Author Topic: HP 3466A restoration - DPDT switches  (Read 7203 times)

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Offline calin

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HP 3466A restoration - DPDT switches
« on: December 14, 2012, 07:41:17 am »
I got an old HP 3466A (with battery option) of Craigslist ...40$. Pretty nice find; and now I am working to bring it back to life.

I have to say these things are pieces of art - I posted just for "porn" a photo of the gold plated PCB of the battery charger.

However, i dug (first day only) and I think I found the issue. Meter powers up, all nice, display etc but looks like the function and range switches are all over the place. I tested everything else and is in the parameters given in the service manual (7 volt logic circuits :) and an micro working at a smashing 200kHz) .

So I got to the stage in which I believe the old switches are the culprit - actually i can see they literally cause buzzing and flickering when I push them.  Parts are listed in the manual .. but fat chance finding something with that part number. Google blah blah ... nothing. I recon I am compete noob - how the heck these "selector switches" are actually called. they are simply listed as DPDT switch in the manual - how the heck are they called. And even more, does anyone have any idea where i can find something like this.

Attached are a few photos; any help is welcome :)



 
 

Offline robrenz

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Re: HP 3466A restoration - DPDT switches
« Reply #1 on: December 14, 2012, 02:15:00 pm »
If at all possible remove switches and dissemble. Thorough wash in your fave solvent. Sparingly lube all the mechanical aspects of the switch with your favorite non silicone grease. Use Caig Deoxit D100L on all the contact areas. If any of the contacts are gold clean off the D100L and apply Caig G100L. Thoroughly cycle the switch and then test the contacts with meter or scope. I suggest taking pictures at every stage of diss-assembly and be very carefull opening the switch so you can see how it works and not lose any flying springs or contacts. A container for all the parts helps also because many of these unobtainium parts will run away from home all by themselves if not constrained. :palm:

EDIT:
If the switch has any crevices that you could spray cleaner and deoxit into then blow out with compressed air it would be worth a shot before doing the autopsy method above.
« Last Edit: December 14, 2012, 02:46:55 pm by robrenz »
 

Offline calin

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Re: HP 3466A restoration - DPDT switches
« Reply #2 on: December 14, 2012, 04:30:56 pm »
He he ... I was thinking to do that but before performing the "surgery" I was hopping there is some pill I can take to fix the thing :)

I think I can pop just the hood open - I mean the top cap of the switch - and clean them that way without de-soldering. The darn things are also in an assembly that makes them work toghether - u know push one the other pops out like in the old channel selectors in TV-s. Oh man remember those :) . The thing is that switches not only select the digital part of the function or scaling (for dsplay) the also select the input circuitry V, amps etc and the input gain. Have these shorted and meter measures nada :( .  I will start with the function ones .. wish me luck.  %-B

As for configuration the things are really simple - each group of 3 has a dumb slider - for exaple de-pressed u have 1&2 shorted and pressed 2&3. No link between sides

Code: [Select]
+-------+
| 6   7|
| 5   8|
| 4   9|
+------+
| 3  10|
| 2  11|
| 1  13|
+------+
 

Offline robrenz

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Re: HP 3466A restoration - DPDT switches
« Reply #3 on: December 14, 2012, 04:42:57 pm »
I have some Tek 7000 series stuff with that same type of switch gang. Same thing here, way to much disruption to remove so I used my edit version 2 method above with great success. IMO the high pressure compressed air blasting is key to having the stuff get thru the switch assy.

Offline calin

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Re: HP 3466A restoration - DPDT switches
« Reply #4 on: December 14, 2012, 05:50:52 pm »
I tried .. no luck. These things are press fit forget about opening them, you just break them.

So ... I will apply the  cleaner then blow the heck out of them strategy. They have some small openings at the end facing the control panel and some on top.

 

Offline SeanB

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Re: HP 3466A restoration - DPDT switches
« Reply #5 on: December 14, 2012, 06:21:55 pm »
Take the front panel off first, along with the knobs if possible. Switch cleaners can be aggressive when applied to the acrylic panels. Best way to get it in is to place the board vertical and drip it in the hole at the rear, then operate it a few dozen times wet. Blow dry, then do again from the front. Finally apply a small drop of thin oil to the latch mechanism to keep it working smoothly.
 

Offline calin

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Re: HP 3466A restoration - DPDT switches
« Reply #6 on: December 14, 2012, 06:26:45 pm »
Yep that's my plan - I just discovered that I've run out of compressed/bottled air. So ..gotta wait a bit till I pass by Fry-s.
 

Offline david77

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Re: HP 3466A restoration - DPDT switches
« Reply #7 on: December 14, 2012, 07:22:35 pm »
Be careful to remove all the dirt and your cleaner of choice after cleaning the switches. I'd also give them a thorough rinse with lots of IPA afterwards and then blow that out with shop (or canned) air. The dirt & cleaning fluid could easily mess with the meters high impedance input. I had some issues with a meter with similar symptoms once.

 

Online nctnico

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Re: HP 3466A restoration - DPDT switches
« Reply #8 on: December 14, 2012, 08:39:06 pm »
I'd get another one which just works and keep this as a parts unit. Years ago I've paid US $39 for my 3466A including postage to NL.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline calin

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Re: HP 3466A restoration - DPDT switches
« Reply #9 on: December 15, 2012, 02:55:43 am »
Oh right so the results are in... the cleanup worked and the oldie is back. In tops the old guy got some kick  - somebody show me a 40$ meter able to do 0.03% precision. Compared with my 85V fluke and is spot on on all functions and ranges. That's the best meter I have around to compare; even if the HP should me more precise.

Thanks for the advice guys, I have now one more nice meter around .. not to count in the cool side of having a meter on the bench almost as old as you :)

 

Offline SeanB

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Re: HP 3466A restoration - DPDT switches
« Reply #10 on: December 15, 2012, 04:30:23 am »
Very nice!  I do like old test gear, have got an Advance signal generator to test and repair for the holidays. New mains cable required, and it will be getting recapped where needed.
 


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