Connect with us

Help identifying item, finding datasheet or replacement

Discussion in 'Troubleshooting and Repair' started by Six_Shooter, Nov 6, 2013.

  1. Six_Shooter

    Six_Shooter

    98
    0
    Nov 16, 2012
    I have an OEM amplifier for my truck that I would like to finally get back to working condition, been putting it off for months since I discovered the problem...

    Well I discovered this was an issue after the battery would be discharged overnight or so, and found it to be the OEM amplifier being the culprit. It was drawing about 400mA (discharge rate difference between the amp being connected and disconnected) or so when it was attached to vehicle and using my Fluke DMM at the battery while looking for the problem.

    Today I decided to get working on it, and when it was connected to my bench supply was indicating about 375mA without being turned on, just power and ground. There is a separate turn on trigger that should be what turns it on and off.

    Anyway, I've traced it down to what I believe is a MOSFET that is what switches the power on to the amplifier ICs, of which there are 3. Once this was removed the current draw went to zero. One side is connected to the 12V input, one pin is connected to a transistor through a resistor that is controlled by the trigger input. The third pin is what then feeds the 3 amplifier ICs.

    I don't know what to make of the markings to start looking for a datasheet to find a replacement, so if some of you electronics gurus can take a look and help me identify this transistor, I would be really appreciative.

    I guess barring finding the original specs knowing what I need to do to spec out a new part to replace it with. From what I understand a MOSFET makes the most sense here to pass relatively high power.

    Anyway, onto the pictures. It is Q701, just to the right of the large diode. I have also included pictures of the transistor itself and what the pads on the board look like with it removed to help in identifying a replacement.

    Don't worry about the Q702, that is the transistor that is controlled by the trigger input, and then triggers this mystery transistor (MOSFET?), you'll notice in one picture Q702 is removed and then replaced in another, it was an initial idea of what was keeping the amplifier powered up. Also C706 has been removed for easier access to the offending transistor (and follow traces).

    Thank you.
     

    Attached Files:

    Last edited: Nov 6, 2013
  2. Six_Shooter

    Six_Shooter

    98
    0
    Nov 16, 2012
    Small update:

    I decided to hook the amplifier back up and find the actual current across this transistor, and I found it to be 54.3 mA @ 12.0V across the source and drain (assuming it's a MOSFET) tabs. Current on the power supply jumps up to 375 mA.

    just as a note, I'm not using my Fluke DMM to measure this draw, since it's at work, I'm using a Canadian Tire brand (Mastercraft) DMM that I have found to be a decent DMM overall. If need be I can take measurements with a few other DMMs I have if a datasheet can't be found, to find a suitable replacement.
     
    Last edited: Nov 6, 2013
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,160
    2,676
    Jan 21, 2010
    One thing to do is to see what sort of device it is.

    If it is a bipolar transistor it will have a diode junction between base and emitter and another between base and collector.

    If it is a mosfet you should find one terminal appears totally isolated from the others, and there is either a short or a diode junction across the others. If you find a short, connect the three terminals together to discharge any gate capacitance and measure it again. If you see other than a diode junction it's probably toast.

    What do you think the markings are? 1Q? I can look that up and see if I can find anything.. Nope, I can't find a 1Q in this package :(
     
  4. Six_Shooter

    Six_Shooter

    98
    0
    Nov 16, 2012
    Yep, tried measuring between the terminals, but they are shorted together, no or very little resistance between the 3 terminals, hence why the amplifier is simply staying on with this transistor in the circuit.

    The markings to me look like 3 vertical dots, next to a 1 or lower case L or upper case I at one end and a Q with a single dot next to it.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,160
    2,676
    Jan 21, 2010
    There are fairly thick traces going to all three pins. This is inconsistent with it being a mosfet or a BJT (but doesn't eliminate the possibility).

    It *might* be a double diode, but I don't thinks that's entirely likely.

    I would trace as much of the circuit around the device as possible. What you're looking for is how the control terminal is controlled, and what it is switching. Both may assist you in determining the nature of the device and possible required specs.
     
  6. Six_Shooter

    Six_Shooter

    98
    0
    Nov 16, 2012
    I've already gone through that and posted it in my post. What it controls and what is controlling it.
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,160
    2,676
    Jan 21, 2010
    Yeah, but I need to know a little more exactly.

    Such as:

    Even better would be to draw all that as a schematic where we can add more to it as we get more information.

    I do note that the traces seem to connect to more than a single part, so the circuit may be more complex.
     
  8. Six_Shooter

    Six_Shooter

    98
    0
    Nov 16, 2012
    This is why I was hoping someone would recognize the markings on the transistor and then I would know which pin is which to label them, from a datasheet.

    The power input is directly to the 12V input to the amplifier from the vehicle. The output goes to the same pin on 3 amplifier ICs that I have not got the part number of yet, since there's a clamping bracket that holds them against the case/heatsink.
    The control pin comes from what looks to be the collector (assuming Q702 is an NPN transistor), through a 2.166k resistor (measured) R702, marked with 222, 2.2K nominal.

    I've attached a close up of the area, with the control path highlighted in blue.

    The 12V appears to connect directly to the input pin, no voltage drop between input pin and this pad, even with a load (amp powered on)

    Output to the amplifier ICs has a direct connection to them as well in a parallel fashion .
    You can see the collector of Q702 is connected through the 2.2K ohm resistor to the control input of this mystery transistor.

    The ground of Q702 is connected through that via to the ground plane on the other side of the board.

    The trigger input to Q702 is through a resistor (not in the picture), then to the anode of the large diode (D703), through C707 and C721, through R704 and then to the base of the transistor. This path is highlighted in pink. Yes, it passes through the vias as jumpers on the other side of the board.

    I'm thinking even for testing purposes I can substitute in a non SMD device (which I'm completely fine with), and would even be fine with that as a permanent repair, I just want to make sure I use the right type of device here.

    I'll mention it again, the current across the 12V in and out to amplifier ICs pin is 54 mA (turning the amplifier on) and an overall draw through the 12V input to the amplifier (from power supply) of about 375 mA, at idle. I can't really test a loaded output since the case is also the heatsink and I'd rather not test the thermal limits of those amplifier ICs. ;) If it's absolutely necessary, I could solder some wires to the pads and re-install in the vehicle to see if that current changes

    I've also attached an overall picture of the amplifier, the area I'm working in is just to the right of the transformer and below the TO-220 packaged 7806.
     

    Attached Files:

  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,160
    2,676
    Jan 21, 2010
    If the connection to the amplifiers is to their power connection, then I'd suspect the device is a P Channel mosfet.

    In this case the source connects to 12V, the drain to the amplifiers, and the remaining pin is the gate.

    I would try a 30V or higher P channel mosfet in what appears to be a SOT-89 package. I'm not sure of the current rating, say a couple of amps? Obviously, ensure the pin connections are correct.
     
  10. Six_Shooter

    Six_Shooter

    98
    0
    Nov 16, 2012
    That's what I've been leaning towards. I don't have any on hand, at least none that I'm willing to sacrifice, since the ones I have are for school labs, though I don't know that we will be doing anything with MOSFETs anytime soon.

    Anyway a friend of mine just informed me he has a box of electronics for me that he got from a co-worker, so I'm hoping there's something in there, even in a through hole type. :D
     
  11. Six_Shooter

    Six_Shooter

    98
    0
    Nov 16, 2012
    Well, I removed the heat sink clamp to get the part number for the amplifier ICs, they are AN7190K amplifier ICs. I found a Panasonic datasheet, with a package that matches what I have.

    Anyway, as I suspected the connection from Q701 to the amplifier IC is the Vcc pin.

    The only thing I'm a little confused by is the difference in measured current overall vs across the Q701 pads. 375 or so mA overall and only 54 mA across the pins to power the amplifier ICs, so there's another 321 mA being used by the Op-amps and the rest of the amplifier.
     
  12. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,264
    Nov 28, 2011
    I agree Steve, it's either a P-channel MOSFET or a PNP transistor (non-Darlington).

    Digikey don't have any suitable MOSFETs in that package (the lowest Rds(on) is 9 ohms), and the best Mouser have is the Zetex / Diodes Inc ZXMN3A01ZTA with Rds(on) of 0.12 ohms: http://mouser.com/ProductDetail/Dio...GAEpiMZZMshyDBzk1/Wi4P4wC6csLMYyqpw%2bGcj9aA=

    As for PNPs in that package, there are lots.
    NXP PBSS5330XZ 30V 3A Vce(sat)[email protected] USD 0.46: http://www.digikey.com/product-detail/en/PBSS5330XZ/568-10409-1-ND/4333338 - this is the cheapest, and one of the best
    Zetex / Diodes Inc ZX5T3ZTA 40V 5.5A Vce(sat)[email protected] USD 0.71 http://www.digikey.com/product-detail/en/ZX5T3ZTA/ZX5T3ZCT-ND/679129 - lower Vce(sat), higher current rating, higher gain.
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,160
    2,676
    Jan 21, 2010
    I reckon there's a connection between the "upper" terminal of the unknown device through to a 2k2 (R701) resistor connected to the control input. The control input is pulled to earth via another 2k2 (R702) resistor.

    This lends weight to it being a mosfet as you would likely not need a pull-up on the base of a PNP BJT.

    It also points to it being a logic level device as the gate is only going to be pulled about 6V more negative than the source.
     
  14. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,264
    Nov 28, 2011
    I'm not sure I agree. I doubt that R701 connects to either the collector/drain of Q701 or to 0V. We can't tell what else connects to the gate/base apart from the two 2k2 resistors, because that signal also disappears into a via.

    It doesn't make sense for R701 to go to ground; the driver, Q702, has its emitter/source connected to ground (as the OP labelled it), so the driver pulls its collector/drain to 0V to enable the pass device (Q701). A 2k2 resistor from Q701 base/gate to ground would permanently enable Q701.

    Also I can't think of any reason why the designer would provide only half of the available 12V to a MOSFET and then choose a low-Vgs device! Even low-Vgs MOSFETs saturate more at higher Vgs.

    The presence of R702 between Q702 collector/drain and the base/gate of Q701 also could imply that it's a transistor, since no resistor (or only a low-value resistor) would be needed for a MOSFET switch.

    At 12V that would give a base current of 5 mA, which is very low for a transistor that's switching a load of 400 mA quiescent. I'd expect the load to be at least a few amps when the amp is playing. Perhaps the transistor is a special high-gain device. I suppose it could be a Darlington, but that would waste significant voltage. So that argues back in favour of a MOSFET.

    There is no protection component across the gate-source, but that's not conclusive.

    I'm curious now! I would like to see the whole circuit.
     
    Last edited: Nov 7, 2013
  15. Six_Shooter

    Six_Shooter

    98
    0
    Nov 16, 2012
    I'll look at more of the control circuit and see what I can map out. It is a multilayer PCB so I might not be able to get everything.

    Just as a quick test last night I soldered in a PNP transistor that I had in my parts bin (2N4403) just to see what happened, yeah I know I should have done some calcs first, but anyway...

    The amplifier turned on with no trigger input, but did not power up the amplifier ICs, so the total I was around 320 mA. Once I triggered the amp current went up, but the voltage to the amplifier ICs was only about 6V. I'm not surprised by that, due to other resistances that would be in the circuit (ri of the amplifier ICs, resistance across Vce of the 2N4403, etc). I think this points even more of a MOSFET that can work more like a switch from what I recall of MOSFET operation.
     
  16. Six_Shooter

    Six_Shooter

    98
    0
    Nov 16, 2012
    Going through parts I have kicking around I have a lot of N-channel MOSFETs, but no P-channel. :facepalm:

    I did recently acquire a few of these: http://datasheet.octopart.com/DM0063-Crydom-datasheet-13117099.pdf

    I'm going to do some testing and see if this will work, barring tha.t I also received a bunch of relays, a couple of which have good specs to work in place of the original MOSFET. I just worry about the flyback voltage not being suppressed well enough with a diode. Trigger to teh diode would come directly from the trigger input and not Q702.
     
  17. Six_Shooter

    Six_Shooter

    98
    0
    Nov 16, 2012
    So I picked up a P-channel MOSFET (IRF9530) today, and it seems to be working as expected. Amp turns on and off when trigger is applied and taken away.

    It's a TO-220 case, but I made it work. At the very least I know that a P-channel MOSFET will do the job so I can look for a proper sized SMD MOSFET if I really want to.

    Time to add some hot glue support to the parts I removed it from and the new MOSFET, since it's kinda hanging in the air. Then I might actually have tunes again!. w00t!
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-