Keithley 179 TRMS DMM Repair/Refurb

[xrunner]

Dropped in a rack onto a concrete floor, so there is no case damage but the insides are heavily jarred. Or on a bench and had a few falls onto a carpeted floor.

Yea could be, because it actually does have case damage and a cracked handle. Those are the next things I'm going to tackle (cosmetics) because it's looking like this meter is going to be a winner. I'll be showing the case damage and how I fix it in the coming days. 

[xrunner]

A quick check shows we got a winner! After all these years and abuse it's not bad! I'll go through the cal procedure later, but I'm very happy that it's going to live again! 

[Vgkid]

Hopefully you are going to adjust that...

[lowimpedance]

Just in case you were wondering what that unused dip socket at the front RHS was for. It was the connection to the optional GPIB interface PCB which was used in a number of instruments ie 179 ser 24000 and up , 177 ser 16500 and up, 480 picoammeter. The model number for the option was 1793.

[Lightages]

It would probably be a good idea to let a drop of superglue wick under each of those lifted pads to get them immobilized.

[McBryce]

Congratulations on getting it running.

Aren't those lifted pads on the pins of the selection switches? They've probably just lifted due to years of being pressed.

McBryce.

[Macbeth]

Just in case you were wondering what that unused dip socket at the front RHS was for. It was the connection to the optional GPIB interface PCB which was used in a number of instruments ie 179 ser 24000 and up , 177 ser 16500 and up, 480 picoammeter. The model number for the option was 1793.

Interesting - Looking at the schematic and a quick flick through the 30535D(Model1793).pdf manual shows it would be very easy indeed to knock up an equivalent with a microcontroller. Ignore all the GPIB stuff like addressing and just implement the talk only mode at 2.5 readings/second. Use an 8 bit data bus to read in OVER, /STROBE, B1, B2, B4, B8, D5 and SIGN from J1008 dip connector and get the +5V power too. /STROBE is the latch. D5 indicates the first digit of five. B1-8 are BCD. Do some simple ASCII conversion to the same spec as detailed in 3.8 DATA FORMAT, and finally send it out a serial port to an opto-isolated RS232 interface much the same as all those cheap DMMs do.

Nice little project. 

[xrunner]

Hopefully you are going to adjust that...

Well of course. Right before it's all ready to be put back together.

Just in case you were wondering what that unused dip socket at the front RHS was for. It was the connection to the optional GPIB interface PCB which was used in a number of instruments ie 179 ser 24000 and up , 177 ser 16500 and up, 480 picoammeter. The model number for the option was 1793.

Thanks.

It would probably be a good idea to let a drop of superglue wick under each of those lifted pads to get them immobilized.

I'll try that thanks.

Aren't those lifted pads on the pins of the selection switches? They've probably just lifted due to years of being pressed.

Maybe, those switches have a lot of pins, and the pins are pretty big wire. But anything's possible.

Interesting - Looking at the schematic and a quick flick through the 30535D(Model1793).pdf manual shows it would be very easy indeed to knock up an equivalent with a microcontroller. Ignore all the GPIB stuff like addressing and just implement the talk only mode at 2.5 readings/second. Use an 8 bit data bus to read in OVER, /STROBE, B1, B2, B4, B8, D5 and SIGN from J1008 dip connector and get the +5V power too. /STROBE is the latch. D5 indicates the first digit of five. B1-8 are BCD. Do some simple ASCII conversion to the same spec as detailed in 3.8 DATA FORMAT, and finally send it out a serial port to an opto-isolated RS232 interface much the same as all those cheap DMMs do.

Nice little project. 

Good info thanks. I'll post some pics later today because I'm starting to restore the case now. Hopefully it will be interesting to some people.

Well here's one. I got an ultrasonic cleaner from Harbor Freight a few years ago. It really cleans things well. I pulled off the button covers and threw them in it. I just put a few drops of dish soap in. It's amazing what dirt flies off when the cleaner is turned on. Highly recommended for cleaning all kinds of things. 

[ivan747]

Good info thanks. I'll post some pics later today because I'm starting to restore the case now. Hopefully it will be interesting to some people.

Well here's one. I got an ultrasonic cleaner from Harbor Freight a few years ago. It really cleans things well. I pulled off the button covers and threw them in it. I just put a few drops of dish soap in. It's amazing what dirt flies off when the cleaner is turned on. Highly recommended for cleaning all kinds of things. 

That looks very interesting indeed:
http://www.harborfreight.com/25-liter-ultrasonic-cleaner-95563.html
But that sort of takes some space on the bench, doesn't it? Anyway, I'll be looking for the before/after comparison. And I guess I'll have to use a toothbrush and soap in my case.

[SeanB]

Careful of the ultrasonic cleaner on some things. it can take paint off and destroy certain plastics.

[xrunner]

And I guess I'll have to use a toothbrush and soap in my case.

Funny you should mention toothbrushes, I took some pics of what I do to some of my used toothbrushes. I like to bend the handles of some, because it makes them easier to use in certain circumstances. Just stick the brush part in a vise and grab a propane torch, and heat right behind the brush part and bend the handle up to whereever you like. The plastic is surprisingly tough, but it will bend.

Some of these bent brushes are really useful - plus, who doesn't like melting plastic with a torch? 

[McBryce]

The third one looks like it would have been good for a few more weeks of dental care

McBryce.

[SeanB]

I just use new tooth brushes. They are cheap enough, and you often find a sale where you get 5 in a pack for the price of 2, or I just order them wholesale. That way you do not get contaminants in the work you are cleaning.

[McBryce]

I use used toothbrushes. It's more important that you have several of them, so that you don't use a toothbrush with etching fluid remnants to clean switch contacts etc. I doubt any "dental contamination" would effect the electronics.

McBryce.

[xrunner]

I just use new tooth brushes. They are cheap enough, and you often find a sale where you get 5 in a pack for the price of 2, or I just order them wholesale. That way you do not get contaminants in the work you are cleaning.

Contaminated with what? My used toothbrushes are only "contaminated" with whatever was in my mouth, which I don't think is contaminated enough to have any effect whatsoever on what I'm using them to clean after I discard them. Even if there was some sort of residue, I can just throw it in my ultrasonic cleaner.

Besides, as soon as you start cleaning anything with a new toothbrush it's contaminated with the dirt you have just loosened. If you want to buy new toothbrushes go for it, but as far as my work goes, my used toothbrushes are just peachy keen. 

[Vgkid]

I really like the idea of bending the handles, will bend some.

[codeboy2k]

I really like the idea of bending the handles, will bend some.

My dental hygienist just bends those same Oral B tooth brushes with her hands.. to reach where she needs to.. she showed me, she said they are designed to bend there.  Maybe heating them up is not necessary?  Now I just follow her, and bend them myself without heating.

[VK5RC]

Hot water works really well to soften plastic without burning.  I recently used an old but 'clean'  toothbrush but ended up getting small amounts of dried toothpaste on the board.  So I have gone new/cheap route.

[xrunner]

My dental hygienist just bends those same Oral B tooth brushes with her hands.. to reach where she needs to.. she showed me, she said they are designed to bend there.  Maybe heating them up is not necessary?  Now I just follow her, and bend them myself without heating.

Oh I can bend them, but they won't stay bent, at least not to the position I want. Hey do it however you want. 

Anyway, moving on from toothbrushes, I'm proceeding to the restoration. I'm going to make it as original and clean as I can. Hence I am gluing back on the label that fell off the transformer. I'm polishing the red plastic window with some DVD disc polish I got from the now bankrupt Radio Shack (R.I.P.). It works really well and makes it like glass. Also, I'm removing all the old cal labels and any other gooy stuff with Goo Gone. Some of the dried label adhesive is very hard to get off, but if you let it set all day it will come off. Another thing you can do is put the Goo Gone on and then place a small piece of saran wrap on top of the Goo Gone so it won't evaporate and leave it all day. This is another use for a toothbrush because the plastic bristles will not scratch the plastic but will scrub well.

[ivan747]

How did you remove the scratch marks from the front panel overlay?

Are you gonna do anything to the 7 segment display? (is it faded?)

[xrunner]

How did you remove the scratch marks from the front panel overlay?

I used as much polish as I dared to use on the overlay, I don't want to damage it. It's about as good as it can get at this point.

Are you gonna do anything to the 7 segment display? (is it faded?)

It works perfectly now that the 5V supply is fixed - good as new.

[ivan747]

I don't think I can get a hold of that goo gone in the DR. I'll have to improvise.

Does anybody reckon this will work?
http://lifehacker.com/5931843/diy-goo-gone

[SeanB]

Do not use the gasoline. Use citronella oil ( or just use a lemon skin and rub it on the label till it is damp with the oil off the skin) and leave for a minute or two for the adhesive to soften. Pretty much any citrus fruit, like lemon, grapefruit or Navel oranges will do, as they all have citronella oil in the sin surface. Just rub the skin outer while squeezing it firmly to release the oil.

[xrunner]

Yea I think it's based on citrus oils. I also saw some substitutes on the web made out of cooking oil or coconut oil, don't know if they would work as well. Just go buy some citrus degreaser and try it. 

[McBryce]

I'd recommend "Displex" for the panel. It's made to remove scratches on mobile phone screens, but it's great for restoring plexiglas surfaces. You can pick it up on ebay: http://www.ebay.com/itm/Displex-Scratch-Remover-Display-Polish-Cleaning-Cloth-For-Clear-Plastic-Screens-/310851033895?pt=LH_DefaultDomain_0&hash=item48602a5b27
I've restored quite a few things with this and it gives great results.

Bryce.