Uninterrupted for a computer do-it-yourself repair

In detail: an uninterruptible power supply for a computer do-it-yourself repair 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 provide emergency power to computers.

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

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

They will not require much effort to eliminate themselves. We will leave difficult cases to professionals.

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

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

If the transistor (or other part) gets very hot, then the marking, usually made with white paint, darkens. In this case, the solder at the soldering point also darkens. If the part is close to the board, then the board itself will darken at the point of contact.

Sometimes characteristic ring-shaped cracks appear around the leads of high-current parts. Contact in such places between the pin 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 faulty, they must be replaced with the same or similar ones.

Next, you should check the fuse. A UPS usually has at least two fuses. The first (which can be accessed 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. It can be removed with a narrow blade screwdriver. Often a fuse holder has a slot 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 bus of the battery. It is designed for a 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 should deliver a current of 250: 12 = 21 A. And this is without taking into account the 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. These fuses are used in cars, so they can be found in the car market if necessary.

Note that most of the fuses do not fail “just like that”. Therefore, before changing them, you need to make sure that other parts are in good working order - rectifier diodes, the same inverter transistors.

Sometimes fuses blowing can be caused by an interturn fault in the transformer, but fortunately this rarely happens.

The transfer of the UPS to battery mode is most often carried out by means of electromechanical relays.A DC relay with a 12 or 24 V coil and powerful contacts is used. Sometimes the contact group of one of the relays fails.

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

Typically, 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 must be infinitely large, and a closed contact must 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, note that a clear click should be heard when the coil is energized. If it is not heard or some "rustles" are heard, there is a mechanical failure, and the relay definitely needs to be changed.

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

Conventional (non-reed) relays have a resource of at least 100,000 operations, which is more than enough for the entire operation time of the UPS.

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

APC Off-line UPS includes Back-UPS models. UPSs of this class are distinguished by their low cost and are designed to protect personal computers, workstations, network equipment, trade and point-of-sale terminals. Power of 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. Main technical data of UPS class Back-UPS

The index "I" (International) in the names of 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 suppressor filters that suppress surges and high-frequency noise in the mains voltage. The devices give appropriate sound signals when the input voltage is lost, the batteries are discharged and overloaded. The utility voltage threshold below which the UPS switches to battery operation is set using the switches on the rear of the unit. Models BK400I and BK600I have an interface port that can be connected to a computer or server for automatic self-closing of the system, a test switch and a beep switch.

The schematic diagram of the Back-UPS 250I, 400I, and 600I is almost completely shown in Fig. 2-4. The multi-tier power grid 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 for battery charging (this circuit uses D4 ... D8, IC1, R9 ... R11, C3 and VR1) and analysis of the mains voltage.

If it disappears, then the circuit on the elements IC2 ... IC4 and IC7 connects a powerful inverter, powered by a battery. The ACFAIL command to turn on the inverter is generated by IC3 and IC4. The circuit, consisting of comparator IC4 (pins 6, 7, 1) and electronic key IC6 (pins 10, 11, 12), enables the operation of the inverter with a log signal. "1" going to pins 1 and 13 of IC2.

The divider, consisting of resistors R55, R122, R1 23 and switch SW1 (pins 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 with frequent fluctuations in the mains voltage resulting in frequent UPS switches to battery power, the threshold voltage should be set to a lower level. The fine adjustment of the threshold voltage is performed by the VR2 resistor.

All Back-UPS models, with the exception of the BK250I, have a bi-directional communication port for communication with a PC. Power Chute Plus software allows the computer to both monitor the UPS and safely shutdown the operating system (Novell, Netware, Windows NT, IBM OS / 2, Lan Server, Scounix and UnixWare, Windows 95/98) while saving user files. In fig. 4 this port is designated as J14. Purpose of its findings:

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

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

3 - CC 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 terminal has a resistance of 20 ohms with respect to the common wire of the UPS.

5 - CC 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 you need to connect a relay to them, then the winding should be shunted with a diode.

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

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

Turn the UPS into battery mode without load. Connect a voltmeter to the UPS output to measure the effective voltage value. By adjusting the VR3 resistor, set the voltage at the UPS output to 208 ± 2 V.

Set switches 2 and 3 on the rear of the UPS to OFF. Connect the UPS to a LATR-type transformer with continuously variable output voltage. Set the voltage at the LATR output to 196 V. 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 to 230 V. Disconnect the red wire to the positive battery terminal. Using a digital voltmeter, adjust the VR1 resistor to 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 - analogs of the most frequently failing components.

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

The function performed by the uninterruptible power supply (abbreviated - UPS, or UPS - from the English Uninterruptible Power Supply) is fully reflected in its very name. As an intermediate link between the mains 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 a power outage can be extremely unpleasant: 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 the charge of the built-in battery is maintained from an external power supply by the charging circuit. In the event of a power failure or a strong deviation from the rating, the UPS output is connected to its built-in inverter, which converts direct current from the battery into alternating current to supply the load. Naturally, UPS runtime is limited by battery capacity, inverter efficiency and load capacity.

There are three design types of uninterruptible power supplies:

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

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

Since the batteries built into the UPS are automatically kept charged, no need for additional charging... If the battery has been completely discharged, a number of UPS models at the moment of switching on may indicate a battery malfunction, but as it gets charged, the indication will stop.

Typically, when the UPS is turned on for the first time, 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 (mistakenly or deliberately can 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 being used for a long time, it is a good idea to run it idle regularly to maintain the battery charge.
Real gel batteries are more expensive, but they tolerate prolonged deep discharge without consequences. At the same time, they are more sensitive to overcharging, which can occur if batteries with a capacity less than designed are installed in the UPS.

Read also: DIY ceiling plaster repair

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

Our tips for self-repairing an uninterruptible power supply cover the most basic problems. If you are unsure of your knowledge and do not have experience of "dealing" with equipment operating at hazardous voltages, it is best to consult a professional. You can find a complete list of repair and modernization services here. If you have any unresolved problems with your PC, then feel free to contact the specialists of our company, we are always ready to take on any difficult work. We work both in the city of Chelyabinsk and in the region.

Uninterruptible voltage supplies 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 supplied by the filtered mains voltage. Filters are used to suppress electromagnetic and interference in the input circuits. If the input voltage falls below or above the set value or disappears altogether, the inverter turns on, which is normally off. By converting the DC voltage of the batteries into AC, the inverter supplies the load from the batteries. BACK UPS of the Off-line class operate uneconomically in power grids with frequent and significant voltage deviations from the nominal value, since frequent switching to battery operation reduces the service life of the latter. The power produced by the manufacturers of Back-UPS is in the range of 250-1200 VA. The scheme of the uninterruptible voltage source BACK UPS is rather complicated. In the archive you can download a large collection of schematic diagrams, and below are several reduced 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 the mains voltage is absent and if the UPS is on, then 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 be enough for up to 10 - 30 minutes, if, of course, the device powers the computer. You can read more about the operation and purpose of UPS nodes in this book.

BACK UPS can be used as a backup power source; in general, it is recommended that every home has an uninterruptible power supply. If the uninterruptible power supply is intended for household needs, then it is advisable to remove the signaling device from the board, it reminds that the device works as a converter, it makes a reminder with a squeak every 5 seconds, and this is boring. The output of the converter is pure 210-240 volts 50 hertz, but as for the pulse shape, 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, although I changed the battery several times, but this is normal. And then the moment came, in the morning, as usual, I wanted to turn it on in order to work at the computer, but the uninterruptible power supply did not turn on, in response, there is not even a squeak, the relays do not click.

I had to untwist and figure out what happened.

value-600e indicated places for self-tapping screws

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

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

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

admission: on the capacitor such marking is F .01J / PD 250V

The power supply to the output is broken (and I would like to supply 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 several types of breakdowns 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, the reason may be broken field-effect transistors - they should be replaced;

• it is possible that the charging circuit “flew” and needs to be replaced.

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

I attach a diagram of the device of one of the UPS models

Repaired 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 fell into my hands for repairs. Since I haven’t had to repair the uninterruptible power supplies yet, I took up the repair with the reservation “to try it,” it will not get any worse.

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

I'll start with its characteristics:

A type - interactive
output power - 600 VA / 360 W (pay attention to wattage (W), not volt-ampere (VA))
Runtime at full load - 5 minutes (although the box says 10-25 minutes for “some computer with a 17” CRT monitor)
Output waveform - signal in the form of multi-step approximation of a sinusoid 220 V ± 5% of the nominal
Battery transfer time - 4 ms
Max.absorbed pulse energy - 320 J

UPS electrical parameters table taken from the manual:

As you can see, there are no bells and whistles: 360 watts, power supply for only two devices, there are no observation options, except for one LED on the front panel and a "buzzer". The slightly older models have additional functions, but these are 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 crashed to the ground, causing the UPS 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 - a 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 (!) Years with a tail. Many will say - it makes no sense to repair it, the battery has long leaked and burst. But no, it is whole, as shown by the autopsy and testing, only discharged to zero.

Disassembling the UPS turned out to be simple: the four screws securing the top cover were removed 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 schematic 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 a shock - these are the battery and the 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 next to each other) should ring. Then thick wires black, red, blue, which are also combined with each other, ring out. Everything seems to be in order with the transformer.

ATTENTION! Be careful! Further work may result in electric shock. The author does not bear any responsibility for the consequences of your actions.

Battery. External examination showed that it was intact - it did not burst or leak. But in order to check its serviceability, you first need to charge it. 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 in the computer power supply there is just 12 V, we just take and power the battery from the power supply unit: the yellow wire to the red terminal on the battery, the black wire to the black terminal. You should not connect the power supply to anything else. If you do not have an extra power supply 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 humble servant felt on himself all the charm of the current flowing through his arm. In this state, the battery and the 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. It was not for nothing that I indicated 11.86 volts above, which are necessary to start the control board. The “brains” of an uninterruptible power supply in the form of a 68NS805JL3 microcircuit are powered by a battery and, based on the table of malfunctions in the manual, at least 10 volts are needed for operation. This table is:

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

The next step was to dial everything that can be called with an ordinary digital multimeter. In fact, there were three broken diodes, which I replaced with similar ones. Which again gave nothing - the uninterruptible power supply was silent as before.

Then the devil pulled me to solder all the unvarnished tracks (from the side of the installation) - what if there was a crack that would open the chain. Somehow I didn't want to measure the voltage for a break when the device was turned on.

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

An interesting fact remains that for more than 4 years the discharged battery has remained intact and perfectly produces almost 12 volts it is supposed to.

Here is a list of files you may find useful:

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

The following tools and materials were used for the repair:

DT838 digital multimeter
Phillips screwdriver
Slotted screwdriver
Soldering iron 60 W
Medical tweezers
Side cutters
Rosin, flux, solder, alcohol, napkins
2 "crocodiles", 2 wires from the old power supply, Molex connector from the old "CD" for connecting the battery to the power supply.

I wish you success in the repair and do not hit you with a current!

I got an APC-420 uninterruptible power supply from the previous administrator, all dirty, it was lying in the closet, among other trash. When he asked what happened to him, he said: "The battery is dead, if you need it, order a new battery." Okay, lying around, and lying around, does not ask for food. Forgot.

About six months later, I stumbled upon him by accident, during another fruitless attempt to restore at least some semblance of order in my sharaga. I connected it to an outlet in order to see what the uninterruptible power supplies with a dead battery say and show. He blinked light bulbs, peeped something, then they called me, and they ripped me off somewhere. In general, I found it again only after a couple of months. 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 mains, it got nervous, squeaked and hummed with tension, continuing to supply 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 he behaves in the event of a power outage - everything is clear, the computer plows, issues warnings (I licked it with a cable on the COM port), and after 7 minutes the computer is cut down, followed by the UPS.

Once, they turned off the voltage, but they did not warn me in advance. Nothing terrible happened, Almost all of them had UPSs, finished their work and began to wait to be turned on. I didn’t cut anything down, I decided to check in “combat conditions” how long the self-powered equipment will last. Along the way, it turned out that Cisco and the TAYNET DT-128 cable momed are connected directly to the network, without any filters and uninterruptible power supplies.
- After 8 minutes, my uninterruptible power supply died, without warnings, and the correct completion of the Windows operation. (This is despite the fact that I hesitated to pick up a cable for it - APC has at least two possible pinouts for COM cables)
- At the 15th minute, two sideboards, powered by one UPS at 700W, were out of order.
- 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 was not provided in principle, so the work was not completed correctly.
- At the 22nd minute, they turned on the napruga and the experiment ended. Three 24-port switches remained in operation, and a server powered by a Smart-UPS 1500.

As a result, after some combinations and shenanigans with rearranging UPS's, 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, until under the fryukha managed to get her to see him. The result of the last of the experiments was that everything ended correctly, but after turning on the power on the APC-420, a red light began to burn constantly - like the battery was dead:

The red light on the uninterruptible power supply began to burn constantly, indicating 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 of such a small size, I got used to the old mains with conventional transistors, but here there were field-effect ones - as a result, the size of the radiators was reduced by more than an order of magnitude:

Nowadays 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 the radiators for transistors - now they heat up less.
The second thing that is already a good thing is the power of the transformer, which, judging by the marking on it, was equal to 430W, which is even more than the rated power of the uninterruptible power supply unit (it is believed that more powerful uninterruptible power supplies are produced in such a case with minor differences in the circuit and more powerful key transistors):

Oddly enough - the trance is made with a margin :) Something, but this from the cross-eyed I did not expect. (albeit with a small one - 30W, but still)
Another interesting crap in the design, which I didn’t even notice before, is the ability to connect a network cable via Smart-UPS for additional protection. Upon closer examination, the scheme 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 unsoldered):

A rather primitive, but effective circuit for protection against high voltage surges:

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

Video (click to play).

Charged up to 14.8 volts, and then discharged it 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 it, I put it in place. When his torment was over, he worked like new. Of course, this did not make him new, but he worked for a long time. In an amicable way - three times is not enough, it was necessary to drive him out like this 5 times, I would have worked much longer (a year later a similar story happened to him, but I did not work there anymore, and I don’t know how everything was decided.).

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