Electronics > Repair
E4407B Tracking Generator Repair
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smgvbest:
Everything is in dB on first photo
Measured with Rigol 1.5 ghz SA
scope probe. Still waiting on sma to make that diy probe you mentioned

Interested in relative values in this case.  Should show if amps working
And IGG5 has same in/out


For VCO I measured with just a 50 ohm lead first. Then probe.  Got same value except probe was lower dB

I’ll check areas you mention.
smgvbest:

--- Quote from: analogRF on September 28, 2020, 09:52:59 pm ---1-what are these numbers? what does -57 mean?
2-what did you measure them with? I mean was it scope or a spectrum analyzer?
3-the most important thing is what probe did you use?

4-for VCO this is very strange! but we dont know what that pin is so please measure the VCO
at the RF input to the mixer (pin 3) and also more importantly measure the IF output
you can measure at pin 2 of mixer but better is to measure at the output of the big filter which is the input pin of the blue "LF3" filter

--- End quote ---

#4,   Pin3 is 182.5Mhz, 600Mhz Pin4  782.5Mhz at input/output of LF3
smgvbest:
HMC346

3dB unlevel, then -10dB reading level
all vDC


--- Code: ---V1 = 0.181/-1.7
v2 =  -4.191/-2.48
I  =  -0.585/-5.85
--- End code ---
analogRF:

--- Quote from: smgvbest on September 28, 2020, 10:25:32 pm ---Everything is in dB on first photo
Measured with Rigol 1.5 ghz SA
scope probe. Still waiting on sma to make that diy probe you mentioned

Interested in relative values in this case.  Should show if amps working
And IGG5 has same in/out


For VCO I measured with just a 50 ohm lead first. Then probe.  Got same value except probe was lower dB

I’ll check areas you mention.

--- End quote ---

you mean regular scope probe with SA?? that will kill all the signal and significantly disturb the signal path whenever you touch it
no need for sma connector, just solder a 450 or 470 ohm resistor to the center of a piece of coax like rg316 (or a rigid coax and then solder the rigid coax to a longer regular coax like rg316 in order to have a solid probe head) and then solder a piece of short wire to the shield of the coax (at the tip where you had the 450 ohm) to use it as your ground lead and your are good to go with 500ohm impedance you are good
use 20dB level offset on your SA in order to read the amplitudes correctly

something that is a bit strange is that between -10dB and +3dB setting the values dont change much. This could be due to attenuator section being
switched in/out so the levels at the TG out change little or it could be symptom of your underlying problem. based on the attenuator that you have at the output and also the range of TG level settings, you should be able to figure out what level at the output of TG must exist to have XdBm
at the front panel connector. Normally (not necessarily) for anything above 0dBm there should be no attenuator switched in but for -10dBm there is perhaps a section switched in like 8dB for example then your BITG must produce -2dBm at output.

anyways, if the closeness of the two measrements are symptom of underlying problem, then since the ALC loop is closed on the A2A1 board (the PWR LVL DAC) then i suggest check the control voltage the comes to the HMC346C8 chip. see the datasheet, there is an opamp on the other BITG board related to this chip. and also the voltage coming from PWR_LVL is 0 to -11V according to A2A1 schematic so it must be transformed into 0 to -2.5V for HMC346 and that is done in the other BITG board.
so you need to do some DC measurements. maybe there is bad opamp on that board!
also see if the PWR_LVL oltage coming from A2A1 is ok  (for example it is not stuck at a value)

smgvbest:
I did check the Bias on the MCL29 which read 3.57vDC and the MCL59 which was 4.7vDC

at the front panel connector. Normally (not necessarily) for anything above 0dBm there should be no attenuator switched in but for -10dBm there is perhaps a section switched in like 8dB for example then your BITG must produce -2dBm at output.

at the -10db it says the 8db attenuator is active. 

I will have to trace the board to find the op amp the pwr_lvl goes to.
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