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Replace power MOSFET in subwoofer plate amp, Sledge STA-1000D

Discussion in 'Troubleshooting and Repair' started by Ninian Fife McAfee, Nov 3, 2017.

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  1. Ninian Fife McAfee

    Ninian Fife McAfee

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    Oct 20, 2017
    Hello -
    This is my first post in the forum.
    I have a Sledge STA-1000D subwoofer plate amp (1000W mono, Class D), used in an SVS PB13 Ultra subwoofer, that failed with both power MOSFETs on the line side of the power supply blown apart (cracked cases), I assume from a surge. (No, I didn't have the volume cranked to eleven.) The fuse also blew.

    The circuit board was made by Formosa Audio, model FMA-990501 Power Supply & Amp, Ver. 4.0. I did contact them, but I doubt that I will get a reply.
    The failed parts are N-type Enhancement-mode power MOSFETs, marked Q101 & Q102 on the circuit board, (D, G, & S are printed on the board next to each pin) and with "SMS1532" and "0932" printed on the transistors - see attached pictures.
    They are TO-247 size transistors.
    I searched for a replacement for "SMS1532", but came up empty.
    I also searched for "1532 MOSFET", and got a hit but it's the wrong part.
    The two transistors are wired together in a "push-pull" configuration (actually "push-push", if I understand what I read correctly); attached is a very simplified circuit diagram (the battery symbol is used in place of the output of the bridge rectifier and a bank of electrolytic capacitors). The gates are both driven by the same chip, but not from the same pin.

    If I am unable to find a datasheet, please help me choose a suitable replacement based on the circuit design and output power.
    Also, any advice on what else to check for failure on the board is appreciated. I already checked all the diodes on the secondary side of the transformer, and the other transistors for shorts. The bridge rectifier on the primary side shows signs of stress on one of its legs, so I will replace it (that part, a GBJ 2506 was easy to find a replacement for). The two failed MOSFETs have protection circuits consisting of two chip resistors and a zener diode on their gates; at least one of those resistors burnt out and will also be replaced.

    Thank you in advance for any and all help.

    GEDC0918-50.jpg
    GEDC0922-50.jpg
    GEDC0924-50.jpg
    schemeit-project.jpg
     
    Last edited: Nov 3, 2017
  2. Ninian Fife McAfee

    Ninian Fife McAfee

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    Oct 20, 2017
  3. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Many MOSFET switching devices have HUGE ratings for little price - a 600V device with 30A rating in a TO247 package shouldn't be difficult to find.... or something like it.

    Sites like this:

    http://category.alldatasheet.com/index.jsp?sSearchword=MOSFET 30A TO247

    have search facilities to allow you to enter the various parameters needed.

    Such volts/amps ratings will likely well exceed those required by the original and given they are used as switching devices their other parameters can (usually) be ignored!

    But before you chose any replacement, have you found out why the originals blew up?
     
  4. Ninian Fife McAfee

    Ninian Fife McAfee

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    0
    Oct 20, 2017
    Thank you for the reply!

    I am hoping that all I have to do is choose a TO247 MOSFET with sufficiently large voltage and current ratings.
    Am I correct that given the circuit design, these are ordinary N-type Enhancement-mode power MOSFETs ????
    Is there anything else that I must take into consideration when choosing replacements, if I can't get the datasheet for the originals?
    Since it's a Class D amp / switching power supply, the switching frequency should be only a few hundred KHz, so no need for a high-frequency rating, correct??
    Also, it's being fed rectified DC straight from the 120VAC mains, as I indicated above, so no more than 180VDC supply, so a 600V rating for the replacement parts is enough, like you mentioned, correct?
    And the amp has a nominal 1000W power rating, and 1000W / 120VAC = 8.333A from the wall, not taking into account that the Power Factor won't be 1, but in any case replacements rated for 30A like you said, or more, should be big enough, right?
    I just hope that the driver IC (U101, 8-pin DIP SMD in the last photo above) is undamaged. Anyone have an idea what this chip is? A simple two-phase oscillator maybe?

    It certainly looks to me like a surge from the power line. The diode in the bridge rectifier that conducts forward from the Hot wire to the +180V supply was weakened (it shows a slightly lower forward voltage than the other three diodes) so it will be replaced, plus those two MOSFETs completed the circuit for the surge to follow to ground. The unit was actually turned OFF when it happened, and luckily it doesn't appear that any of the surge voltage made its way to the secondary. There is an MOV across the 120VAC mains input that looks untouched, so apparently it stood by idly and let the surge pass unimpeded, so it too will be replaced, then punished most severely for dereliction of duty.
    None of the six capacitors on the line side of the supply show any signs of damage, like bulging tops or leakage.
    The two MOSFETs were mounted to the heatsink, but insulated with "rubber hoods", which certainly didn't help them to dissipate any heat; I am thinking of replacing that with a more conventional insulator, provided the breakdown voltage is high enough. Is that a good idea?
     
    Last edited: Nov 4, 2017
  5. Ninian Fife McAfee

    Ninian Fife McAfee

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    Oct 20, 2017
    BTW, the unhelpful answer to the similar problem posted at the other site, was to use a 14-pin DIP TTL quad AND gate, based on the fact that the part numbers are similar. :eek:
     
  6. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    Is this your subwoofer ?
    If so,
    look at the last page find costumer support info there,try them.
     
    Last edited: Nov 4, 2017
  7. 73's de Edd

    73's de Edd

    2,805
    1,176
    Aug 21, 2015
    Sir Ninian Fife McAfee . . . . . .

    MY OBSERVATIONS and SUSPICIONS . . . .
    With just a quick rundown of those markups.

    The left YELLOW boxed area . . . with the BLUE PCB within . . . is the units class D amps small signal portion which feeds via the ribbon cable, to the input of the bootstrapped power amplifier, a pair of power transistors at the smaller YELLOW and PINK rectangles to then output to the larger PINK and YELLOW where those L and C components filter all of the digital artifacts and other crap out . . . to then re create a concurring power analog audio signal again.
    I suspect the two LIME GREEN connectors to be an alternative audio power output, such as is being the large RED and WHITE wire connectors routing into the cabinet.

    Now we come to the vertical FUCSIA division line of the power supply section.
    Far right is the ORANGE AC line input that passes down to the mechanical power relay and then to the right and then moves up thru noise cancelling line inductors, X caps and Y caps and eventually goes into the LIGHT BLUE FWB rectifier unit and it outputs its pulsating DC over to the HUGE main capacitor bank within the RED rectangle. It feeds into the primary center tap lead of the main power transformer and two transformer connections are routed to go over to each of the unidentified POWER switching semiconductors.
    They receive their drive from the BROWN rectangle area with the electronics mainly located on the bottom side of the board with some corrective feed back coming from the two black isolators seen on the top side of the board.
    Also I am expecting the small transformer shown up there, with U103 and its companion driver FET on the transformers primary winding, to be providing for the constantly on LV standby supply.

    With main B+ supply present and a set of alternatively driven main POWER FETs, expect voltage out of the secondary of the main power transformer to then be rectified and feed out two polarities of voltages . . .+ - . . . to store within the BLUE rectangle capacitor sets.
    Expecting somewhat less than the 100 VDC max voltage spec on the caps and a whole bunch of amps, in order to be able to achieve this units fierce wattage specs.
    I certainly do not recognize the casing aspects but expect the LV secondary diode sets to be within the WHITE rectangle area. (Although they are resembling porcelain cased power resistors to me )

    Lastly . . . . . inspect the photos LIGHT BLUE rectangular area vewy-VEWY-VEWY carefully . . . Now don't these OEM transistors shown, seem to be METAL heat sink tabbed ? . . . possibly only using a thin mica insulator and thin film of heat sink compound.
    And its not being your insulated series of transistor casing being shown to us . . . . . unless its metal tab is partially exposed on the hidden side and is being mounted against the heat sink proper.



    You say . . .

    I just hope that the driver IC (U101, 8-pin DIP SMD in the last photo above) is undamaged. Anyone have an idea what this chip is?


    BTW, the unhelpful answer to the similar problem posted at the other site, was to use a 14-pin DIP TTL quad AND gate, based on the fact that the part numbers are similar.

    Our response could be expected only be less . . . since you didn't entrust us enough to even give US that number


    BTW, the unhelpful answer to the similar problem posted at the other site, was to use a 14-pin DIP TTL quad AND gate, based on the fact that the part numbers are similar.

    No WAAAAAAAAAAAY


    If this is solely a driver (s) its most likely to be akin to the units below . . . .

    http://www.ti.com/lit/ds/symlink/ucc27424.pdf

    http://www.microchip.com/ParamChart...hID=9010&mid=11&lang=en&pageId=79


    HEAVEEEEE CONSIDERATION . . . . is that U101 chip will be the Power controller AND driver combined.
    Note the two optical couplers within my BROWN rectangle, do they eventually route over to this U101 chip, if so I suspect controller and driver are both within this 8 pin U101 chip.

    GIVE US 'DA NUMBER ON IT.

    We pwomise that we will not tell you that its being a SIXTEEN PIN equivalent piece of TTL crap from the '70's.

    ASIDE:
    Indeed . . . .your units "flat plate" is being offered in bulk six packs to be shipped to California . . . . stuffed into a Sledge and being resold.

    https://translate.google.com/transl...CN&tl=en&u=http://formosaaudio.en.b2b168.com/

    Lastly . . . . . . Those shore are some impressive specs on the low end . . . . of course my old ears couldn't hear it . . . . but I 'soitanly could feel it compressing my chest and be watcing the nails wiggling out of the sheetrock.



    REFERENCING PHOTO . . . . marked up . . . .

    [​IMG]



    73's de Edd
     
    Last edited by a moderator: Nov 9, 2017
  8. Ninian Fife McAfee

    Ninian Fife McAfee

    8
    0
    Oct 20, 2017
    Hello -

    Yes, as I indicated at the beginning of my first post, it is the amp from an SVS PB13 Ultra subwoofer.
    Yes, customer support would be more than happy to sell me a whole new STA-1000D module for a mere $600 U.S.:

    https://www.svsound.com/products/replacement-amp-sledge-sta-1000d-pb13-ultra

    I would like to think that I can fix mine for a whole lot less than that, especially if I get some help here.

    Thank you for the reply.
     
  9. Ninian Fife McAfee

    Ninian Fife McAfee

    8
    0
    Oct 20, 2017
    Hello 73's de Edd -
    I appreciate your help.
    The reason that I did not give you the number for IC U101 is quite simple: I didn't have the number myself; it was buried under a layer of goo / glue / flux / leaked magic fluid / whatever, as you can see in the picture that I posted above.
    However, you are of course correct, that number would probably be useful, so I cleaned the gunk off the top of the chip, and it revealed: SPD07
    Here is the picture:
    GEDC0934-40.jpg

    I googled, but I was unable to find a MOSFET driver chip by that number.
    I determined that pins 5 & 7 (top row in the picture) are the outputs, and are coupled to the gates of the power MOSFETs through a resistor divider.

    ****HOWEVER****, could we please return our attention to my first and primary problem, how to choose a replacement for the obviously-failed power MOSFETs??
    (Both MOSFETs are cracked; I don't know that the U101 driver has even failed.)

    Am I correct, given the circuit design, that these are enhancement mode, N-channel power MOSFETs?
    Am I correct that the switching frequency is only a few hundred KHz?
    I searched Mouser for TO-247 N-type Enhancement-mode power MOSFET, and the Vishay SIHG47N65E-GE3 has the sturdiest specs, 650V Vds and 47A drain current, from their inventory.
    But I also need to know Vgs, the Gate-Source Threshold Voltage - should I choose 2, 3, 4, or 5V?
    Which brings us back to the driver chip U101; I bet if I knew the specs for that chip, then I would know its output drive voltage, and thus the Vgs needed in the replacement MOSFETs, right????
    How else can I determine the needed Vgs if I can't get the specs for the driver chip?
    Or should I just go with a Vgs of 2V, and the hell with it??
    Is there anything else that I must take into consideration when choosing replacements for the MOSFETs?
    THANK YOU AGAIN

    ***********************************************************************************************************
    As for your helpful description of the circuit functions, you are mostly correct, with the following clarifications:

    1. The line-level (either balanced or unbalanced) signal actually enters through the small square blue PCB at the bottom of your "Referencing Photo" (with "DC-Signal" printed on it), then travels through the rainbow ribbon cable to the rectangular blue PCB in the yellow boxed area, which is a DSP circuit, with an LCD display and a knob and buttons to let the user choose crossover frequency and slope, low end extension, volume boost, phase, etc.

    2. The two lime green connectors aren't an "alternate audio power output", they are the primary and only output, that connects to the 13" subwoofer driver unit itself, the top connector in that photo being positive, and the bottom being negative. I am surprised that you thought that "the large RED and WHITE wire connectors routing into the cabinet" was also an "alternate audio power output", because that is the 120VAC mains power connector. Again, there is no "alternate audio power output", nor need for one. I would be quite happy just to get it to drive the one subwoofer again.

    3. Yes, correct that "the LV secondary diode sets to be within the WHITE rectangle area. (Although they are resembling porcelain cased power resistors to me )". The diodes, like the failed MOSFETs are encased in grey rubber hoods, which is why they appear like porcelain power resistors in the photo. All the diodes were tested and found to be good.

    4. "Lastly . . . . . inspect the photos LIGHT BLUE rectangular area vewy-VEWY-VEWY carefully . . . Now don't these OEM transistors shown, seem to be METAL heat sink tabbed ? . . . possibly only using a thin mica insulator and thin film of heat sink compound."
    No, they are not. I can understand why you think that from the photo, but not correct. The MOSFETs are both in grey rubber hoods, and being held against the heatsink with curved metal brackets. Look again closely and you can see the grey rubber hoods under the brackets. The brackets themselves are further encased in black heat shrink tubing.
    A very stupid design if you ask me, because why would you need rubber hoods when a thin mica insulator and a thin film of heat sink compound would provide much better heat conduction, and still provide more than enough insulation between the heatsink and the MOSFETs, correct?? I fear that the failed MOSFETs were weakened over time from heat stress and thus were easy targets for the surge that destroyed them.
    This is why I am asking if I can replace the rubber hoods with conventional, thin mica insulators.
    (I wouldn't have asked if they were already mounted with thin mica insulators!!)
    I cannot understand, given the circuit design and function, why they went to such extremes to insulate the MOSFETs from the heatsink. The transistors are passing less than 200V, not thousands of volts, and as for spikes caused by the transistors switching on and off, the MOSFET should have an "integral reverse junction diode" (quoting from the Vishay SIHG47N65E-GE3 datasheet) to clamp those, so what were the designers thinking????
    (A similar argument could be made for removing the hoods from the diodes on the secondary side, and likewise replacing them with thin mica insulators, but they didn't fail.)

    5. "Note the two optical couplers within my BROWN rectangle, do they eventually route over to this U101 chip"

    Yes, that's correct - through a small network of discrete components that I did not attempt to map out.

    6. "Lastly . . . . . . Those shore are some impressive specs on the low end . . . . of course my old ears couldn't hear it . . . . but I 'soitanly could feel it compressing my chest and be watcing the nails wiggling out of the sheetrock."

    Yes, the SVS PB-Ultra are quite an earth-moving experience, literally. :D

    Thank you again.
     
    Last edited: Nov 7, 2017
  10. kellys_eye

    kellys_eye

    4,277
    1,146
    Jun 25, 2010
    The 'goo' is a conformal coating used to keep moisture out, often slapped around circuits of high impedance that may be affected by environmental conditions.

    MOSFETs are usually driven into saturation and often have very low Rds(on) values (drain-source resistance in the order of milli-ohms when fully on) such that the power they dissipate internally is very low compared to your usual bi-polar semiconductor transistor arrangement. Accordingly the heat sinking is dramatically reduced and a rubber 'boot' clipped to a plate is quite common.

    That said, peak switching currents can be 10's or 100's of times larger than the average power and are worse in inductively driven loads anyway. The peaks are the 'destructive' parts of the signal and checking that replacement parts can handle such is as important as their V/I ratings.
     
  11. 73's de Edd

    73's de Edd

    2,805
    1,176
    Aug 21, 2015
    That cryptic "house number " on the 8 pin IC is as useless as the like crypic numbering on the power FETS.
    I really don't know of any 8 pin controllers that alternatively feed TWO power FET's . Am I correct in not seeing any other IC's nearby to U101?
    On the power wiring . . . . I was imagining the RED / WHITE going into a speaker housing . . . . while in reality it is routing through a flap towards the front panel.
    I am correct on the push on terminals though . . . since some POWER does need to pass thru them .

    I also would be using mica and heat sink compound. . . . i just can't equate with silicone booties or silicone pads being their thermal equivalent.

    " grey rubber hoods"

    Put a HOT soldering iron or flame to one and you will then soon see the need to correctly upgrade its materiel status on up to SILICONE rubber hood.( or tubing)

    I really like AAVID black anodized thin aluminum plates if not using HIGH voltage.

    That power supply section has to have its controller IC . . . .not just a mere driver.

    Still researching a U101 equivalent or unit with ONLY 8 PINS and the possibility of what it is .

    I determined that pins 5 & 7 (top row in the picture) are the outputs, and are coupled to the gates of the power MOSFETs through a resistor divider.

    From the photo, I am not able to confirm pin 1 indexing . . . what is it . . . a dot-dimple -slot ?.
    Can you also confirm all grounds to it and possibly, its VCC connection into it .

    I
    Will still be looking for an 8 pin units possibility.

    73's de Edd
     
    Last edited: Nov 8, 2017
  12. Ninian Fife McAfee

    Ninian Fife McAfee

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    0
    Oct 20, 2017
    Thank you very much, kellys_eye & 73's de Edd. You are very helpful indeed!

    I will look carefully at peak Ids (Drain-Source current; I don't know how to do subscripts here) when choosing replacement MOSFETs.

    I am not able to confirm pin 1 indexing . . . what is it . . . a dot-dimple -slot ?.

    Nor was I; I just went with the orientation of the code on the chip to assume for descriptive purposes only, that pin 1 was the lower left pin in the picture, with pins 8-7-6-5 across the top row, L-R in the picture.

    Can you also confirm all grounds to it and possibly, its VCC connection into it .

    Yes of course, right after lunch.

    I Will still be looking for an 8 pin units possibility.

    Thank you. However, I have an idea: With the two failed MOSFETs removed from the PCB, why don't I power up the amplifier and observe the activity on pins 5 & 7 of the driver IC? Yes, I will use an isolation transformer to power the DUT (the amplifier), and Yes, I will exercise extreme caution around the high voltage, and Yes I will be sure that the capacitor banks are fully discharged after the test is done and the unit is unplugged, before proceeding any further.

    Observing the outputs of the driver IC (pins 5&7) should answer all remaining relevant questions, correct?? Specifically: Is the low voltage power supply (brown box section) operational? Is the driver IC still operational? What is the voltage of the drive signals (to choose Vgs for the replacements)? And, if the driver IC has failed, is there a drive signal of some sort present on its input(s)?
    I am hoping and assuming that the driver IC is powered by the low voltage power supply, and will thus be powered continuously, instead of "bootstrapped" with a pulse at power up and needing the switching supply to be operational to remain powered up, like in a more conventional switching power supply that doesn't have a stand-by circuit.
    I am also assuming that with the main power supply disabled by the absence of the switching MOSFETs, there is no need for an 8 ohm dummy load across the speaker output terminals (but couldn't hurt).

    Is that a plan? (Yes, I understand that I proceed at my own risk around high voltage.)

    Thank you again!
     
  13. kellys_eye

    kellys_eye

    4,277
    1,146
    Jun 25, 2010
    No reason why you shouldn't power up and make relevant tests and measurements. You seem to have all the bases covered as far as safety is concerned.

    If you can 'scope the signals that we 'think' may be driving the MOSFETs then so much the better!
     
  14. 73's de Edd

    73's de Edd

    2,805
    1,176
    Aug 21, 2015
    I think that I see what they were doing.

    I need your eyes on the board to confirm that the gate drive resistors are 220 ohm units and being unharmed and completely intact.

    HOWEVER . . . of the two snubbers placed across the FETs, that one has its resistor blown, and the light relection on the photo prohibits positive confirmation, but is it a 10K resistor blown as the left SM resistor. R115 device . . . .when you are reading its companion at R118 ?.
    Also need to see if the 6 pin U103 IC in the area above has a legible part coding on it . . . and hopefully is not going to be as useless as the prior ones were.
     
  15. Kons

    Kons

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    Sep 19, 2019
    SMS 1532. 0932.( N-ch.Mosfet) Vgs (on) 4.280 V aT Id 5.02mA
     
  16. WHONOES

    WHONOES

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    174
    May 20, 2017
    Don't get bogged down with the Gate Source Threshold voltage. Mosfets invariably require 10V on their gates to become fully enhanced. The VGs threshold is largely immaterial in a switching circuit. They are either on or off. The driving device will be designed to accommodate this.
     
  17. deimar

    deimar

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    0
    Nov 25, 2019
    Hi Ninian Fife!
    Were you able to replace the IC U101 SDP07 and finish repairing the module successfully?
    I have the same problem here in Brazil and we are not getting this replacement IC nor the DataSheet
     
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