[sebhc] DeOxit and other things to help revive old systems

[Jack Rubin]

Take a look at http://www.caig.com - DeOxit is only one of their
products for cleaning and lubricating contacts. The stuff is magic! 

I prefer Nye Lubricant's Nyogel to Caig's contact grease and Dwight
makes a good case for a silicone lubricant, but deoxidizing components
and sockets, and cleaning and lubing connectors can solve a bunch of
mysterious intermittent problems.

Jack

> -----Original Message-----
> From: sebhc at sebhc.org [mailto:sebhc at sebhc.org] On Behalf Of 
> Carroll Waddell
> Sent: Friday, May 07, 2004 4:39 PM
> To: sebhc at sebhc.org
> Subject: Re: [sebhc] Re: H8 data record format
> 
> 
> I heard someone talk about Deoxit. What is this, what does it do, and 
> where do you get it?
> Carroll
> 
> Lee Hart wrote:
> 
> >>Anyone have experience reviving old gear? Mine's been boxed 
> for over a 
> >>decade. Any precautions I should take before I try to power 
> up another 
> >>unit?
> >>    
> >>
> >
> >Patrick Rigney had some good ideas. Here is my contribution.
> >
> >The main offenders are old batteries (but the H8 doesn't have any 
> >unless you have added a real time clock board), electrolytic 
> >capacitors, and tantalum capacitors, and high-current 
> connectors. These 
> >parts all age (get much worse over time), and can fail in dramatic, 
> >dangerous ways.
> >
> >Batteries
> >
> >Any batteries over 5-10 years old should automatically be 
> replaced. On 
> >some equipment, they will be little cylindrical or coin 
> cells hiding on 
> >a clock board somewhere. They will leak, and short or 
> corrode traces to 
> >cause all sorts of bizarre circuit behavior.
> >
> >Electrolytic capacitors
> >
> >Electrolytics have two main problems; they dry out, and they 
> lose their 
> >dielectric forming.
> >
> >Dryout means they have lost water, which increases internal 
> resistance 
> >and reduces capacitance. Dryout is proportional to *operating* time; 
> >the amount of time the equipment has been turned on and 
> working. High 
> >voltage and high temperature drastically increase the rate! For 
> >instance, a 25vdc 85 deg.C rated electrolytic will last 10 years at 
> >16vdc 45 deg.C -- but only 2 months at its full ratings; 25vdc 85 
> >deg.C! (Now you can see why you shouldn't use electrolytics at their 
> >full rated voltage or temperature).
> >
> >An electrolytic that has dried out isn't really working as a 
> capacitor. 
> >It allows excessive noise and ripple in the circuit that will cause 
> >other parts to malfunction or fail. It will also get hot. If the 
> >heating gets bad enough, it will leak or explode! So, if the 
> equipment 
> >has spent a lot of time turned on and tends to run hot, replace the 
> >electrolytics.
> >
> >An aluminum electrolytic consists of two aluminum plates in 
> a caustic 
> >water-based electrolyte. During manufacture, they apply a DC voltage 
> >until a small current flows. Like a battery, this current 
> "reduces" one 
> >plate (makes is pure aluminum) and "oxidizes" the other 
> (coats it with 
> >aluminum oxide). This is called "forming" the capacitor. 
> Since aluminum 
> >oxide is an insulator, the current stops when the plate is 
> completely 
> >coated, and you have a capacitor.
> >
> >If the capacitor is not powered for a long time (years), this oxide 
> >coating gradually goes away. When you later apply voltage, 
> it isn't a 
> >capacitor; it's a *resistor*! It will get hot, and if hot enough to 
> >boil the water inside, it will vent or even explode!
> >
> >So, if the equipment has not been used for several years, 
> power it up 
> >slowly, with a light bulb or variac or light dimmer in the primary. 
> >Start at about half voltage, and crank it up slowly over a 24-hour 
> >period. This allows time to re-form the oxide layer so it will work 
> >again.
> >
> >Tantalum capacitors
> >
> >Tantalum capacitors are similar to electrolytics, but with tantalum 
> >oxide forming the dielectric. Their problem is that their breakdown 
> >voltage gradually falls as they age, usually from high 
> temperatures or 
> >tiny cracks or damage to their case during assembly. When 
> the breakdown 
> >voltage gets down to the applied voltage, they suddenly fail 
> shorted. 
> >If they happen to be connected as filter capacitors right across a 
> >high-current power supply, they explode with a violent bang!
> >
> >There's no way to fix them, and they are usually reliable 
> enough that 
> >it's not worth blindly replacing them. But be prepared for a sudden 
> >"bang!" shortly after you put an old piece of equipment back in 
> >operation. The good news is that tantalums are tiny, and 
> rarely do any 
> >real damage unless your eyeball is in the path (running with 
> the boards 
> >exposed. Then, you have to find the place where the tantalum 
> capacitor 
> >is now missing from a board, and replace it (easy with Heathkits, 
> >thanks to their magnificent documentation).
> >
> >Connectors
> >
> >Equipment stored in basements, garages, attics, and other 
> "dirty" areas 
> >will suffer from corrosion damage to connectors. The effect is much 
> >worse if you live in a city or other area with high air pollution 
> >levels.
> >
> >Connector problems mainly cause intermittents and flaky 
> operation. But 
> >a high-current connector can melt down or even burn up. As a 
> >preventative, I generally unplug and re-plug all the 
> connectors in an 
> >old piece of equipment; the friction helps clean them up.
> >
> >It's generally *not* a good idea to do this with cheap IC sockets, 
> >though. Many of them that Heath used are really garbage-grade, and 
> >you'll create more intermittents than you fix if you 
> plug/unplug ICs in 
> >these sockets more than a few times.
> >
> >There are contact lubricants and greases that help prevent these 
> >problems, as have been mentioned previously. But they don't do much 
> >good once the connection is already bad. You may have to just 
> >mechanically clean or replace any connectors that get hot or are 
> >discolored or corroded.
> >  
> >
> 

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