NRG GUARD 2000A UPS, NOT STARTING REPAIR
This UPS came in my hands after an unsuccessful repair attempt from another technician. The symptom it showed right after powering it was no reaction at all. The front and back views of this UPS are shown below:
Well, as I almost always work without any schematics, I removed the main PCB from the unit and as a first step I watched carefully what the previous technician did on it.
The unit was generally in very good condition. It suffered an overvoltage at its input and blew a 3A power diode and a power transistor in the battery charging circuit along with its input fuse of course. The main board is shown below:
The previous repairer had replaced the power transistor shown at the right side of the electrolytic capacitor located at the middle of the PCB, behind the blue cable, along with the 3A power diode nearby (all of them shown better in the below photo) and also repaired a part of foil trace of the PCB which was lifted and melted due to the excessive fault current that passed through it.
In the above photo you can see the power transistor which replaced the original (for which I don’t know what type it was). It is the Q13, TIP 31C located in front of the electrolytic cap at the middle of the PCB. Also the new 3A diode (shown in front of the right side of the first relay, or at the right side of Q13) is a 1N 5404 replacement of the original one (for which, again, I don’t know what type it was).
Below is a better view of the location of the power diode. It’s the one between the blue cable and the current transformer, at its left side. He also replaced the small signal transistor (Q26) shown with the yellow sleeve in one of its terminals (Base), at the right side of the heatsink shown, around its middle.
Well, this transistor caused me enormous trouble for the reason I will give you further explanation later on…For the moment keep in mind that the one shown below is my own replacement and not his…
Well, as usually, I checked all the semiconductors of the circuit along with all the electrolytic capacitors and found another small signal transistor (Q25, 2SC945) in the relay area to be defective. In fact it was a relay driver. I was then sure that I had finished the repair, but this was not the case. You can see the replacement transistor in the photo below, having reverse orientation from the original as marked on the PCB. It is the one located just above the single one at the middle of the PCB, downwards. I put a yellow sleeve in one of its terminals (Base):
After a new test, I had only the improvement that when pressing the power switch I could hear a click of a relay, a long beep sound and then nothing at all.
Believe it or not, I “swept” the entire PCB again and again. I checked everything on it. I used magnifier lenses to search for “non typical failures” like cold joints or broken PCB foil traces. All went in vain. No result at all. Everything was in perfect condition and yet the device refused to start. So, I left it for a few days sitting on my bench and smiling ironically at me…
After that (indeed very useful for me) interval, I decided to go on with it. Only this time by trying to get any useful electrical measurements of dynamic conditions, neglecting the static component measurements which one way or another were perfect and all they brought me was an equally perfect confusion…
During the troubleshooting procedure, I noticed that the device when trying to start it was giving at the battery cables an output (charging) voltage of the order of 14V D.C which was not enough for a normal charging of the 2x12V batteries connected in series in its circuit. Half of the needed voltage was missing. Then I thought that the processor “sees” this inadequate voltage output and stops the entire system.
With this in mind as a good starting point, I removed the main board again, located the components involved in battery charging and rechecked them again one by one. It was that time when I noticed that the transistor for which I said above I owe you a further explanation was giving me the right indications about its B-E and B-C forward voltage drops, but the physical arrangement of its terminals was different from the other, same type, transistors used in the circuit.
What happened with this transistor was: correct replacement in terms of electrical equivalence and at the same time wrong replacement because the previous technician took care only for the electrical parameters of the equivalent transistor he put there without paying any attention to its terminals’ arrangement which was different from the original transistor. The original had an E-C-B arrangement and the replacement had an E-B-C arrangement. That’s why you see this transistor in the photo above with different orientation and a plastic sleeve in one of its terminals (Base). I had to interchange the C-B terminals end therefore to insulate the Base terminal with a plastic sleeve as I had to bend it and place it in the collector’s place. The collector’s terminal was also bent to reach the place of the base, but now it was in front of the base terminal. The sleeve was put there therefore to prevent any likely short circuit of the B-C terminals by accidental bending of the entire body of the transistor. I did exactly the same when I replaced the original relay driver (small signal transistor Q25, 2SC945). The replacement transistors I used were of BC546 type in both cases.
Well, after the rearrangement of the Q26 transistor’s terminals the device started normally after the self tests, giving an output of 27 Volts in the battery terminals. After a full charging (overnight test) of its batteries and when being in stand by status thereafter this voltage was absolutely stable.
The problem was finally eliminated and the UPS was ready for normal use again.
This article was prepared for you by Paris Azis from Athens-Greece. He is 59 years old and has more than 30 years’ experience in electronics repairs, both in consumer and industrial electronics. He started as a hobbyist at the age of 12 years and ended his professional carrier as a senior electronics technician. He has been a specialist in the entire range of consumer electronics repairs (: valve radio and BW TV receivers, transistorized color CRT TV, audio amps, reel and cassette tape recorders, telephone answering and telefax devices, electric irons, MW cooking devices e.t.c) working in his early stages at the official service departments of National-Panasonic first and JVC afterwards, at their premises in Athens.
Then he joined the telecoms industry, working for 20 years as field supporting technician in the sector of DMRs (: Digital Microwave Radio transmission stations), ending his carrier with this subject. Now he is a hobbyist again!
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Note: You can check out his previous repair article below:
https://www.jestineyong.com/farfisa-art-4821-door-entry-intercom-repair/
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albert
October 16, 2015 at 11:52 am
Tremendous job !!!
Paris Azis
October 17, 2015 at 2:01 am
Thank you Albert.
Robert Calk
October 16, 2015 at 12:46 pm
Nice job, Paris! You never know what you will find when someone else has "worked" on it...lol
2000A??
Paris Azis
October 17, 2015 at 2:05 am
Unfortunately this is always true Robert. Thank you for your support.
Best Regards
Yogesh Panchal
October 16, 2015 at 2:54 pm
Sir,
Good effort for repair .This article lead us never give up hope,effort and patience and you will get favourable Result.
Paris Azis
October 17, 2015 at 2:20 am
Hello Yogesh
Please try to call me simply Paris. “Sir” is too heavy for me. (I am neither a Knight or a Lord or anything similar)… Of course I respect your politeness, but this “Sir” is not necessary here (I think).
And yes, this should be the motto: “Never give up with it”. Every possible alterative must be first examined and if things show that there is no chance for the apparatus to survive by anyone of them, then of course the effort naturally ends there…
Best Regards
Chris
October 16, 2015 at 4:11 pm
My congratulation for the good article and well explanation.
Question:
Is that 2000A maybe 2000VA? I hope that is not a 2000Amp. UPS? 🙂
Paris Azis
October 17, 2015 at 2:27 am
Thank you Chris. Your articles are fascinating as well.
2000A is the model type written in its back label and it is 2000VA indeed. If it was 2000A I would sell electric power in all over my neighborhood here making lots of money, but that is not the case…Unfortunately…
Best Regards
Albert van Bemmelen
October 16, 2015 at 4:26 pm
You solved another repair after another previous engineer couldn't! Funny thing that the previous repairer did all the work again but messed up at doing everything right. Thanks Paris for this also well written article!
Paris Azis
October 17, 2015 at 2:38 am
Hello Albert
Thank you for your warm comment. Guess who did this repair! The same person who repaired the Konig amplifier! But I don’t blame him at all. He is a very good friend of mine and a very nice man. He is an expert in mechanic constructions and he likes electronics very much. His problem is that he is not educated at all and due to his age (same with mine) it is too late for him to learn even the basics now…
He is in my mind a spoiled talent…”So ist das leben” my dear Albert…
Best Regards
SAJID RAUF
October 16, 2015 at 6:38 pm
Dear Paris Axis,
Hello,
I just earlier read your article.Really very interesting, informative, and much more motivational that never ever give up. Weldone great job.keep it up.
I made last year and 3 band valve radio,it's MW&SW1 are not working.Shall you help me in this regard.
SAJID Rauf Raja
Leeds UK.
Paris Azis
October 17, 2015 at 3:00 am
Hello Sajid
Thank you for your warm comment. I would be pleased to help you, although I don’t know how to do this…I also didn’t clearly understand what exactly the problem with this valve radio is.
Anyway, if SW2 is working good (as I understood) chances are for the band selector switch to be defective. Before doing anything with it, no matter if the switch is a single-rotary and multiple pole type or a bank of three separate switches one next to the other, you must buy a contact cleaning spray (from a local shop selling electronic spare parts) and then open the device and wash the switch(es). Let it then dry and plug it on the power afterwards.
Take great care while working with it, especially if you are inexperienced as I imagine. The device should be out of power (completely disconnected) as long as you work with it. Reconnect it for test after it is completely dried.
If the problem still exists, I don’t think that there is much to do for it as you will not find any spare parts for it, due to its age…
I hope these guidelines will work for you.
Best Regards
Anwar Shiekh
October 16, 2015 at 9:57 pm
Unfortunately repair is a dying art; I only repair for my own use as the time needed does not make it a profitable endevour.
Robert Calk
October 16, 2015 at 11:36 pm
I repair devices for the fun of it, although it kills my back sometimes, and to save myself, family, and friends some money.
Albert van Bemmelen
October 17, 2015 at 4:34 pm
Hi dear Robert, I used to have back problems 24/7 every week, or better said every second of the day. But nowadays I'm almost cured from it because I went at least 15 times to a Chiropractor. Who also told me to use 2 pillows under my knees in Bed every night so my backmussles can loosen up while sleeping. And the funny thing is that I went there because I thought he could help me get rid of my Migraines because my stiff shoulders and Neck. But in the end he freed me from my nagging backproblems. And I watch out doing any heavy work, which also helps. And I avoid riding in too small cars (I am 6 feet 5 you see). Also I do al lot of walking when I can, or use my Bike if I'm in a bit of hurry. And I think that the hartpills I take helped me from my migraines. (The hart problems I got from my neighbor above me who is an Alcoholic amongst everything else who keeps me awake almost every night the past 22+ years now).
Robert Calk
October 17, 2015 at 8:04 pm
Hi Albert, Wow, you're a big man! I hate to hear about your heart problems - I'll pray for you.
My pain is not muscle pain. I have arthritis in my back and it's inoperable. But I can't stand to do nothing everyday like kids do playing video games. I guess I'm old fashioned and believe that people should always strive to be useful in some way.
Albert van Bemmelen
October 17, 2015 at 11:57 pm
Me too Robert. Guys - like my upstairs neighbour - who only are making it harder for the community are a pain in the ... (you know what! Hint: I meant to say 4 or 3 characters beginning with a B or an A LOL). He is always making noises at night with is TV set or CD player long after midnight over and over again. And he simply refuses to use a headphone on his deaf ears. I agree with you that doing nothing isn't helping anyone. And probably only the best remedy against Alzheimer or Dementia. Cheers!
Jestine Yong
October 18, 2015 at 3:16 pm
HI Albert,
You are very tall. I'm only 6 feet 1. Once a while I will also have back pain but after some back exercises the pain will go away.
Jestine
Albert van Bemmelen
October 18, 2015 at 7:35 pm
Hi Jestine, 6 feet 1 inch = 1 mtr 85 cm. that is not bad? (only 4 inches less than I am).
Jestine Yong
October 18, 2015 at 7:43 pm
HI Albert,
You are right and I guess the air at your level is much more fresh ha-ha.
Jestine
Albert van Bemmelen
October 19, 2015 at 3:20 am
Once there was someone at my pre-technical school who called me the "Eifel tower". I told him "then you must be the little elevator" LOL.
Paris Azis
October 18, 2015 at 1:32 am
Hello Robert
I do the same as you do for the five last years!
Best Regards
Paris Azis
October 17, 2015 at 3:17 am
Hello Anwar
I fully agree with your opinion about professional repairers…I was one of them in the past and things were very different at the old days. Buying new equipment was not so easy to do and therefore repairs had their place within the useful life of the electronic products. I remember that when buying a new device, within its package you could find its electronic schematic diagram. Especially talking about TVs, Radios, tape recorders etc home appliances, the schematic was always there.
Well, I have now an LG 32” TV completely dismantled, the model is 32 LG 500-ZA and belongs to a very good friend of mine. He asked me to repair it. It has a “not starting” symptom. I searched and found in the web its servicing manual. Now guess what! There are only block diagrams in there…If you follow their instructions, they simply end up with “replace the PSU”…
The difference from the old time is apparent.
Best Regards
Albert van Bemmelen
October 17, 2015 at 4:43 pm
Recently I repaired a SHARP LCD TV that also had the same problem you mentioned. I noticed a 2200uF 16V capacitor on the PSU Board that was Bulging. Replacing it by a new 3300uF 16V one fixed the Sharp TV again.
We didn't have any service manual but didn't need it in the end. So if you are lucky too it is a simple component replacement thing.
Paris Azis
October 18, 2015 at 12:50 am
Hello Albert
Unfortunately this one is not a bulged capacitor's problem...
I already found a defective I.C, and keep on searching for more problematic components...
Albert van Bemmelen
October 18, 2015 at 12:13 am
Hi Paris. On ElektroTanya I found a corresponding service manual that was 99 pages long. Probably that Manual is the complete Service Guide for the TV Set you mentioned above?
Paris Azis
October 18, 2015 at 5:16 pm
I'll try it Albert. Meanwhile, a second file I saved from the web gives some elementary information about the internal circuits, although I typed "schematic diagram" for searching it.
The first one was excactly the same, without these two lasp pages with the elementary schematics...
Jestine Yong
October 17, 2015 at 2:47 pm
Hi Anwar,
I personally do not think repair is a dying art. If you are referring to consumer electronics then probably yes but to industrial electronics it is well alive and kicking. The reason I say this is because the students that has attended my repair course mainly were in the industrial circuit board repairs. Their technology changes are not as fast as the consumer electronics. Many still use the analogue circuit board. Even their switch mode power supplies are still using old design. Not only that, many came because they seems to have an inbuilt desire to learn electronics repair either for hobby purpose or to be a better repairer. I had a student just discovered that he likes electronics repair and his age was 52! In another case, a retired police officer started to repair equipment at the age of 56 after attended my course. You can read his article below:
https://www.jestineyong.com/audio-alchemy-dac-in-the-box-repaired/
Although there are not many people like us out there who like repair, I still believe many of them still want to learn about electronics repair and surely it will never be a dying art.
Robert Calk
October 17, 2015 at 4:18 pm
I agree with you Mr. Yong. But consumer electronics repair gets better when the economy goes down. When people start having less disposable income, they start looking for ways to save money. Also, repair shops need to advertise more.
Paris Azis
October 18, 2015 at 12:45 am
I fully agree Robert. This is exactly the situation in my country during the last few years...
Corriete
October 16, 2015 at 10:27 pm
yes that was a big mistake from the previous and so called technician. Let us realize that we need to be careful in all joints of repair.Good job sir for identifying the legs configuration.
Paris Azis
October 17, 2015 at 3:25 am
Hello Corriete
Please take a look at my answer to Albert van Bemmelen above…And (please again) try to understand such cases. They need our support instead of our curse (I humbly believe)…
Best Regards
Aydn
October 17, 2015 at 6:29 am
Inserting a transistor with incorrect pin configuration is possibly due to human error, and the same lack of attention to detail by an aircraft maintenance engineer caused the aircraft windscreen to blow out and the captain to be sucked out of the aircraft - Also 2SC945 is a common transistor used in Sharp and Toshiba TVs
https://www.youtube.com/watch?v=ONGzvBvu6gA
Paris Azis
October 18, 2015 at 12:55 am
Thank you Ayd
This is what happened in this case. A human error.
Fortunately this device was not an airplane...!
Best Regards
Peter O
October 17, 2015 at 9:36 am
A very determined repairer & eventual satisfactory outcome.
Since we don't know how the original failure occurred it would seem wise to think about additional circuit protection. I am a bit surprised that this was not considered.
Nevertheless an excellent repair!
Paris Azis
October 18, 2015 at 1:18 am
Hello Peter O
Most likely a melted PCB foil is the common proof that the device has suffered an excessive overvoltage. And the usual causes of this are the discharges of lightings on the utility network. From there the damage enters the various connected devices. And finally there are no practical countermeasures to protect those devices in an absolute manner...
Thanks for your comment.
Mohammed Kasim
October 17, 2015 at 12:41 pm
Very Good case history. When you will post about that short circuit finder (using OP amp to amplify the voltage drop in the circuit....) I am waiting for that
Congratz
Paris Azis
October 18, 2015 at 1:22 am
Hello Mohammed
I know that this is left behind, but I will finish it soon. Just stay here...
Best Regards
Waleed Rishmawi
October 17, 2015 at 4:04 pm
good job on the repair. i have been in that situation before and it took me forever to get it fixed because a technician tried to fix it and instead, he made it worse. that is why I good thing to do is to go over what the other technician has done and check his work. many times I refuse to repair a device that was taken to another guy for repair because most of the time, the device is worse than before and sometimes it takes forever to get it fixed.
Paris Azis
October 18, 2015 at 1:25 am
The usual picture...You are right Waleed. I cannot deny that...
Best Regards
aziz
October 17, 2015 at 9:13 pm
Thanks mr Paris
Paris Azis
October 18, 2015 at 1:27 am
Thank you too Aziz.
Best Regards
Chris
October 18, 2015 at 6:51 pm
When I found a trace of a repairing attempt of another technicians in a repairing equipment what I have to fix, first a stop the repairing process.
Try to roll back the unit into a factory stage. I mean, I search for the schematic or try to make one on papers what are separated from each other.
Lets say the audio amp circuit I brake down in power circuit, filter circuit and at the end the main input and output circuit. Then I check does the technician before me eventually changed components or not.
After the roll back process I start to analyse and repair the unit.
If the roll back process need to much time then I stop the whole repair process and give me a try in one hour repair. If no result in one hour then it would be expensive for the customer to repair the device and will talk to the customer and make some deal with him/her.
If I repair a unit but for some reason I could not repair it I will leave a message in the unit what i changed and why on a paper. If some other technicians try to repair they can see what I changed or measured...
Paris Azis
October 19, 2015 at 12:29 am
Nice tactic Chris
I liked it, especially your last paragraph.
Once upon a time, there was a TV technician in the place I have grown up (a relatively small city in the north-west Greece) who was misalighning every adjustable I.F transformer he was seeing in case he could not repair a device. He thought that he was protecting his good reputation in this way, since "none else could make any repair on this device after him"...Of course after some time the police took good care of him and his business came to end...
That's why I said I liked your last paragraph so much...
Best Regards
Raul Jose Go
October 19, 2015 at 2:44 am
Hello Paris Azis, ever this is the best repair i had known, i am 63, first time to have knowledge of such defects, most probably that same happened to some electronics appliances of which i was not able to fix.so many thanks and gratitude to you as well as other technicians who contributes their expertise in this forum, again i congratulate everybody as well as Jestine Yong. Raul, Philippines.
Paris Azis
October 19, 2015 at 7:15 pm
Hello Raul
Thank you for your warm and supporting comment. It is really encouraging me to go on and improve my technical presentations through this blog of Jestine.
Most valuable of anything else is the positive feeling I get through this feedback from the readers of my articles that they learned something they didn’t know before reading them.
And I find this to be both exciting and invaluable, at least for myself.
Moreover I hope that these technical articles, not exclusively mine but of all the writers in this blog, to work as motivation factors for new electronics’ repairs’ technicians in order to keep this work object alive, either as hobby or as profession…
It’s a pity to find out that an apparatus was thrown away only because of a burned out fuse…And I have seen this so many times up to now…Let alone what happens to the environment as a result of the so called “electronics garbage”…This must at least be reduced to a minimum if not stopped at all (which is a wish of mine)…
Best Regards
Samantha Perera
October 19, 2015 at 1:43 pm
Nice explanation Mr Pariz Thank you.
Paris Azis
October 19, 2015 at 7:19 pm
Hello Samantha
Thank you too for your support.
The opinion of a woman involved in electronics’ repairs’ is for me of doubled value!
Best Regards
Ulises Aguilar Pazzani
October 21, 2015 at 8:15 am
Mr Paris Azis,
Very curious Job and very profecional always read Your articles keep uo Sir
Paris Azis
October 22, 2015 at 2:25 am
Hello Ulises
Thank you too for your support.
Best Regards
Ulises Aguilar Pazzani
September 2, 2016 at 12:10 pm
Mr Paris Azis great repair job , and good diagnostic Sir