PLLDAC errors

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Jan 5^th, 2010 at 3:35pm

Gentlemen,

Can please someone explain to me, what are the PLLDAC errors ?

Thanks !

Jan 5^th, 2010 at 6:01pm

Possibility: Read last two messages here FLL DAC ERROR

Best regards, Eric.

Jan 5^th, 2010 at 9:36pm

Thanks for your reply

Basicly I dont know what needs to be replaced, either the netmodem or the BUC, I think that Advantech 200W BUCs have their LO PLLed onboard and dont need the modem to do that, so I guess I might be looking into replacing the BUC,
how does that sound to you ?

Thanks again

Jan 5^th, 2010 at 10:14pm

Where does the PLL DAC alarm come from ?

PLL DAC suggests to me Phase Lock Loop Digital Analogue Converter.

A BUC contains a local oscillator, phase locked to an external 10 MHz reference. If the PLL loses lock then the BUC will normally mute (stop the output) and a BUC alarm will be given- typically "PLL unlock alarm". This occurs if there is loss of the 10 MHz input, but could be hardware fault/damage, perhaps due to overheating.

In the iDirect hub is something that gives FLL DAC alarms. See the other forum topic. It seems to be associated with a calibration table associate with an oscillator in the line card. Mabe if the crystal itself drifts too far the DAC gets to the end of its range and gives an alarm. Try adjusting the crystal back to nominal; it probably has a small adjustable trim capacitor. Ask iDirect to help if under warranty.

Try switching to alternative redundant hub devices an attempt to isolate the problem.

Best regards, Eric.

Jan 7^th, 2010 at 3:09pm

This current problem is instability in the Modem FLL/PLL segment
which is reported to imonitor as FLLDAc drift.

Jan 7^th, 2010 at 3:50pm

Is the modem in an extremely hot or cold place ?

Replace the modem with a good one and verify that the FLLDAC fault alarm disappears.

Test the faulty modem and find the relevent oscillator component and see it has drifted off frequency a long way. Use a freq counter with a coupled atomic standard, GPS or Radio frequency reference. Retrim back to nominal and watch it for a week, power cycling from time to time. It may be failing. Check it starts every time and warms up normally. If there are problems with the oscillator, replace it. Leave running for a week and retrim.

Best regards, Eric.

Jan 9^th, 2010 at 3:13pm

1. Modem type?
2. Are you seeing PLLDAC errors or FLL DAC errors?
3. Are you noting errors on other modems in the same network?

Keep in mind that the 3100 does not have an ovenized oscillator. So, as Eric is eluding to, if this modem is operating in a place where the temperatures are fluctuating radically (very warm days, and cold nights) the output of all crystal oscillator could be affected by the temperature changes...thus causing errors.

Temp changes are just one culprit of such errors.

Other considerations: The modem could be in need of calibration or the frequency reference to the Tx Line card could be very inaccurate (hence the reason why I asked you if any other modems were exhibiting the errors). The latter is unlikely, so I would think your problem is either calibration or temp swings.

Email me:eric@satsig.net

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