Electronics > Repair

E4407B Tracking Generator Repair

<< < (4/27) > >>

analogRF:

--- Quote from: smgvbest on September 24, 2020, 03:46:17 pm ---
--- Quote from: analogRF on September 24, 2020, 03:23:06 pm ---maybe I missed something but why dont you just simply start by checking the levels at the major LO connections? I mean the LO in/out levels at the control board and the LO in at the TG module (which is the same as LO out from control board)? just vary the center frequency at zero span
and vary the TG amplitude and monitor the LO levels at these 2 points (one at a time) it should be fairly easy to rule out one of the modules

since the error occurs at some intervals , it seems to me the problem could be either an electronic attenuator somewhere OR an electronic RF switch which changes the signal path depending on the level requested (more likely in my opinion). I think I saw a couple of them in one of the pictures. I need to look again. But the circuits are very simple and easy to diagnose. there is no need for schematics

--- End quote ---

Hi,

So a few thing on that.   the only SA I have that can look at the LO is the E4407B.  when you enable the TG it turns on the LO to the TG and your range is reduced to 0-3Ghz.  if you go outside the 3Ghz range which you need to for the LO (starts around 3.9 Ghz if I recall) the TG LO is turned out so you can't view it on the SA itself.

Second item is there are 2 errors associated with the TG
Source LO Unlevel (whcih I am not getting) and points to the LO being a problem on the Control Board.
Source Unlevel (which I am getting) points to a problem on the A2A2 (BITG) board.   

I've disconnected and terminate the LO coming from the control board and still get same errors. 

The only reason to check those FETS and PIN diodes was because at least a few of the FETS had been replaced and that's me doing my due diligence it looking at them

the good thing with the BITG is it sits high enough that if I leave the shield off I can likely probe the board.

I've spent most my time right now documenting these board as there's nothing out there on the TG.

Now that I have its time for troubleshooting.

I welcome any advice I can get here.   RF is not my specialty by any means.   I think I see the signalpath (not trying to steal their name or anything) so there's not many places I can see it could go bad on the BITG

--- End quote ---

so clearly the problem is only inside the A2A2 and in that module the entire section behind the RF output (marked by yellow color below) is 0-3GHz and you should be able to probe it. The level problem is more than likely happening in this section and not in other sections (there are scenarios that it can be traced to other sections but the most likely cause of unlevel issue must be the section I have highlighted with yellow color here)

there are only two RF gain blocks (check their supply first) and if they are ok the only problem is the IGG hybrid which does the level detection
and RPP  :( :palm:  if someone applied RF power or DC to the tracking gen, the IGG5 is gone  :palm:

just to make sure, you can also check the AD620 opamp that is most likely connected to the IGG5 and completes the level detection and probably generates the error signal based on some reference value.

suj:
Maybe try to set the TG frequency quite low and try to check the level with an oscilloscope? In this case, I prefer the 3 GHz HP 85024A probe, but I have other SA's at my disposal. Maybe diode detector with additional resistor at the input??

smgvbest:

--- Quote from: analogRF on September 24, 2020, 06:01:27 pm ---so clearly the problem is only inside the A2A2 and in that module the entire section behind the RF output (marked by yellow color below) is 0-3GHz and you should be able to probe it. The level problem is more than likely happening in this section and not in other sections (there are scenarios that it can be traced to other sections but the most likely cause of unlevel issue must be the section I have highlighted with yellow color here)

there are only two RF gain blocks (check their supply first) and if they are ok the only problem is the IGG hybrid which does the level detection
and RPP  :( :palm:  if someone applied RF power or DC to the tracking gen, the IGG5 is gone  :palm:

just to make sure, you can also check the AD620 opamp that is most likely connected to the IGG5 and completes the level detection and probably generates the error signal based on some reference value.

--- End quote ---

Thank you for the analysis. that's very helpfull. 
I've been collecting datasheets so here they are for reference


my thought was with HMC346, the variable attenuator.
The area you mention is much easier to probe though.  my other sa's go to 1.5Ghz (Rigol) and 2.7 Ghz(Agilent Base Station)



analogRF:
I would start by checking the output section. any unlevel issue most likely happens in there (+ probably the opamp on the upper right of the IGG5)

if that section is fine, then we can think of other scenarios.

1.5GHz SA is fine. I believe your unlevel errors happen at any frequency, right? or do they happen at certain frequencies?!

if they happen at certain frequency ranges, then perhaps that HMC346 is a better place to start. But I thought your errors were happening at all frequencies

analogRF:
not sure if the golden mixer is HMC129. The packaging does not match. still it could be an old version of hmc129 with different specs...

another peculiarity here is that MNA6 (bottom right) is specified as 0.5-2.5GHz amplifier. So the signal in that path cannot be 3.92GHz as we expect.
I am thinking maybe that path is 1.96GHz and the golden mixer H129, actually does a harmonic mixing (mixing with the second harmonic of 1.96) ?
I wish you could do some tests and verify what frequency is there..

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod