HP equipment fuse in N connector

[tkamiya]

I'm stuck in stupid place.

Troubleshooting sweeper cartridge, I traced the issue to be the N connector on front panel.  It's SMA inside, N outside.  There is no continuity.  Replacing it with my spare fixed the problem. 

I know the fuse is easily replaceable, if one knows how.  Does anyone know how?  There is no obvious "Twist Here for Fuse" sign anywhere.  I see there are 3 dots if I look inside the N side of barrel.  That means there is a special tool for it.   Pouring over manuals for last 3  hours didn't help me any.

Help!

[pbarton]

and the model number of the HP sweeper is....?

[jfphp]

If it is a 8359XX plug in, a 834XX..., there is a capacitor Inside between input sma and output N (and the connector is not serviceable). Purpose is to block the DC driving the pin switch in the YTM. Suppression of the DC block will destroy the pin switch and eventually the DC coupled spectrum analyzer connected.
A fuse existed in the old 608A-95A fuseholder.

[tkamiya]

It is indeed 83590A.

Oddly though, the one that does not have DC continuity, I cannot get any output.  One with continuity, it works normally.

[tkamiya]

I measured 1500pF from SMA side to N side.  No DC continuity.  Placing it inline between sweeper and specAn, there is RF coming out.

This requires further investigation.  My plugin did not work with this DC isolated version but did work with DC connected kind.  I am not sure if there are multiple design changes?

Just to be sure, I measured DC output at sweeper.  Zero volt.  So nothing is coming out as far as DC is concerned, even with one with DC continuity.

[MarkL]

I've had N connectors where the center pin broke off internally.

There may not be a fuse, but it does look like there are two types of N connectors HP installed on these units according to the service manual, one of them being AC coupled.

Relevant page attached below; extracted from:

  http://literature.cdn.keysight.com/litweb/pdf/83590-90005.pdf

EDIT - Sorry - wrong!  That's an APC-7 connector, not an N connector.

[tkamiya]

Wow, thanks!  That's a really helpful information!

I was just retracing my steps.  Logically thinking, either version should work as 1500pf is large enough for few MHz to pass.  One thing I noticed is that looking at it from N fitting side, the color of insulator is different.

BLACK insulator version passes DC
BROWN insulator version does not pass DC

PART NUMBER ARE THE SAME!!

I am wondering what prompted the change.  Does the fact this unit have an attenuation installed mean something?  If this is to block DC, it's pretty bad way to do it.  Sure it works but for a technician, there is no way to tell which one is right for a particular unit.

[MarkL]

Sorry, my mistake!  That second connector is option 005 which is an APC-7 connecctor.  It's not an N connector.

[tkamiya]

But take a look at the part number and description for J-1.  I think the pictorial above it is showing APC but it may equally apply to N as well.  (as J-1 describe both connector assembly)

I still don't think relying on capacitor IN connector is a bad design.  I would put independent module inline.

Thank you for your keen eyes. 

[tkamiya]

Now, I replaced the N connector to what was in there before.  It works!

I hate this.  I thought it was THE problem.  Now it's gone.

[MarkL]

It could be (what I mentioned before) the center pin is broken off inside the connector housing.

When this happened to me the connection was intermittent, like you're describing.  After I figured out it was definitely the connector, I also noticed the center pin was loose enough to spin, so you could check for that.

[tkamiya]

I tested for "rotation" and they both have none.  What I didn't mention was I have two unit with similar problems.

I found one possible theory.  I didn't mention this, but I have two unit with similar symptoms.  Inside each unit is a directional coupler with 3.5mm connector.  To it, rigid connector with SMA connects to it.  On unit "B", the center conductor on 3.5mm was destroyed.  I didn't check on unit "A" but I do recall it being lose, so I tightened it to proper torque. 

Maybe that was the issue...?

Unit B is now strictly a parts box.  Rotary encoder is broken, no output, directional coupler is damaged.  I got both for $25 so nothing is lost. 

Now, I have to figure out why UNLEVEL comes on.  The light is consistent on all band, (0 to 4) but goes away on retrace.  There is an extensive process on troubleshooting on manual.  So it should be fixable.