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Power Transistor Location

Discussion in 'Boxers/TR/M' started by bpcurtis, Feb 10, 2020.

  1. bpcurtis

    bpcurtis Rookie

    Nov 5, 2003
    30
    Dickinson, TX
    Full Name:
    Burnell Curtis
    My 87 TR AC and Heater blower motor works only on high. There is a strong suggestion that the power transistor is bad. On Tav. 127 number 14 there is a power transistor shown. Does anyone know where it physically is? I have searched under the dash and can not find it.
     
  2. Rifledriver

    Rifledriver Two Time F1 World Champ

    Apr 29, 2004
    26,845
    Austin TX
    Full Name:
    Brian Crall
    I have very big hands but I still can reach it through the center dash vent once removed. If you look under the dash for the 3 wires that come out of the ducting near the A/C box and the 2 pop rivets holding it in, Thats it.

    Check also the fuse in the fan speed controller.
     
  3. bpcurtis

    bpcurtis Rookie

    Nov 5, 2003
    30
    Dickinson, TX
    Full Name:
    Burnell Curtis
    I do and the fan runs on max but when switched to lower speed the fuse blows.
     
  4. bpcurtis

    bpcurtis Rookie

    Nov 5, 2003
    30
    Dickinson, TX
    Full Name:
    Burnell Curtis
    Thanks, I hope my hands are small enough.
     
  5. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    18,733
    Texas
    Full Name:
    Steve Magnusson
    #5 Steve Magnusson, Feb 10, 2020
    Last edited: Feb 10, 2020
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  6. Rifledriver

    Rifledriver Two Time F1 World Champ

    Apr 29, 2004
    26,845
    Austin TX
    Full Name:
    Brian Crall
    I assure you they are smaller than mine.
     
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  7. Motob

    Motob Formula 3
    Professional Ferrari Technician

    Nov 11, 2003
    2,149
    Berkeley, CA
    Full Name:
    Brian Brown
    I tap threads in the aluminum frame for the transistor, so that I can bolt it back in place instead of using pop-rivets. A good replacement for the transistor can be purchased at an electronics store at a very low price. I am sure that there are many threads on this topic.

    Brian Brown
    San Francisco Motorsports
     
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  8. bpcurtis

    bpcurtis Rookie

    Nov 5, 2003
    30
    Dickinson, TX
    Full Name:
    Burnell Curtis
    Thanks everyone. After much neck pain I found the power transistor, removed it, found it good, replaced it anyway, and now the blower still works only on high but does not blow the fuse in the switch. My guess is that I have a bad connection somewhere or one of the relays is bad. Any suggestions?
     
  9. Motob

    Motob Formula 3
    Professional Ferrari Technician

    Nov 11, 2003
    2,149
    Berkeley, CA
    Full Name:
    Brian Brown
    Time to properly diagnose the system. Have you measured voltages at the base/emitter and collector of the blower speed transistor while varying the setting of the speed control? The workshop manual and the wiring diagram manual have good diagrams of how the system is wired. Ferrari made some changes over the years, using different speed controllers with slightly different wiring, so take that into account when looking at what you have.

    Brian Brown
    San Francisco Motorsports
     
  10. xplodee

    xplodee Formula Junior

    Jan 3, 2017
    845
    Allentown, PA
    Full Name:
    Tim
    I had an issue where a pad lifted on the circuit board of my fan speed switch. It prevented the fan from working at any speed below max. Took two minutes to fix once I identified it as the issue
     
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  11. bpcurtis

    bpcurtis Rookie

    Nov 5, 2003
    30
    Dickinson, TX
    Full Name:
    Burnell Curtis
    I have now found that the switch is bad. One of the pots on the board is bad. A replacement switch is $750. which I find insulting. Anyway, has anyone found a replacement for the pots or the switch itself. An electronics friend of mine says it is possible but will take time so I thought I would ask and not repeat work.
     
  12. bpcurtis

    bpcurtis Rookie

    Nov 5, 2003
    30
    Dickinson, TX
    Full Name:
    Burnell Curtis
    I have now found that the switch is bad. One of the pots on the board is bad. A replacement switch is $750. which I find insulting. Anyway, has anyone found a replacement for the pots or the switch itself. An electronics friend of mine says it is possible but will take time so I thought I would ask and not repeat work.
     
  13. bpcurtis

    bpcurtis Rookie

    Nov 5, 2003
    30
    Dickinson, TX
    Full Name:
    Burnell Curtis
    I have now found that the switch is bad. One of the pots on the board is bad. A replacement switch is $750. which I find insulting. Anyway, has anyone found a replacement for the pots or the switch itself. An electronics friend of mine says it is possible but will take time so I thought I would ask and not repeat work.
     
  14. vincenzo

    vincenzo F1 Rookie

    Nov 2, 2003
    2,673
  15. xplodee

    xplodee Formula Junior

    Jan 3, 2017
    845
    Allentown, PA
    Full Name:
    Tim
    You'll need to measure the resistance across the pot at the various taps. If I remember correctly it wasn't a common style of pot either, but you can likely just sub it out for one good enough. I can understand why an OEM switch would be so expensive, but the reality is you don't need to replace the whole switch and can just repair them.
     
  16. bpcurtis

    bpcurtis Rookie

    Nov 5, 2003
    30
    Dickinson, TX
    Full Name:
    Burnell Curtis
    The pot closest to the knob is good. The other pot is open at all points, which is strange.
     
  17. xplodee

    xplodee Formula Junior

    Jan 3, 2017
    845
    Allentown, PA
    Full Name:
    Tim
    can you provide a pic?
     
  18. bpcurtis

    bpcurtis Rookie

    Nov 5, 2003
    30
    Dickinson, TX
    Full Name:
    Burnell Curtis
  19. xplodee

    xplodee Formula Junior

    Jan 3, 2017
    845
    Allentown, PA
    Full Name:
    Tim
    Yours is different than mine. Do you have pics of the circuit board itself? Thats where the parts are likely to fail. Can the pot go back together? I wouldn’t have bothered to take it apart, maybe more harm than good there
     
  20. bpcurtis

    bpcurtis Rookie

    Nov 5, 2003
    30
    Dickinson, TX
    Full Name:
    Burnell Curtis
    I could supply a picture of the printed circuit board but the second pot, the closeup one, is not working. It has no measurements(open) on the carbon trace, which is why I took the whole thing apart. I could put it back together and put it on the board but I see no reason to do that now. If someone had a similar switch and could tell me the values of the second pot, then there is a possibility that I could fix it. Otherwise, I am stuck.
     

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