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TR AC Power Transistor Voltages?

Discussion in 'Boxers/TR/M' started by curtisc63, Aug 15, 2008.

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  1. curtisc63

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    #1 curtisc63, Aug 15, 2008
    I am in the process of replacing the Power Transistor on my 88.5 US TR. It is desplaying the classic signs - fan blows all or nothing. I have searched the forums and found everything I need - or so I thought. I replaced the transistor last night - buttoned things back up temporarily to test, reconnected the battery, turned on the key, and pressed the AC button. Nothing. Rotated the speed selector to full and "click" the relay takes over and I get full speed fan. Eergh. Searched the forums again and found a post from a couple years back where our great friend and contributor Steve (91TR) talked about voltages going to the transistor:

    Green/Red - 12V
    Yellow/Green - to Ground
    Orange/Red - a SMALL VARIABLE "+" VOLTAGE that would change with rotation

    I am wondering what the SMALL voltage should be - in my case it was 0.4V down to about 0.2V That just seems really small to me.

    Can anyone assist with what the voltage should be? And, since the transistor swap did not do the trick what should I look for? Is there a way to troubleshoot the rotary switch?

    Should I just put it back together and live with it all or nothing?

    Curtis
     
  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #2 Steve Magnusson, Aug 15, 2008
    I don't recall the context of the prior thread (why I suggested measuring "voltage" and not "current"), but the real thing to measure is the DC current flowing into the base (i.e., the DC current flowing in the orange/red wire) as you move the speed control knob requesting different speeds -- if things are working, this would be a small current (mAs) that would increase as you turn the speed control knob from a low variable speed to a higher variable speed. The fact that you have some voltage present on the base terminal (the orange/red wire) is better than having nothing at all, but I'm unsure what the value should be (if you can dig up a thread giving a manufactures PN for the transistor, or something near equivalent, maybe the manufacturer's data sheet would give a typical design value for Vbe).

    IIRC, they changed the TR speed control ECU twice so you might go to the TR SPC and first determine if you've got the 1st, 2nd, or 3rd type. From other's posts, I'm fairly certain that the 1st version has a small fuse that often blows giving this same symptom, and I know the 3rd version (which I have) has no fuse, but not sure about the 2nd type.

    One other thing to do is to take a jumper wire and connect the collector (the green/red wire) to the emitter (the yellow/green wire) -- the fan should run full speed (this checks the wiring associated with the transistor). If that works, and you confirm that you have no changing small DC current flowing in the orange/red wire when requesting different variable speeds, that would be a bad sign for the speed control ECU if it's fuse (if any) is OK. Does yours have the tiny fuse?
     
  3. curtisc63

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    #3 curtisc63, Aug 15, 2008
    Thanks Steve - maybe you did say Current in the previous thread - this was a couple years ago - and it was late last night while I was searching. I will check current next.

    No fuse on my switch - just a white plastic surround with 4 wires coming out - red, yellow, green and black. There is a hole in the side with what looks like an adjustable pot inside it. I have not touched this.

    I did short out the emitter and case last night by accident - thought I had fixed it! Fan ran almost full speed (discernable difference in sound) and did not vary with rotating the knob. Transistor got very hot, I have the blister to prove it.

    CC
     
  4. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #4 Steve Magnusson, Aug 15, 2008
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  5. jselevan

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    #5 jselevan, Aug 15, 2008
    Curtis and Steve - Do you know if this is a PNP or an NPN type transistor?

    Steve's suggestion of shorting the collector to emitter is simply a way of temporarily removing the power transistor from the circuit. It should run at full speed without any heat eminating from the transistor.

    If you inadvertantly shorted the emitter to ground, this should not have been a problem if the transistor is a NPN type. I assume that the emitter is already grounded. Hence, that the transistor got hot suggests that this might be a PNP (somewhat odd?).

    The rheostat (variable resistor) likely acts as a voltage divider on the base of the transistor. Hence, measuring the voltage at the base input as the rheostat is turned should provide information about the limits of full on and full slow base driving current. The PN or NP junction at the base-to-emitter drops approximately 0.7 volts. Thus, one can calculate and derive the base current from the transistor data sheet, however, this is unnecessary I suspect.

    Any power transistor should work. It should be capable of driving the fans. If there is a 16 amp fuse, then use this as your upper limits for the collector-emitter current. You can find these in most Radio Shacks or local hobby electronic shop.

    Jim S.
     
  6. Steve Magnusson

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    #6 Steve Magnusson, Aug 15, 2008
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  7. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #7 Steve Magnusson, Aug 15, 2008
    Last edited: Aug 15, 2008
    I'm pretty sure it's an NPN -- EZORED and Vince (vincenzo) had posted the PN (or maybe it's an equivalent PN) and a link to the data sheet in these threads -- 2N5886:

    http://ferrarichat.com/forum/showthread.php?t=191719

    http://ferrarichat.com/forum/showthread.php?t=190887

    which does make it seem strange about the heat Curtis noted when shorting the case (collector) to the emitter -- but, if the thing used as the jumper had some resistance (like a steel screwdriver shaft), it would heat up, and the heat would get conducted into the case pretty quickly -- just a thought...
     
  8. Mr.Chairman

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    #8 Mr.Chairman, Aug 16, 2008
    I am having the same issue with my a/c fan selector. How does the center plate on the console lift up so I can check. Which one of these units is the one with the fuse. I would like to start there first.

    R
     
  9. curtisc63

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    #9 curtisc63, Aug 16, 2008
    Last edited by a moderator: Sep 7, 2017
    Guys,

    Thanks for all jumping in on this. My Italian girlfriend has consumed my week. I had to spend time with my American girlfriend last night. It was worth the time away - I was getting quite frustrated. Below are the pin locations on my switch and a pic. Heading to a Ferrari picnic today - in my Miata (head hung in shame)

    It is the same style connector in a different numbering orientation. The label on the pin diagram is on the opposite side of the switch. BTW - An Alligator clip had shorted the pins. I was using another new resistor temporarily without soldering.
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  10. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #10 Steve Magnusson, Aug 16, 2008
    Last edited: Aug 16, 2008
    I wonder if yours is the 2nd style ECU (the pics I posted are 1st = 134128 and 3rd = 140151) -- does your SN decode to a different PN in the SPC?

    Also, could you please tell me what the wire colors are on the wiring harness side? I.e., pink wire on the ECU is connected to ? wire in the wiring harness; black wire on the ECU is connected to ? wire in the wiring harness; etc...

    TIA
     
  11. curtisc63

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    #11 curtisc63, Aug 17, 2008
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    Steve,

    Back in the garage today. Below you will see the labelled wires for the harness side. The bottom Yellow/Green Banded wire location has two wires coming from it. One goes off into the harness and the other loops back to the upper location noted.

    So when connected we get the following matchings, starting at the alignment notches and going clockwise when viewed from the switch side:

    OPEN => Double Yellow/Green Band
    Pink => Brown
    Black => Orange/Yellow Stripe
    Yellow => Single Yellow/Green Band
    Green => Pink/yellow stripe
    OPEN => Green

    I am far from an electronics genious, but the above table makes little sense to me...
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  12. curtisc63

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    #12 curtisc63, Aug 17, 2008
    Jim S.

    I purchased the following Transistor which was listed as an equivalent at my local electronics supply store:

    NTE181
    T-NPN, Sl, High Power Audio Amp

    CC
     
  13. curtisc63

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    #13 curtisc63, Aug 17, 2008
    BTW - The SPC (PDF Copy) I have does not list different part numbers for this switch. My serial number is 76802.
     
  14. curtisc63

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    #14 curtisc63, Aug 18, 2008
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    OK, I have admitted my lack of electronics so let me ask a question. Should or how should the transistor be isolated from the aluminum mounting plate? Is it not that important since the aluminum plate is mounted to plastic? I think it should because the case is actually taking the 12V from the switch. Right?

    Upon disassembly I found the below mounting.

    Where I label plastic I mean there was a thin, clear plastic wafer betwen the transistor and the mounting plate. This interface had some heat sink compound on it. There were also plastic isolating washers between the nuts and the mounting plate. I realize the screw is in contact with the case which is in contact with the wire end and nut. But why all the precautions???

    Wire from "Base" is orange with red bands. Orange did not come through in posting...
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  15. Steve Magnusson

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    #15 Steve Magnusson, Aug 19, 2008
    Last edited: Aug 19, 2008
    Even though you could probably get away with not using the "isolation" pieces for the transistor mounting on this TR application, that mounting is pretty much the standard design for the TO-3 transistor package -- because, as you noted, the case is "hot" (electrically), but also if used in a high frequency switching application, you don't want the heat sink acting like a big antenna. That thin sheet insulator is mica or a mica-substitute material (electrically insulating, but thermally conductive) and not typical "plastic".

    Thanks for giving the wire colors for the harness side. I checked the schematic, and it seems to all work out OK -- e.g., you show that the pink wire on your ECU connects to the brown wire in the harness, and the 509/88 schematic shows that the brown wire on the 140151 ECU connects to the brown wire in the harness, and the pink wire on your ECU is in the same position as the brown wire on 140151. I.e., 140151 should work OK in place of your ECU (even though the wire colors and placements seem different). I've got a spare 140151 so let me know if you need one and have a hard time getting one from the usual suppliers (last I heard they were getting scarce).

    You must have an early TR SPC. The later TR SPC shows:

    http://www.eurospares.co.uk/partTable.asp?M=1&Mo=624&A=2&B=35195&S=

    item 21 (the fan speed ECU)
    131473 for LHD up to SN 73475 (after looking up the "Heater Unit" PNs on a different page)
    134128 up to SN 79903
    140151 SN 79904 and after

    so you've got the second one, 134128, if it's never been replaced (and I wrongly stated that 134128 was the 1st one earlier).
     
  16. curtisc63

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    #16 curtisc63, Aug 20, 2008
    Is there no way to test the switch that you are aware of other than trying to measure the current from the ECU to the base?

    Secondly, if I put a new switch in place and the problem is somewhere else, will it fry the new switch?

    Curtis
     
  17. Steve Magnusson

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    #17 Steve Magnusson, Aug 20, 2008
    No. Your fan motor is already telling you that the current flow in the collector-to-emitter path is not working correctly (and you've replaced the transistor), so measuring the current behavior in the base-to-emitter path is the only other thing that I know to do.

    This is always a risk -- and why electrical parts sales are final ;). Since your fan works correctly at full speed, and when using the collector-to-emitter jumper, that's a good sign that you don't have anything seriously wrong with the wiring so little risk IMO that you would hurt a new part -- but please make your own decision. Welcome to the downside of complexity ;)
     
  18. curtisc63

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    #18 curtisc63, Aug 21, 2008
    Steve - I certainly understand that all of the advice given here is meant in good faith and that I take any and all responsibilities for any decisions I make. Thus so many questions and trying to make sure I understand as much as possible.

    Is there no other component to check between the switch ECU and the connector that leads to the transistor? I have tried to trace everything but I get lost lying upside down under what is left of my dash - I know there has to be something there as the wire color changes...

    BTW - you have a PM regarding your extra switch.

    Curtis
     
  19. curtisc63

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    #19 curtisc63, Aug 28, 2008
    Last edited: Aug 28, 2008
    New Switch in place and still no love...

    I might have made progress though. I decided to solder up a new transistor as it could only be the switch right??? Put the new switch in place, turn on the ignition, fan runs on high, rotate selector below 7/8 and fan stops. Cr@p! But wait, there is a rythmic "click-click" coming from deep in the dash near the floorboards. Checking the schematic there are a couple relays that seem to be invloved in the emitter circuit of the transistor. Could these be the culprit? Varying the position of the speed selector switch has no effect on the frequency of the "click-click".

    I am at my wit's end on this one AND I have a favored rally to attend Saturday. I will likely button up and go back to Full Speed or nothing operatio until winter. Eeeerrrghh!

    Any other ideas? How to troubleshoot/isolate if the relays can be the root of my problem? Please help.

    Thanks.

    Curtis

    Using the old speed selector switch results in the same "click-click" - so it looks like I have a spare switch now.
     
  20. Steve Magnusson

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    #20 Steve Magnusson, Aug 28, 2008
    Last edited: Aug 29, 2008
    It's never easy is it ;)

    However, I think that you are misreading the schematic somewhat. Although the ground line going to the emitter is also connected to some other components, they are not involved in operating the transistor/motor -- the emitter should just always be connected to ground. Try adding a jumper wire directly from the emitter to a known good ground and see if that has any effect -- your comment in post #3 about the "Fan ran almost full speed (discernable difference in sound)", rather than true full speed, when you had the collector jumpered to the emitter is maybe a sign that the emitter's connection to ground is not that good.
     
  21. curtisc63

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    #21 curtisc63, Aug 29, 2008
    You can say that again. Misreading schematics is not a far stretch either - with me it is like following a maze blindly and hoping to stumble my way out into the open - or at least find some cheese...

    Emitter to ground with jumper made no difference.

    I should be sleeping but really want to get this sorted by the week end. Any idea what the Clicking is? Something to wiggle or clean connections?
     
  22. curtisc63

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    #22 curtisc63, Aug 29, 2008
    Figured out what the Click-click sound was - the solenoid for temperature control. Rotate the knob, clicking changes rate. It was much cooler in the garage last night than previous nights.

    So, back to square one gosh darnnit...

    One question for the schematically gifted among us - Where do the wires from the climate control harness go (speaking specifically of the fan speed control unit to the power transistor) prio to re-emerging bundled with the hot air sensor wires (Orange/white and black/white) and terminating in a female 3 prong connector, which then goes to the transistor. The wiring colors have been thoroughly documented previously in the thread and they are not the same when they re-emerge. I ask this because I am not able to measure any current to the base leg of the transistor. I will use a better multi-meter this week end if I can lift one from work as I am not sure about the one I have. I do not recall all the colors in the 3 prong female connector as it was pretty late last night when I packed it in. The one I do recall was one all black wire. I will post connections later today - once I slip out of work with a multi-meter under my shirt...

    CC
     
  23. Steve Magnusson

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    #23 Steve Magnusson, Aug 29, 2008
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    They don't give the wire colors on the AC unit itself, but fortunately they put small "C", "E", and "B" labels on the transistor -- the "base" wire in the harness is SG (pink/yelllow):
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  24. curtisc63

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    #24 curtisc63, Aug 29, 2008
    How many times can I say thanks for helping out, Steve? I was trying to trace wires last night until I just couldn't take it anymore. I was checking connectors, wiggling wires, etc. until the big pink bunny in the corner of the garage finally threatened me with his light saber equipped right ear - that is the right ear when looking from behind the bunny, to be clear in the orientation. After "seeing" that I figured it was time to go to bed.

    My other fear is that the "New" switch I purchased could also be bad. The packaging and condition of the post where the knob mounts makes me wonder as to its previous life...

    CC
     
  25. Izzo02

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    #25 Izzo02, Jul 8, 2025
    Clearly this is a very old post… wondering if there was ever a solution?
     

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