Mechanic+high voltage circuit= please help!

Discussion in 'The Projects Forum' started by barefootstu, Nov 17, 2010.

  1. barefootstu

    Thread Starter New Member

    Nov 17, 2010
    8
    0
    I've recently started learning some basic electronics but I'm just starting out and haven't fully grasped all of the theories or component functions yet.

    My buddy runs an automotive carburetor repair shop where I am employed/apprenticing. We have an older industrial sized ultra sonic cleaner that recently quit working.
    New, this machine cost thousands of dollars and I am really really hoping to get it working again as it is very useful for cleaning delicate parts and we can't afford to replace it. Were using a smaller unit to get by, but it is no where near large enough to house the larger pieces we work on.
    So any help will be greatly appreciated!

    About the machine:
    Everything functions on the control panel, and all the switches show correct voltage on the volt meter, but the ultra sonic 'transducer' doesn't function because the power generator box keeps blowing fuses. (8amp 250volt glass tube type).
    I did a really bad thing and put a 15amp 250volt fuse in it and caused got a really good POP!.
    The bridge rectifier blew (as is evidenced by the black marks on the circuit board...).
    At this point I know I have to replace the blown bridge rectifier and possibly the transformer placed next to it on the circuit as it has some black marks on it aswell. :(

    [​IMG]
    Heres the box that is inside the machine. The dials are preset at the factory and you can't see this box without removing the side panel and exposing the relays and what not.

    [​IMG]
    Here is the beginning of the device: the top of the photo is the power cord (120 volt) inlet and the fuse holder. The wires run to a on/off switch and split off to the cooling fan (115 volt) and the board you see in the photo with the round doo hickey, some capacitor looking things and the big coil. the black and white leads continue out from this circuit to another circuit board mounted on a large heat sink.
    [​IMG]
    The circuit starts on the upper left where the black and white leads connect where the large disc type capacitor is.
    [​IMG]
    Here is my current problem area, imediatelly after the disc capacitor is the leads for the bridge rectifier (its mounted underneath the board against the heat sink) and the small transformer with eight pin leads. Only 1,4,5 and 8 are connected to the circuit. 1 being the top left, 4 the bottom left, 5 the top right and 8 the bottom right.
    So, how can I identify or test the transformer so I can verify that its not destroyed, or replace it so I know it works and can move on trouble shooting this circuit?
    The leads from the large coil packs on the right connect to the output connector that runs to the transducer unit.

    Also, can anyone explain to me what this circuit is doing and how to go about finding out why this device keeps blowing fuses?

    Finally, the third and final circuit of the device that has pin connectors running from it to the second board and to the two dials on the front of the unit is pictured below:
    [​IMG]
    Hopefully my post makes some sort of sense, as I am lost in a sea of confusion! But, I'm really hoping to learn from this project and gain a working knowledge of electronics and start building and tinkering with bigger and better projects.
    I will post more photos upon request and any other info I can give!
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,761
    924
    can you get another picture of that area near BR2?

    It looks like smoke tracks on the board below the TO220 device(voltage reg?) with the Heat sink attached. I would look there first.
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    That is not a disk capacitor, but a surge arrester. That could be shorted. See what your meter says about it.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Ultrasonic Power Corporations' website is here: http://www.upcorp.com/ultrasonic.html

    They would be your best bet for obtaining schematics, a service manual, or provide servicing for your unit.

    Looking at the label, your unit is rated for 500 Watts power. An 8A fuse with 120v in would take 960 Watts of power to blow, or nearly twice the units' rated power. That 15A fuse really was a bad idea.

    In the 4th image down, do you see the integrated circuit with "SG3524N" (I think, can't tell for certain if the last digit is a 4) on it, in between the two smaller caps and the one larger capacitor? That's a regulating pulse width modulator, used in switching power supplies. Q6, just above the large capacitor, is a MOSFET or transistor that switches power to the small transformer, the black rectangular object to the left of Q6. There's another MOSFET/transistor just like it below the large cap that's also driven by the SG3524.

    From the date codes on some of the parts, I'm going to guess that the supply was manufactured around late 1999 to early 2000. If the machine sits idle for long periods of time, it could be that the electrolytic caps lost their dielectric, and started shorting out - but those don't exhibit any sign of bulging at the tops, which is an indication of overheating due to low internal resistance.

    Your machine might be a victim of a power surge or spike. Such transients can cause semiconductors to short out or open up.

    What are the two items below C10 & C11? I'm suspecting that they are low voltage regulators. If you look to the right of the lower item (with the heat sink on it just above the transformer), you will see a small round object labeled BR2, which is another bridge rectifier.

    Does the transformer smell burnt? If so, you'll most likely need a replacement.

    Have you removed BR1 yet? If not, do so - carefully. Large bridge rectifiers can be a pain in the neck to remove without damaging the board. If you overheat the board causing the traces to lift, it's ruined.

    After you get BR1 out, you might try re-assembling it, and replacing the fuse (with an 8A or lower, 250v rated one), to see if the fuse still blows. If it doesn't blow, measure the AC voltage on BR1's AC inputs and see what you get.

    The large round orange thing below BR1 is most likely a MOV, or Metal Oxide Varistor. It's job is to "clamp" high voltage transients to prevent damage to the rest of the circuit. You might get an idea of what the transformers' output voltage should be by reading the part numbers from the MOV; it'll likely be rated 10% to 30% higher than the transformer's normal peak output.
     
  5. barefootstu

    Thread Starter New Member

    Nov 17, 2010
    8
    0
    Wow, thanks for the great feedback guys!
    I'm really glad I found this board now :)

    Ok, heres some more pics to help answer all of your questions.

    [​IMG]
    Heres a close up of BR2.

    [​IMG]
    Heres the bottom side of the board where BR1 was mounted. You can see the smoke marks where it exploded. I don't see any other marks on the board, just some dusty areas.

    The large orange disc is a MOV SgtWookie.
    When I put one of the leads of my volt meter on each leg of the MOV I get no continuity.
    It's model number is 130L20 and googling the part # its rated at 130 volts.
    http://www.datasheetarchive.com/130L20-datasheet.html

    I removed the BR1 without much trouble, leaving the contacts and traces unharmed :D
    I'll pick up some more fuses tomorrow and do what you suggested.

    The transformer doesn't smell burnt, it just has some black marks underneath the plastic covering the first coil as seen in the photo below:
    [​IMG]

    Is there any way to tell if it is functioning now that I have removed from the board?
    Are you saying that it is possible that I could replace it with another unit that is rated 10-20% less than the MOV voltage and not necessarily the exact same part?

    The two items below c10 and c11 are MC7915CT and LM2940CT-15 and googling says that they are regulators like you thought.

    You are right, this machine is about ten years old according to my friend who bought it originally. I would say he bought it in 2000. As far as I know, it has seen regular use since then.


    :eek:
    Man I had no idea what i was doing putting the 15A fuse in there. Lesson learned!

    Thanks again for helping me out!
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    It's just about impossible to take good photos of circuit boards indoors unless you have professional lighting equipment. Flash units just don't cut the mustard; they produce images with harsh glare and very high contrast, which makes it very difficult to divine useful information from them.

    About the best lighting you can get is outside on a cloudy day; the lighting is very bright, even, and shadow-less.

    If your flash unit can be rotated, then you can "bounce" the light off of a white sheet, pillowcase, or white cardboard/poster board to produce reasonably even lighting. Direct flash will give poor results.

    It might be that the BR1 bridge rectifier being shorted is/was the main problem. However, it could also be those four devices on the bottom of the board, which could very well be thristors, such as SCRs or TRIACs. Is there a screw/bolt going through their tabs that you can remove so the part number(s) can be read?

    I tried Googling the HP 3100 ICs and some datasheet search engines, but all I came up with was printers; no datasheets.
     
  7. barefootstu

    Thread Starter New Member

    Nov 17, 2010
    8
    0
    Yeah, I searched for the HP3100 ic aswell and couldn't find anything worth noting, just a lot of dead ends.

    Ok,
    the four devices on the bottom of the board are APT 4016BVR Mofset's.
    http://www.datasheetcatalog.org/datasheet/AdvancedPowerTechnology/mXttwwy.pdf

    I removed one from the board without much trouble.

    I'm thinking I'll order all the suspect parts and replace them on the board, then see what happens?
    I figure most these components are cheap enough to warrant throwing parts at the board to try and cure the problem :D

    Problem is the APT 4016 is out of stock at digikey and mouser.
    Digikey gave me these close, but not direct replacements:
    IXFH32N50 , STW30NM50N and STW26NM50

    Thanks!
    -Stu
     
  8. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    MOSFETs are pretty robust while in their circuits, but are damaged very easily by ESD (electrostatic discharge) when out of the circuit. If the voltage on the gate referenced to the source terminal exceeds +/-20v, they are instantly destroyed. Static is a big problem during the winter. If you don't have an anti-static mat and wrist strap, you'd better get them; they're a lot cheaper to buy up-front rather than destroying lots of parts.

    If you can feel a tingle when you touch something metal, that's about 3kv of static charge.
    If you can see a spark and hear a snap when you touch something metal, that's about 10kv.
    Remember, MOSFETs will die with as little as 21v static discharge. You'd never feel it.

    Have a look at this MOSFET: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=IXFH42N50P2-ND
    Better-than specifications from the ones that are installed; Vdss is higher (500v vs 400v), total gate charge is lower, and Rds(on) is lower, in the same TO-247 package.
     
  9. barefootstu

    Thread Starter New Member

    Nov 17, 2010
    8
    0
    Thanks SgtWookie,

    I don't see any reason those mofset's wont work :)
    I'm gonna grab 8 of them.

    What about this component?
    Is this a capacitor?
    [​IMG]
    [​IMG]
    I cant find any info on it with the part number printed on it.
    I hit it with the soldering iron and burned through the white coating so I wanted to replace this item with a new one as well.

    I really appreciate the help, and I'm learning a ton from this experience.
    I'm really hoping to see this unit function again!
     
  10. barefootstu

    Thread Starter New Member

    Nov 17, 2010
    8
    0
    ok,
    so i talked to digi-key tech help and they sent me this: http://orangedrop.sbelectronics.com...ay i could seal it up again? Thanks again!
     
  11. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Electronic Goldmine has these:
    http://www.goldmine-elec-products.com/prodinfo.asp?number=G2304
    400v, 4.7uF. They'd probably do the trick; a bit over the original specification, but that's usually not as bad as under spec. E.G. has a $10 minimum order, so you can poke around and look at other stuff, or buy 4 of these caps.

    I don't think you'll get away with putting some sealer over the gash; looks like you nicked into the caps' plates, so it's likely shorted - or just might be shorted once power is applied.
     
  12. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
  13. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,761
    924
  14. barefootstu

    Thread Starter New Member

    Nov 17, 2010
    8
    0
    Thanks sgtwookie and kermit2 for the info.

    I got 2 capacitors from newark and ordered everything else I needed from digi-key so next week I should be able to reassemble everything and see what happens!
     
  15. barefootstu

    Thread Starter New Member

    Nov 17, 2010
    8
    0
    Hey guys!
    its been a really long time.... but, I soldered all the new components in and reassembled everything and Success! for about ten minutes.
    Then the fuse started popping again. :mad::confused:

    So... I'm not sure what to think, but what is the purpose of the big coil and capacitors that are before the circuit board?
    [​IMG]
    http://lh6.ggpht.com/_RIbmMUoIPgE/TNy3Pyx6CmI/AAAAAAAACwg/pMbj4gbZz4A/s800/20101111203850.jpg

    The power from the outlet comes into this cluster at the bottom of the photo via the on/off switch. at the top the black and white wires proceed to the circuit board where I replaced the voltage regulator, bridge rectifier, two large capacitors and the four mofsets.

    Any thoughts?

    Thank you very much for any help!
    -Stu
     
  16. wayneh

    Expert

    Sep 9, 2010
    12,083
    3,021
    It's a very good sign that you got 10 minutes on it before the fuse blew. I think you're at least back to where you started.

    Did anything get hot? It's a simple and telltale clue, but of course you need to stay safe when feeling around. Safety first.

    Another tool could be a small hall-effect current sensor to tell you where the current is.

    Have you ruled out the transducer? IMHO, that's a prime suspect. Can you tell if it was operating before the fuse blew?

    And it's been suggested before; call the company and ask them why the fuse would be blowing.
     
  17. barefootstu

    Thread Starter New Member

    Nov 17, 2010
    8
    0
    Thanks Wayneh.
    I don't think its the transducer because I have it disconnected, and unfortunately the fuse still blows.

    With the unit on the bench and the transducer disconnected the fuse blows immediately.

    When it was working, I tested it twice on the bench for a minute with the transducer connected and it worked fine with the transducer buzzing away like normal, so I reassembled everything into the machine and we filled it up with fluid and tested it by letting it run. It ran a good 10 minutes before the fuse blew.

    Now, like I say, the fuse blows immediately, even with unit out of the machine on the bench and the transducer disconnected. as soon as I turn on the switch, POOF!

    Ill be calling the company tomorrow and I'll let you guys know what they say.

    Thanks!
    -Stu
     
  18. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    NEVER try to seal up a bad cap, if it blew it's because the insulation has broken down.

    Take an ohmmeter and test everything you can both passive and active first, replace any that that needs replacing then go from there.

    That's a 0.4 uF @ 400V cap, specifically designed to take mains AC voltage and they are different from regular caps. Toss it, get something at least 0.22 uF rated as an AC suppression cap such as http://www.mouser.com/ProductDetail...EpiMZZMvQAn3cSZoTr%2bBQwT%2bBXvKipn3YhYEk5Pg=

    Rated for 630V or 253V AC on mains.

    Worst case the manufacturer may provide a whole new board for less than you think, just write them.

    NEVER replace an AC suppression cap with a plain one, with any luck that thing blew and saved the rest of your active components but I'd darn sure check everything else out. I realize there's some discrepancies regarding cap markings but I'm pretty darn sure I'm correct on this. A 406 would equate to a 4 uF and there's no way they'd use that value across AC mains and even 0.4 uF is too large as far as I'm concerned. 0.22 - 0.39 would be quite sufficient. I rarely go over 0.22 uF on any line filters but I ALWAYS use caps that are rated for line suppression, the higher the voltage the better thus my recommendation.

    Figure out the reactance, subsequent current and you'll see what I mean.
     
    Last edited: Feb 2, 2011
Loading...