Electronics > Repair

E4407B Tracking Generator Repair

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smgvbest:
here's an update RF board where signals go
note the labels PD+/PD- in the peak detector that go to the AD620.

analogRF:

--- Quote from: smgvbest on October 18, 2020, 03:50:31 am ---Would this be of any value in doing.

my Rigol 815 only goes to 1.5Ghz.
I need to look at signals up to 6hgz (LO)

I go have a Divide by 4 that's good up 8Ghz
what if I ran my probe into the /4 then into the SA. adjust reference to give good readings

The 3.92Ghz would come out at 981.875Mhz if present.   

I would also be able to see the LO sweeping

I know its not ideal but working with what I have would that be useful to do?

--- End quote ---

why do you need to do this? I think we concluded long ago that LO was present and working
in fact your TG is working normally most of the time except some short dips in amplitude
which you must find out their correlation with other signals to see what is causing them
other than that between those blips, the TG is working normally. Obviously if you didnt have LO coming in
this would not have worked at all
So i dont see the point of this test. Besides, if anything, you would need to know the precise amplitude of coming LO
which this test will not tell you but you measured that with power meter and it was alright.

analogRF:

--- Quote from: smgvbest on October 18, 2020, 03:41:24 am ---at peak detector I did have a typo
this is the correct value
1-2   1.3908v/0.1447v

in PICT0042-1.jpg

the Cap did clean up as seen and the LCR at 10Khz says 9.65pF

--- End quote ---

so there are two separate schottky diodes in one package, one for peak detection and one for the temp and V_fwd compensation. It's a classic RF peak detector circuit. But the part number I could find for "D" was a single diode which makes no sense so it must be a different part...

analogRF:

--- Quote from: smgvbest on October 18, 2020, 04:08:58 am ---here's an update RF board where signals go
note the labels PD+/PD- in the peak detector that go to the AD620.

--- End quote ---
B1 and B2 are power supplies for the RF ampliiers.

C8 is the output of peak detector and must eventually become ALC_MON after further processing on the other board

you need to find out the relationship between V1/V2 and PWR_LVL signal coming from A2A1

is there any jump/dip in OSC_PWR consistent with the dips in the TG output power?

analogRF:

--- Quote from: smgvbest on October 17, 2020, 11:16:33 pm ---
--- Quote from: analogRF on October 17, 2020, 12:28:35 pm ---
--- Quote from: smgvbest on October 16, 2020, 11:29:44 pm ---Looking for help in identifying some components
in PICT0007.jpg   looking to identify all marked ones.  the one I put a D on,  the D is the only marking on the component.   I think this is a dual diode package for the peak detector.

I loose allot of power at the point of this component.   like -25dB.   this is suppling the 786.5hz RF to the Mixer (5x that but I can't measure on my 1.5Ghz SA)
in  IMG_2867-1.jpg

--- End quote ---

the white elements are most likely resistors. you can check with multimeter
the "D" element is most likely HMPP-3890 single schottky diode by Agilent/Avago but are you 100% sure about the marking? sometimes it is tricky to read the labels
seems that all 4 pins of it have been used  ??? also for a good temperature compensated peak detector it makes sense to have two diodes in one package but if the marking is only a "D" then I couldn't find anything other than HMPP-3890 which is still applicable...

the element with red dot is what is used to generate 5th harmonic if i remember correctly from previous discussions, so it is probably a diode of some kind.

--- End quote ---

The White elements do read as resistors of 50 and 125 ohm

for the part with the D marking.   see image for best I could get 
Using the Diode test here are reading for all 4 pins (see image for pin numbering used)  all reading Vdc

1-2  1.3908v/1.447v
3-4  1.6304v/0.1447v
1-3  0.0691c/0.0691v
2-4  1.4398v/1.3723v

for the damaged element

Did multiple checks
Resistance Open
Capacitance 0
Diode open

see image for better view

--- End quote ---

I dont think the marking on the dual diode package is "D". It must be 2 letters and "D" seems to be the second letter which is a date code
there is a very faint letter before "D" it's either "B" or "C" i think
you need to look carefully at proper angle

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