How to Detect Damaged Resistors/Capacitors in a Circuit without Desoldering (Beginner Tips)

I am a beginner. I have a question how to check if the resistor / capacitor are whacked since they are soldered into the entire system. Do you need to desolder it to be sure? Even when the resistor is burnt, the meter can show us the resistance of the rest of the system seen from the side of the terminals of this burnt resistor. And even when it is not burnt, the value shown on the meter may be the value resulting from the parallel connection of the resistor and the resistance of the rest of the system. capacitors can always be determined visually ? If possible, how (e.g. how to distinguish an electrolyte leak from the glue used to assemble the kit?)

You reason correctly - the easiest way is to desolder a resistor or capacitor and check it with a meter - you can also desolder, for example, only one leg of the element, and then check the element with a meter.

As for the visible damage to the resistors - sometimes it can be difficult to determine whether they are damaged, because there are resistors that are broken, but visually they look good. Of course, I omit the fact that the resistor is all black, has burnt paint, and sometimes you can't even figure out what its value was...

As for electrolytic capacitors: as you can see that there is a bulging sheet at the top, or a cork from the bottom - the capacitor is already damaged - although not always. Sometimes it's just dried up, it looks OK visually, but the meter shows a value much much lower.

And as for the transistors. How to know that they are burnt. There seems to be a short circuit between the collector and the emitter then, right?

In principle, this short-circuit can be in different ways: BE, CE, BC or between all three

Read here: https://www.elektroda.pl/rtvforum/topic12376.html

As for transistors, it's best to check with a diode tester. Knowing where we have individual EBC pins and npn or pnp polarity, you can easily identify a burnt transistor. We treat the transistor as two diodes connected. In the direction of conduction, the meter shows a voltage drop at the junction, i.e. about 600-1000 mV, and in the reverse direction it shows a break!!! four measurements with a meter and everything is clear

The basic method of detecting damage to resistors and transistors is to measure voltages
constants - e.g. a transistor in a typical system has a voltage of 0.7V between the emitter and the base;
transistors do not always short-circuit when they are damaged - often a break on the emitter.

And as for checking the desoldered transistor - four measurements (EB and BC in both directions)
it may not be enough - how to short EC (e.g. wire E touches C).

As for the original damage - I had a case that the NPN transistor was damaged so
that it turned into a properly functioning PNP transistor; it was a BF194 CEMI.

And when it comes to distinguishing drain - source in FETs - there is probably no simple method,
maybe like this: when the gate is shorted to one of them, the one-way transistor works as
current limiter - reliably limited current depends on whether the drain or the source,
and even more surely the impedance of this limiting is higher, when we short-circuited the source;
relatively certain results should give: measurement of the slope of the characteristic - as we will replace
drain with the source, then we will get smaller; and breakdown voltage measurement (GS less).

Also, it can be difficult to tell the difference between emitter and collector - not all types
transistors have forward voltage difference EB and CB, you need to measure beta,
or the breakdown voltage of the junctions (the latter is easier than in FETs).

I have one more question about the capacitors. Will we get a value by testing the capacitor desoldered from the system with an ohmmeter because I sometimes get, for example, 40 Kohm. When this resistance is small, can it be assumed that the capacitor is damaged? How small?

It all depends on the meter, its range and measurement time. A good capacitor at the beginning of the measurement should have almost a short circuit, and after a period of time depending on the range of the meter and its current efficiency in this range, it should charge and show max (the smaller the range, the faster). dried - it will not show "almost a short circuit" or break at the operating voltage (and we do not have such in the meter). Aha - the smaller the capacity, the higher the range of the ohmmeter, with picofarads you can only check if it is not shorted.
As for the transistors, with a little practice, you can check their diode transitions at the base-collector and base-emitter junctions without desoldering, one way about 450 Ohm, the other max (taking into account the surrounding elements. EC should be high resistance in both directions. If EC there is no short-circuit, and BE and BC behave like diodes, it is highly probable that the transistor is operational (does not apply to MosFet, Fet and other field effect transistors)
Regards J

If it's not electrolytic, and if the ohmmeter shows that resistance constantly, it's a capacitor
it's damaged; when measuring a capacitor with a larger capacitance, the ohmmeter can
especially in the high range, show some resistance for a while - until the capacitor
when it is charging it has current flowing through it if you have a 10 megohm ohmmeter and a capacitor
with a capacitance of 10uF, the current should flow about 100 seconds.

With electrolytic capacitors a more complicated matter - if the voltage
with the ohmmeter is in the wrong direction, the best capacitor will let through
current (and you may have trouble distinguishing a low capacitance capacitor from a diode,
both pass current in one direction and not in the other); besides the right one
the capacitor also lets some current through - but it should be a few uA at most
(for small capacitance capacitors; there are some standards that define it more precisely,
but I don't have more precise data here), if the capacitor lets more through, then you can
suspect it's not the best, but it's a good test to plug it in
some time under DC voltage, then disconnect, wait a minute, and measure the voltage.
If it is more seriously damaged, there will be almost no voltage, it will be very good
held the voltage for hours - make a few measurements with different waiting times, and you know.

There is also such a phenomenon as drying up of electrolytic capacitors. You can see this in 10 - 12 year old TV sets that start to behave strangely: first they stop firing, then the colors change, strange stripes appear on the screen, etc. Just replace the old capacitors and ok.

Right. How do their parameters change then - decrease in capacitance, increase in resistance?

Hello!!!
When I read these arguments about the measurements of ordinary passive elements, my brain likes it, gentlemen! do a little digging in the old press
Radio Amateur and electronics and you will see how easy it is

We amateurs already have it... Lack of books and other professional sources.

I have a collection of electron magazines. since 1969, but unfortunately I did not earn enough
still a scanner. I advise buying a clock multimeter at the marketplace
for PLN 10 and the matter is settled, these digital ones indicate what they want, unless they are high-class professional from PLN 500 and above.
For example, I will show how I check electrolytic capacitors with a dial meter: discharges the end cap and ohmmeters, measures depending on the capacity, the pointer swings by a certain value and returns to O. If it does not return, the end cap is shorted. I have been checking this for years and this method has not failed me yet, what do I know if kndek is 5 m or 7 m and has a tolerance of 20%. exposure