Anritsu MG3633A signal generator teardown and repair log

[capt bullshot]

So I've started to tear down and repair the loot from the Duesseldorf trip
http://wunderkis.de/mg3633a/index.html

This is work in progress, first unit is fixed, two more to go, stay tuned for updates.

Some of us might remember DC1MC and me picked up some stuff there:
https://www.eevblog.com/forum/buysellwanted/%28deeu%29-group-sale-of-5-anritsu-mg3633a-signalgenerators-%2810-khz-to-2700-mhz%29/

[capt bullshot]

Update #1:
Some more circuit analysis and fault location happened to unit #2, not yet repaired but root cause of malfunction located:

http://wunderkis.de/mg3633a/repair2.html

[DC1MC]

Excellent tear-down and repair detective story, recommended for everybody who wants to see a properly done and documented repair  .
Also the generator construction is really a wonder of Japanese technology, I had some kind of electrogasm looking at that gold attenuator !!!

Keep on the good work,
DC1MC

[capt bullshot]

One more update for today:

Unit #1 is no more wacky: http://wunderkis.de/mg3633a/repair1.html
Unit #2 is "undefekt" now: http://wunderkis.de/mg3633a/repair2.html
Unit #3 is diagnosed: http://wunderkis.de/mg3633a/repair3.html

Two out of three, that ain't so bad?

[DC1MC]

One more update for today:

Unit #1 is no more wacky: http://wunderkis.de/mg3633a/repair1.html
Unit #2 is "undefekt" now: http://wunderkis.de/mg3633a/repair2.html
Unit #3 is diagnosed: http://wunderkis.de/mg3633a/repair3.html

Two out of three, that ain't so bad?

Hey capt, are you taking apprentices ? 'Cause my unit is still in need of some love, I can haul it back to you some time for some spiritual healing 
But excellent job indeed, done in a very German way  !!
 
I have this strange idea, if you mix the outputs of the two guys that are OK, will this become an even higher frequency generator ?
And second, less wacky idea, if those guys will be feed in their reference input from a rubidium 10MHz source, will they become some craz stable generators ?

 Cheers,
 DC1MC

[capt bullshot]

I've added some thoughs about the rather subtle cause of the ceasing oscillation within this PLL (refering to repair #2):

In the end, we've got a nasty but innocent looking electrolytic capacitor causing all this inconvenience. I'm slightly not amused now, but happy because the unit is up and running again. Alas, the culprit suffered from desoldering and cutting it off the board (the bottom side of the PCB isn't accessible in an easy way), so I couldn't investigate further on the failure mode of this component. For sure, it'll be properly widlarized then.

I guess that little electrolytic was dried to some extent, and changed its ratio from C to ESR / ESL somewhat. The ESR must have been still low, otherwise there would have been too much damping, but the ESL apparently formed a resonant tank with the paralleled ceramic cap, resonating in the ballpark of 300MHz. This is the low level oscillation that I could observe when the desired 95MHz oscillation ceased. The damping ratio of these concurring tank circuits must have gone critical here, so the parasitic one could take over.

I remember Jim Williams warning about paralleling electrolytic and ceramic caps for decoupling purposes (it's written up in one of his famous app notes), just because this tank formed
by the high Q ceramic and the electrolytic's ESL could create serious ringing.

[capt bullshot]

I've done some timenuttery with the two working ones now:

Using a simple power splitter, one can add (not mix) the outputs of two signal generators to see the beat frequency on a scope.
Both units set to 100MHz, the scope shows about 2Hz - meaning the OCXOs match to 2*10E-8

Adjusting one generators frequency to 100MHz - 2.05Hz results in a constant amplitude (meaning the frequencies are the same), resulting to 2.05*10E-8 oscillators.
The reference oscillator of the CMU200 is just about the same accuracy - quite nice for about 1992 vintage instruments.

I guess, now I need a GPSDO ...

[capt bullshot]

Update on unit #3:

http://wunderkis.de/mg3633a/repair3.html

Short story: It came to life again, I've replaced some blown up and obsolete components by modern stuff.

[DC1MC]

Capt, wie immer (as always), an excellent repair job, nicely illustrated and with good and cost effective solutions found. 
This puts my lazy old a$$ to shame, you've repaired 3 and I was only able to repair the PS of the SA and order a CRT rejuvenator to see if the tube can survive a bit more or it's the LCD time.
I definitely have to meet you again or put my behind in movement.

 Congratulations and keep up the good work,
 DC1MC

P.S. If you need rejuvenate some of your CRTs, I have the professional solution coming  .

[capt bullshot]

That was a pretty quick reply, have you been sitting all the time and waiting for this post? 

[DC1MC]

That was a pretty quick reply, have you been sitting all the time and waiting for this post? 

Told you', lazy a$$ 
I was just logging in and looking at the replies to my posts while crunching some toxic blue chips from Kaufland  , we probably reach home around the same time.

 Cheers,
 DC1MC