How to quickly check all the capacitors on the board. Simple ESR Probe

How to identify a faulty electrolytic capacitor?

Most common cause of failure in radio electronic equipment – failed capacitorsand it is far from always possible to identify them with a multimeter.
The fact is that in addition to capacity and operating voltage, capacitors have ESR (or equivalent series resistance) – one of the most important parameters capacitors, characterizing its active losses in the AC circuit.

Normally, ESR is very small – from tenths of an ohm to several ohms. But when a capacitor fails, it builds up, which can cause the rest of the circuit to malfunction or malfunction.

You can also purchase a ready-made tester to measure the ESR parameter, but I suggest that you assemble a simple and reliable ESR tester from the available components with your own hands. It is characterized by a reliable design and the ability to measure directly on the board, without desoldering components and risking damage to the device.

On one of the forums, I found a diagram and decided to repeat it.

During setup made some improvements – namely, he changed the winding data of the transformer, removed the 10 kΩ resistor from the secondary winding circuit and left only a 10 kΩ trimmer. Also, in the base circuit of the transistor, I replaced the 100kΩ resistor with a trimmer 10kΩ. I made these changes for the reason that the circuit did not work with the original values.

Transformer wound on a toroidal ring, primary winding 50 turns with a tap from the center, and secondary 50 turns, wound with 0.25 mm wire, turn to turn. I insulated the secondary with a piece of cloth and wound 6 turns of 0.5 mm wire over it for the measuring winding. All windings were wound in the same direction. I impregnated the finished transformer with quick-drying varnish.

Dial indicator I used the one that was at hand – from the recording level indicator from the Soviet tape recorder, you can take any other suitable one. The transistor is BC547B, but you can experiment and try any other low power reverse conduction.

Assembled the structure on a breadboard bought in a store for 40 rubles.
For the body, I took an old Soviet case from a ruler, cut out parts of the required size from it, smoothed the edges with a file, and glued them together with dichloroethane.

Probe sockets I found in my stock from an old oscilloscope. The probes themselves were made from medical needles – I cut off part of the cap, made a hole in it for the wire, put it on the wire. I bit off the plastic part of the needle so that it went into the cap. The needle itself was bitten off with wire cutters to half the length. I soldered the wire to the base, inserted the needle into the cap, and poured B7000 glue through the hole to fix the structure. The wire was taken thick enough stranded so that its resistance was minimal. I took the connectors from an old Chinese thermocouple.

On the left in the case I made holes for adjusting the tuning resistors. Put the power switch on the right. The device is powered by one AAA battery, I bought a battery holder in a radio store for 25 rubles.

Let’s test the resulting device in action.

Turn on the power. When turned on, the arrow of the device deviates to the extreme left position – this should be understood as follows – the resistance at the terminals of the device is maximum at the moment. When shorting the probes, it returns to the far right – the resistance is minimal.

Now let’s take two capacitors the same capacitance – 1 microfarad. One is modern and the other is Soviet.

We take modern, in blue isolation. We apply it with contacts to the probes and see how the arrow deviates to the extreme right position – the capacitor has a minimum resistance to alternating current, which means it is serviceable and suitable for use.

Now let’s take old soviet capacitor. We apply it with contacts to the probes and see that the arrow only slightly deviates from its original position – this capacitor has a high resistance to alternating current and most likely caused the breakdown of the device in which it once stood. Unfortunately, now its place is only in the trash.

This device you can check the capacitors not only individually, but also within the circuit, since the resistance of the circuit in the vast majority of cases is too high for the device to respond to it, and the AC voltage at the output of the ESR meter is too low for the transistors to start opening. In the event that the capacitor was not discharged, then the discharge will occur on the measuring winding, and since the transformer filters out the direct current, it will not enter the device circuit either.

Demonstrate how the device works on the example of two boards found in their bins – all the capacitors on them turned out to be serviceable. But the other day I had to repair a CRT TV, and this ESR meter helped to quickly identify the problem. Within half an hour, a couple of dried electrolytes were replaced, the TV is now back in service and pleases parents.