Posted on February 24, 2013 at 19:45Thanks for your answer clive1 !
Well, R21 and R22 are already mounted.
The JINGYUXING tech crystal ST recommends on the schematics offers these specs :
- 6pF, 20ppm freq accuracy, and 50KOhms of motional ESR...
pretty much the same as the T6 Seiko crystal I've salvaged :
min 3.7pF max 6.0pF, 20ppm, 55kΩ ESR.
To be fair, I'd say the SEIKO rice grain one is even more prone to oscillate under such tenuous drive currents, as it claims to start oscillating with a drive asweak as 10nW ! It's a VT-200-FL type, for low power apps, designed to be used on wristwatches.
Fact is, I wouldn't have chosen a 49U crystal from some random 8086-operated PCB, as I had in mind to find a match for what usually is a button-cell-feeded piece of circuitry.
But you've dropped a dime here : aren't my load caps a bit too ''big'' ???... 15pF instead of 6.8pF... ( since I don't have lower values in stock anymore). Maybe they're choking the OSC32 drive.
Even worse: maybe I did overheat the crystal while soldering it back on the discovery board. These have crappy plastic leads spacers, that tends to short to the metal casing. *sigh*
Pfew ! I would never have guessed I'd have such a hard time driving such a slow oscillator !
