Semi manufacturer takeover - do parts change?

Hmm any other changes to the pcb? New layout, different caps?

George H.

Does it start at a harmonic or a completely different frequency?

Faster rise time or lower drive impedance parts can sometimes cause curious effects and 32kHz xtals tend to react badly to being overdriven.

What's the exact symptom? The 4046's oscillator will generally work over a range of more than 100:1 (often even 1000:1) but the guaranteed specs aren't what you'd call microscopically precise.

Cheers

Phil Hobbs

Are you still getting a part labeled HEF4060B or one labeled 74HC4060?

(The 74HC4060 datasheet says, "... _pin_ compatible with the HEF4060.")

It's quite possible that the fab facility was changed. Some years ago I was involved in moving all of ON-Semi's 'HC line to a different process house. The hardest part to match new-to-old performance was the 'HCU04 inverter... commonly used for crystal oscillators.

You may need to adjust the values of the drive resistor and the "pi" capacitors. ...Jim Thompson

Excellent point, Martin. I wonder if the crystal manufacturer rather than the IC manufacturer has changed something.

Gate-based XOs are always tricky. The crystal parameters, the external caps, and the gate behavior all interact, so things need to be tweaked to work, and an apparently OK tweak could be marginal. The semi process could have changed, for instance the new gate could be faster than in the old process, have less phase shift, and not oscillate with your old parts.

Play with the caps and any resistors in the circuit, to get you back to marginal operation.

I always buy packaged oscillators, which always oscillate.

Parts change. Like JT and JL said, analog functions implemented on digital processes have the most trouble.

Two or three decades without a problem is pretty good, actually.

I was in charge of maintaining a board for a while that had an MC1594 on it: at least once a year the factory would change the process, which changed the offsets or gains, which required tweaking resistors on the board. So your life could be much worse.

Well, this happens all the time, unfortunately! One thing is, you may have to change the resonating caps on the crystal to get the crystal to start up un the right harmonic or fundamental. If the oscillator completely fails to start, a resistor across the crystal may be needed. if it starts at the wrong frequency, then the resonating caps are wrong. A few pF up or down may be all it needs to fix the problem. A small change to the chip layout or packaging technology could cause a few pF change in terminal capacitance.

Jon

Nope, all EXACTLY the same. Some work ok some don't.

It starts up at roughly twice the fundamental.

Its the same part number - HEF4060B.

It's used in a battery supplied low power design. 4060's from other vendors were tested but the current consumption is too high with the alternatives.

Less drive power and a low pass filter should fix it.

As one of my dodgier mentors would say "slug it with a bit of extra R and C" (it was his fix for anything that misbehaved - amazingly it worked more often than not because he was very good at figuring out exactly where to put it). His fix for things mechanical was a bit of bent tin. He left a trail of things that worked but were ugly.

I suspect the xtal loading capacitance is now too low and the output drive power too high so a bit more series resistance and some more capacitance ought to prevent the second harmonic from resonating.

I'd bet the new part is faster with a lower output capacitance and smaller chip geometry. JT has explained why this happens.

Thanks Martin - more food for thought.

Yep. For the 'HCU04 replacement I had a helluva time matching the new gain-bandwidth-phase against the old... but I succeeded. Some "reworkers" may not be so dedicated. ...Jim Thompson