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Question for the group..

Started by Dave April 18, 2013
I have an automatic battery charger which is totally non-functional, 
apparently not sensing when it is connected to a load, and the first thing I 
note about it is that it makes prodigious use of the 2N3904 transistor on 
its main control board.  And one of these (2N3904) has an odd 
characteristic- it measures .676 VDC from emittor to collector, rather than 
the typical OL that the others measure, or that I get from a 2N3904 out of 
stock.  (Note that this is with the negative or black lead from the DMM on 
the emittor and the positive or red on the collector, that I get a .676 VDC 
reading on the DMM.)

Anybody have any idea as to what this would indicate about the particular 
transistor in question?  It's been too may years since I've done this on a 
regular basis, and I'm having to clean the cobwebs out of the attice to try 
and figure it out.  MANY THANKS for any feedback.

Dave


"Dave" <db5151@hotmail.com> wrote in message 
news:CKSdnQkD39KYpu3MnZ2dnUVZ_hmdnZ2d@posted.internetamerica...
>I have an automatic battery charger which is totally non-functional, >apparently not sensing when it is connected to a load, and the first thing >I note about it is that it makes prodigious use of the 2N3904 transistor on >its main control board. And one of these (2N3904) has an odd >characteristic- it measures .676 VDC from emittor to collector, rather than >the typical OL that the others measure, or that I get from a 2N3904 out of >stock. (Note that this is with the negative or black lead from the DMM on >the emittor and the positive or red on the collector, that I get a .676 VDC >reading on the DMM.) > > Anybody have any idea as to what this would indicate about the particular > transistor in question? It's been too may years since I've done this on a > regular basis, and I'm having to clean the cobwebs out of the attice to > try and figure it out. MANY THANKS for any feedback. > > Dave > >
Just realized, I am talking about using the DMM in DIODE-TEST function, but I didn't indicate that. D
On 4/18/13 11:29 AM, Dave wrote:
> > "Dave" <db5151@hotmail.com> wrote in message > news:CKSdnQkD39KYpu3MnZ2dnUVZ_hmdnZ2d@posted.internetamerica... >> I have an automatic battery charger which is totally non-functional, >> apparently not sensing when it is connected to a load, and the first thing >> I note about it is that it makes prodigious use of the 2N3904 transistor on >> its main control board. And one of these (2N3904) has an odd >> characteristic- it measures .676 VDC from emittor to collector, rather than >> the typical OL that the others measure, or that I get from a 2N3904 out of >> stock. (Note that this is with the negative or black lead from the DMM on >> the emittor and the positive or red on the collector, that I get a .676 VDC >> reading on the DMM.) >> >> Anybody have any idea as to what this would indicate about the particular >> transistor in question? It's been too may years since I've done this on a >> regular basis, and I'm having to clean the cobwebs out of the attice to >> try and figure it out. MANY THANKS for any feedback. >> >> Dave >> >> > > Just realized, I am talking about using the DMM in DIODE-TEST function, but > I didn't indicate that. > > D > >
If there is no other voltage across the circuit, this sounds like a defective transistor with a short in it. Measure it with the ohm setting. In theory, with no voltage, VCE should be infinity ohms. With a .676v drop, it sounds like it is acting like a diode, rather than a transistor.
"Daniel Pitts" <newsgroup.nospam@virtualinfinity.net> wrote in message 
news:KhXbt.60885$iT2.58548@newsfe01.iad...
> On 4/18/13 11:29 AM, Dave wrote: >> >> "Dave" <db5151@hotmail.com> wrote in message >> news:CKSdnQkD39KYpu3MnZ2dnUVZ_hmdnZ2d@posted.internetamerica... >>> I have an automatic battery charger which is totally non-functional, >>> apparently not sensing when it is connected to a load, and the first >>> thing >>> I note about it is that it makes prodigious use of the 2N3904 transistor >>> on >>> its main control board. And one of these (2N3904) has an odd >>> characteristic- it measures .676 VDC from emittor to collector, rather >>> than >>> the typical OL that the others measure, or that I get from a 2N3904 out >>> of >>> stock. (Note that this is with the negative or black lead from the DMM >>> on >>> the emittor and the positive or red on the collector, that I get a .676 >>> VDC >>> reading on the DMM.) >>> >>> Anybody have any idea as to what this would indicate about the >>> particular >>> transistor in question? It's been too may years since I've done this on >>> a >>> regular basis, and I'm having to clean the cobwebs out of the attice to >>> try and figure it out. MANY THANKS for any feedback. >>> >>> Dave >>> >>> >> >> Just realized, I am talking about using the DMM in DIODE-TEST function, >> but >> I didn't indicate that. >> >> D >> >> > If there is no other voltage across the circuit, this sounds like a > defective transistor with a short in it. Measure it with the ohm setting. > In theory, with no voltage, VCE should be infinity ohms. > > With a .676v drop, it sounds like it is acting like a diode, rather than a > transistor.
AAahhh. Thank you, that is what it sounds like I guess. Over half of the 2N3904s on the main control board are exhibiting this particular characteristic, which makes me wonder what other demons lurk within. One of them even shows a 1.6 VDC characteristic across the emittor/collector. Wondering now if all the ICs on the board are likely trashed, but I guess I'll see to that after I get the transisors replaced. Thanks again. I'll check them with the OHMS setting. Dave
On Thu, 18 Apr 2013 13:27:18 -0500, "Dave" <db5151@hotmail.com> wrote:

>I have an automatic battery charger which is totally non-functional, >apparently not sensing when it is connected to a load, and the first thing I >note about it is that it makes prodigious use of the 2N3904 transistor on >its main control board. And one of these (2N3904) has an odd >characteristic- it measures .676 VDC from emittor to collector, rather than >the typical OL that the others measure, or that I get from a 2N3904 out of >stock. (Note that this is with the negative or black lead from the DMM on >the emittor and the positive or red on the collector, that I get a .676 VDC >reading on the DMM.) > >Anybody have any idea as to what this would indicate about the particular >transistor in question? It's been too may years since I've done this on a >regular basis, and I'm having to clean the cobwebs out of the attice to try >and figure it out. MANY THANKS for any feedback.
If it's a "diode-connected" setup (base and collector connected) then you will get that typical diode drop voltage in the usual diode-test mode on the multimeter. That configuration is used as a temperature sensor, which might reasonably show up in a charger control circuit.
On 4/18/13 12:13 PM, Dave wrote:
> "Daniel Pitts" <newsgroup.nospam@virtualinfinity.net> wrote in message > news:KhXbt.60885$iT2.58548@newsfe01.iad... >> On 4/18/13 11:29 AM, Dave wrote: >>> >>> "Dave" <db5151@hotmail.com> wrote in message >>> news:CKSdnQkD39KYpu3MnZ2dnUVZ_hmdnZ2d@posted.internetamerica... >>>> I have an automatic battery charger which is totally non-functional, >>>> apparently not sensing when it is connected to a load, and the first >>>> thing >>>> I note about it is that it makes prodigious use of the 2N3904 transistor >>>> on >>>> its main control board. And one of these (2N3904) has an odd >>>> characteristic- it measures .676 VDC from emittor to collector, rather >>>> than >>>> the typical OL that the others measure, or that I get from a 2N3904 out >>>> of >>>> stock. (Note that this is with the negative or black lead from the DMM >>>> on >>>> the emittor and the positive or red on the collector, that I get a .676 >>>> VDC >>>> reading on the DMM.) >>>> >>>> Anybody have any idea as to what this would indicate about the >>>> particular >>>> transistor in question? It's been too may years since I've done this on >>>> a >>>> regular basis, and I'm having to clean the cobwebs out of the attice to >>>> try and figure it out. MANY THANKS for any feedback. >>>> >>>> Dave >>>> >>>> >>> >>> Just realized, I am talking about using the DMM in DIODE-TEST function, >>> but >>> I didn't indicate that. >>> >>> D >>> >>> >> If there is no other voltage across the circuit, this sounds like a >> defective transistor with a short in it. Measure it with the ohm setting. >> In theory, with no voltage, VCE should be infinity ohms. >> >> With a .676v drop, it sounds like it is acting like a diode, rather than a >> transistor. > > AAahhh. Thank you, that is what it sounds like I guess. Over half of the > 2N3904s on the main control board are exhibiting this particular > characteristic, which makes me wonder what other demons lurk within. One of > them even shows a 1.6 VDC characteristic across the emittor/collector. > Wondering now if all the ICs on the board are likely trashed, but I guess > I'll see to that after I get the transisors replaced. > > Thanks again. I'll check them with the OHMS setting. > > Dave > >
Note that your DMM is applying voltage to the circuit, so it could be that if you aren't isolating these components, the reading is actually expected for the circuit. Ohms setting likely applies less voltage (though I'm not certain about that), so it may be "more accurate" indicator of a problem. If multiple transistors are showing this "short", then I suspect its a problem with the measurement rather than the device. Now, here is the disclaimer. I'm very amateur, so take all my advice with a hunk of salt.
Dave wrote:
> "Dave" <db5151@hotmail.com> wrote in message > news:CKSdnQkD39KYpu3MnZ2dnUVZ_hmdnZ2d@posted.internetamerica... > >>I have an automatic battery charger which is totally non-functional, >>apparently not sensing when it is connected to a load, and the first thing >>I note about it is that it makes prodigious use of the 2N3904 transistor on >>its main control board. And one of these (2N3904) has an odd >>characteristic- it measures .676 VDC from emittor to collector, rather than >>the typical OL that the others measure, or that I get from a 2N3904 out of >>stock. (Note that this is with the negative or black lead from the DMM on >>the emittor and the positive or red on the collector, that I get a .676 VDC >>reading on the DMM.) >> >>Anybody have any idea as to what this would indicate about the particular >>transistor in question? It's been too may years since I've done this on a >>regular basis, and I'm having to clean the cobwebs out of the attice to >>try and figure it out. MANY THANKS for any feedback. >> >>Dave >> >> > > > Just realized, I am talking about using the DMM in DIODE-TEST function, but > I didn't indicate that. > > D > >
You need to detach it from the circuit for a proper test. Just unsolder a couple of legs.. You could have a diode in the circuit that is giving you a false reading. Jamie

"Dave" <db5151@hotmail.com> wrote in message 
news:CKSdnQkD39KYpu3MnZ2dnUVZ_hmdnZ2d@posted.internetamerica...
> I have an automatic battery charger which is totally non-functional, > apparently not sensing when it is connected to a load, and the first thing > I note about it is that it makes prodigious use of the 2N3904 transistor > on its main control board. And one of these (2N3904) has an odd > characteristic- it measures .676 VDC from emittor to collector, rather > than the typical OL that the others measure, or that I get from a 2N3904 > out of stock. (Note that this is with the negative or black lead from the > DMM on the emittor and the positive or red on the collector, that I get a > .676 VDC reading on the DMM.) > > Anybody have any idea as to what this would indicate about the particular > transistor in question? It's been too may years since I've done this on a > regular basis, and I'm having to clean the cobwebs out of the attice to > try and figure it out. MANY THANKS for any feedback.
You say "not sensing when its connected to to a load" as if the load was something other than a battery. Your "fully automatic battery charger" senses a voltage produced by the battery to detect correct polarity - obviously a "load" will not produce a voltage for the "fully automatic battery charger" to sense. A totally dead flat battery will also not provide a voltage for polarity detection. I keep an old iron cored transformer to get things started just in case I encounter a dead flat battery.
"Ian Field" <gangprobing.alien@ntlworld.com> wrote in message 
news:K%Zbt.26871$9T.9571@fx22.fr7...
> > > "Dave" <db5151@hotmail.com> wrote in message > news:CKSdnQkD39KYpu3MnZ2dnUVZ_hmdnZ2d@posted.internetamerica... >> I have an automatic battery charger which is totally non-functional, >> apparently not sensing when it is connected to a load, and the first >> thing I note about it is that it makes prodigious use of the 2N3904 >> transistor on its main control board. And one of these (2N3904) has an >> odd characteristic- it measures .676 VDC from emittor to collector, >> rather than the typical OL that the others measure, or that I get from a >> 2N3904 out of stock. (Note that this is with the negative or black lead >> from the DMM on the emittor and the positive or red on the collector, >> that I get a .676 VDC reading on the DMM.) >> >> Anybody have any idea as to what this would indicate about the particular >> transistor in question? It's been too may years since I've done this on >> a regular basis, and I'm having to clean the cobwebs out of the attice to >> try and figure it out. MANY THANKS for any feedback. > > You say "not sensing when its connected to to a load" as if the load was > something other than a battery. > > Your "fully automatic battery charger" senses a voltage produced by the > battery to detect correct polarity - obviously a "load" will not produce a > voltage for the "fully automatic battery charger" to sense. A totally dead > flat battery will also not provide a voltage for polarity detection. > > I keep an old iron cored transformer to get things started just in case I > encounter a dead flat battery.
Hmm. That's interesting. How do you make use of the transformer? Thanks... D
"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in message 
news:lRZbt.544910$kp4.259294@newsfe09.iad...
> Dave wrote: >> "Dave" <db5151@hotmail.com> wrote in message >> news:CKSdnQkD39KYpu3MnZ2dnUVZ_hmdnZ2d@posted.internetamerica... >> >>>I have an automatic battery charger which is totally non-functional, >>>apparently not sensing when it is connected to a load, and the first >>>thing I note about it is that it makes prodigious use of the 2N3904 >>>transistor on its main control board. And one of these (2N3904) has an >>>odd characteristic- it measures .676 VDC from emittor to collector, >>>rather than the typical OL that the others measure, or that I get from a >>>2N3904 out of stock. (Note that this is with the negative or black lead >>>from the DMM on the emittor and the positive or red on the collector, >>>that I get a .676 VDC reading on the DMM.) >>> >>>Anybody have any idea as to what this would indicate about the particular >>>transistor in question? It's been too may years since I've done this on >>>a regular basis, and I'm having to clean the cobwebs out of the attice to >>>try and figure it out. MANY THANKS for any feedback. >>> >>>Dave >>> >>> >> >> >> Just realized, I am talking about using the DMM in DIODE-TEST function, >> but I didn't indicate that. >> >> D >> >> > You need to detach it from the circuit for a proper test. Just unsolder > a couple of legs.. You could have a diode in the circuit that is giving > you a false reading. > > Jamie >
I pulled it out and got the same reading, so replaced that transistor. Had enough trouble doing this I decided to leave the others alone, as they didn't seem as troubled. Figured I would wait and see how it functioned when I hooked it back up to an actual battery... If need be I'll tackle it again. Thanks to all for the input. Dave