Do-it-yourself uninterruptible computer repair

In detail: do-it-yourself uninterruptible power supply for a computer from a real master for the site my.housecope.com.

Today we will talk about helping the first friend of computers - an uninterruptible power supply.

An uninterruptible power supply (UPS) is designed to protect and emergency power computers.

This is such a "savior". But sometimes the “rescuer” himself needs help. After all, a UPS, like any equipment, can break down!

In this article, we will consider only the simplest malfunctions that occur during operation.

They don't take much effort to get rid of. Let's leave the difficult cases to the professionals.

High-current parts are, first of all, inverter transistors. Most often, powerful field-effect transistors (FETs) are used in inverters, the open channel resistance of which is in hundredths and thousandths of an ohm.

This is a very small resistance, but currents of tens of amperes can flow through transistors. Therefore, they are installed on radiators (or on one common radiator).

If the transistor (or other part) gets very hot, then the marking, most often made with white paint, darkens. At the same time, the solder at the place of soldering also darkens. If the part is closely adjacent to the board, then the board itself will darken at the point of contact.

Sometimes characteristic annular cracks appear around the leads of high-current parts. Contact in such places between the output and the printed circuit board has increased resistance, which leads to even more heating.

All bad and suspicious soldering should be carefully soldered!

After an external inspection, it is necessary to check the inverter transistors with a tester. To do this, you need to read the article "What is a field effect transistor and how to check it?"

If the transistors are found to be defective, they must be replaced with the same or similar ones.

Next, check the fuse. The UPS usually has at least two fuses. The first one (which is accessible from the outside) is via a 220 V network. It has a rating of several amperes, which depends on the power of the UPS. The more powerful the UPS, the higher the rating.

Most often, it is located in a special socket, in the immediate vicinity of the power cord connector. You can remove it with a screwdriver with a narrow blade. Often the fuse holder has a socket for another fuse (spare) and the fuse itself. So a blown fuse can be quickly replaced.

The second fuse is installed on the board along the +12 V circuit, in the positive battery bus. It is designed for much higher current (30 - 40 A and more). The fact is that when the voltage disappears, the inverter starts to work, and the battery must give a large current.

Video (click to play).

For example, with an active power of 250 W of the load connected to the UPS, the battery must give a current of 250:12 = 21 A. And this is without taking into account losses in the inverter!

Usually this fuse has a rating of 30 or 40 A. In more powerful UPSs, there may be two of them, while they are installed in parallel. Such fuses are used in cars, so they can be found in the car market if necessary.

Note that fuses for the most part do not fail "just like that." Therefore, before changing them, you need to make sure that other parts are in good condition - rectifier diodes, the same inverter transistors.

Sometimes blown fuses can be caused by an inter-turn short circuit in the transformer, but fortunately this rarely happens.

Switching the UPS to battery mode is most often carried out by means of electromechanical relays.DC relays are used with a 12 or 24 V coil and high-power contacts. Sometimes the contact group of one of the relays fails.

This can be manifested by the fact that the uninterruptible power supply does not turn on at all or does not switch to batteries when the mains voltage fails. If you suspect such a malfunction, you should unsolder the relay and check the resistance of the closing contact with a tester.

As a rule, such a relay has one changeover contact.

When voltage is applied to the coil, contacts 1 - 3 open, and contacts 2 - 3 close.

The resistance of an open contact should be infinitely large, and a closed contact should have a resistance of the order of tenths of an ohm.

If it is equal to several ohms (or tens of ohms), such a relay must be replaced.

In conclusion, we note that when power is applied to the coil, a clear click should be heard. If it is not heard or some “rustles” are heard, there is a mechanical malfunction, and the relay definitely needs to be changed.

Let's also say that an electromagnetic relay is most often a reliable and durable thing.

Ordinary (not reed) relays have a resource of at least 100,000 operations, which is more than enough for the entire duration of the UPS.

In the second part, we will continue to get acquainted with the simplest malfunctions of uninterruptible power supplies.

Off-line UPSs from APC include Back-UPS models. UPSs of this class are characterized by low cost and are designed to protect personal computers, workstations, network equipment, retail and cash terminals. The power of the manufactured Back-UPS models is from 250 to 1250 VA. The main technical data of the most common UPS models are presented in Table 1.

Table 1. Back-UPS main technical data

The index "I" (International) in the names of the UPS models means that the models are designed for an input voltage of 230 V. The devices are equipped with sealed lead-acid batteries with a service life of 3 ... 5 years according to the Euro Bat standard. All models are equipped with filter-limiters that suppress surges and high-frequency mains voltage interference. The devices give the appropriate sound signals when the input voltage is lost, the batteries are discharged and overloaded. The mains voltage threshold below which the UPS switches to battery operation is set by switches on the back of the unit. Models BK400I and BK600I have an interface port that connects to a computer or server for automatic self-closing of the system, a test switch and a horn switch.

The schematic diagram of the Back-UPS 250I, 400I and 600I UPS is almost completely shown in fig. 2-4. The multi-stage mains noise suppression filter consists of varistors MOV2, MOV5, chokes L1 and L2, capacitors C38 and C40 (Fig. 2). Transformer T1 (Fig. 3) is an input voltage sensor.

Its output voltage is used to charge batteries (D4…D8, IC1, R9…R11, C3 and VR1 are used in this circuit) and to analyze mains voltage.

If it disappears, then the circuit on the elements IC2 ... IC4 and IC7 connects a powerful inverter running from the battery. The ACFAIL command for turning on the inverter is generated by IC3 and IC4. The circuit, consisting of a comparator IC4 (pins 6, 7, 1) and an electronic key IC6 (pins 10, 11, 12), allows the inverter to operate with a log signal. "1" coming to pins 1 and 13 of IC2.

The divider, consisting of resistors R55, R122, R1 23 and switch SW1 (terminals 2, 7 and 3, 6) located on the rear side of the UPS, determines the mains voltage, below which the UPS switches to battery power. The factory setting for this voltage is 196 V. In areas where there are frequent fluctuations in mains voltage, resulting in frequent switching of the UPS to battery power, the threshold voltage should be set to a lower level. Fine tuning of the threshold voltage is performed by resistor VR2.

All Back-UPS models except the BK250I have a bi-directional communication port for PC communication. Power Chute Plus software allows the computer to perform both UPS monitoring and safe automatic shutdown of the operating system (Novell, Netware, Windows NT, IBM OS/2, Lan Server, Scounix and UnixWare, Windows 95/98) while preserving user files. On fig. 4 this port is labeled J14. Purpose of its conclusions:

1 - UPS SHUTDOWN. The UPS shuts down if a log appears on this output. "1" for 0.5 s.

2 - AC FAIL. When switching to battery power, the UPS generates a log on this pin. "one".

3 - SS AC FAIL. When switching to battery power, the UPS generates a log on this output. "0". Open collector output.

4, 9 - DB-9 GROUND. Common wire for signal input/output. The output has a resistance of 20 ohms relative to the common wire of the UPS.

5 - SS LOW BATTERY. In the event of a battery discharge, the UPS generates a log on this output. "0". Open collector output.

6 - OS AC FAIL When switching to battery power, the UPS generates a log on this output. "one". Open collector output.

Open collector outputs can be connected to TTL circuits. Their load capacity is up to 50 mA, 40 V. If a relay needs to be connected to them, then the winding should be shunted with a diode.

A normal null modem cable is not suitable for this port, a suitable 9-pin RS-232 interface cable is supplied with the software.

To set the output voltage frequency, connect an oscilloscope or a frequency meter to the UPS output. Turn on the UPS in battery mode. By measuring the frequency at the output of the UPS, adjust the resistor VR4 to 50 ± 0.6 Hz.

Turn on the UPS in battery mode with no load. Connect a voltmeter to the output of the UPS to measure the effective voltage value. By adjusting the resistor VR3, set the voltage at the output of the UPS to 208 ± 2 V.

Set switches 2 and 3 located on the back of the UPS to the OFF position. Connect the UPS to a LATR type transformer with smooth adjustment of the output voltage. Set the voltage to 196 V at the LATR output. Turn the VR2 resistor counterclockwise until it stops, then slowly turn the VR2 resistor clockwise until the UPS switches to battery power.

Set the UPS input voltage to 230 V. Disconnect the red wire going to the positive battery terminal. Using a digital voltmeter, by adjusting the resistor VR1, set the voltage on this wire to 13.76 ± 0.2 V relative to the common point of the circuit, then restore the connection to the battery.

Typical malfunctions and methods for their elimination are given in Table. 2, and in table. 3 - analogues of the most frequently failing components.

Table 2. Typical Back-UPS 250I, 400I, and 600I UPS Problems

The function that an uninterruptible power supply performs (abbreviated as UPS, or UPS - from the English Uninterruptible Power Supply) is most fully reflected in its very name. As an intermediate link between the power grid and the consumer, the UPS must maintain the power supply to the consumer for a certain time.

Uninterruptible power supplies indispensable in cases where the consequences of power outages can have extremely unpleasant consequences: for backup power supply of computers, video surveillance systems, circulation pumps of heating systems.

More about UPS

The principle of operation of any uninterruptible power supply is simple: as long as the mains voltage is within the specified limits, it is supplied to the UPS output, while at the same time the charge of the built-in battery is maintained from an external power supply by the charge circuit. In the event of a power outage or a severe deviation from the nominal value, the UPS output is connected to the inverter built into it, which converts the DC current from the battery into AC power to the load. Naturally, UPS runtime is limited by battery capacity, inverter efficiency, and load power.

There are three constructive types of uninterruptible power supplies:

We offer you to get acquainted with the UPS device using the example of the APC Back-UPS RS800 model

Since uninterruptible power supplies are primarily used for backup power to computers, they often have USB outputs for connecting to a PC, which allows you to automatically put the computer into a low power mode when switching to backup power. To do this, just connect the UPS to a free port on the computer and install the drivers from the included disk. Old models of uninterruptible power supplies can use the COM port for this, which has practically disappeared on the PC.It must be remembered that the load power in watts connected to an uninterruptible power supply must be at least one and a half times less than its rated power in Volt-Amps multiplied by 0.7 (the power factor that determines the losses in the source itself) to avoid overloading the inverter. For example, a 1 kVA inverter will be able to power a load of no more than 470 watts without overload, at the peak - up to 700 watts.An example of a possible connection scheme: Image - Do-it-yourself uninterruptible computer repair

Since the batteries built into the UPS are automatically maintained in a charged state, no need for additional charging. If the battery has been completely discharged, a number of models of uninterruptible power supplies may indicate a battery malfunction at the time of switching on, however, as they gain charge, the indication will stop.

As a rule, when you first turn on the UPS, it needs 5-6 hours to fully charge the battery. A number of operating nuances depend on the type of battery used:

The cheapest batteries made using AGM technology (misleadingly or intentionally may be called gel by sellers) are not recommended to be left discharged for a long time, as this leads to their degradation and loss of capacity. If the UPS is not used for a long time, it is worth turning it on regularly to keep the battery charged.
Real gel batteries are more expensive, but without consequences they endure a long deep discharge. At the same time, they are more sensitive to overcharging, which can occur when a battery with a capacity smaller than calculated is installed in the UPS.

If there is a need to charge the battery from an external charging source, it is extremely important to limit the charging current to a value of no more than 10% of the nominal capacity (for example, a battery with a capacity of 4 Ah can be charged with a current of no more than 0.4 A).

The main failure of the uninterruptible power supply that you have to deal with is due to the fact that UPS does not go offline. It can be caused by the following reasons:

Subject to the same rules for operating the uninterruptible power supply, all its maintenance will be reduced to the timely replacement of batteries.

A friend at the company threw away a non-working APC 500 uninterruptible power supply. But before using it for spare parts, I decided to try to revive it. And as it turned out, not in vain. First of all, we measure the voltage on the rechargeable gel battery. For the operation of an uninterruptible power supply, it must be within 10-14V. The voltage is normal, so there is no problem with the battery.

Now let's examine the board itself and measure the power at key points in the circuit. I didn’t find a native APC500 uninterruptible circuit diagram, but here’s something similar. For better clarity, download the full diagram here. We check powerful olefin transistors - the norm. Power for the electronic control part of the uninterruptible power supply comes from a small 15V mains transformer. We measure this voltage before the diode bridge, after, and after the 9V stabilizer.

And here is the first swallow. The voltage of 16V after the filter enters the microcircuit - the stabilizer, and the output is only a couple of volts. We replace it with a model similar in voltage and restore the power supply of the control unit circuit.

The bespereboynik began to crackle and buzz, but 220V output is still not observed. We continue to carefully examine the printed circuit board.

Another problem - one of the thin tracks burned out and had to be replaced with a thin wire. Now the APC500 uninterruptible power supply device has worked without problems.

Testing in real conditions, I came to the conclusion that the built-in squeaker signaling the absence of a network yells like a bad one, and it would not hurt to calm it down a bit. You can’t turn it off completely - since you won’t hear the state of the battery in emergency mode (determined by the frequency of the signals), but you can and should make it quieter.

This is achieved by including a 500-800 ohm resistor in series with the sound emitter. And finally, a few tips for owners of uninterruptible power supplies. If it sometimes disconnects the load, the problem may be in the computer's power supply with “dried” capacitors. Connect the UPS to the input of a known good computer and see if the trips stop.

Uninterruptible sometimes incorrectly determines the capacity of lead batteries, showing the status OK, but as soon as he switches to them, they suddenly sit down and the load “knocks out”. Make sure the terminals are tight and not loose. Do not disconnect it from the network for a long time, making it impossible to keep the batteries on constant recharging. Avoid deep discharges of batteries, leaving at least 10% capacity, after which the uninterruptible power supply should be turned off until the supply voltage is restored. At least once every three months, arrange a “training” by discharging the battery to 10% and again charging the battery to full capacity.

Everyone knows that power surges are dangerous for household and computer equipment, as well as electronic components of power tools and industrial equipment. Unfortunately, power surges are not uncommon in the power grids of our cities, and even more so in villages. To protect equipment from these phenomena, the UPS device was invented, which is an abbreviation of its name: an uninterruptible power supply. UPS is his English. abbreviation. Thanks to modern technologies, the UPS effectively smooths out voltage fluctuations and radio frequency interference, and in the event of a complete power outage, it switches to powering consumers from a backup battery.

Today there are three main types of UPS:

off-line - This is the cheapest version of the device, which does an excellent job of protecting home appliances and computer equipment. When the voltage drops below a critical level, the device switches to the battery within a few milliseconds and feeds the devices of rated power connected to it through the inverter. As the voltage returns to normal, the device switches to mains power, simultaneously recharging the battery.

The disadvantage of this type of “uninterruptible” is the lack of a built-in stabilizer, therefore, with an unstable voltage in the network, frequent switching to the battery and back occurs, which quickly disables the battery.

line-interactive - this is an UPS with a built-in stabilizer that smooths out voltage drops without resorting to the “services” of the battery. The presence of a stabilizer and smoothing filters leads to a significant increase in the range in which the TBP can operate without a battery. This type of UPS is ideal for networks with frequent voltage fluctuations. When choosing an IPB of the Line-interactive class, one should give preference to well-known brands that have proven themselves in the domestic market, since the repair of an IPB of this type can reach 70-100% of its cost.

As a disadvantage, one can note the cost, which is somewhat higher than that of Off-line devices.

Online - These are the most expensive UPSs, with complex voltage inversion. This type of protection device is mainly used for the most sensitive industrial equipment.

The use of this type of UPS for home use is not expedient and economically unprofitable.

Despite the fact that the "uninterruptible" is intended to protect the equipment, he himself is electronic equipment, which can also fail and require repair, regardless of its type and performance. As a rule, the repair of an uninterruptible power supply is carried out at a service center or in a specialized workshop, but some types of breakdowns can be fixed at home without resorting to the services of expensive specialists. It is about such malfunctions that can be eliminated, as they say "on the knees" and will be discussed in this part of the publication.

The uninterruptible power supply beeps. There can be three reasons for this phenomenon: “everything is fine”, when switching the device to a battery; “everything is bad” if the uninterruptible power supply did not pass the self-test; and "overload". On any UPS for diagnostics, an LED or LCD indicator is provided.
The UPS does not turn on. In fact, there are a lot of reasons for this phenomenon: the network cable is damaged, poor contact in the socket, the fuse is blown, the battery is completely discharged. Most often, after a long storage of the UPS, it is the battery that has completely lost its charge.
The device does not support the load. There are only two types of possible malfunction: the battery has failed or the electronics have failed. In the first case, you can try to charge the battery. In the second - definitely a service center.
The uninterruptible power supply turns off after a short period of operation. The reason for the shutdown may be a high load that exceeds the maximum power of the "uninterruptible" itself. The reason for the shutdown may be other UPS malfunctions, but their diagnosis and elimination should be carried out exclusively by the service center specialists.

Who is to blame for the main problems of the UPS has already been suggested, now it remains to decide what to do. It turned out almost like Shakespeare!

Our tips for self-repairing an uninterruptible power supply cover the most basic problems. If you are not sure of your knowledge and you have no experience of "communication" with equipment operating from dangerous voltage, it is best to contact specialists. You can find a full list of repair and modernization services here. If you have any unresolved problems with the operation of your PC, then feel free to contact the specialists of our company, we are always ready to take on any difficult job. We work both in the city of Chelyabinsk and in the region.

Uninterruptible voltage sources use a closed helium or acid battery. The built-in battery is usually designed for a capacity of 7 to 8 Amperes / hour, voltage - 12 volts. The battery is completely sealed, which allows you to use the device in any condition. In addition to the battery, inside you can see a huge transformer, in this case 400-500 watts. The transformer operates in two modes -

1) as a step-up transformer for a voltage converter.

2) as a step-down mains transformer for charging the built-in battery.

During normal operation, the load is powered by filtered mains voltage. Filters are used to suppress electromagnetic and interference in the input circuits. If the input voltage becomes lower or higher than the set value or disappears altogether, the inverter turns on, which is normally in the off state. By converting the DC voltage of the batteries into AC, the inverter powers the load from the batteries. Off-line BACK UPSs do not work economically in power grids with frequent and significant voltage deviations from the nominal value, since frequent switching to battery operation reduces the battery life. The power of Back-UPS manufactured by manufacturers is in the range of 250-1200 VA. The BACK UPS uninterruptible voltage supply circuit is quite complicated.In the archive you can download a large collection of circuit diagrams, and below are a few smaller copies - click to enlarge.

Here you can find a special controller that is responsible for the correct operation of the device. The controller activates the relay when there is no mains voltage and if the uninterruptible power supply is on, it will work as a voltage converter. If the mains voltage reappears, the controller turns off the converter and the device turns into a charger. The capacity of the built-in battery can last up to 10 - 30 minutes, if, of course, the device powers the computer. You can read more about the operation and purpose of uninterruptible units in this book.

BACK UPS can be used as a backup power source, it is generally recommended that every home have an uninterruptible power supply. If an uninterruptible power supply is intended for domestic needs, then it is advisable to unsolder the signaling device from the board, it reminds that the device works as a converter, it makes a squeaking reminder every 5 seconds, and this is annoying. The output of the converter is pure 210-240 volts 50 hertz, but as for the shape of the pulses, there is clearly not a pure sine. BACK UPS can power any household appliances, including active ones, of course, if the power of the device allows it.

I have a Value 600E uninterruptible power supply for my computer, I bought it for a long time, it served correctly, though I changed the battery several times, but this is normal. And then such a moment came, in the morning, as usual, I wanted to turn it on to work at the computer, but breaker did not turn on, in response, there is silence, not even a squeak, the relays do not click.

I had to unpack and figure out what happened.

value-600e places for self-tapping screws are indicated

I checked the voltage, then the battery is fine. I completely unscrewed the board to make an external inspection, but everything was fine. I began to ring the chain and as a result found broken capacitor 0.01 uF 250V in C4 (103k) and in cliff resistor 1.5 kOhm 2W on the R5 circuit

made a screen from the circuit (below is a link to the complete circuit diagram of the Value 600E) indicated the culprits with red arrows:

I replaced the burned-out elements, assembled it and it worked (repaired), I hope my experience will be useful.

Note: the capacitor is marked F .01J / PD 250V

Broke down, no power is supplied to the output (and I would like to put a more powerful battery now 7AH) Maybe someone knows a sensible page on the network?

To repair an uninterruptible UPS (UPS), you will need a multimeter and an accurate determination of the element of the device that has broken. Here are some types of breakdown and, accordingly, repair tips:

• it is possible that the fuses have blown and need to be replaced;

• it is necessary to check the network cable, which may have a break;

• when there is no voltage at the output, broken field-effect transistors may be the cause - they should be replaced;

• perhaps the charging circuit has “flew” and needs to be replaced.

However, I must warn that the cost of repairing a UPS in a service shop after the user has tried to repair it himself is usually up to 50% of its price.

Attached is a diagram of the device of one of the UPS models

I did some repairs and decided to unsubscribe on this topic. So I got a Powercom Black Knight BNT-600 uninterruptible power supply with a difficult fate full of falls (literally) and disappointments. Naturally he got into my hands for repairs. Since I have not yet had to repair uninterruptible power supplies, I took up the repair with the reservation “to try”, it will not get any worse.

This bespereboynik, let's say, is not the best, in general, one of the simplest.

Let's start with its characteristics:

A type – interactive
output power – 600 VA / 360 W (pay attention to the power in watts (W), not in volt-amperes (VA))
Operating time at full load - 5 minutes (although the box says 10-25 minutes for "a certain computer with a 17" CRT monitor)
Output waveform – signal in the form of a multi-stage approximation of a sinusoid 220 V ± 5% of the nominal value
Switchover time to battery - 4 ms
Max. absorbed pulse energy – 320 J

Table of electrical parameters of the UPS taken from the manual:

As you can see, there are no bells and whistles: 360 watts, only two devices are powered, there are no surveillance options, except for one LED on the front panel and a tweeter. Models a little older have additional features, but this is all lyrics. Now let's move on to the actual history of this UPS.

This UPS was purchased back in 2005, but did not have time to work - it was slammed to the ground, which caused the besperebonik to have a huge crack on the back wall, through which all the power connectors fell out. Eyewitnesses claimed that before the fall, he still managed to work a little - the computer worked through him all day. After the fall, he completely refused to work. And in this state, he stood in the closet for 4 (!) With a tail of a year. Many will say that it makes no sense to repair it, the battery has long since leaked and burst. But no, it is whole, as the autopsy and testing showed, it is only discharged to zero.

Disassembling the UPS turned out to be simple: four screws securing the top cover were unscrewed with a regular long Phillips screwdriver. We remove the cover and see: the battery itself, the transformer and the control and signaling board. Here is a diagram of the internal (cable) connection of the battery to the board and to the transformer.

Electrical circuit diagram Powercom BNT-600

Everything is extremely simple and there should be no questions about the connection. When you turn on the uninterruptible power supply to the network either under load or without load, the latter does not show any signs of life. First of all, we check those parts of the UPS that could fail from impact - this is a battery and a transformer.

The transformer for breaking the windings is checked as follows - the wires going to the connector are ringing: black and green, as well as black, red and blue (located side by side), should ring among themselves. Then thick wires black, red, blue are called, which are also interconnected. Everything seems to be in order with the transformer.

ATTENTION! Be careful! Further work may result in electric shock. The author is not responsible for the consequences of your actions.

Battery. An external examination showed that it was intact - it did not burst or leak. But in order to check its serviceability, it must first be charged. I charged it from a computer power supply - this is the only thing that was at hand. The battery indicates that it gives out 12 volts and 7 amperes, and the computer PSU just has 12 V, just take and power the battery from the power supply: yellow wire to the red terminal on the battery, black wire to the black terminal. You should not connect the power supply to anything else. If you do not have an extra PSU at hand, then you need to turn it off and pull it out of the system unit. The power supply itself is turned on by shorting PS-ON (green) and COM (any black) on the ATX connector. Be careful. For your obedient servant felt on himself all the charm of current flowing through his hand. In this state, the battery and power supply must be left for several hours, I charged it for three days for 5 hours, this was enough for the battery to give out 11.86 volts - which is quite enough to start the control board.

While the battery is charging, let's move on to the next part of the UPS - this is the PCB, the control board. I inadvertently indicated above 11.86 volts, which are necessary to start the control board. The “brains” of the uninterruptible power supply in the form of a 68NS805JL3 microcircuit are powered precisely from the battery and, based on the fault table in the manual, at least 10 volts are needed for operation. Here is that table:

The thought came to me: maybe that's why the uninterruptible power supply does not turn on! But looking ahead, I’ll say that upon reaching a normal charge, the installed battery was only able to shock me, but the besperebonik did not start. So the problem is not low voltage. Moreover, a fully charged UPS did not want to start immediately after the fall.

The next step was to ring everything that can be called with a conventional digital multimeter. In fact, there were three broken diodes, which I replaced with similar ones.Which again did not give anything - the uninterruptible power supply was silent as before.

Then the devil pulled me to solder all the unvarnished tracks (from the installation side) - and suddenly there was a crack that broke the circuit. I somehow did not want to measure the voltage for a break on the switched on device.

As a result, it turned out that when it fell, it was the crack in the board that failed, because the soldering of the tracks helped!

Interesting is the fact that for more than 4 years, the discharged battery has remained safe and sound and perfectly gives out almost 12 volts to it.

Here is a list of files that you might find useful:

Schematic diagram (pdf): [hide][attachment=110][/hide]

The following tools and materials were used for the repair:

Digital multimeter DT838
Phillips screwdriver
Screwdriver
Soldering iron 60 W
Medical tweezers
Side cutters
Rosin, flux, solder, alcohol, wipes
2 alligator clips, 2 wires from an old power supply, a Molex connector from an old CD to connect the battery to the power supply.

I wish you success in the repair and yes, do not beat you current!

I got an APC-420 uninterruptible power supply from the previous administrator, all sniffy, it was lying in the closet, among other rubbish. When he asked what was wrong with him, he said: “The battery is dead, if you need it, then order a new battery.” Okay, lying around, and lying around, he doesn’t ask for food. Forgot.

About six months later, I accidentally stumbled upon him, during another fruitless attempt to restore at least some semblance of order in my sharaga. I connected it to the outlet in order to see what they say and show uninterruptible power supplies with a dead battery. He blinked his lights, squeaked something, then they called me, and they tore me off somewhere. In general, I found it again only a couple of months later. It stands peacefully, a green light is shining, they say, everything is in order with the voltage in the network. I disconnected it from the network, it got nervous, squeaked and buzzed hard, continuing to apply voltage to a non-existent load :). After waiting 5 minutes for control, I turned it off and connected my computer through it. I tried how it behaves in the event of a power failure - everything is clear, the computer plows, issues warnings (I slobbered it with a cable over the COM port), and after 7 minutes the computer is cut down, followed by UPS.

Once, they turned off the voltage, but did not warn in advance. Nothing terrible happened, Almost everyone had UPSs, completed the work and began to wait to be turned on. I didn’t cut anything, I decided to check in “combat conditions” how long the equipment will last on autonomous power. Along the way, it turned out that Cisco and the cable momed TAYNET DT-128 are connected directly to the network, without any filters or uninterruptible power supplies.
- After 8 minutes, my uninterruptible power supply died, without warning, and the correct termination of the work of Windows. (This is despite the fact that I hesitated to select a cable for it - APC has at least two possible pinouts of COM cables)
- At the 15th minute, two sideboards, powered by one UPS at 700W, went crazy.
- At the 15th minute, the proxy for FreeBSD died, which had a small Back-UPS 475, and on this model a cable for communicating with a computer is not provided in principle, so the work was not completed correctly.
- At the 22nd minute, they turned on the voltage and the experiment ended. Three 24-port switches remained in operation, and a server that was powered by Smart-UPS 1500.

As a result, after some combinations and manipulations with rearranging UPSs, I got the 700th smart, and FreeBSD got mine, which was kind of dead, but with an RS-232 interface (COM port) for pairing with a computer. He fought for a long time, while under the fryuha he managed to ensure that she saw him. The result of the last of the experiments was that everything ended correctly, but after turning on the power on the APC-420, the red light began to burn constantly - like the battery was dead:

The red light on the uninterruptible power supply began to burn constantly, showing that it was time to replace the battery - like dead.
The first thing that surprised me after disassembling the UPS was that the radiators on transistors are so small, I got used to the old bass switches with ordinary transistors, and here they turned out to be field ones - as a result, the size of the radiators decreased by more than an order of magnitude:

Now they began to use field-effect transistors - they heat up much less than ordinary ones, so the radiators have become very small.
The transition to field-effect transistors made it possible to reduce the size of radiators for transistors - now they heat up less.
The second thing that is already good is the power of the transformer, which, judging by the markings on it, was equal to 430W, which is even more than the nameplate power of the uninterruptible power supply (it is believed that more powerful uninterruptible power supplies are also produced in such a case with minor differences in the circuit and more powerful key transistors):

Oddly enough, the trance was made with a margin :) Something, but I did not expect this from cross-eyed. (albeit with a small one - 30W, but still)
Another interesting thing in the design, which I had not even noticed before, is the ability to connect a network cable via Smart-UPS for additional protection. Upon closer examination, the circuit turned out to be quite simple, and only two pairs are protected through which data is transmitted (for a telephone pair, the protection is divorced, but not soldered):

A rather primitive, but effective scheme for protecting against high voltage surges:

To restore the battery (12V 7.0Ah, the banks seem to be intact, none of them swelled.), A simple circuit was assembled for charging with an asymmetric current (I previously discharged it to 10.8 volts with a 21W light bulb):

Video (click to play).

Charged up to 14.8 volts, then discharged again. And so three times. The charging current was about 0.5 A. The first time it was discharged very quickly - literally in an hour. From the second call - for two with a penny, the third time I did not discharge, put it in place. When his torment was over, he worked like new. Of course, he did not become new because of this, but he worked for a long time. In a good way - three times is not enough, it was necessary to drive him away like that 5 times, he would have worked much longer (a year later a similar story happened to him, but I didn’t work there anymore, and I don’t know how everything was decided.).

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