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One think I learned long ago and somewhat mentioned previously is A - caps for some reason are not on your mind in repairing a bad circuit, it seems I always refused to consider them, and B - they more often than not are what begins a circuit failure, often taking out other parts when they go. Virtually always the failure is a short circuit, even disc ceramic in lower voltage than their ratings situations. Something you would not think probable but I often see 50 volt disc caps shorted in 8 volt circuits. Clearly the most likely reason is some defect in manufacture. Tantalums likewise probably manufacturing defects most often. Or they short because they just do not like you for no apparent reason. This leaves electrolytics, I think I only recall one or two poly or mylars over the years failing without a reasonable cause. The problem with electrolytics is temperature or storage. Storage is the most often cause of the 10 volt blues I mentioned previously. They transfer the oxide from one side to the other over time when unpowered. Years later you turn it on, and usually fairly quickly they short from electrochemical action. A much more rare failure for liquid dielectrics in low voltage circuits is drying out and 'losing their capacitance'. This failure mode usually is in high voltage filters combined with heat, typically they lower in uF as they increase in leakage until you blow HV diodes. The single best way to maintain electrolytics in equipment is to take it out of the closet at least once a year and power it for an hour or two. This can greatly multiply their survival time to decades.
Do not randomly replace tantalums with electrolytics unless you have a clear understanding of their circuit function in a given location. In many circuits they are critical because types such as electrolytics while providing high capacitance per unit size have much greater leakage. In the wrong location this can bring proper circuit function to a halt. As I mentioned before usually in power filtering functions in low voltage circuits probably you will not have a problem. In other areas needing somewhat high capacitance yet very low leakage tantalums are critical. If you do not understand in depth the circuitry do not substitute one type for another. If you have a precision filter network in a high impedance opamp circuit putting in a cheap disc ceramic instead of a poly or mylar can cause you much grief. As a rule if you are not engineering savvy stick with what the engineer used and trust they knew more than you.
If your quest is to go in depth into circuit repair I also suggest you look for a transistor tester which indicates not only beta but also leakage down to 1 or 2 micro amps, and works on both low power and high power devices. I have owned an old Sencore TR-15A for over 40 years and I still use it daily. Not portable but I prefer it to a half dozen modern portable models some of which were in the 500 dollar price range. None of them are as good on a power transistor looking for 1 to 5 uA specs in an RF amplifier device such as a 2SC2879. I do use a cricket and a B&K for quick lead identification and good/bad/leaky (kinda, not so accurate as my Sencore), have 3 or 4 more really good ones I seldom take out of a box, and most often I like my Fluke 23 beep for fast searching of junction defects. Curve tracers are nice also but labor intensive if you do massive amounts of repair.
Do not randomly replace tantalums with electrolytics unless you have a clear understanding of their circuit function in a given location. In many circuits they are critical because types such as electrolytics while providing high capacitance per unit size have much greater leakage. In the wrong location this can bring proper circuit function to a halt. As I mentioned before usually in power filtering functions in low voltage circuits probably you will not have a problem. In other areas needing somewhat high capacitance yet very low leakage tantalums are critical. If you do not understand in depth the circuitry do not substitute one type for another. If you have a precision filter network in a high impedance opamp circuit putting in a cheap disc ceramic instead of a poly or mylar can cause you much grief. As a rule if you are not engineering savvy stick with what the engineer used and trust they knew more than you.
If your quest is to go in depth into circuit repair I also suggest you look for a transistor tester which indicates not only beta but also leakage down to 1 or 2 micro amps, and works on both low power and high power devices. I have owned an old Sencore TR-15A for over 40 years and I still use it daily. Not portable but I prefer it to a half dozen modern portable models some of which were in the 500 dollar price range. None of them are as good on a power transistor looking for 1 to 5 uA specs in an RF amplifier device such as a 2SC2879. I do use a cricket and a B&K for quick lead identification and good/bad/leaky (kinda, not so accurate as my Sencore), have 3 or 4 more really good ones I seldom take out of a box, and most often I like my Fluke 23 beep for fast searching of junction defects. Curve tracers are nice also but labor intensive if you do massive amounts of repair.
I don't have a tester so it would be easier/ cheaper to just replace it. 8 pin holes are in the board so at least that is easy. Problem is I can't find one. According to Mouser NTE7144 might be a possible replacement for a CA3140 but nothing on a CA3140s (unfortunately a 2 week delay time and $7 to ship anyways). There are some different varities of according to Digikey. Here is the link:
Anyone have any ideas? I'd rather order it as the same time as the caps to save on time and shipping. Thanks
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