Orion MK II - Unstable frequency

DL8LAQ
Posts: 57
Joined: Sun Apr 09, 2017 3:28 pm

Orion MK II - Unstable frequency

Postby DL8LAQ » Tue Jun 26, 2018 7:02 pm

Hi guys,

two week ago I did repair a 7000DLE with a toasted RX2 input (on the PA board) and a frequency stability fault.

The 10-MHz-REF-input on the OrionMKII did not work properly. Without external ref connected the TCXO was not supplied with 3.3 VDC, but 1.6 VDC instead. That was caused by a defective Q4 at the input amp (diff amp). I replaced Q3 and Q4 to fix this. After that the switching from internal to external ref worked fine again.

73, Norbert - holidays in JM57NH - CT7/DL8LAQ
73, Norbert - DL8LAQ - ANAN-7000DLE
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w-u-2-o
Posts: 1744
Joined: Fri Mar 10, 2017 1:47 pm

Re: Orion MK II - Unstable frequency

Postby w-u-2-o » Tue Jun 26, 2018 7:53 pm

Here is a snippet of the schematic showing the external clock input and automatic selection circuit.

The jumpers at the input provide options with respect to a differential or single ended input (J24) and a 50 ohm or high impedance termination (J22), whichever your external clock source requires. If you are having problems first ensure that these jumpers are configured properly for your external clock source.

Next up is a sine to square wave converter formed from a two-transistor differential amplifier. This allows the use of either sine or square wave external clock sources. The resulting square wave goes to IN0 on the 74LVC1G97 which acts as a switch.

The square wave also goes to a circuit that derives a logic level for IN2 on the 784LVC1G97. When an external clock is attached that level will be high and the output of the switch (Y) will be sourced from the external clock on IN0. When no external clock is present that level will be low and the output of the switch will be sourced from TCXO U26 on IN1.

The same logic level on IN2 also is applied to the gate of Q1, and when high due to the presence of an external clock, will drive the P-channel FET to cutoff and turn off power to the on-board TCXO.

Image

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