RESTORATION of TEK 7603 Scope w 7A18 amp + 7B53A timebase

[robrenz]

This is my restoration of my first scope from 32 years ago. The story of getting it back 32 years later is  this thread  It had very little use  during the roughly 30 years it was not in my possession but was very dirty inside and out yet was fully functional.

The main cosmetic issue was serious corrosion under the nickel plating on the front and rear frame bezels. The main covers were just dirty and needed some body hammer work from heavy items that gently bowed the tops in the perforated areas and some light dents. Magic sponges and simple green were extremely effective at removing the dust that very firmly attached itself to everything. Armor all was used on all the exterior plastic and vinyl parts. The plastic CRT filter needed a wet sand and plastic polish treatment to remove some mild scratches.

The main functional issues were the very dirty and corroded bnc connectors and the normal scratchy pots and switches. I disassembled the pots that were bad and ultrasonic cleaned all the parts in IPA. Then cleaned all the contacts and wipe areas with Deoxoit D100L on a soft wood stick. Clean with IPA again and lube the gold wipe areas with Deoxit G100l and the actual pot wiper with Caig Faderlube. The mechanicals were lubed with Triflow grease. The gang switches were flushed with IPA and then Deoxit D100L was blasted thru them with compressed air. The drum switches in the amplifier and timebase were disassembled and all the gold finger contacts were individually cleaned with D100L on paper pulled thru the contact area, cleaned with IPA and lubed with G100L.  I also replaced the power cord that was pretty stiff.

I have many more pictures but I am trying to restrict this thread to things that are not in your typical restoration. I will start with just before and after shots and then post more details following.

Front before, the poor(er) photo quality was not intentional.


Front After


Top right before


Top right after


Rear before


Rear after


bottom after


After top and handle


After left top


After top


After side

[david77]

Great! I was looking forward to reading your restoration on this scope. As soon as I can find one in reasonable shape and at reasonable price I'll get one.
A small electronics shop here has a couple of them for sale, in unknown condition without plugins for 550,00 EUR a piece non negotiable - I think not  .

[robrenz]

More before and after shots. All the knobs went into the ultrasonic with waterbase cleaner. Front panels were removed cleaned and replaced. Armor all got rid of oxidation on the black portions of the knobs and the AC-GRND-DC switches.

Finshed back.


Since I had to refinish all of the frame I was able to match the bottom extrusions to the front and rear bezels at the bottom.


Very dirty 7A18 vertical amp.


Crusty bnc connector.


After 7A18




Very dirty 7B53A timebase



After 7B53A timebase

[alm]

Very impressive results!

[robrenz]

The Frame bezels are nickel plating over a copper flash on the base aluminum die casting.  I thought I could just glass bead blast it off but the plating thickness varies greatly because of the current density variations in the plating bath. So all the sharper corners are plated thicker. So I had to file all the nickel off on all the areas that are exposed when assembled. After all the body work and sanding of the exposed areas it went into my glass bead blast cabinet for that uniform frosty finish. The frame and CRT bezel were then washed in solvent and sprayed with Permalac  sealant.  Very high performance stuff with a price to match.  All this work may seem extreme but I think the final results are worth the effort.

Heavily corroded spot


General peeling


General funk


Filing thru the corner. Nickel then copper flash then the base aluminum.


Precisely filing all the nickel off. Several hours of work followed by several more hours of contour filing and sanding.


220 wet or dry silicon carbide paper glued to a cast iron surface plate. This allows me to flatten the face of the bezel.


I put black marker on the face to check when it is all cleaned up. I am about half done, have to sand until all the black is gone.


This is the bare aluminum with a glass bead blast finish and sealed with the Permalac.


The CRT bezel fortunately was not plated so it only needed some filing, sanding and bead blast before the Permalac

[robrenz]

Much to my dismay the screen printed text on the rectangular push buttons wiped off with just water.  So I pondered many other bad fix methods before realizing I could engrave the buttons and fill them with black epoxy.


Engraver set up with quick fixture to repeatably locate the buttons. Ratio is set to match the original text size.


Quick fixture made with toolmakers vise and parallels glued to the vise to nest the button.


It just so happens the engraver font I have is the same as the button text.


I sharpened the engraver cutter to a narrower than usual included angle so I could get some substantial depth without the cut getting too wide. This cut is about .01" deep.


These have the original text still on and I have used the same engraving cutter to cut the horizontal line in these buttons.


Mixing 20 min epoxy with carbon black to fill the engraving.  The milligram scale allows precise ratio mixing of very small quantities.


Epoxy was spatula-ed into the engraving and cured under the luxo lamp.


All the buttons have been filed and then wet sanded on 6 micron diamond film. This also removed all of the yellowing of plastic on the buttons


Button after polish with Meguires plastic cleaner on woven nylon metalographic pad.


At normal viewing distance I don't think anyone is going to know these are not original.

[T4P]

Extreme machining comes into practice here - Great work rob! 

[SeanB]

Very nice work there, looks better than when it left the assembly line all those years ago.

[Shuggsy]

Amazing looking work robrenz. Did you have to replace any parts or was it all "just" (BIG quote marks there, a LOT of work involved!) cleaning? Those buttons look particularly great. Tek should have made them that way!

[firewalker]

Awesome!!!

Alexander.

[muvideo]

Wow, hats off to you, wonderful work !

Fabio.

[Soertier]

Awesome restoration!!

[TerraHertz]

I'm speechless! Awe and envy at your skills. Beautiful work.

(So *that'* how to shine up dirty BNCs. I never was able to do even that terribly well.)

[robrenz]

Thanks All for the kind words. It is easy to do when it is a labor of love.

Did you have to replace any parts or was it all "just" (BIG quote marks there, a LOT of work involved!) cleaning? Those buttons look particularly great. Tek should have made them that way!

The only replacement was the red center knob on the timebase dial and I broke one switch on the timebase circuit board. (I had another timebase to rob from)

(So *that'* how to shine up dirty BNCs. I never was able to do even that terribly well.)

Speaking of BNC connectors, Never dull is what I used on the outside of the connectors. This stuff is a cotton wadding that is very damp with some magic cleaner/polish.


This is the secret to the super clean BNC insides. I mount a very hard felt cylinder in a Dremel tool running at 5000 rpm. In "manual lathe mode" take an exacto knife and bore a hole in the felt that clears the teflon insulator of the BNC. Also turn down the outside diameter of the felt to be a snug fit into the BNC.  This can be a very dangerous thing,  apply all your wood turning skills here. Soft felt won't work, it will fly apart before you get the shape you need.


Wet the outside of the felt with Gaig Deoxit G100L and slide into the BNC and then turn on the Dremel at 5000 rpm. Oscillate the felt and apply light side pressure in a full circle.  The whole thing will be done in about 3 seconds.


The inside of the center connector is cleaned with a Microbrush in the Dremel at 5000 rpm.  I wet the Microbrush with G100L and insert it into the BNC before turning it on so it doesn't throw all the Deoxit off.



I wrap a kimwipe or a piece of toilet paper around a 1/4" dowel so that its outside diameter is a snug fit in the BNC. Wet that with IPA and clean all the residue out. The paper needs to extend past the dowel far enough that it reaches the bottom of the BNC. Clean all the BNC's this way and then use a fresh wipe and repeat until the wipe stays clean after doing all the BNC's Then a flush of IPA in the center connector and a air blast to remove all the IPA. Finally a light coat of Deoxit G100L outside and inside.


This was the worst of the BNC's,  before


After (OK not the same BNC but the same amp, this is channel 1)

[grenert]

Wow, this should be stickied as the "Ultimate Instrument Restoration Techniques!"  Very, very impressive.  Those restored buttons are done similar to the old HP calculator buttons (don't know if they used the same technique in their instrumentation).

Two questions:
What are magic sponges?
Where do you get those tiny, tiny brushes for the BNC connectors?

[robrenz]

Two questions:
What are magic sponges?
Where do you get those tiny, tiny brushes for the BNC connectors?

Magic sponges are Melamine foam. A brand name is Mr Clean magic eraser (most expensive way to buy them).  google magic sponge for lots of sources. They wear out quickly but one sponge did this whole restoration. They really are magic!

There is a hyperlink (underscored blue text) right in the thread that will take you to the Microbrush site.

[SeanB]

Links are inline in the text for the Eshops. Lovely work there, I normally just use brass polish liquid ( leave it in the tin for a week so it settles out from the abrasive) and a cloth. Learnt that from cleaning ceremonial uniform brassware so it would shine, I also made a sheet plate to act as a cloth protector for the buttons, so I did not have to remove them every week to polish. I did pay to send a set in to be gold flashed, never needed to polish them again, but they were for special parades only.

[robrenz]

For some reason Tek did not provide power for the illuminated pushbuttons on the 7603. I followed the instructions from the update kit PDF for installing a LM309K to provide the 5V to the main interface board that the plugins plug into.  I made up the mounting bracket out of aluminum angle.



The EMI shield strips were all pretty dull with a heavy oxide layer. These things are very thin material and easily kinked. So I sanded down a paint stir stick to precisely match the shape of the EMI strip so it would be a press fit.


I used Astonish cleaner to polish these because it is a fairly aggressive abrasive as cleaners go. (don't use on BNC's it will remove the nickel if you polish very long). I used a felt pad and I could bear down on the strips since they were fully supported by the custom wooden mandrel.


Before (an especially corroded example)


After


I have lots of other pics of the internals but It would be the same stuff as other rebuild threads on here so not much point in posting.
The End. 

[SeanB]

Any reason for using the TO3 part over the TO220 other than it matches the rest of the unit construction? Lovely finish on that angle there, you probably got better surface finish than the original heatsinks have.

[ModemHead]

Truly awesome work.  Thanks for sharing your techniques with us.  It reminded me that I have some of that wadding polish, I had forgotten about it and never thought to use it on things like BNC connectors.  Interestingly mine is called "Ever Brite" as opposed to "Nevr Dull".

[mamalala]

Wow, fantastic work! I seriously envy you for you handicraft. Me, i'm rather unable to do much mechanical work. Give me a file and a piece of metal, and you get back a flat file and an unchanged piece of metal.

Again, really fantastic what you are doing there. This takes the word "refurbished" to a whole new level.

Greetings,

Chris

[robrenz]

Any reason for using the TO3 part over the TO220 other than it matches the rest of the unit construction? Lovely finish on that angle there, you probably got better surface finish than the original heatsinks have.

None other than that is what I had on hand.  That reg is left over from the original project from 32 years ago   

I have an obsession about deburring and chamfering,    I like very precise chamfers and well rounded corners that will pass the aerospace white glove tests. Abrasive sponges really do a nice job on blending corners and the glass bead finish can make anything look good.

[lewis]

Sir, that is absolutely awesome. Truly a labour of love. It's great to see classic instruments brought back to showroom condition. Extremely impressed 

[FenderBender]

Fabulous work! I think I know what I'll be doing with my 465 this Christmas break.

[BravoV]

Thank you so much for sharing this, one the best thread about old scope restoration ! 

Thread bookmarked, and 5 stars rating given (geezz.. c'mon folks, why I'm the 1st who clicked the 5 stars rating)  %-B