Need Diehard battery charger schematic

Discussion in 'General Electronics Chat' started by BillD, May 7, 2008.

  1. BillD

    BillD Thread Starter New Member

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    I have a faulty Sears Diehard Battery charger Mod. # 200713101 and cannot troubleshoot it without a schematic. I have been in contact with the customer service dept. at Sears several times over the past week but the only help they have been is to make available the PDF download version of the Owners Manual which contains top level wiring diagram but no schematic. I am convinced that a schematic, and perhaps a maintenance manual, exists for the unit but it is like fighting the windmills to deal with the Sears personnel. In the first place I haven't talked to anyone yet who gave me the impression that they know the difference between a schematic and a wiring diagram. I have tried to get to talk to a repair technician but apparently they aren't allowed to talk to customers, or some other nonsensical reason. If anyone can help I would greatly appreciate it. Thanks, Bill.
  2. beenthere

    beenthere Retired Moderator

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    What is the nature of the problem?

    It is common for details like schematics to be considered as intellectual property, and so not be available to the public.
  3. pfofit

    pfofit Member

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    Why don't you just reverse engineer your own. Even the "automatic" ones only have a handful of components and are not that complicated and would take must less time than trying to get something that does not exist in sears world.

    Sears makes nothing, they are distributors that slap their name and logos on stuff.

    cheers
  4. BillD

    BillD Thread Starter New Member

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    Thanks for the responses. I am in the process of "reverse engineering" as suggested and have made good progress in spite of the fact that the control board contains 7 transistors (2N4401 & 2N4403) plus a "shunt regulator" (TL431 that I never used or even heard of) and an unnumbered SCR. However the CB doesn't seem to be the problem.
    The problem has been narrowed down to the transformer windings. A very close inspection has shown that there is no sign of wire breakage, heating, or any form of contact problems or connector melting. The secondary seems simple, center tapped with two rectifiers feeding the SCR with a circuit breaker in the + output lead.
    The primary appears to be the problem. It has two separate coil areas and a total of 14 leads exiting the coils which go to two different switches; A spdt for 6v - 12v operation and the other for selecting charging rates: 2 amp, 10 amp and 60 amp (engine start). Without a drawing it is hard to explain the wiring problem, but I'll try. The hot contact from the power plug goes to the center contact of the spdt 6v-12v switch of which one pole goes to one end of a primary coil and the other pole goes to the other end of the same primary coil. There are no other wires connected to either end of this coil. This means that 110v ac is applied to one end of the coil in one position and to the other end of the same coil in the other position, always leaving one end open. This makes absolutely no electrical sense. So, without a schematic which shows the windings of the transformer, I am left with three alternatives, 1) junk the thing and stop wasting my time, 2) unwinding the transformer in the reverse engineering process (impractical), or 3) cut up my Sears credit card and mailing it to the Sears CEO with a nasty note about their lack of customer support.

    The reader of this has probably deduced that I am retired and don't give up easily. I am also a good electronic troubleshooter and hate to throw in the towel.
  5. pntrbl

    pntrbl Active Member

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    I'm a single minded old fart like your self BillD, and please don't take my words a pearls of wisdom, but that sounds like it could be a normal primary to me. The Xfmer has to step 110VAC down to 6VAC and 12VAC respectively for rectification. The switch allows you to select between the two.

    Just my 2 cents and I'm not sure it's worth that much!

    SP
  6. SgtWookie

    SgtWookie Expert

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    The TL431 has the nickname of "Adjustable Zener" - because that's how it acts ;)

    It's a reasonably stable voltage reference. Basically, all you need to set one of them up is a current limiting resistor on the high side, and then a pot to set the Vref.

    You're probably aware that the Radio Shack "grab bags" of 15 PNP and 15 NPN transistor assortments usually have several 2N4401 and 2N4403's in them - just in case you need a quick source.

    Don't give up on it just yet. Check those switches over really well, and particularly the power cord. Power cords are easy to overlook. So are outlets - and extension cords.
  7. thingmaker3

    thingmaker3 Retired Moderator

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    Bill, please note that your option #3 is not mutually exclusive with the other two options.;)

    What about finding a second charger from Craig's List or EBay or some such?
  8. beenthere

    beenthere Retired Moderator

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    It would still be helpful if we knew what the charger was/was not doing. What does your meter indicate?
  9. 104kerry

    104kerry New Member

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    Hi Bill,

    While I'm not retired, I seem to have the same tenacity as yourself. I have the same charger and have what sounds like the same problem. I have replaced the SCR without any luck.

    I would appreciate an email if you figure this beast out, I will do the same.

    Thanks,

    Kerry
  10. 104kerry

    104kerry New Member

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    Hi Bill

    I have figured out what my problem was. It was the SCR. I tested without screwing it to the heat sink. After I thought about it, I figured to complete the circuit, the case would have to be grounded. Put some new heat sink material behind it and screwed it tight. Working great. I purchased the SCR through Mouser, their part number 519-S2055W. Mouser.com or phone 800-346-6873.
  11. eskort

    eskort New Member

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    Bill, did you ever figure out the schematic? I have one that has acted funny for years. I opened it up only to find a blob of solder on the component side of the board from when it was manufactured--it shorted something out.

    Just hoping to save some time.
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