Author Topic: HP 6114A Precision Power Supply Restoration  (Read 16400 times)

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Offline robrenz

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HP 6114A Precision Power Supply Restoration
« on: July 13, 2013, 09:06:34 pm »
Thanks to PedroDaGr8’s heads up thread, I picked up a very dirty but nice HP 6114A power supply.  I thought I would document the restoration. Other than a cranky V/A meter switch, it was fully functional despite being shipped in a single layer corrugated box that had no packing material except a half inch of clearance on each end filled with some packing peanuts.  Quite a testament to the old HP build quality.  This first post will focus on Physical restoration other than inside pictures and the decade switch clean and lube.  Calibration and testing posts will follow.

Quick general specs. 0-20V, 2A/20-40V, 1A 
CV specs. Load Reg. 0.0005% + 100µV  Line Reg. 0.0005% + 40µV   Ripple and noise 40µVrms/100µV p-p (up to 20MHz)  8 hour drift 0.0015% + 15µV  Output accuracy 0.025% +1mV 
CC specs.  Load Reg. 0.01% + 500µA  Line Reg. 0.005% + 40µA   Ripple and noise 200µArms/1mA p-p  8 hour drift 0.25% + 7mA

Before


After


Top before


Top after. Cleaned with Simple Green Crystal at 1.5:1 and magic sponges. That white patch at the back is very old duct tape residue. It took a while but it got the residue off without damaging the vinyl coating. IMO magic sponges (Melamine foam) can clean things that nothing else can, try them! I used a short bristle paint brush to scrub the insides of all those cooling holes by hitting then at an angle from 4 different directions on both sides. I used a body hammer and a soft foam mat to remove some depressions and generally flatten the cover. On these types of covers you want a slight bow that will keep the center of the cover tight when installed. A final treatment with Armor All gives that new vinyl finish.


Side panel before.  This whole unit was covered in a brown sticky film like cigarette smoke or rosin flux residue.


Side panel after. Same treatment as top


Top at tape residue patch before.


Top at tape residue patch after.  Magic sponges are able to get into the crevices of that vinyl and make it look new.


Meter face before.  Not in too bad shape, no visible scratches just a general haziness.


Meter face after. I will discuss polishing later below.


Voltage decade switch before.  This plastic had that lamp black soot matte look that some old plastics get.


Voltage decade switch after.  After disassembly and ultrasonic cleaning, a rubdown with ArmorAll minimized that matte look and also lubricates the mechanism.  The clear windows were also polished both inside and out with ArmorAll on a wad of Kim wipe held in hemostats. I filled the + and – symbols on the pushbuttons with white craft acrylic paint using a sharpened bamboo skewer for a paintbrush (under the stereo microscope). Knob took a dump in the ultrasonic and toothbrush scrub with ArmorAll at the end.  The graphic panel looked clean after washing with Simple green but the white text did not get really white until I gave it a light scrub with the magic sponge and simple green.


Output jacks and current limit dial before.  In really good condition, just dirty.


Output jacks and current limit dial after.  IPA wash with toothbrush scrub. IPA on Cotton swab in jack holes. ArmorAll on jack plastic. Pot knob removed and internals oiled. Outside of pot given a wipe with WD-40


Total front panel before. Other than stickers and grime, excellent condition with all text and graphics in perfect condition. The top aluminum extrusion has a few paint only scratches thru the paint on the edge.


Total front panel after.  I sanded out the few scratches on the top aluminum extrusion and an IPA wash before giving a coat of paint that approximately matched the original HP color. If you don’t sand out the scratches first they will show thru the new paint!  The stickers peeled off easily but left that dried out sticker residue behind. Xylene or GOO gone removed the residue and did not attack the text or graphics. IPA cleaned off all the other crud and toothbrush got into all the crevices. I had the unit disassembled at this point so I could clean the whole bottom panel section without the side panels or meter and decade section attached.  Again there were a few brown spots that did not budge until a Magic sponge hit them with the IPA. Then a buff with Armor all and all is well.


Bottom after.  It had some mild dents and it got the same treatment as mentioned for the top. Under the 4 new stick on feet were square holes that probably held the original feet of the unit. I am obsessive but I don’t care if they are original or not, just functional.


Bottom view of the massive two piece heat sinks and transformer and main caps.


Top view of the main board.


Side view of the Daughter board.


Continued on next post

EDIT: added Melamine foam and link
« Last Edit: January 21, 2014, 06:21:19 pm by robrenz »
 

Offline robrenz

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Re: HP 6114A Precision Power Supply Restoration
« Reply #1 on: July 13, 2013, 09:07:19 pm »
Continued :)

Right half of the daughter board.


Left half of the daughter board.


Top front showing the back of the decade switch circuit board and the back of the panel meter.


Top back with the huge heat sink and ribbon connection to the rear panel connections.


Rear connections for output, remote sense, remote voltage programming, remote current programming, case ground.


Frame sides removed for refinishing.


Refinish tool lineup clockwise from top right, fine grit sanding sponge, WD-40, fine flat file, sanding stick with 220 silicon carbide paper, magic wadding polish, Grey fine scotch brite. Fortunately these HP frames are just polished aluminum, not nickel plated like the Tektronix frame in my scope restoration.  Edges of frame are first filed for uniform edge radius and smooth corners. Then using the sanding stick kept wet with WD-40 the edges are all sanded keeping the lay of the sanding straight with the edges to a uniform sanded finish. Next the sanding sponge wet with WD-40 does wonders giving a very uniform texture to the aluminum again, keeping the lay of the sanding straight with the edges. Then a final polish with the magic wadding polish and a dunk in the ultrasonic cleaner.


I wanted to disassemble and clean and lube the decade switches but they have to be removed from the circuit board to take them apart. Fortunately they are just connected with a solder bridge/fillet between the boards. Here is the board with all the solder removed with solder wick. I find solder wick works even better when you wet the section you are using with more liquid flux before use.


This is the back of a decade section showing removing the heat staked plastic edges that hold the circuit board in place with a small chisel.


Here are the internals of one of the decades the gold was in perfect shape but had caked and dried lubricant on it. I wiped it and the wipers clean with IPA followed by a scub with Deoxit D100L then a rubbed in application of Deoxit G100L.


All these parts went into the ultrasonic and then were rubbed down with ArmorAll to renew and lube the plastic. There are two holes in the back that you can put a “U” shaped piece of wire into to hold the detent arms back while you insert the number wheel. Very fiddly bits that like to explode out of the case when least expected.


All of the number wheels wiped clean and looked like new just using a dry Kim wipe, until this one where half the zero wiped off.



So under the microscope with a bamboo skewer sharpened to a point to us as a fine paint brush and some white acrylic craft paint. Not perfect but at normal viewing distance no one will notice. Fortunately that was the only occurrence.


Decade stack back together and held with two bands of Kapton tape about 3 layers deep each. The original was held with a woven tape much like a heavy medical tape. Because I cut off all the plastic heat staking that held the circuit boards in place. I had to put several layers of tape on the back of each circuit board in strategic places/thickness to have the mating switch body press the circuit boards down tight when assembled.


All the solder bridges/fillets redone.


Example of the plastic oxidation from whatever was in the air or lighting. That matte chordal shaped area is what is exposed when the meter is assembled.


The graphic panel was originally contact cemented down and held by the pot nut. I used two strips of thin double stick tape for the restore.


Lifting the bezel ears allowed removal to get to the clear part.


Removing one clear “U” clip at the top of the meter allowed the clear part to just fold right off the back. I just did a light polish with Meguires plastic polish on a felt pad to remove the light haze on the lens. A final polish with a Kim wipe both outside and inside left it perfectly clear.  Be very careful about what you polish with. Most general paper products (toilet paper, paper towels, etc.) will scratch very fine soft surfaces. Kim wipes are designed to be totally nonabrasive and lint free on optical surfaces. That is why I use them for this. A microfiber towel may also be used.


About 8 hours FUN to go from surplus store condition to fresh off the HP assembly line. Calibration and testing next.
« Last Edit: January 21, 2014, 06:22:38 pm by robrenz »
 

Offline quantumvolt

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Re: HP 6114A Precision Power Supply Restoration
« Reply #2 on: July 13, 2013, 09:51:17 pm »
Very nice job.

Strange you got got the same stupid "Flat Rate Box" or similar as me. But in my case, several fins were broken, and front panel with knobs and posts were damaged.

When you work with the manual, I am sure you understand why I say that these HP PSUs are in a class far above PD when regarded as professional laboratory equipment.
 

Offline uoficowboy

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Re: HP 6114A Precision Power Supply Restoration
« Reply #3 on: July 14, 2013, 05:00:55 am »
That's really nice work man.

I wish Power Designs used 10 turn pots for the current limit like this device used. You can't have enough 10 turn pots in a device IMHO.
 

Offline Vgkid

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Re: HP 6114A Precision Power Supply Restoration
« Reply #4 on: July 14, 2013, 05:25:26 am »
Very nice job on your power supply restoration. Those old HP's are very accurate.
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Offline BillyD

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Re: HP 6114A Precision Power Supply Restoration
« Reply #5 on: July 14, 2013, 08:49:05 am »
Very nice job indeed, a great example of what can be achieved with skill and patience - and cleaning products and elbow grease!
Thanks for sharing.


 

Offline saturation

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Re: HP 6114A Precision Power Supply Restoration
« Reply #6 on: July 14, 2013, 12:12:12 pm »
Great job, most excellent, as always!
Best Wishes,

 Saturation
 

Offline quarks

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Re: HP 6114A Precision Power Supply Restoration
« Reply #7 on: July 14, 2013, 02:34:10 pm »
Great work, thanks for sharing.
 

Offline c4757p

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Re: HP 6114A Precision Power Supply Restoration
« Reply #8 on: July 14, 2013, 02:36:56 pm »
I wish Power Designs used 10 turn pots for the current limit like this device used. You can't have enough 10 turn pots in a device IMHO.

I love PD, but those little screwdriver knobs on single-turn pots for current limit are freaking retarded. What where they thinking...?
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Offline saturation

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Re: HP 6114A Precision Power Supply Restoration
« Reply #9 on: July 14, 2013, 03:45:47 pm »
..it is c1960s technology .. :-//

I wish Power Designs used 10 turn pots for the current limit like this device used. You can't have enough 10 turn pots in a device IMHO.

I love PD, but those little screwdriver knobs on single-turn pots for current limit are freaking retarded. What where they thinking...?
Best Wishes,

 Saturation
 

Offline c4757p

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Re: HP 6114A Precision Power Supply Restoration
« Reply #10 on: July 14, 2013, 03:56:22 pm »
I assure you, there were knobs in the 1960s! And they were still doing it well into the 70s...
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Offline saturation

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Re: HP 6114A Precision Power Supply Restoration
« Reply #11 on: July 14, 2013, 04:25:22 pm »
My apologies, I see what you mean like on the HP 6114a, a screwed pot instead of a knob pot.  IIRC some ye olden day designers thought that would prevent accidental adjustment of the current limit and that folks wouldn't use it much, so they made it more difficult.  In other models like the precision PD ones, they are all knob'd.  In this PD generations photo, the older PD has a separate set and adjust button, in black in the unit on the upper right, the other 3 are pull to adjust knobs.



I assure you, there were knobs in the 1960s! And they were still doing it well into the 70s...
Best Wishes,

 Saturation
 

Offline robrenz

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Re: HP 6114A Precision Power Supply Restoration
« Reply #12 on: July 14, 2013, 08:35:37 pm »
Thanks everyone for your kind words. I find the whole process very relaxing and enjoyable.

The 10 turn current pot is an option 008 so there are many 6114A units with a single turn pot for current just like the PD precisions. On the other hand the single turn pot on the 6114A covering 10mV is not as good as the single turn pot on the PD precisions covering 1mV.  In  both cases 10 turn pots are not readily available in these low values 20ohm for the HP and 1 ohm on the PD.

The 6114A is definitely better on CC accuracy and stability as it was designed with that in mind since it has specifications for CC operation.  The PD precisions only consider this as a current limit control.  Some tests done on the POWER DESIGNS thread show that is the case. The shunt resistor tempco is not nearly good enough to have accurate CC regulation.

Offline robrenz

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Re: HP 6114A Precision Power Supply Restoration
« Reply #13 on: July 15, 2013, 04:54:34 pm »
Clarification on "Magic sponges"

Someone PM'd me if the "magic sponge" they found on amazon was what I used.  It was a microfiber sponge which is not what I am talking about.  If you search for "Magic sponge eraser" or "Melamine foam"you will get the correct thing which must be Melamine foam. 

wikipedia link

Offline PedroDaGr8

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Re: HP 6114A Precision Power Supply Restoration
« Reply #14 on: July 15, 2013, 11:07:41 pm »
WOW! That thing looked MUCH worse than mine did and came out looking much better.  These PSUs are beautiful works of art.  I checked the images before posting that thread in the BST section. I noticed they seemed to be in pretty good shape albeit dirty as all get out. I liked your tear down of the switches. I'm debating going into mine and doing that.

I got lucky on mine in that there were no real dents and only a few small scratches. Mine weren't even dusty inside. Everything else was just adhesive residue and finger oils. I used Weiman Gas Range degreaser on a paper towel + elbow grease seemed to take care of the adhesive residue.

One thing I can mention on the restoration: Mothers Back To Black works REALLY well on the switch buttons. I let it soak in much longer than the usual time frame (I actually ended up doing two-three applications) but when done they look basically like new.


Also, there seem to be a few revisions to these. On some they use a vertical dial to set the last digit (it is rotary not decimal like the others), then some use all red/black banana plugs while others use the gray with red/black tips, then lastly on older ones the power switch is very small at the bottom, while newer versions replace that with a larger switch centrally mounted.
« Last Edit: July 15, 2013, 11:21:01 pm by PedroDaGr8 »
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Offline calin

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Re: HP 6114A Precision Power Supply Restoration
« Reply #15 on: July 16, 2013, 12:06:49 am »
Wow, why i did not think at magic eraser sponges before ... BTW .. they are calles "Mr Clean magic eraser" sponges ... That's it I am off to home depot to get a bunch to clean my old hP gear :)


BTW, awesome job Rob .. looks like new !!!
 

Offline JimmyMz

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Re: HP 6114A Precision Power Supply Restoration
« Reply #16 on: July 16, 2013, 12:36:04 am »
Nice restoration; I enjoyed all the before and after shots.

"Goo Gone" (citrus based) works wonders on adhesive residue. A squirt to cover the area, 30 seconds, and wipe off...and it gets it all.  :)
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Online BravoV

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Re: HP 6114A Precision Power Supply Restoration
« Reply #17 on: July 16, 2013, 03:23:58 am »
Great work and thanks for sharing !  :-+  :clap:

Offline free_electron

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Re: HP 6114A Precision Power Supply Restoration
« Reply #18 on: July 16, 2013, 06:20:44 am »
Well done! Looks like brand spanking new!
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Offline robrenz

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Re: HP 6114A Precision Power Supply Restoration
« Reply #19 on: July 16, 2013, 10:38:01 am »
Thanks again everyone and glad these restorations and tips are appreciated.

@ PedroDaGr8,  thanks again for the heads up and I will have to try that "mothers back to black". Its description sounds like it is the same thing as Armor All but it may be better.  I agree that this seems to be a later model than what is shown in the manual with a analog pot for the millivolt setting and a more modern power switch.

@ calin,  The Mr Clean ones work great but the generic ones are the exact same material and are cheaper in bulk.  These things disintegrate pretty quickly in use so you can go thru one sponge on one restoration.

@ free_electron,  I am glad your great distaste for antique electronic equipment did not extend this far ;D

@ BravoV,  This is partly your fault ;)

Offline JuiceKing

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Re: HP 6114A Precision Power Supply Restoration
« Reply #20 on: July 16, 2013, 11:05:05 am »
Very nice! I have the 6115A (the 50/100V) version, picked up for very little from eBay in very grubby condition but not so hard to clean up and works great.

For those now keen to find one of these, take note that prices vary widely, but they are plentiful. It pays to be patient. Dirty but working units come up all the time. Mine also has the 10-turn pot for current control, and as nice as this is, it's not desperately important. I wouldn't pay the big premium for it that some sellers seem to hope for.

Just ordered a bunch of those magic sponges...a great tip. Thanks!
 

Offline PedroDaGr8

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Re: Re: HP 6114A Precision Power Supply Restoration
« Reply #21 on: July 16, 2013, 02:39:23 pm »

@ PedroDaGr8,  thanks again for the heads up and I will have to try that "mothers back to black". Its description sounds like it is the same thing as Armor All but it may be better.  I agree that this seems to be a later model than what is shown in the manual with a analog pot for the millivolt setting and a more modern power switch.

I follow auto detailing quite a bit. Armor-All is used for protection and giving a surface shine (though even for that there are better ones like 303 aerospace). Back to black and a few others are specifically designed to restore sun damaged plastics. It has more of a lotion like consistency than a liquid like Armor-All and it lasts much much longer.

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Offline robrenz

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Re: HP 6114A Precision Power Supply Restoration
« Reply #22 on: July 16, 2013, 02:51:14 pm »
Thanks, I will get some and try it.

Offline aholtzma

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Re: HP 6114A Precision Power Supply Restoration
« Reply #23 on: July 19, 2013, 04:03:57 pm »
Did you clean the PCB as well? If not, it sure was in good shape. Mine has a nice coating of sticky dust.
 

Offline robrenz

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Re: HP 6114A Precision Power Supply Restoration
« Reply #24 on: July 19, 2013, 04:47:24 pm »
I thought it would be sticky since the outsides were but it blew right off with an air hose and light brushing. the pictures of the insides are actually as received before I dusted it off.

I take it you got the other one?  Was yours packaged as poorly as I described?

Edit: Welcome to the forum aholtzma
« Last Edit: July 19, 2013, 05:25:23 pm by robrenz »
 


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