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Thread: 856XE Fractional N spurious


Permlink Replies: 7 - Pages: 1 - Last Post: Mar 12, 2014 4:50 PM Last Post By: techfreakz Threads: [ Previous | Next ]
David Sudry

Posts: 37
Registered: 05/14/07
856XE Fractional N spurious
Posted: Jun 25, 2012 7:51 AM
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Hi,

I have seen several 8563E, 8561E spectrum analyzers with about 500KHz spurious at a level of -50dbc.
I believe the spurious is generated at the Fractional N Synthesizer at the A14 Frequency Control Assembly.

Has someone noticed this and found a cure for it?

Is there a simple way to reduce this spurious level? Replace the The Fractional N divider?

I have the schematics for this Assembly and I am willing to share it with someone that can help.

Regards,

David Sudry
Carmel Wireless
Shoresh, Israel
dhamilton

Posts: 136
Registered: 02/01/08
Re: 856XE Fractional N spurious
Posted: Jun 25, 2012 7:54 AM   in response to: David Sudry in response to: David Sudry
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David,

Your problem is in the power supply. There is a service note out on that problem. Check the Agilent website.
David Sudry

Posts: 37
Registered: 05/14/07
Re: 856XE Fractional N spurious
Posted: Jun 25, 2012 10:17 AM   in response to: dhamilton in response to: dhamilton
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Dear dhamilton,

I searched the Agilnt Service notes site for "856" .
I found nothing on the subject.

I have a current case of this spurious which showed up after power supply has been replaced.

can you provide a link to the service note?

Thanks,

David Sudry
David Sudry

Posts: 37
Registered: 05/14/07
Re: 856XE Fractional N spurious
Posted: Jun 30, 2012 2:10 AM   in response to: David Sudry in response to: David Sudry
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Hi,

Problem traced to a faliure in the power supply regulator assembly p/n 08564-60009.
I have replaced the regulator assembly and the spurious disappeared .
I will troubleshoot the regulator assembly and will advise about the required repair.

Regards,

David Sudry
Shoresh, Israel
techfreakz


Posts: 5
Registered: 03/05/14
Re: 856XE Fractional N spurious
Posted: Mar 5, 2014 4:13 PM   in response to: David Sudry in response to: David Sudry
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Hello all,

I'm trying to repair an 8563E spectrum analyzer for personal use and I'm also seeing the exact same spurious signal at 480-500kHz offset (about -57dBc) on the 300MHz CAL OUTPUT. I get similar levels looking at an external signal generator.

I'm guessing its the 6th harmonic of the ~80kHz switch-mode supply getting on to the 100MHz/300MHz/600MHz board and modulating the outputs?

So, is the fault generally caused by failing 2700uF, 6800uF and 220uF smoothing capacitors or do also need to replace the dual diode rectifiers (e.g. VHE2402A) as per Section E "OUTPUT RECTIFIER" of the schematic (See attached)?

Best regards,

Alex
jlubecky

Posts: 15
Registered: 08/20/13
Re: 856XE Fractional N spurious
Posted: Mar 5, 2014 8:10 PM   in response to: David Sudry in response to: David Sudry
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Attachment 8560E-17.pdf (151.7 KB)
The 300KHz spurs are from the A6A2 regulator assembly. They (Agilent) added 2 - 220pF caps. I attached the service note that was referenced.

Joe L
techfreakz


Posts: 5
Registered: 03/05/14
Re: 856XE Fractional N spurious
Posted: Mar 6, 2014 3:46 PM   in response to: jlubecky in response to: jlubecky
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Hello Joe,

Thank you for taking the time to reply.

I now have a set replacement capacitors on order from Farnell for all the electrolytics on the A6 PSU board and I will patch some additional 220uF capacitors on to the -5V line of A6A2.

Thank you also for attaching the service note - there seems to be many documents for the 8563E that don't appear in search engines!

Best regards,

Alex

P.S. I will post back here if the fix works with details of the parts used for the benefit of others.

Edited by: techfreakz on Mar 6, 2014 3:46 PM
techfreakz


Posts: 5
Registered: 03/05/14
Re: 856XE Fractional N spurious
Posted: Mar 12, 2014 4:50 PM   in response to: jlubecky in response to: jlubecky
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OK,

So I've replaced the capacitors and now I appear to have a different PSU issue.

Does anyone have a schematic or CLIP for the A6A2 module? (08564-60009)

With only a few of the main PCB's plugged on to the J1 ribbon the unit starts up, but as I plug-in more boards the +5V rail and the +15V rail start to drop (settling at about 2.8V and 8V respectively. The PSU is also "squealing" a little and the N-ch IRFZ40 FETs & 220uF output capacitors are getting rather toasty (probably due to the ripple current as the FETs turn on and off). The unregulated voltages heading in to the A6A2 module appear to be the expected average levels (+6.8V and +17V), but they droop when then N-ch FETs turn on.

Either another fault has developed on one of the main PCBs attached to J1 ribbon or the PSUs ability to deliver current has diminished.

Does anyone have any suggestions or insight before I start ordering replacement ICs for the A6A2 board and output regulator FETs?

Thanks again for your help,

Alex

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