| Author | Message | ||
| Carl Rose (Carl_rose)
Junior Member Username: Carl_rose Post Number: 87 Registered: 10-2002 |
Successful diagnosis today. Removed RH heater blower switch (part# identical to A/C) and plugged into A/C harness. Variable control of fan speed returned. Disassembled the A/C fan switch again - composed of a two connected potentiometers on a circuit board. Resistance values directly from the potentiometer out-leads indicate proper change in resistance with increasing rotation of shaft, leading me to believe a component on the board is faulty. Certainly would welcome any advice from EE folks but figure time has come for new switch. Do these cross-reference with any standard-type switches, or must I buy Ferrari-specific? (once again my automotive problems fall into that 1%/+3 SD bracket...sigh) Thanks for everyone's help. I'll finish up editing & post procedure.  Carl | ||
| Carl Rose (Carl_rose)
Junior Member Username: Carl_rose Post Number: 86 Registered: 10-2002 |
Thanks JRV. With your experience suspect you're right about this, I'm still determined to be a good mechanic (not a "parts-changer"). Interchanging the fan switch is a (relatively) simple job to avoid spending $$ replacing component that may not be at fault. Heater blower motors both function correctly. LH LEDs work properly, noticed about two days ago the RH temperature rocker LEDs didn't light - plan to delve into that next. As the circuits are independent figured separate etiologies (will start at heater valve & motor). Your point about replacement/original transistors having different lead configurations is a good thought. I'll check replacement/spare/originals tonight with ohmmeter.This would certainly make sense with your previously having to switch a wire to fix. My understanding of this system (reading wiring diagram) is that it is essentially a "ground control", with fan switch lead controlling amount of input voltage bled off through ground lead? (excuse my ignorance if I am incorrect) Carl | ||
| JRV (Jrvall)
Intermediate Member Username: Jrvall Post Number: 1030 Registered: 11-2002 |
I'm trying to remember what my orig problem was when doing this workaround. You might need to check the flow path of the generic transistor, seems like I remember something about the generic lead positioning & the original being switched or reversed. Essentialy Carl the system is just an electronic variable reostat...eveything in the middle (below high speed) is controlled via switch micro circuits and transistor... Of course it's always possible something new can go wrong....but I've never seen the symtom you describe being anything other than the transistor power unit. Is your heater system working properly? | ||
| Carl Rose (Carl_rose)
Junior Member Username: Carl_rose Post Number: 85 Registered: 10-2002 |
Hi Mr. Magnussen, You are correct - part #126854 is transistor for heaters/#126856 is for A/C. Heater fan & A/C fan switches listed as same part # (with superceding # for all) so expect they will interchange. Plan to try to test this evening if I get home at a decent hour. Thanks for all your help; as usual, my automotive endeavors always seem to be more "challenging" than the norm... Carl | ||
| Steve Magnusson (91tr)
Intermediate Member Username: 91tr Post Number: 1459 Registered: 1-2001 |
Carl -- As far as swapping the controls, I'd say "might work but need to be sure". My brief exposure to the 328 SPC indicates that the 328 heater blower motors and the 328 AC blower motor have similar ECU/power transistor/motor set-ups (and I'd guess that the two 328 transistor PNs that Jeff H. listed might only be different in heatsink design/mounting -- one for the AC, the other for the heaters), but you'd really need to confirm on the schematic beforehand IMO. IIRC Steve Jenkins has an '89 328 wiring diagram on his site if you want to pursue. Did you try the simple test of jumpering the collector to the emitter? | ||
| Carl Rose (Carl_rose)
Junior Member Username: Carl_rose Post Number: 83 Registered: 10-2002 |
(This is a family conference - any help is appreciated Mr. Rochlin!) I have pictures at home but transistor is basically 2N5886/TO-3 configuration attached to an aluminum bracket sandwiching a mylar insulator. When installed, transistor is in A/C ducting airflow tract; assume cooling air & aluminum bracket designed to function as heat sinks. Carl | ||
| Steven R. Rochlin (Enjoythemusic)
Junior Member Username: Enjoythemusic Post Number: 185 Registered: 4-2002 |
Hi, (Warning, i am an audio electronics geek) While not familiar with the exact transistor or how it appears on the board, is there room to attach a heat sink to the transistor? If so, then i'd highly recommend installing one with the appropriate installation technics. Just trying to help. Enjoy the Drive, Steven R. Rochlin | ||
| Carl Rose (Carl_rose)
Junior Member Username: Carl_rose Post Number: 82 Registered: 10-2002 |
Thanks guys for sticking with me on this. Although I would be the first to admit I could have resoldered wires in incorrect orientation, in this instance not only did I make a diagram but - since I intend on posting in maintenance section took sequential pictures - in reviewing the "pre-disassembly" versus "post" wires in proper position. There is always the possibility this was manufactured wrong, but if wires were switched would the motor function at all? (non-EE speaking) JRV your point about checking mylar insulator below transistor is well-taken. Will check. Steve, I'll check voltages & resitances as suggested & report back. Any thoughts on removing console & substituting heater blower switch? Thanks once again, Carl | ||
| JRV (Jrvall)
Intermediate Member Username: Jrvall Post Number: 1026 Registered: 11-2002 |
I concur with Steve...also make sure the insulators are in their proper places... I'm pretty sure I had the same problem once and I had a wire on wrong or something. After rechecking everything I switched a wire and got it working...however, I've just ordered them from Ferrari for quite a few years now , plug them in and move on. But since you have a spare you might as well keep going this way. | ||
| Steve Magnusson (91tr)
Intermediate Member Username: 91tr Post Number: 1458 Registered: 1-2001 |
Carl -- If your 328 transistor set-up is like the TR, try connecting the collector to the emitter with a short (stout) jumper wire (which would simulate the transistor conducting) -- the blower motor should run at full speed. If that works, then you'll have to get into looking at what's going on (or not going on) in the base-emitter path. Have you tried measuring the voltage at the base terminal or the current flow into the base terminal as you turn the speed control knob? | ||
| Carl Rose (Carl_rose)
Junior Member Username: Carl_rose Post Number: 81 Registered: 10-2002 |
The plot thickens... Disassembled and removed old transistor & soldered in new & reassembled. No change in symptoms - A/C blower continues to run on high setting only. Appears the heater blower switches are identical part # to A/C fan; considering removing console & interchanging to see if switch is at fault? Any other suggestions to proceed? Thanks once again, Carl | ||
| Carl Rose (Carl_rose)
Junior Member Username: Carl_rose Post Number: 80 Registered: 10-2002 |
This board and its participants continues to be a superb resource. I was actually able to locate & purchase the proper transistor (and a spare) from a local electronics supply house ($11). On call this evening, will try and replace in next few days & post illustrated procedure & results. (Not adverse to spending $ on my mechanical child...just very "determined" [<-- other words may be substituted here] mechanic!) (smile) Carl | ||
| Jeff Howe (Ferrari_uk)
Junior Member Username: Ferrari_uk Post Number: 139 Registered: 12-2002 |
Hi all. I come up with 2 part numbers for the transistor by selecting 328, aircon and putting 'transistor' in to the search engine on the Owners' Site parts area: 126854, �43.40 or about $68.71 and 126856, �97.80 or about $154.85 Hope this is of use. | ||
| JRV (Jrvall)
Intermediate Member Username: Jrvall Post Number: 1023 Registered: 11-2002 |
At one time I was able to locate an indentical replacement transistor for about $20 from a large wholesale Electronics Wharehouse. This failure is very, very common. And if you ever touch a working transistor and see how much heat it sheds you'll know why. | ||
| Steve Magnusson (91tr)
Intermediate Member Username: 91tr Post Number: 1451 Registered: 1-2001 |
Carl -- Unfortunately, the F part number for the 328 power transistor assembly is different than the TR power transistor assembly 127014 (but it wouldn't surprise me if the difference is in the heatsink/mounting rather than the transistor itself). For reference, the TR power transistor case is marked: BDY29 which shows up via a brief internet search as a SI-N 100V 30A 220W transistor and I believe it is hooked up in a common emitter configuration: The case is the collector and would measure +12V with the ign. key on, the grounded terminal is the emitter, and the terminal hooked to the speed control switch is the base. Any similar markings on the 328 power transistor? | ||
| Steve Magnusson (91tr)
Intermediate Member Username: 91tr Post Number: 1446 Registered: 1-2001 |
Carl -- While I appreciate your desire to avoid the replacement syndrome, I think you could go for a fresh blower power transistor with no regrets now even if it isn't the problem -- i.e., better to buy a new one now (if the price isn't crazy) rather than do the labor again in the near future anyway. I think based on our collective experience it's clear that this transistor dissapates a lot of power so it gets a lot of thermal stress and doesn't age well. I've never tried sourcing just the transistor itself, but it couldn't hurt to talk to Radio Shack, etc. (maybe the case markings are enough for identification). Do you have a wiring diagram to identify base, collector, emitter? (I can't recall if the TR schematics show that detail, but I'll check tonight). | ||
| JRV (Jrvall)
Intermediate Member Username: Jrvall Post Number: 1018 Registered: 11-2002 |
This is an easy one, new resistor..it's shot. | ||
| Carl Rose (Carl_rose)
Junior Member Username: Carl_rose Post Number: 79 Registered: 10-2002 |
Hi everyone, Searched the archives for about 90 minutes unfortunately no direct answer. Symptom: A/C blower operates on high only (knob at full clockwise), no slower speeds. Removed & cleaned console switch with electrical contact cleaner to no avail. Removed "power transistor" in duct...appears OK (i.e. to us non-EE folks "no burning look/odor!) one lead is 12v hot, one to ground, other to A/C switch. 1. What is the best way to comprehensively test either switch or transistor (trying to avoid the "diagnosis by replacement syndrome")? 2. Per archives transistor is most frequent etiology. Can just the small silver disk-shaped unit (attached to bracket) be sourced at an electrical supply house? Thanks very much in advance for everyone's help. Plan to post removal procedure (pictures/text) once I have a moment to edit. Carl |