Broadcast PLL - Veronica NRG 2025

[jvok]

How/what or were do I check or measure that ?

Not easily. Is the circuit identical to the original NRG? If it is then check carefully for faulty/incorrect components, bad solder joints or shorts, especially in the circuit between IC3 and the varactor. If not then you're probably best changing it to match the original.

Also when you say it doesn't lock, have you actually measured the frequency? Or are you just basing that on the lock LED not coming on? Could be that its locking fine but something in the lock detect circuit isn't working.

Sorry I posted the wrong results before... should be

Cold = +5.0211V
Warm = +5.0279

Looks fine so not that then.

Out of interest, what happens if you turn it off, short out all the caps in the loop filter to discharge them, then turn back on again? Does it lock up straight away or take ages again?

[BriansBrain]

To add to the checklist: try replacing C4.

Also double check C4 is the right way round.

C6 is another candidate for leakage although ceramics are usually better than electros

So... last thing last night... took the board out of the case
Firstly - looked and yes C4 was the right way round
Then... I replaced C4 & even C6
Put it back together in the 19" rack - turned on - it locked quickly as usual when hot
Adjusted VC1 to a perfect 3.2V @ emitter of TR1.
Turned OFF and finished in the workshop for the night.
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This morning when it was cold, turned ON.... and - BINGO - it locked up in just +/- 5 Seconds

Looks like I have found the slow lock-up problem guys - thanks a lot for the help

Unfortunately both capacitor sustained damage during removal so any testing would be pointless

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