Electronics > Repair

E4407B Tracking Generator Repair

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analogRF:

--- Quote from: smgvbest on October 01, 2020, 05:58:49 pm ---
--- Quote from: analogRF on October 01, 2020, 02:22:25 am ---4-since the failure moves to lower amplitude as time passes, it is probably affected by heat. Why dont you spray some freeze spray (aim very locally) at different components and see if the error goes away. starting with that IGG5!

--- End quote ---

Did this.   the only component that had effect using cold spray was the HMC346 it only shifted it down (lower db reading)  but unlevel condition continued
tried the other board on the TG (one with OPAMPS and Analog Switch) , no effect there either

--- End quote ---

did you also try freezing the the capacitor and the schottky diode of the peak detector circuit?

based on the table you provided before, you should have got unlevel error even at -2dBm because the ALC_MON drops below -1V
and according to the schematics of A2A1 this will set the unlevel error. it is puzzling that you didn't get that.

something is happening between -3dBm and -2dBm. Can you try to measure the RF amplitude at these twi levels and see if the
RF actually drops? because the ALC_MON is reporting that it drops quite a bit instead of increasing by 1dB. So check the actual RF amplitude
(assuming IGG5 is ok, you can do it at the SMA port) if the actual RF amplitude does not drop then the problem is in the ALC_MON reporting
and the circuit between the schottky peak detector (and its ceramic cap) and the ALC_MON pin must be checked (most probably the opamp on the top right)
but if the amplitude does indeed drop, then I think the HMC346 is the main suspect.

by the way, is the frequency spot on?
 

smgvbest:

--- Quote from: analogRF on October 02, 2020, 04:17:27 pm ---did you also try freezing the the capacitor and the schottky diode of the peak detector circuit?

--- End quote ---

Yes,  no effect noticed.


--- Quote from: analogRF on October 02, 2020, 04:17:27 pm ---based on the table you provided before, you should have got unlevel error even at -2dBm because the ALC_MON drops below -1V
and according to the schematics of A2A1 this will set the unlevel error. it is puzzling that you didn't get that.

something is happening between -3dBm and -2dBm. Can you try to measure the RF amplitude at these two levels and see if the
RF actually drops? because the ALC_MON is reporting that it drops quite a bit instead of increasing by 1dB. So check the actual RF amplitude
(assuming IGG5 is ok, you can do it at the SMA port) if the actual RF amplitude does not drop then the problem is in the ALC_MON reporting
and the circuit between the schottky peak detector (and its ceramic cap) and the ALC_MON pin must be checked (most probably the opamp on the top right)
but if the amplitude does indeed drop, then I think the HMC346 is the main suspect.

--- End quote ---

Will do this.
I did trace and verify that indeed the via pointed in the peak detector circuit does go to the input of the AD620 as indicated.
I also did more tracing of the RF board and its 2 10 pin connectors.  i've got most pins traced out. will post image with labels shortly for reference


--- Quote from: analogRF on October 02, 2020, 04:17:27 pm ---by the way, is the frequency spot on?

--- End quote ---

yes it is

analogRF:
one other thing you can test, if you set the TG ALC to External and dont apply any DC to the Ext ALC
the output should stay fixed at around 0-1dBm I think. At least this is how it worked in 8590 series I remember
I dont know what DC levels can be applied to the EXT ALC to control the TG output level. Maybe it's somewhere in the manual....

smgvbest:
I've been trying to figure out what's happening at the AD620.
but overall its looking like the Reference voltage is fluctuating and the output of the detector is stable at about .0446vDC.   so the output of the AD620 is also fluctuating.

also the output is not very stable as read at same time as the input to the AD620.   which kind of aligns with the output of the AD620.
So is the AD620 causing the Reference to fluctuate or is the Reference to the AD620 the problem
I need to record the rest of the reading for my table here.  hopefully latter I can do this
also as the unit warms up it more seems to change behavior.   the notable items is the output from the detector seems stable. so this to me so far is pointing to the AD620 or Reference to the AD620

more info to come


--- Code: ---Attenuation dBm Min dBm Max dBm AVG (A)in
3dB -3.020 1.200 -0.910 0.0447
2dB -1.720 1.220 -0.250 0.0446
1dB -0.940 1.220 0.140 0.0447
0dB -2.840 0.620 -1.110 0.0446
-1dB -0.910 -0.390 -0.650 0.0447
-2dB -1.990 -1.370 -1.680 0.0446
-3dB -3.420 -2.490 -2.955 0.0447
-4dB -4.370 -3.560 -3.965 0.0446
-5dB -5.110 -4.540 -4.825 0.0447
-6dB -6.140 -5.560 -5.850 0.0446
-7dB -6.670 -6.680 -6.675 0.0447
-8dB -7.780 -7.750 -7.765 0.0446
-9dB -9.660 -8.750 -9.205 0.0447
-10dB -10.110 -9.470 -9.790 0.0446

--- End code ---

analogRF:
what are these numbers?

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