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RV power converter Todd PC40 -- insulator problem

Discussion in 'Electronic Repair' started by Michael Caplan, Sep 24, 2003.

  1. Does anyone have information on or experience with the PC40, 40 amp
    converter made by Todd Engineering Sales of Tucson (now out of business)?
    I'd sure like to get hold of a schematic, but my main interest right now is
    in identifying the special insulator used under the mosfets.

    The power supply is used to provide the 12 DC used in recreational travel

    It's basically three paralleled SMPS's mounted inside a large aluminum heat
    sink (which is also the case), one of which, as far as I can tell, is the

    The unit came into my shop with no output. After getting the case opened
    (it's all pop-riveted) and pulling out the master board, I found the IRF740
    mosfet on this board shorted and the resistor next to it open (looks like
    0.24 Ohms, 2 Watt -- red, yellow, silver, then gold on a gray body). I
    also found signs of arcing from the mosfet to the heat sink. The arcing
    appears to have been through the mosfet's insulator, and that is where I am

    The mosfet, an IRF740 in a TO-220 type case, is insulated from the heat sink
    by a piece of what at first looks like a standard silicon rubber heat
    conductive insulator. However, I was attracted to the fact that there is a
    grounding wire soldered to the insulator. On much closer examination I
    confirmed that the insulator has a metallic core ("middle of the sandwich").
    The point where the heat sink was marked by the arcing corresponds to the
    narrow edge of the insulator where the metallic core is now exposed.

    I suspect that the insulator is compromised and should not be reused. But I
    haven't seen this type of insulation material before and was wondering if
    anyone has come across it. Is there a description and trade name for it?
    What about sources?

    Michael Caplan CET
  2. Mike,
    I am working on the same unit. I am trying to find out the part number of U2
    on the main PCB. It is a 3 terminal TO-92 plastic device, it burned up and I
    can not read the markings.. My unit has a standard insulator, no wire
    soldered to it. The main board near the large chassis terminal has a spade
    terminal soldered to the PCB and held in contact with the heatsink with a
    clip. Also do you know if the telephone type connector is required to turn
    the unit on.

  3. Marshcollins


    Sep 5, 2009
    PC40 phone connector

    I have a manual for the PC40 which indicates the phone connector is for a jumper which switches the voltage from 14.1 vdc output to a lower voltage for when you are continuously connected to shore power. Higher voltage with the jumper installed.
    TIMmORON and Arthur Bryant like this.
  4. timotb


    Oct 29, 2009
    Todd PC30 Charger

    Could someone tell me if I can use the Todd 12 volt 30 amp model PC30 as a full time battery maintainer. Does this unit have the circuitry to shut off and not over charge a battery if always plugged in and connected?
  5. Reitan


    May 5, 2010
    Todd Engineering Sales, Inc. Model PC 40 Power Source


    I have successfully repaired a Todd Engineering Sales, Inc. Model PC 40 power source. I drew a schmatic diagram and I would be delighted to share that with those of you that would like to have one.

    I found two open 62K ohm resistors that are in parallel in the zener voltage regulator circuit that powers the PWM IC circuit. Also a N channel power MESH MOSFET was bad in one of the PC boards.

    In exchange I am searching for a schmatic diagram to a Todd Engineering Sales, Inc. power source battery charger/ power supply, model PC30B.

    I hope this will be of some help.

    Arthur Bryant likes this.
  6. Reitan


    May 5, 2010

    I has repaired this power supply and I may have some answers to your questions. Please feel free to contact me.

  7. pomonabill220


    Jun 8, 2010
    Hello Tony;
    I have a PC30E that my father gave to me (not working... BIG inductor got REAL hot and chared the pcboard) BUT my U2 (a T0-92 package) has SiLR 645 stamped on it. Also, the board is labeled U2 RT2 OT. NOTE also that right next to this device is a long rectangular (about 1/2 inch tall) mechanical thermostat, THAT might be the RT2 OT NOT the SiLR 645,,,, so take note! So it might be a solid state temperature sensor. All three leads are used (traces).
    I hope this helps.
    IF you have a schematic for the PC30E, I would appreciate seeing your work!
    Last edited: Jun 8, 2010
  8. lambiasow


    Jun 30, 2010
    Does the manual include a schematic?

    can you post the manual to this site?


  9. pomonabill220


    Jun 8, 2010
    U2 (the TO-92 package) is a "smps startup regulator". It has a max input of 450volts and output of 15 volts for the switcher drive. After the supply starts, a winding on the transformer is used to supply the logic and the U2 is shutoff. The logic supply uses a power resistor to limit current, a diode to rectify and a zener to regulate the 15 volts. My supply had a bad LM393 (dual comparitor) as well, but it would still run. The comparitor is probably used to current limit, or overcurrent protection, or just for voltage selection... havent found out yet.
    It also appears that the mechanical thermostat is for over temp, and the comparitor shuts down the supply if it gets too hot (yeah right!), or turns the fan on. Just a guess as I learn more.
    over temp is kind of a joke... why did the output inductor in mine cook the board and melt the tape wrapped around it then?!?!?! I got mine with the fan frozen!
    Last edited: Jun 30, 2010
  10. berger316


    Jul 7, 2010

    I am also having issues with my PC40 unit.
    Could you send me a copy of your schematic.

  11. icabod2


    Jul 8, 2010
    I would love a copy of your schematic please. I have a model PC 45 which I am sure must be similar.
  12. ROMOAS


    Sep 28, 2010
    please send me a sch and a parts list i have all the parts i need but 2 items i can not identify mine fryed big time but the transformers are ok so i'm just repairing it for fun i have the PC40 thank you
  13. linetrash75


    Oct 20, 2010
    I have a todd engineering PC40 that is not working, the most i,am capable of is checking in ternal fuse. CZould somebody walk me though this or possibly fix it if i shipp it to you.

    Thanks Jed
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