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R&S SMP02 ERR233 YPLL unlocked - repair

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BeamDump:
Hi

I have a SMP02 20GHz unit with a YPLL unlocked error (233). The unit does output the target frequency but it drifts, so the YIG/YFOM has to be operational and it's either the YIG-PLL, Sampling or Synthesis cards (which is most of the unit).
Opened up the A21 sampling module with the YIG/YFOM assembly and saw a scorch mark on a motorola IC. Can anyone help identify the parts marked 3866, 5160 and also parts marked 420 and A08?

KeBeNe:
The 3866 might be an MRF3866, the 5160 might be an EL5160, the MMIC's are probably less special.

BeamDump:
Thanks! MRF3866 is spot on, the other is MRF5160. R&S apparently use the same sampling design for their hfh2-z2 loop antenna.
Too bad the transistors weren't the problem. Started measuring the YIG RF output directly by feeding it -5 to 0V to the PINYFO. I can't measure over 4GHz but from what i see 2-4GHz is the output power never exceeds 6 dBm and it jumps allot:

2.1 = 3 dBm
2.2 = 0.2 dBm
2.3= 2 dBm
2.4 = 6 dBm
2.5 = 5 dBm
2.6 = 2 dBm
2.7 = 0.7 dBm
2.8 = 3.3 dBm
2.9 = 5.9 dBm
etc...

Will see if the YIG driver board is at fault, maybe poor transistor or voltage regulator but the RF output power should be at least 15 dBm at any given time from what i understand.

Coil resistance measures 7.1 ohm on Main coil, 1.1 ohm on Tracking and 0.5 on FM coil (suppose to be 1.5 ohm?)

Meanwhile, some photos of the YFOM module opened.

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