only sometimes will the red unlock led light if I tune the vco, what i’m not seeing however is the pll working (usually instant red then flicker green and eventually go solid green, but currently i’m seeing the opposite) also the dip switches are having no effect.
I measure the voltage of pin 15 suggested above and I get 7.44v (i’m guessing this is acceptable and close enough to 7.5 to still work).
I’ve ordered a new vco trimmer (although it does allow tuning and I can get it to hit my desired frequencies I feel it’s a little temperamental and it’s not smooth it sticks in places as it turns/ )

I don’t have a scope but I do have a small freq counter (will that be enough to test the output freq of the pll clock?)

Thanks all

[Albert H]

Yes - your counter should show 6.25 kHz from pin 15 of IC1.