Backlight Inverter

Discussion in 'General Electronics Chat' started by the alchemist, Aug 7, 2005.

  1. the alchemist

    Thread Starter New Member

    Aug 7, 2005
    Recently the backlight inverters on both of my LCD monitors fried. I found a place nearby that sells the inverter board and bought the last one they had. It had been refurbished so I could see exactly where components had been replaced.

    I removed the two inverters from the monitors, replaced 1 with the one I purchased and as expected, the monitor worked again. Then I decided I'd see if I could make 1 working one from the two dead inverters. Like an idiot, I didn't make a note of which components I had to replace so I opened up the working one again identified the parts. Since it was pretty clear to me that only a few parts had been replaced I made the assumption that the same parts on an other part of the board would be ok. So I desoldered them and soldered them on the other card - put the monitor back together and it worked!!! Then I put the previously working monitor back together again only to find the same blown inverter symptoms as before.

    Crap! Ok so maybe I forgot to reconnect something - apart it went once again and sure enough I had left a small cable disconnected. I plugged it in put the monitor together again but no luck - the monitor shows an image for a split second and then goes black - although the power light stays green. I did notice that the board I purchased was using replacement parts that didn't look the same as the originals. I assumed the place I bought it from did that either because there is no difference in how they behave or perhaps because these were better thus preventing that problem from happening again.

    Ok so I assume I might get eaten alive for being such an ignoramus but I would like some very basic questions. You can insult me if you like but if so at least provide me with some answers.

    I'll add a bit of non related info and mention that I really know very little about electronics although I have a bit of a knack for fixing complicated things... For example, several years ago (like 12 to be precise) I had a Mac SE30 that died on me and I didn';t have the money to fix it. Reading everything I could find I narrowed my problem down to a fried chip known as the WOZ chip. It sat between the internal disk controller and the external drive connector. Not being apple certified at the time, getting a replacement part was impossible so I went to a place that is best decscribed as an electronics graveyard and bought 2 or 3 SE motherboards, desoldered the chip in question and Voila, my mac was working again! Other similar escapades include repairing cell phones and even my mom's t.v. when I was 12 yrs. old. Suffice it to say that I have pretty good intuition but what I don't have is theoretical or factual knowledge. I even lack, as my questions will show, the knowledge of what different components are called... I don't know how to use my multimeter and haven't found anything online to help me figure it out. What I have found is pretty dense and tells me little about the "how to" part.

    Ok so my questions -

    1. First - is it possible that by forgetting to connect that one set of wires, I managed to fry the parts again?

    2. The parts I replaced were as follows - a). small rectangular black with 3 points. On the top it is labelled 619 - on the card I purchased it had been replaced with a larger one labeled DK QA ( or OA) - The second type was also small, black, rectangular with two points and labelled 1.25A -(is that called a resistor, transistor, fuse? ) On the board I purchased it had been replaced with a green rectangular part labelled S - 2b). Are these other parts compatible? Better? Worse?

    3. If I were to use my multimeter to try and find out what happened how would I do it? I have a micronta auto range digital multimeter.

    I'm not content with simply having a knack and not knowing what the heck I'm doing anymore so I'd really like to learn enough to at least help me stop sounding like a total moron. I've noodled for many years and managed to be pretty succesful without knowing anything by simply looking at things and comparing to other things or detecting parts that look like they may be burned out. I've read whatever I can find but perhaps someone can suggest a web site or reading materials that can help me pick stuff up relatively quickly and without too much peripheral theory, I am interested in practical info to help me with projects I work on, or for instance fixing a couple dead music effects processors I have etc...

    Sorry for such a long post - I hope at least you got a good laugh out of my ignorance and I would very much appreciate any tips and help.

  2. atferrari

    AAC Fanatic!

    Jan 6, 2004
    Sure I am not the one to help you but could you post a couple of pictures.

    Macro pictures are easier with digital cameras nowadays. Perhaps you could too.
  3. the alchemist

    Thread Starter New Member

    Aug 7, 2005
    well the picture will probably be useless - I circled the 3 parts I replaced on the other one that works - Ok and I faked on in photoshop ....hope it helps...
  4. mozikluv

    AAC Fanatic!

    Jan 22, 2004


    have you check your soldered area for grounds? use a magnifyying glass. it's very easy to destroy a work just by having a poorly soldered leg connect to another part.

  5. freetek

    New Member

    Aug 10, 2005
    Hi there,

    The individual item pictured is a surface mount fuse with a 1.25 Ampere rating and you apparently replaced two of them.

    The third item I cannot see well enough to identify but is quite likely the culprit.
    Fuses will blow without any other reason than metal fatigue but this type can be damaged by being heated too long.
    Any ohmmeter or continuity tester will tell you if they are intact - they should act like a piece of wire until blown or open from heat.
    The unidentified item should have some kind of part number on it that might help unless it is a house number assigned by the display manufacturer.

    Be careful to be static-free if poking around with meter leads, there will be numerous circuits sensitive to static damage.

    Steve A.