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PCB not functioning

Discussion in 'Troubleshooting and Repair' started by partyanimallighting, Oct 31, 2012.

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  1. partyanimallighting

    partyanimallighting

    319
    4
    Oct 22, 2012
    Hi, I have a couple of these PCB's in need of repairs. They work with very high voltage, up to 500 volts, and I've gotten a very lively shock from one of them already when I tried to troubleshoot so I would love to get some advice from the wise ones in the forum before I electrocute myself. The company was kind enough to send me all schematics and diagrams but I am not knowledgeable enough to read them. Can anyone help me?
     

    Attached Files:

  2. MrEE

    MrEE

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    Apr 13, 2012
    what are these boards and in what way they don't work? What is it they are supposed to do and are not doing? Can you post the schematics?
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,411
    2,779
    Jan 21, 2010
    If you have the schematics and you are able to post them, it would help immensely.
     
  4. partyanimallighting

    partyanimallighting

    319
    4
    Oct 22, 2012
    These boards are for strobe lights. I removed them for repairs as the lights were no longer functioning. When they are working, there are 2 LED's, one green, signalling power, and one red, that flashes when the lamp flashes. The quality of the schematics is terrible because I had to reduce the resolution to decrease the file size.
     

    Attached Files:

  5. partyanimallighting

    partyanimallighting

    319
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    Oct 22, 2012
    I am also not too excited about getting shocked again so any help will be greatly appreciated.
     
  6. QuantumCheese

    QuantumCheese

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    Apr 27, 2012
    Page 2 of that schematic would be useful, p1 only has the logic and none of the HT things.
    Also - what is the fault? for openers, what do the LED's do now?
     
  7. partyanimallighting

    partyanimallighting

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    4
    Oct 22, 2012
    Hi QC, the LED's do not light at all on one pcb and the green LED lights and dims on the other on startup. As I mentioned before, these PCB's are for strobe lights and the socket for the lamp is in the center of the pcb. When the PCB's function perfectly, the green LED lights constantly and, when DMX signal is applied to the unit, the red LED flashes in sync with the flash rate of the lamp. Presently I get no response at all off these defective PCB's. If you need any information at all let me know as I have been waiting on a response on this and other pcb's for some days now and I was getting worried. I will have to private message you the schematic if that's OK as the size is larger than what is allowed and if I decrease the size, the quality is really terrible.
     
  8. partyanimallighting

    partyanimallighting

    319
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    Oct 22, 2012
    Hi QC, the private messaging does not have the option to attach the .pdf. What's the best option here? Please bear with me, I'm new to all this.
     
  9. partyanimallighting

    partyanimallighting

    319
    4
    Oct 22, 2012
    Hi QC, I attached two schematics before. Did you check both to see if they are what you need?
     
  10. CocaCola

    CocaCola

    3,635
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    Apr 7, 2012
  11. partyanimallighting

    partyanimallighting

    319
    4
    Oct 22, 2012
  12. QuantumCheese

    QuantumCheese

    73
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    Apr 27, 2012
    Hi,
    Okay, I looked at the previous attachments, but as i said the front end supply section and presumably also the bit you got a shock off would appear to be on page 2 of 2?

    Also, when you say 'strobe lights' traditionally i think of a arc-ing strobe with a trigger of 8 or so kV, the transformer in the picture is clearly not going to do that so what kind of 'bulb' goes into the socket?

    edit: missed your posting of the full schematics. i'll be back.
     
  13. QuantumCheese

    QuantumCheese

    73
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    Apr 27, 2012
    Right, so it is what i would call a arc-ing strobe light.

    First of all, you've already had a 'nip' off this circuit, looking at the schematic you were quite lucky. this circuit uses un-isolated mains voltages for the DC rail, unless your trying to fix this with it plugged in via a 1:1 isolating transformer, i'm outta here.
    Secondly it quite cramped and you need to have it firmly fixed down to something before you start making any kind of power-on measurements.

    Failure to observe standard precautions while working on a circuit such as this can cause instant death

    Please confirm that you know what your doing before i go any further.
     
  14. partyanimallighting

    partyanimallighting

    319
    4
    Oct 22, 2012
    OK QC. FULLY UNDERSTOOD!!! DO NOT FOOL AROUND WITH THIS UNLESS I AM THOROUGHLY AWARE OF ALL THE DANGERS INVOLVED!!!!

    Got it.

    How do I proceed from here? First of all, I can secure the PCB firmly to an insulated surface, probably a piece of plywood lined with a piece of electrical insulation paper. From there I can make all the necessary power on readings that you suggest. From the schematics I assume this PCB will output as much as 500 ~ 650VDC so I am very aware of the dangers involved. Please remember that I'm not very versed at reading schematics so please bear with me. Also, as I am attempt to "self-teach" myself to repair a variety of faulty PCB's from different units, what tools would you recommend? I have all necessary hand tools (pliers, screwdrivers etc), a Fluke 77 multitester and a 12V and 24V power source on my workbench. I was thinking about getting a capacitance tester also. What do you think?
     
  15. QuantumCheese

    QuantumCheese

    73
    0
    Apr 27, 2012
    It's not really that, I would rather you didn't kill yourself 'fully aware of the dangers or not'. there is a very real difference between 500V and 500V UN-isolated mains. one makes you go ouch, the other much worse.

    The first 'tool' you need to acquire when working on things like this is an isolation transformer. you plug the mains in one side and your repair job in the other.

    Then with the circuit now isolated, i would start by checking the low voltage rails - 5V and 12V as provided by vr1 and vr2. The power led that doesn't light would indicate the 5v rail is at fault. the one that's dim could well be similar

    A bench, a supply and a meter is a good start. a cap meter can be useful but not essential, or not as essential as an Isolation Transformer - Google it.
     
  16. partyanimallighting

    partyanimallighting

    319
    4
    Oct 22, 2012
    Hi QC, I did the necessary research on the isolating transformer and I fully understand it's necessity for this type of repair. However......I checked around at quite a few electrical suppliers for this type of transformer and the majority are clueless as to what I'm asking for. However, one major electrical supplier had available but these were industrial types weighing close to 1000 LBS. Not something I would consider putting on my workbench. I'll check around again tomorrow at some electronic repair and parts suppliers and see what gives. I do remember seeing these types of transformers around decades ago but can't recall the last time I saw one, especially with the 110V power cord at one end and the 110V socket on the other. If I am not successful in sourcing this transformer, can I still attempt to repair this PCB? As for the other necessary tools, I have a sturdy non-conductive bench with switched 12V, 24V and 110V supply, good work light and a trusty Fluke 77. Will add the isolation transformer once I can source it.
     
  17. QuantumCheese

    QuantumCheese

    73
    0
    Apr 27, 2012
    Hi, Glad you now see my point. Yes they {isolation transformers} can be quite pricey but its worth it. I used to have one of those 'big yellow things' under my bench, but i now have to make do with a transformer i lifted from a skip that had a number of windings on both primary & secondary, it's not quite 1:1 but it's close enough and it was free! just add your own sockets.
    other options are things like this chap did
    - http://www.mhennessy1.f9.co.uk/isolating/index.htm

    in the mean time if your real careful (see below). attach the -ve lead of your fluke with a crock-clip to the tab of vr1, then measure 5v status on pin 28 of U3. this should give use somewhere to start.

    When making the measurements - "Use the old electricians’ trick of keeping one hand in your pocket. This lessens the chance of a closed circuit across your chest and through your heart."
    Remembering also as my old Safety & Measurements lecturer once said, but don't lean back on a radiator while your doing it :eek:
     
  18. partyanimallighting

    partyanimallighting

    319
    4
    Oct 22, 2012
    Hi QC, I might get my hands on an old isolating transformer from a client, probably over the course of this weekend so if I do, I can start testing. I was wondering if you could advise me on another pcb? I posted before on these other pcb's, I got a little assistance but I haven't gotten any feedback since. I'll post the pictures of the pcb and, if you can help me, that would be great. They've been sitting on my bench about 3 weeks now and I haven't been able to resolve the problem.
     
  19. QuantumCheese

    QuantumCheese

    73
    0
    Apr 27, 2012
    I commented on that 'PCB' already, in it's original thread and you never replied?

    As i said before, a schematic would be very helpful here - especially as that control device appears to have lost it's descriptive printing. the rest of the circuit 'looks' pretty straight forward.

    on the Right there are a pair of transistor arrays that are driven by what ever the big IC is. bottom there is a 555 so on one pin of that you ought to be able to find some pulses - google ne555 for a pin-out description.
    data sheets are readily available and have examples of most configurations so you can even work out what it's supposed to be doing too

    below the two large caps looks like a linear reg be it 7815/7812/7805 i can't read round corners need schematic!

    the led however, and i'm guessing here, appears to be connected to the input pin on the reg, so if it's not lit there is a fairly fundamental issue at the front end of the supply (or the LED's popped). though i could be wrong, it's not easy to tell with a picture of a populated double sided PCB what's connected to what.

    If you can get a schematic for this board i might be able to help a bit more.
    As this is off-topic for this thread and you already have a thread for this, please continue it there - I have posted this reply there also

    QC
     
  20. partyanimallighting

    partyanimallighting

    319
    4
    Oct 22, 2012
    Hi QC, first thing I did was check the voltages at the legs of VR1 and VR2 first and I got 12VDC and 15VDC on VR1 and -1.6VDC and 16VDC on VR2. I then checked the voltages from the tab of each one, VR1 and VR2, to Pin 28 on U3 and I got (-)0.5VDC on VR1 and (-)1,6VDC on VR2. I hope this is a start to a positive result.
     
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