WTB: OPT001 Board for HP/Agilent 33120A

[ZGoode]

I am looking to buy the option board for an HP/Agilent 33120A function generator.  I can't seem to find anywhere online, so if anyone has one, or even a broken 33120A that they can pull it from I'd be interested in buying it.
I was looking into making a replacement board, but I can't seem to find a suitable replacement for the oscillator used on the board since I can't even find a datasheet for the original one used.

[Zucca]

I am 99% sure your read this, but just in case
https://www.eevblog.com/forum/testgear/agilent-33120a-option-001-phase-lock-external-10mhz-standard/

Posting the schematics somewhere in this forum and asking for help nicely could push you in the right direction to make it one yourself.

[indeterminate]

Theirs a dead 33120a with option 001 on flebay now
115710775753

[Qw3rtzuiop]

I cloned the option board. If DIY is an option for you. Details are available here:
https://github.com/Qw3rtzuiop/33120a-option-001

[ZGoode]

Theirs a dead 33120a with option 001 on flebay now
115710775753

I mean thats pretty much what I'm looking for, but they want pretty much the price of a working unit and its freight shipping

I cloned the option board. If DIY is an option for you. Details are available here:
https://github.com/Qw3rtzuiop/33120a-option-001

Probably going to look more into this since I'm not against spinning my own.  I was looking to make a 1:1 copy of the original board, but can't source the crystal they used.  Literally every other part is something that can still be bought on Digikey except for that stupid miscellaneous 40MHz crystal.  Qw3rtzuiop, I'm assuming that's why your version uses a 10MHz OCXO instead of the original 40MHz?

[ZGoode]

I am 99% sure your read this, but just in case
https://www.eevblog.com/forum/testgear/agilent-33120a-option-001-phase-lock-external-10mhz-standard/

Posting the schematics somewhere in this forum and asking for help nicely could push you in the right direction to make it one yourself.

Yup, I did see that one.  Once I look a bit more into Qw3rtzuiop's design I'll probably start a post for that

[Qw3rtzuiop]

Qw3rtzuiop, I'm assuming that's why your version uses a 10MHz OCXO instead of the original 40MHz?

Yes. I wasn't able to source a 40 MHz oscillator for a reasonable price. And these used OCXOs are cheap.

[ZGoode]

What's the difference between your version 0 and version 1?  Or is it just adding on the changes from those bodge wires you mentioned?  I'm debating whether or not to deep dive this, or just order and assemble your design and call it a day since I want this option, but I have other projects I would rather work on

[Finnegan1]

Zgoode - I sent you a PM on how to source built and tested units.

[Qw3rtzuiop]

What's the difference between your version 0 and version 1?  Or is it just adding on the changes from those bodge wires you mentioned? 

Yes. Rev. 1 contains the bodges I had to make on rev. 0

[Qw3rtzuiop]

Zgoode - I sent you a PM on how to source built and tested units.

Why not posting it here for others to see too?

[ZGoode]

Zgoode - I sent you a PM on how to source built and tested units.

Why not posting it here for others to see too?

He just told me to buy the SCSKits board on Ebay, which while that seems like an ok solution, I don't know what quality of components are used and how it compares to the original.  At least with spinning my own from the github you provided, I can select high quality components and know how the specifications stack up to the original option.

[ZGoode]

Hey Qw3rtzuiop,
Do you happen to remember the part numbers of the CR108 and T101 for your version?  Those are the only parts I have not been able to make sure I have the right version for yet.  Also how long did you make the IDC ribbon cable?  I was planning on ordering a premade one off digikey and wanted to make sure I had one at least the minimum length

[Qw3rtzuiop]

Hey Qw3rtzuiop,
Do you happen to remember the part numbers of the CR108 and T101 for your version?  Those are the only parts I have not been able to make sure I have the right version for yet.  Also how long did you make the IDC ribbon cable?  I was planning on ordering a premade one off digikey and wanted to make sure I had one at least the minimum length

CR108 is a SMCJ43CA in the original schematics. I used an 18CA that was in my parts box. T101 is TC1-1T+ from Mini Circuits. In my case its useless at the moment because i didnt use isolated bnc jacks. Th cable length is 15cm but its almost too long.

[ZGoode]

Awesome!  I thought that was the transformer used, but wanted to make 100% certain.  I plan on using isolated BNC's if I can find some for RG316 so that will be useful for me.  As soon as I get all the parts and boards I'll assemble one and let you know how it goes!

[Qw3rtzuiop]

If you find isolated bncs for RG 316 please link them here.

[ZGoode]

If you find isolated bncs for RG 316 please link them here.

These here on Digikey are the ones I was looking at using:  https://www.digikey.com/en/products/detail/amphenol-rf/112252/2627853

[monz]

I've built Qw3rtzuiop's board. I'm running in to some difficulty. I had to lower R112 to 56K to get CR105 led to come on when synced with a reference - I assume this LED means it's synced and the other means reference input is detected. This works fine and the generator's output is perfect when the reference is connected.

However, I'm having trouble with when the reference isn't connected, running on it's own with the XCXO. It provides the 40MHz signal fine and the generator works, but I'm not able to calibrate it. It looks like pin 2 on the ribbon cable provides the voltage to adjust it and the 4066 switches to use that to generate that voltage which appears to get through the 4066 ok. Attempts to calibrate with calibration option 86 results in "cal error" "value range" no matter how small of an adjustment and no change in control voltage. Same thing with calibration option 00. Maybe I'm doing something wrong or there's some other problem? Any ideas?

[Qw3rtzuiop]

Attempts to calibrate with calibration option 86 results in "cal error" "value range" no matter how small of an adjustment and no change in control voltage. Same thing with calibration option 00. Maybe I'm doing something wrong or there's some other problem? Any ideas?

I tried that again but im only getting this error when im leaving the tuning range of the ocxo. Are you sure your ocxo is okay?

[Qw3rtzuiop]

But what i observed is that i needed more than 10-15 calibration runs (setup 86) after i intentionally selected a frequency correction by 1 KHz. But I did not get the range error when approaching my reference ocxo (53131 opt. 010, calibrated against a gpsdo).

I guess the tuning range of the ocxo i selected is way smaller than the tuning range of the original vcxo.

[ZGoode]

I've built Qw3rtzuiop's board. I'm running in to some difficulty. I had to lower R112 to 56K to get CR105 led to come on when synced with a reference - I assume this LED means it's synced and the other means reference input is detected. This works fine and the generator's output is perfect when the reference is connected.

However, I'm having trouble with when the reference isn't connected, running on it's own with the XCXO. It provides the 40MHz signal fine and the generator works, but I'm not able to calibrate it. It looks like pin 2 on the ribbon cable provides the voltage to adjust it and the 4066 switches to use that to generate that voltage which appears to get through the 4066 ok. Attempts to calibrate with calibration option 86 results in "cal error" "value range" no matter how small of an adjustment and no change in control voltage. Same thing with calibration option 00. Maybe I'm doing something wrong or there's some other problem? Any ideas?

I just finished building my board the other day.  I'll try and cal it to let you know if I can reproduce your errors.  I'll calibrate it against my Rubidium GPSDO
What are you using as a reference source?  Your reference might not be in spec.  Your OCXO on your board could also be bad.  I have had a lot of Chinese OCXO that are way past their lifespan and have drifted down outside of the adjustment range.

[monz]

I tested the OCXO before installing it and I think it's ok. I awas able to adjust it to 10MHz via it's control voltage input using another 33120a set to output DC, it ended up being 2.115V, the range it can be is 2-4V. When the board is synced with an external source, it ends up being about this voltage. When not, the voltage being provided to it is about 4.5V. maybe the voltage being applied is just starting out too high.

I do get the value range error even when setting to 1 above or below at the LSB displayed - all 9's or 10 and all zeros with 1 at the end.

I have a GPSDO that a I built as a reference. The calibration procedure outputs 10MHz then you tell it what it's actually putting out.

I also have a 53131a with an option 010 that I built as well that I'm using to check with that matches the GPSDO.

[monz]

I did some more testing tonight. It seems it might be a problem with the 33120A itself. I have a second one that has option 001, so i took it out and installed in in this one and it does the same thing. The only calibration setting to not give an error isentering 10.00000MHz. I also tried via SCPI, similar results, it appears to take the new value, but it changes back when moving to another cal setting or power cycle.

Not sure why it won't take any other value. The DAC (pin 2) is putting out -2.560V - possibly the lower limit. The DAC and the op ap that makes up the sample/hold for that voltage seem fine - the DAC multiplexes multiple voltages from its output. Maybe configuration in flash memory is corrupt since it wont store the new value.

[ZGoode]

I managed to calibrate my 33120A (at least frequency, I wasn't going to bother with all 80+ tests right now) with no problems using my 53131A and my Trak 8835-3M Rubidium GPSDO.
I think the first step to figure yours out is to run the self test and see if there are any errors.  On power up hold down the shift button for 5 seconds to run the full test.  If it fails remove the opt 001 board and rerun the test.  I did find that if the SMB/SMA connectors are not fully seated it can cause errors.  Also make sure your ribbon cable is wired correctly.
Right now the only calibration steps that are critical for the opt 001 board are 00, 01, and 86 as far I can tell from the manual.

[monz]

Still no luck getting past the error, suspecting a maybe a bug in the software since it detects the board. Since calibration just sets the voltage supplied to the XCXO to set its frequency, so I decided to provide that voltage myself. The XCXO has a 4v reference voltage, which should be very stable. I connected a 10 turn potentiometer across it and ground and am using that to provide the resulting voltage to the junction of R128 and R127, with those two resistors removed. This works very well and was easy to adjust. So far it's been very stable and working fine.