DIY voltage stabilizer repair

Recommendation points

• About the internal structure and types of stabilizers
• Typical faults of relay devices
• Broken servo stabilizers
• Common problems of electronic devices
• General recommendations

Today we will consider a list of basic malfunctions of voltage stabilizers of various types with a description of the causes and methods of their repair. After all, not every breakdown of a voltage stabilizer requires service repair, especially after the expiration of the warranty period..

About the internal structure and types of stabilizers

Of all the varieties of voltage stabilizers, there are three most common topologies with rather specific conversion principles. Among them, it is impossible to single out the most reliable one, too much depends on the nature of the power supply and the type of load, as well as on the quality factor of the device. In our review, we will consider servo, relay and semiconductor converters, features of their operation and typical malfunctions..

In a servo-driven stabilizer, the main functional element is a linear transformer with many terminals of the midpoints of the secondary, and sometimes the primary winding – from 10 to 40, depending on the accuracy class. The ends of the leads are assembled into a collector comb, along which the collector carriage moves. Depending on the effective voltage on the power line, the stabilizer corrects the position of the carriage, thereby adjusting the number of involved turns and, accordingly, the transformation ratio. At the output of the circuit, a more subtle voltage adjustment can be carried out, for example, using integrated semiconductor stabilizers.

Relay transformers are designed in a similar way. The number of transformer terminals is smaller; instead of smooth regulation, the fine tuning is achieved by recombination of the windings included in the operation. Power relays with a complex configuration of a relay group are responsible for operational switching. As in the previous case, additional filters, stabilizers and protection devices can be at the output, however, the main work is performed by a transformer and relay assembly under analog control.

Electronic voltage stabilizers can be based on two conversion principles. The first is switching the transformer windings, but with the help of symmetrical thyristors, not relays. The second principle is the conversion of current into direct current, its accumulation in buffer capacitors (capacitors), and then the reverse conversion into “alternation” with a pure sine wave by means of a built-in generator. At first glance, the circuit seems quite complicated, but this provides an unprecedented high stabilization accuracy and high-quality line protection..

Of course, there are other stabilizer schemes, including hybrid ones, but due to their highly specialized use or archaic nature, we will not consider them. Each of the three most common families has so-called childhood diseases or congenital defects in technology. And therefore, the most important task before sending the device to the service center is to determine whether the breakdown is the cause of non-compliance with the maintenance standards or an ordinary malfunction for this type of stabilizer..

Typical faults of relay devices

Relay stabilizers are characterized by an optimal ratio of cost and reliability. The relay group is exposed to the main wear, and with frequent or constant operation under increased load, also the dielectric insulation of the transformer windings.

It is quite easy to diagnose a relay as the cause of a malfunction. The first step is to dismantle the components from the printed circuit board; they can be distinguished by a compact rectangular case, sometimes made of transparent plastic, with at least six pins. To determine the purpose of the terminals and the switching scheme, you can refer to the circuit diagram or technical specification for a specific type of relay according to the marking on the case. You can make a test switch on the relay, for which the operating voltage is applied to the coil contacts, as a rule, it is indicated on the product case. The absence of a click when connecting is a clear sign of a burnt coil or stuck contacts. If a click is heard, but when the group of main contacts is ringing, the circuit for their switching is not observed, the problem is most likely in the mechanism of kickback and pressing, or in charred contact pads.

A significant part of electronic relays has a collapsible case and can be serviced: restoration of the mechanism, cleaning the contact pads from carbon deposits with an eraser, sometimes even replacing a faulty coil. However, the best solution would still be to purchase new relays to replace those that have failed according to the article number or pinout.

The loss of the dielectric strength of the transformer due to overheating is accompanied by interturn short circuits and is externally observed as darkening or destruction of the winding insulation. The main symptom is a significant decrease in resistance below the passport standards. Since most budget stabilizers have one solid primary winding and a multi-pin secondary, rewinding is not particularly difficult. In each link, the number of turns is small, they can be neatly laid even without a spindle or other winding devices. The most important thing is to accurately observe the number of turns and the direction of laying, as well as to correctly determine the initial resistivity of the conductors, and not just purchase a winding wire by diameter.

Another type of transformer malfunction is the operation of a semiconductor thermal fuse, which is usually included in the rupture of one of the windings. To replace a semiconductor element, it is enough to clarify its series or basic parameters in order to select an analogue. Usually, the thermal fuse is connected in series with the first link of the secondary winding, so all the outer turns will have to be removed to access it. The problem is diagnosed simply: between the beginning of the winding and the first tap, the circuit does not ring, but all the other turns are in perfect order.

Broken servo stabilizers

The main reason for the failure of servo drives is obvious: wear of the collector assembly. It is this shortcoming that is included in the category of childhood diseases that cannot be eliminated in most models of budget technology..

There are two types of slip mechanisms. At low loads, conventional spring-loaded brushes do an excellent job of switching the windings. The device completely repeats the principle of operation of the collector motors of the power tool, except that the collector itself is deployed from a cylindrical position to a plane. The second type of current collectors has a brush assembly in the form of a roller, due to which friction during movement is reduced, which means that there is no intensive wear of the lamellas. At the same time, the wear rate of plate and roller brushes is approximately comparable.

The disadvantage of a slip ring stems from its geometry. The contact spot is very small – only the line of contact of the cylindrical roller to the plane. True, in the most technically advanced models, the lamellas have radius grooves, although this solution is not entirely justified: as the graphite roller wears out, the contact area inevitably decreases. Depending on the intensity of use, replacement of brushes is required at intervals of 3 to 7 years. The situation can be aggravated in the presence of a large amount of dust and carbon deposits – up to the closure of several windings or a complete loss of contact.

Although servo regulators are also susceptible to overload operation, their transformer will wear less. Unlike relay devices, in which voltage and current surges occur regularly during switching, the collector unit adjusts more smoothly, due to which the mechanical effect of the current is minimal. The varnish insulation of the windings still dries up and becomes brittle, but does not crumble.

Basically, the principle of operation of the servo stabilizer is extremely transparent. If, when turned on, there is an indication of the input voltage, but the device does not respond, the malfunction lies either in the drive itself or in the control and measuring circuit. In the latter case, a faulty circuit element can be easily detected purely visually or by dialing. If there is no voltage at the output, the transformer is faulty, if the proper stabilization accuracy is not ensured, the presence of an interturn short circuit in the secondary winding, collector contamination, wear of the current collector brushes or the lamellas themselves.

Common problems of electronic devices

Inverter stabilizers are considered the least maintainable at home. There are several reasons for this, but the primary one is the need for special knowledge in circuitry and, in particular, the principles of operation of switching power supplies. It will not be possible to do without an appropriate material base: soldering equipment with temperature control, as well as measuring instruments. The set of diagnostic tools goes far beyond the limits of a conventional multimeter, you will need a device with an extended set of functions for measuring capacitance, frequency and inductance, and it is also desirable to have a simple oscilloscope at your disposal.

The most common cause of malfunctions in inverter stabilizers is a malfunction of the clock generator. It is necessary, based on the rated power of the device and the parameters of the transformer, to determine the optimal operating frequency of the pulse converter, and then compare it with the real parameters. Frequency failure is usually caused by a malfunction in the reference oscillating circuit connected to the corresponding pins of the clock IC..

Complete device failure is possible for a number of reasons. If there is no built-in diagnostic system or it is impossible to determine the breakdown by its indications, most likely the cause of the malfunction was the failure of the field or IGBT keys, which is quite simple to determine by the appearance of the case. Another characteristic cause of malfunctions is the breakdown of the built-in power supply of the control circuits; this part of the circuit is most vulnerable to voltage fluctuations, especially impulse.

It will not be superfluous to make a continuity of all circuits, their conductivity must correspond to the circuit and electrical diagrams of the device. The most vulnerable elements include input and output rectifiers, transformer snubber circuits (for suppressing surges), as well as a power factor corrector, if any..

General recommendations

Electronic components are found not only in inverter stabilizers, they can be used in control and measuring circuits or indicating and self-diagnosis devices. This mainly concerns passive elements and microcircuits with a low degree of integration: operational amplifiers, logic elements, combined transistors, current and voltage stabilizers. Failure of these elements can most often be determined purely by external signs: burnt out transistors and diodes have a cracked case, resistors – traces of burned varnish, capacitors simply inflate. Therefore, a close external examination of the printed circuit board is the first stage in determining the malfunction..

If it is not possible to visually determine the cause of the breakdown, a sequence of control measurements should be made. First, the conductivity and quality of the dielectric insulation of the circuit is checked in the off state. After that, when power is applied, voltages are measured at key points: at the connection terminals, after the fuse, on filters and stabilizers, transformer windings, and the main nodes of the control circuit. If the described diagnostic methods do not give a result, it is better to contact the service center, because even a simple breakdown can be very specific, despite the fact that amateur knowledge in electrical engineering and home conditions is not enough to eliminate it.