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50" Mitsubishi Rear Projection Help

Discussion in 'Electronic Repair' started by DogP, Oct 26, 2005.

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  1. DogP

    DogP Guest

    Hi,

    I've got a dead 50" Mitsubishi Rear Projection that I'm trying to get
    working again. I'm familiar with rear projection monitors, but by no
    means an expert... I've fixed 4 so far, but none have been anything
    very complicated (one was a bad PIP card, another was just adjusted
    wrong, one had a cable loose, and the last needed the tubes
    rejuvenated). I'm very familiar with standard CRT monitors though, and
    good with electronics, and I know what I can and can't touch ;) .

    Anyway, this one is on a Wave Runner arcade game (like:
    http://www.klov.com/game_detail.php?letter=&game_id=10414 ), and when I
    turn it on, I hear it click, it sounds like there's HV, then shuts down
    after about a second. It's missing the back door, so I don't know what
    the model number is... the only numbers I can find are PB7539 (on the
    Power Supply) and PB7538 (on the HV/Deflection board). It says it was
    manufactured in 1998 and it's a medium resolution monitor only (no TV
    tuner). Is there any hidden place that a model number would be? Or if
    I took a pic of the boards, would anyone here be able to identify what
    the model is?

    I'm just looking for any ideas on what I can check. I've read about a
    bunch of problems with Mitsubishi monitors, mostly bad solder joints,
    bad capacitors, and blown HOT, but they're always specific about which
    capacitor is bad, and since this model is different, I don't know which
    capacitors to check (C914 is the one I always hear about, but I don't
    have a C914). I don't think the HOT is bad, since that should have
    blown a fuse, and there are no blown fuses.

    I've already pulled the power board and inspected/resoldered the large
    pins, and that didn't help any... I've tried turning down the screen
    controls (I've had one that would shut down in the past if those were
    too high). I'm planning on resoldering the points on the flyback next,
    but I'd like some tips on a more systematic approach to troubleshooting
    this. What would cause the shutdown? I know on CRT monitors, a high
    B+ would cause it, but where do I measure the B+ at on these monitors?

    I'd appreciate any help or tips anyone can give me. Thanks,

    Pat
     
  2. DogP

    DogP Guest

    Anyone have any ideas? I was just looking at it some more, it looks
    like maybe the B+ is low. I found a small pin on the HV/Deflection
    board marked +B, and when I turn it on, it goes up to about 60V, then
    drops when it shuts down (after about 2 seconds). I tested all of the
    voltage pins I could find on the power board and they all tested good.

    What I guess I'm wondering is if I'm chasing the right problem with the
    B+? Or does it normally take a while for it to get up to the correct
    voltage, and the monitor is just shutting down too quickly? And would
    a B+ being too low actually cause it to shut down (I know too high
    does, I've never had too low of a B+ cause a shut down).

    What is the B+ typically on one of these montors? And I assume it
    comes directly from the Power board and not derived later on the
    HV/Deflection board?

    Oh, if this helps any, here's some pics of the monitor:
    http://dogp.home.comcast.net/waverunner/DSCF0671.JPG , and
    http://dogp.home.comcast.net/waverunner/DSCF0672.JPG .

    Thanks,

    Pat
     
  3. DogP

    DogP Guest

    Alright, I'm making some progress... I think. I believe that the HOT
    is blown, when I tested across the Base and Emitter, it was nearly
    shorted, and was the same way after I pulled it (out of circuit). I
    don't have another exactly like it (the original is a 2SC5143), but I
    did have one that was very close in specs to it (and same specs as ones
    that were crossed to my part), so I popped it in, and it appears to
    have blown the same way.

    What would blow these things like that? I guess my part could have
    been too weak, but it didn't act any differently, so I believe that it
    blew almost instantly, meaning something is really messed up. I'm
    going to be ordering a few of the correct parts soon, but what can I do
    to keep these from blowing while I figure out what's blowing them?
    I've heard about putting a light bulb in series, should I try that? Or
    I read on one of the pages to add a 33ohm 1/4 watt resistor in parallel
    with the base/emitter... is this a common modification? I know on X-Y
    monitors, unhooking the yoke takes the load off the deflection
    transistors, would that work the same here? Oh, btw, I did test the
    yokes and they all seem to test fine.

    Does anyone have any ideas? Am I in the wrong place? ;-) Thanks,

    Pat
     
  4. Guest

    I am not going to be much help here but I think I have the same game
    and I just gutted a similiar game. What about the flyback? if that
    thing goes wacko isn't it going to directly affect the HOT? I just got
    a Sencore HA2500 which is made to test HOTs. If it is pretty tough to
    test the HOT because of the problems you mention. This thing is
    suppose to help directly with this issue. I just got it so I haven't
    even used it yet.
    Russ
     
  5. DogP

    DogP Guest

    Russ,

    Thanks for the reply (at least I know SOMEONE is reading this ;-) ). I
    don't think the flyback is bad since when I turn it on, I do get HV for
    the two seconds that it turns on, but I could be wrong, which is why
    I'm posting here. But it doesn't look like I'll be using an HA2500 to
    test it any time soon ($2900!!! O_O). I'm used to smaller monitors
    where when the flyback or HOT blows, it immediately blows a fuse (or in
    the case of a G07, the flyback explodes :p). That's why the blown HOT
    threw me off in the first place.

    Do your monitor boards look like the pictures that I posted? If so, do
    you have the model number of the monitor (it should be on a sticker on
    the back door, which is usually a pegboard sort of material). If I had
    the model number, I might be able to get a schematic or service manual
    from Mitsubishi.

    As always, any replies are appreciated :). Thanks!

    Pat
     
  6. DogP

    DogP Guest

    No rear projection techs out there? I ordered some 2SC5143's and got
    them yesterday... I pulled the whole chassis out and noticed that
    there's another 2SC5143, and it was blown too! It looks like one goes
    to the flyback, one goes to the yokes. So, I pulled both and replaced
    just one, hooked it up with a light bulb in series with the main power,
    and it still blew :-( . I only bought 4 replacments, thinking I only
    needed 1 >_<.

    Any idea what I could check to see what's causing these to blow? I've
    checked all of the large transistors and diodes that I could find, and
    made sure that none of the large capacitors were shorted. I really
    don't know what else I can check, or what the next step in
    troubleshooting this is.

    Thanks,
    Pat
     

  7. There are lots of us out here. Responses have more to do with whether
    someone has much to contribute than whether we are here. You might get more
    help if you post the model number in the subject line. Some of us don't
    catch every thread from the start and I personally won't go digging up the
    previous posts to see if you had the relevant info. Some Mitsubishi sets
    have been known to have repeated HOT failures due to a bad coil. Not
    knowing what set or chassis you have makes it impossible to search for
    specific info.

    In general, repeat failures in outputs in RPTV is not different from direct
    view sets. Problems in the base circuit such as intermittent drive or
    impedance problems or load problems such as a bad flyback or bad cap are
    most likely. Typically with Mitsubishis the problems have been drive
    related as opposed to load.

    Apparently this is a set with separate HV and H outputs. If both are
    blowing it seems pretty obvious to be looking to the drive circuits or the
    power supply. Since the Mits sets are pretty unlikely to operate with
    excessive B+, I'd be leaning to a h-drive problem.

    Leonard
     
  8. Pat,

    What's the model #?

    --
    ==========================
    Jeff Stielau
    Shoreline Electronics Repair
    344 East Main Street
    Clinton,CT 06413
    860-399-1861
    860-664-3535 (fax)

    ========================
     
  9. DogP

    DogP Guest

    Sorry guys, this is in a Wave Runner arcade game, and it's missing the
    back panel where the model number should be :-( . I have a Top Skater
    with a similar monitor (model P502SG), but it's definately not the same
    chassis. I have pics of the chassis here:
    http://dogp.home.comcast.net/waverunner/DSCF0671.JPG and
    http://dogp.home.comcast.net/waverunner/DSCF0672.JPG .

    The only numbers I can find are PB7539 (on the
    Power Supply) and PB7538 (on the HV/Deflection board). It says it was
    manufactured in 1998 and it's a medium resolution (24KHz RGB) monitor
    only (no TV
    tuner). If there's any place I can buy a service manual or schematic,
    that'd be great, but I'd assume that I need the model of the actual
    monitor, not just those boards.

    I did check the voltages at all of the test points (that I saw) on the
    power supply and they all tested good, and with the shorted
    transistors, the B+ would climb up to only about 60V. With the shorted
    transistors, I did hear HV for the couple of seconds that it stayed on
    though, so I think that the flyback is good (and I don't see any
    obvious signs of damage).

    So you would suspect something in the H-Drive circuit? What is a
    typical failure with something like this? Is there usually an IC that
    goes bad, a transformer that opens/shorts, a resistor that opens, a
    single transistor that shorts, or any of the above / something else?
    Are they usually large components that cause it, or is there a small
    signal section that could cause it? As far as I know, I've tested all
    large transistors, resistors, and diodes. I haven't checked every
    inductor or transformer yet.

    Should I just trace back between the two large transistors and see what
    is common with the two and suspect those components? Would that be a
    reasonable way of troubleshooting this? Or do you have any other
    suggestions, or diagrams of a circuit similar to this so I can get an
    idea of what to expect?

    Thanks guys, I really do appreciate the help.

    Pat
     
  10. I don't even recognize that chassis from any of the consumer models!

    Searching my repair database for the 2SC failures you mention shows nada!

    You may want to try posting these images on the rec.games.video.arcade
    newsgroup to see if anyone has the service info or model cross reference.

    --
    ==========================
    Jeff Stielau
    Shoreline Electronics Repair
    344 East Main Street
    Clinton,CT 06413
    860-399-1861
    860-664-3535 (fax)

    ========================
     
  11. kip

    kip Guest

    Its a commercial unit...Good Luck

    kip
     
  12. DogP

    DogP Guest

    Jeff,

    Thanks for checking your database... I'll post a message on RGVAC about
    it, but every time anyone posts about rear projections in video game
    groups, they seem to always send them over here :-( . I know that this
    is a strange beast, so I figured I'd only get generic help, and the
    tips Leonard gave me should help since I now know what section to
    suspect first. Like I said, I don't have a lot of experience
    troubleshooting rear projection stuff like I do standard RGB CRT
    monitors, but I can usually figure this kinda stuff out, so if anyone
    has any other tips, they would be greatly appreciated. Thanks,

    Pat
     
  13. Guest

    Neither of the 2SC's you tested were bad. Standard HOT type of
    transistors which those are have around a 30 ohm resistor internal
    between the base and emitter and a damper diode across the collector
    and emitter.

    As for any service manual, given the limited type of production those
    were in, you really need to contact the manufacture of the unit.

    Try posting the exact symptoms the unit gives.
     
  14. DogP

    DogP Guest

    Wow! I think you're right! These are the kind of tips I was looking
    for! I just tested one of my new ones and it tested 30 ohms across the
    base and emitter. I was sure that I checked that before, but I must
    not have. I wondered why a blown HOT wasn't blowing any fuses, but I
    figured they had some sort of protection for that on these newer
    models.

    The symptoms of the unit:

    Turn it on, makes a couple of clicks, has HV for about a second,
    nothing shows up on the screen, then the monitor turns itself off.
    Won't turn immediately back on, I have to wait about 10 seconds.

    Checking the B+, it looks like it only ever gets up to about 60V (I
    manually set the range on my meter trying to get a quicker reading, but
    I guess it's possible that it's just not fast enough too). When it
    shuts down, it seems to shut the whole thing down (I know at least +5V
    shuts off to the Video/Conv board).

    So far, I've tested most/all of the big caps, resistors, and
    transistors on the Def/HV board, and I've checked the yokes, and all of
    the voltage test points that I could find on the power supply. As far
    as all that goes, everything has tested good.

    I'm not really sure what else to describe. Do you have any ideas as to
    what would cause those symptoms? Should I be suspecting the power
    supply more than the Def/HV board? Or should I suspect the Video/Conv
    board maybe shutting it down because it doesn't think there's a signal
    (even though there is)? Is there usually a shutdown override somewhere
    to see if the B+ ever stabilizes to the correct value, and whether
    anything is displayed if it would just stay on? I assume finding the
    relay that is kicking off and manually jumpering it is a bad idea?

    Once again, thanks for the help, this is definately progress!

    Pat
     
  15. Guest

    If you can turn it back on without unplugging it, that pretty much
    rules out a protect shutdown situation.

    Most RGB monitors use a main B+ that only runs at 60V, not the usual
    130V as a typical tv set.
    Use an O'scope to confirm the actual peak voltage you are getting.

    Most RGB monitors will auto-shutdown if they are not getting a proper
    signal that includes the H-sync and V-sync.
    Probably where you need to start troubleshooting.

    With the board layout of the chassis, you really need to try and buy a
    service manual for it to know what to look at.
    There just is not enough information you are going to be able to find
    without it.
     
  16. DogP

    DogP Guest

    Oh, sorry, I am plugging and unplugging it to turn it on and off.
    There is no manual on/off switch (that I see at least), and the remote
    has never worked (the batteries are good, I've never tested the output
    of the remote though). I have had it where a rear projection monitor
    would shut down if the flyback controls were up too high, but I've
    tried turning them all the way down and it doesn't seem to help any.

    That's good to know about the B+ voltage though, and I know the game
    PCB is outputting a good signal because I tested it on my test monitor,
    so I'll try to somehow get a manual, and make sure all of the
    connections are correct to the inputs on the front of the monitor.

    There are a lot of well labeled test points on the chassis though, so
    in the mean time, I'll hook it all back up and at least try probing a
    bunch of them checking for anything abnormal, and lug my scope up to
    the garage to check the proper B+ and any other waveforms.

    Thanks a lot for the help so far, there has been a LOT of stuff cleared
    up today, and I feel like I'm at least starting to go in the right
    direction.

    Pat
     
  17. Bill Jr

    Bill Jr Guest

    Pat,

    If that's the model I'm thinking it is you may be wasting your time looking
    at the wrong board.
    Check all the discrete components on the convergence output board.
    A couple of discrete mosfet transistors (not the outputs) like to burn up
    causing this symptom.

    I may be off base here but then again it doesn't hurt to check.

    Good Luck,
    Bill Jr
     
  18. DogP

    DogP Guest

    Wow, Thanks! Actually, I was working on this late last night and the
    more I looked at it, the more it seemed that the whole power supply was
    shutting down... so I started unhooking connectors from the power
    supply, and when I unhooked the power to the convergence board and it
    fired up! Of course the convergence is WAY off, but that's a good
    sign. I tried testing some of the components, but I was really tired,
    so I didn't get a chance to dig deep into it.

    Do you know which mosfets typically burn up? And do they usually short
    or open? I quickly checked all of the large transistors, and I didn't
    see any shorted, but I'll definately go back and check again now that
    you say this is common. It's the large ones that burn up, not any of
    those 50 or so small ones, correct?

    Thanks again, you guys have been a huge help.

    Pat
     
  19. DogP

    DogP Guest

    Okay, I've gotten the monitor to stay up with the convergence board
    hooked up now... it ended up being an opened resistor at the -15V line
    on the convergence board. It's a 2 ohm appears to be a 1W resistor,
    which I didn't have, but I had lots of other low value resistors, which
    I hooked up to get within the 5% allowed of the original resistor.

    Anyway, now it comes up, but the convergence is WAY off. Of course
    this has no manual pot adjustments, so I guess I have to adjust it all
    through the menu. I do have the remote, but it doesn't seem to be
    allowing me to change any of the convergence manually. It'll let me
    change size and position, but when I follow the instructions for
    adjusting convergence that I found online, it just sits there doing
    nothing.

    You can see a pic of how bad it is here:
    http://dogp.home.comcast.net/waverunner/DSCF0741.JPG

    BTW, sorry, I assumed that this was a Mitsubishi, because the outside
    looked exactly like my other Mitsubishi arcade monitors, but looking at
    the remote, and the sticker on the EPROM, this is actually a Toshiba.

    Does anyone know why when I hit the adjust buttons, nothing happens?
    Would it be something with the new resistor I put in, or would
    something else be blown, or is there some sort of protect switch or
    something?

    Should I make a new topic on adjusting convergence on Toshiba rear
    projections? Ugh, even with how much of a pain it is adjusting the
    convergence with the thousand pots on a regular old style rear
    projection, I'd rather do that than go through all of the trouble I've
    gone through with this "automatic" convergence stuff :-(.

    Thanks again,

    Pat
     
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