Repair/Restoration Tips & Tricks
Some helpful (hopefully) notes on tips, tricks, and techniques that have worked well for us when doing repairs and restorations on equipment. .
Flat spots on hard rubber rollers
What has worked well for me in most instances has been the following:
Remove the rollers from the water and dry. In most cases the rollers will return to their original shape. In some extreme cases you may need to repeat the process. You may notice a slight flatness remaining, but this will work itself out with use.
In working on equipment such as that shown on these pages, you can expose yourself to voltages that can be hazardous or lethal! If you are not properly trained in working on or around electrical components and high voltages, you should not attempt any of the repairs or tests outlined in this section without the assistance of properly trained personel.
The information presented here should not, and may not be used as a substitute for proper training in the procedures and techniques needed to safely service electrical equipment. No attempt is made here to provide training in these procedures or techniques. All information presented here is only to be considered second-hand advice which may be used only as a suppliment to formal training and knowledge.
If you are not comfortable with the level of your personal knowledge and training in this area, or if you do not have access to the proper tools and supplies needed to safely perform work on equipment of this type, you should not attempt any repair of electrical equipment such as shown on these pages!
Contributors to these pages assume no responsibility for the use or misuse of the information presented here. All information presented here must be used with due consideration to electrical industry standards for training and safety procedures established for working on equipment of this type.
It should be noted that some items that may be found in older electrical equipment (transformers, capacitors, etc...) may fall under the catagory of 'hazardous waste' and must be handled and disposed of properly. Consult your local governing bodies for further information.
Use of proper safety equipment and proper safety procedures should be observed at all times! All items, parts, or components removed or replaced should be disposed of according to established standards for electrical equipment and chemical items. when in doubt of the proper method for disposing of any item, consult your local officials.
(I can't believe that I actually have to say all this! - - - Now, back to our normally unscheduled program...)
Power Supplies and aging
The good side of this is that linear power supplies are pretty simple to troubleshoot. Check the fuses, the output from the transformer, a few diodes, and the final output. Very few mysteries here.
However... there is a down side! The large electrolytic capacitors used in these supplies to smooth the D.C. output of the power supply (reduce ripple, absorb spikes, etc...) do not (to a large extent) age very well, and when they start to go bad all sort of odd things can begin to happen. (especially under load)
There are some straight forward methods that can be used to identify suspicious electrolytic capacitors, not only in the power supplies, but also in the many other places where they are used. Following is a list of a few things you can use to help root out defective electrolytic capacitors...
Visual inspection: take a good look at the capacitor. (I'm not kidding) Nearly all electrolytic capacitors are contained in a light metal shell or 'can'. The sides should be smooth, ends flat, and the plastic insulator wraps tight and secure over the ends. If the shell appears to be deformed (bent, cracked, or bulging) or the end caps are cracked or visibly out of place (pushed out at an angle rather than flat), or the insulator wrap is cracked or discolored, replace that sucker!
Also; larger electrolytic capacitors will often have 'vents' in the end cap to relieve pressure within the capacitor. If you see a gel or paste like substance oozing from the vent, replace that one as well! Something nasty has happened to that capacitor.
Operating temperature: Electrolytic capacitors should not get noticibly warmer than surrounding components unless overloaded or defective. If you find one that is noticibly warmer (hotter) that surrounding components, find out why!
Multimeter test: Take your trusty multimeter, set for resistance/diode conductance testing (conductance testing will provide higher current that most normal resistance tests), and connect to the capacitor in question, observing proper polarity. (and insuring that the capacitor has been discharged first!)
You should initially see a low resistance indicated, which will start to increase as the capacitor charges. If you see zero resistance and this does not quickly start to increase, the capacitor or something in the surrounding circuit is most likely bad. (shorted)
Use of a capacitor tester: Nice if you have one!
After all this, if you are still not sure... consider replacing the capacitor in question, particularily if it is over 6-8 years old. (if in doubt, check the date code markings on the part) Capacitors are inexpensive enough in most cases and is may save you many headaches later.
Thanks toThe Computer Garage