NRG PLL Pro III - will not lock

[LeeCavanagh]

IC1 supply (pin 16) should be around 7.5V. This is a CMOS 4060B. It’s supplied from it’s own 7.5V Zener Diode. The 74 series chips are supplied from the 5V rail (as is the HC4059).
When you tried to use your frequency counter on the logic signals, did you connect the counter ground to the PCB ground ?

Yes i used pcb ground

[LeeCavanagh]

Ok I have purchased a scope

When I put it into ic1 pin 16 I do get a square 6.25
My green led is still lit all the time (except for when I put my finger onto vc1, but i’m still getting,85 instead of.80 on fm radio, which I can tune out till it warms more
Also still getting heat on R37
R48 tests as 96k which is likely within tolerance
I’ve replaced C69 with a new 30pf

Now I have the Scope can this help me fix ???

And pointers where to go next

I also replaced c45, c46, c47 c48, c48,,c53, c62

I could replace c51,,c52. ??

Any ideas maybe around the pll ??

[jvok]

What do you get on IC3 pin 9?

[LeeCavanagh]

What do you get on IC3 pin 9?

I don’t get a reading on ic3 pin 9

[Shedbuilt]

How about IC3 pin 6 ?

[LeeCavanagh]

How about IC3 pin 6 ?

Nothing
But I do get 6.25 on ic3 pins 14, 12, 10. (Maybe another down that side which I have forgotten between the office and my bed)

Thanks

[jvok]

Some other places to check:

IC2 pin 11
IC2 pin 6
IC5 pin 23
IC5 pin 1
IC4 pin 6
IC4 pin 3
IC4 pin 8
IC4 pin 11

[Shedbuilt]

How about IC3 pin 6 ?

Nothing
But I do get 6.25 on ic3 pins 14, 12, 10. (Maybe another down that side which I have forgotten between the office and my bed)

Thanks

Sorry. Should have read IC2 pin 6, not IC3 pin 6 (half asleep myself).

[Shedbuilt]

If you have nothing at IC2 pin 6, it means IC2 is not receiving the divided down output from the 4059. I was following the same methodology as jvok (if nothing at IC2 pin 6, check at IC5 pin 23 (other end of the PCB track), IC5 pin 1 is the input to the 4059, coming from IC4 pin 6 (commoned with IC4 pin 2) etc, working back, through the logic, towards the oscillator. Some of this will depend on what type of scope you have, frequency capability etc.

[LeeCavanagh]

Ic5 pin 23 nothing

Details of my small scope are (i will revisit the faulty board after some lunch, thanks for your advice. Deffo not getting anything on ic2 pin 6, line jumps up but 0hz, (rms 4.99v) where as ic1 pin 15 does show 6.25
I notice on a working Board i get 12.5 on one of the pins on ic3 i dont get that on the faulty board.

Will try your advice after food, as nothing good comes from an empty stomach.


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[jvok]

Right if you're getting nothing on IC5 then check pin 11 on IC4. You should get half the output frequency there. Just like shedbuilt said your tracing the signal path through the divider chain from the VCO to the pll and seeing where it disappears.

120mhz analog bandwidth should be good enough for this. Even if the signals don't look perfect your just trying to see if theres something there or not.

[LeeCavanagh]

Getting 50.2 (rather than 50.4) on pin 11 ic4

Nothing still on ic5 pin 1 or 23

I have to keep pressing auto on the scope for it to lock onto a new freq.

Driving me nuts it is, i’m going to have to put it to one side for a while as squinting has giving me a migraine

Thanks for all the info
I’m wondering if ic4 has some solder hidden beneath the chip socket.

[shorty]

You said you have a working pro3 board, why not remove the ic's one at time from the non working board and try it in your working pro3, see if you working unit will still function with ic's from the problem transmitter.

Could be a duff ic, if your good transmitter no longer works you'll know which ic to replace.

[jvok]

Ok the fault is definitely IC4 or something near it. Check for any shorts or loose solder joints on/near the ic first, if not then most likely the chip is bad. Good thing is you can still get nos 74als74 on ebay, or you could replace it with a brand new 74AHCT74 (has to be the AHCT version, normal 74hc might not work).

Worth a try pulling IC4 out first and check to see if r37 is still overheating, if not then thats a fairly good sign the ic is dead. Oh and maybe feel the top of IC4 with your finger and see if its getting hot too

[LeeCavanagh]

You said you have a working pro3 board, why not remove the ic's one at time from the non working board and try it in your working pro3, see if you working unit will still function with ic's from the problem transmitter.

Could be a duff ic, if your good transmitter no longer works you'll know which ic to replace.

That’s true of course, but I worry sometimes the ic legs can snap even being gentle pulling them out with ic extractors

[LeeCavanagh]

Ok the fault is definitely IC4 or something near it. Check for any shorts or loose solder joints on/near the ic first, if not then most likely the chip is bad. Good thing is you can still get nos 74als74 on ebay, or you could replace it with a brand new 74AHCT74 (has to be the AHCT version, normal 74hc might not work).

Worth a try pulling IC4 out first and check to see if r37 is still overheating, if not then thats a fairly good sign the ic is dead. Oh and maybe feel the top of IC4 with your finger and see if its getting hot too

Yes pulling out ic4 does stop r37 cooking (god only know why that fuse isn’t designed to kick in with this kinda thing)
Anyway, thanks for yours and everyone’s patience, I recall mentioning that I thought a wire or some blob of solder was present when I got it, and turns out some solder had remained around pins 3/4/5 ish,hidden away I was able to refit the ic holder after removing the excess solder and swapping out the ic as old one rendered useless,, and viola she is alive once again.

Thanks all
I should have gone with my gut nearer the start, would have saved on some components but I do plan on finding a couple of project that they will come in handy for

I now have 2 working pll pro 4, and 1 working pll pro 3
And Albert convinced me to get the scope so that will come in useful in the future no doubt

Thanks all

[Albert H]

Lee - you're blind without a 'scope! Even a basic one can give a useful visual representation of what's going on in your gear. It's well worth spending some time learning how to use it properly. You'll find (for example) that the trigger sensitivity setting will have a radical effect on how clear your display is!

[LeeCavanagh]

Lee - you're blind without a 'scope! Even a basic one can give a useful visual representation of what's going on in your gear. It's well worth spending some time learning how to use it properly. You'll find (for example) that the trigger sensitivity setting will have a radical effect on how clear your display is!

i agree, i will watch a few youtube videos, thank you

[Shedbuilt]

Good news there. R37 will limit current, to the point that it will prevent enough draw to blow the regulator. If you put a dead shirt on the 5V rail, R37 would blow. Resistors used in this way (sacrificial in the face of a short circuit), are often raised on ceramic standoffs (sometimes sleeved around the resistor body too), to prevent carbonisation of the board if they overheat and blow.

[Albert H]

I used to HATE the fusible resistors that Bext and a couple of other manufacturers used to install. If they failed, they ALWAYS caused excessive damage to the components around them! I've got a couple of Bext driver boards here that can't really be returned to service (even though the basic problem is fixed) because they look wrecked - burnt, smoke-damaged and obviously overheated, usually with some of the thinner nearby PCB tracks peeled away from the fibreglass!