Just finished - Anritsu MS420K Network / Spectrum Analyzer restoration - Page 1
Forum section: electronics / testgear

author: precaud
author_rank: Frequent Contributor
timestamp: October 09, 2017, 08:24:46 pm
content: Back in the mid-90's I used one of these for a project and really liked it. Was sad when the day came to return it.In '08-'09, during the economic downturn, I bought two of these MS420K's on eBay for a song, both were guaranteed to have issues, and the price reflected that. The seller was so anxious to get rid of them he offered me free shipping if I took them both (these are heavy beasts). On arrival, they both acted similarly when powered on - fans turned, no display, one didn't respond to key presses. I set this one aside and got the other one running but its crt proved to be too weak to use. Eventually I set them both aside and forgot about them.A couple months ago, I decided I want a VNA to do PDN measurement and other impedance analysis, hopefully up to 10MHz. I decided to open this one up and see what its problems are. If you're not familiar with these older Anritsu's, the build quality is impressive. This one was clean as a whistle inside. It's prior owner did some pretty dumb things to it. It had signs of having been intentionally sabotaged. DC supply wires neatly snipped. They didn't have a key for the on-off switch, so they cut the mains wires and hardwired it on. The crt circuits were WAY out of adjustment, as if purposely; the image never came on-screen! And some calibration pots were full-on and full-off, which in practice is rarely the case. Anyway, over the last couple months I've sorted it out in my spare time, and finished the calibration last night.And now we have a fully functional VNA. Crt still has an issue; it cold-starts off-screen, but at least now it centers and stabilizes when warm. I can take my time troubleshooting that issue.First up is to evaluate some isolation transformers for the impedance project. It is the perfect tool for it.

author: Xtremexp
author_rank: Regular Contributor
timestamp: December 14, 2020, 02:34:15 am
content: Such a beautiful snapshot of MS420K. I also got one in my hand, physically it is in great shape but I want to recalibrate it. where can I find the calibration steps? It would be great if someone can help me to find documentation on the calibration.Thanks.

author: precaud
author_rank: Frequent Contributor
timestamp: December 14, 2020, 12:56:45 pm
content: Hi,Congrats on your MS420K. The service manual is huge. I'll look at it today and see how long the cal section is. I'm not well set up for copying things.An extender board is definitely needed to do a cal.

author: precaud
author_rank: Frequent Contributor
timestamp: December 15, 2020, 04:04:59 am
content: Quote from: Xtremexp on December 14, 2020, 02:34:15 amI have the service manual. The cal section is 46 pages, many of them 11x17, I think my old scanner can handle that. I can scan it but the question is when.

author: Xtremexp
author_rank: Regular Contributor
timestamp: December 29, 2020, 04:16:17 am
content: Thank you for the reply. I love this beast and really want it to restore this historical piece.

author: precaud
author_rank: Frequent Contributor
timestamp: December 29, 2020, 12:38:28 pm
content: I have it set out so I don't forget...

author: Xtremexp
author_rank: Regular Contributor
timestamp: February 15, 2021, 05:30:22 am
content: Hi,I am wondering if you were able to scan copies. Really appreciate your help. Thanks.

author: precaud
author_rank: Frequent Contributor
timestamp: February 24, 2021, 05:59:06 pm
content: Here's a first installment, 3 pages TOC and the 1st 18 pages of the chapter. Note that zip changed the correct order, but file names = page numbers. Missing pages were blank.

author: Xtremexp
author_rank: Regular Contributor
timestamp: February 24, 2021, 07:55:22 pm
content: Thank you so much!!

author: precaud
author_rank: Frequent Contributor
timestamp: February 25, 2021, 04:21:14 pm
content: Another dump.

author: precaud
author_rank: Frequent Contributor
timestamp: March 02, 2021, 04:37:59 pm
content: And here is the final batch. Good luck with your cal !

author: Saskia
author_rank: Super Contributor
timestamp: March 02, 2021, 07:04:01 pm
content: Thanks a lot for providing the manual.

author: Xtremexp
author_rank: Regular Contributor
timestamp: March 04, 2021, 05:46:28 am
content: Thank you so much for the document. Really appreciated.

author: precaud
author_rank: Frequent Contributor
timestamp: March 04, 2021, 11:47:28 am
content: You're welcome. Sorry for the delay. Do you have an extender board for the side slots?

author: Saskia
author_rank: Super Contributor
timestamp: March 04, 2021, 02:51:56 pm
content: unfortunately no.

author: precaud
author_rank: Frequent Contributor
timestamp: March 04, 2021, 02:55:36 pm
content: They're becoming harder to find.