Electronics > Repair

DSO6014A PLL Unlocked error. Help needed.

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simonov:
Hello,
My deal on DSO5014 didn't go well and I purchased this used DSO6014A. The seller parted with it for just $280. The scope needed a lot of cleaning inside so it was disassembled and I gave it a bit of a TLC.

The scope does power up and boot. The boot sequence on the front panel seems OK. The scope then shows the following: " The oscilloscope setup defaulted because a software fault occurred. Please report the following diagnostic information: PLL Unlocked"

The front panel controls do not respond. The scope doesn't do anything else. The Auto trigger blinks (on the screen). From time to time (if I hold start button while powering up) the scope boots into battery power mode (although it has no battery).

I've tried providing the scope with external 10MHz reference from my rubidium standard but the result was still the same. The main power board works fine and gives +15V which should be fine.

Any thoughts on this would be welcomed.

Bud:
Identify the clock generator on the board and look around it, maybe you knocked off a capacitor or inductor while cleaning the board. You can post a good res photo of the board here so people can help you find the PLL chip (if there is hardware one).

simonov:
Hi Bud,
thanks for the reply.
Just to clarify - the scope was in this condition when I purchased it. I knew about this error beforehand and It was present before I opened the scope. I will upload more photos soon.

simonov:
I've taken some photos. The PLL is located below the ADC's. It is the LMX2306:
https://www.farnell.com/datasheets/4907.pdf

The main oscillator is V515ME01-LF
http://en.planetec.com/product/datasheet/V515ME01-LF.pdf

The digital logic around those is supplied by the local regulator U1912 which gives 3.3V. The supply voltage is OK. When powered off the DC resistance around the capacitors in this rail is suspiciously low - around 40 Ohm. The regulator is very hot. The capacitor around U1905 is not looking good. It has some yellow goo around it. It looks bad.



It is possible that some bad caps are causing the problems.

Bud:
OK so now you  have something to work with. Per the datasheet, pin 14 may be configured to output lock detect signal, check what you have on pin 14 as per section 1.3.2 in the Datasheet.

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