A look inside of an Agilent E4400B signal generator - Page 1
Forum section: electronics / testgear

author: feedback.loop
author_rank: Frequent Contributor
timestamp: February 22, 2016, 02:31:31 am
content: Check it out. Another lucky find from eBay. This Agilent E4400B generator has some problem with fractional PLL. It seems to be unstable, so the instrument periodically shows error 508 "Frac-N Loop Unlocked". The synthesizer was inspected, the block diagram was discussed and the blocks were located on the board. Unfortunately, there was no definite solution to the problem due to lack of appropriate equipment at the moment. If there will be any developments, another video might follow.Calibration guide:http://literature.cdn.keysight.com/litweb/pdf/E4400-90325.pdfDocument with the block diagram. It is for a different model, which seems to use the same synthesizer:http://cp.literature.agilent.com/litweb/pdf/E4400-90014.pdfhttps://youtu.be/JPEmbvUx0JQ

author: TheSteve
author_rank: Unknown
timestamp: February 22, 2016, 03:19:14 am
content: I have not watched the video at all, just wondering if any Avago MMIC parts are part of the chain in the problem area - perhaps marked A06 or A07.

author: feedback.loop
author_rank: Frequent Contributor
timestamp: February 22, 2016, 05:34:15 am
content: Quote from: TheSteve on February 22, 2016, 03:19:14 amThere are a few micro-x packages marked A0x. U15 marked A07 and U16 marked A06 seem to be a part of the buffer, which might be in the PLL loop. There are a few A03 ones in the buffer and divide by 2 section, and one more in the VCO. What about them? Why did you bring them up? Are they known for failing? Can you identify them in the photo? Do you happen to have data sheets?Thanks.

author: TheSteve
author_rank: Unknown
timestamp: February 22, 2016, 05:52:58 am
content: I have no experience with the unit you have, but have seen the Avago parts fail before in similar devices. I have seen them still pass/amplify a signal but it will be noisy which can make it hard to diagnose.The full part numbers of the various parts are A07=MSA-0786, A06=MSA-0686 etc.

author: feedback.loop
author_rank: Frequent Contributor
timestamp: February 22, 2016, 08:29:42 pm
content: Quote from: TheSteve on February 22, 2016, 05:52:58 amI am looking at the data sheets. The package is sot86, not micro-x. MSA-0786 is rated up to 0.8GHz. So if you are right that A07 in this generator is MSA-0786, I wonder why it is used up to 1GHz. I hope they are not at fault since they are not available neither on Digikey nor on Mouser.

author: nctnico
author_rank: Super Contributor
timestamp: February 22, 2016, 09:47:23 pm
content: I'd try and find where the lock signal is generated and trace back from there. I think most of the HF stuff is there to generate a sine wave between 250MHz and 4GHz. The output frequency is divided in several ranges and this may affect the PLL as well so the first thing to check is whether the error occurs on all ranges or only at a certain frequency.

author: feedback.loop
author_rank: Frequent Contributor
timestamp: February 24, 2016, 07:23:43 am
content: By the way, look at the info: the unit has 32K hours on it, which is about 3.6 years, about 1.5K power cycles and about 3.8M (!) attenuator cycles.Regarding the unlock problem. I put the synthesizer back together, and couldn't reproduce the problem since. I run the unit for several hours from time to time. No errors so far.

author: Pete2
author_rank: Contributor
timestamp: October 16, 2023, 01:03:43 pm
content: I am looking at a faulty 4400B on Ebay with the same error you had: 508 Synthesizer Unlocked. Sadly, it doesn't help that your unit repaired itself. Not much experience in repairing RF stuff so maybe fixing a possibly faulty Synth module is too much for me. Although I don't know if there's a supply rail missing as well. Working modules on Ebay cost more than broken units!

author: R-1125F
author_rank: Regular Contributor
timestamp: October 16, 2023, 09:04:57 pm
content: Have a look at this thread on the HPAK group. There is a problem with some frac-n chips.https://groups.io/g/HP-Agilent-Keysight-equipment/topic/synthesizer_module_in_esg/28079593

author: Pete2
author_rank: Contributor
timestamp: October 18, 2023, 03:26:43 am
content: Quote from: R-1125F on October 16, 2023, 09:04:57 pmThanks for this. Seems like getting the unit is a big risk and even if the same chip is faulty the replacement would cost 150 eur on top of the unit that is about $450 + VAT for my country (24 %) including shipping. I asked the seller if there is the unlevel error as well which MAY indicate a missing supply rail but does not gurarantee an easy fix. Explains why noone has still not bought the unit.