512TR Airco problem

So I've decided to replace the transistor as a first attempt as it seems the most probable cause. I took apart the vent panel (easy to do, 2x 8mm bolts holding it on, hidden behind the vents), and reached and and found the transistor. Its within easy reach and using my phone camera I took this quick video of where it is - you get a very clear image:
[ame=http://www.youtube.com/watch?v=RCbuYH1hS0U]512tr power transistor - YouTube[/ame]

Looks like the transistor is bolted onto a little platform, held on by what looks like a few 6mm nuts/bolts. The platform looks to be riveted on, but I would think I could remove the transistor with a bit of patience. Will go and order one....

 

Thanks for the video and good luck with the repair.

 

Finally got round to attempting this repair. Good news is it worked perfectly (or good enough).

I ended up removing the lower section of the dash in order to drill out the two rivets holding in the "mounting plate" the transistor sits on. This is very simple to do, a couple of notes on it:
1. First remove the small cover (2 screws) under the steering wheel.
2. You don't need to remove the unit with 3 gauges (clock) etc from the center of the dash - this comes away with the main lower dash. It has a simple connector to disconnect the wiring.
3. The main dash itself is held on by approx 8 bolts (10mm). You may have to peel back the carpet a bit to get access, but fundamentally a very simple job.

Once the dash was off I could see the rear of the 2 rivets. With hindsight (and with my plans for reattaching) you possibly could simply lever out the rivets from inside the vent rather than remove the whole dash. Once these were off I simply snipped the wires to the transistor and extracted the transistor and mount.

Pics below are of the rivets and the removed transistor.....continued below.....
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I had already bought the 2N3055 transistor - in fact I ended up with a dozen of them as they were 17p ($0.20) each and I had to buy enough to get them posted out!

Before I removed the old transistor from the mounting plate I put on a little bit of masking tape and marked the wire colours/locations.

Then its a (fairly) simple task of soldering on some new wire. I'm not sure of the max amperage going through the transistor - should be about 15A max, and I had some 30A cable so used that - I expect the actual amperage used will be less than this.

Note - when removing the old transistor it is important to capture the little clear mica film which sits between the transistor and mounting plate and reuse it. The mounting plate is in fact metal and is effectively a heat sink.

Here are a couple of pics of my replacement transistor mounted:
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I just used three simple bullet connectors (rated to 15A) to connect the wires - obviously marking which wire connects to which. The small connectors are useful as they will have to be pushed through the small hole in the side of the inside of the vent. I've also left plenty wire available as I'd rather tie up the extra underneath the dash and have the ability in future to simply pull the transistor forward out of the vent with the spare wire to be worked on/replaced.

My plan is to place a pad of velcro (hook & loop) inside the vent and simply attach the mounting plate with this rather than riveting into place - my feeling being that it will be more than strong enough to hold the plate in place, but allows the transistor to be replaced in under 30 mins in future if required.

A quick test now shows the fan is OFF when the stop button is down and I can adjust the fan speed from nothing to max with the rotary control.

The only slight thing which perhaps makes this not a perfect replacement is that the rotary dial seems to do nothing/very little for about the first 40% of its travel - I can't remember if this is the same as the original control and put it down to slightly different characteristics of the transistors. In any case it that last 60% of travel I can very the fan speed all the way from nothing all the way through full-on, so its not a concern as I have 100% functionality (the benefits of analogue electronics I suppose!)

As Melvok said above, the transistor (and mounting plate) get VERY hot very quickly.

I didn't mind taking off the dash as I have a couple of other issues to do with the stereo and alarm systems I want to correct and tidy the wiring under the dash, but if you're interested in a 512TR without the lower dash, it looks like the pic below.

Overall very pleased that a 20p part and a couple of hours on a sunday afternoon fixed this issue....who says these old cars are expensive to run!
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The blower motor in my 512TR wasn't working except on high so I knew I had this issue, here are some threads I found useful with various transistor related issues.
http://www.ferrarichat.com/forum/boxers-tr-m/241464-fan-speed-switch-90-tr.html
http://www.ferrarichat.com/forum/boxers-tr-m/143661-testarossa-blower-motor.html
http://www.ferrarichat.com/forum/boxers-tr-m/190887-pictures-fan-transistor.html
http://www.ferrarichat.com/forum/boxers-tr-m/209296-tr-ac-power-transistor-voltages.html
http://www.ferrarichat.com/forum/technical-q-sponsored-algar-ferrari/102194-tr-fan-control-new-fuse-2-new-transistors.html

The board (part#127014) is NLA but no matter as there were TWO of these already installed, the original and another one presumably installed by a dealer when it failed.
So I removed one to make space for a new FET attached to a larger finned heatsink shown below (the largest that would fit).
Testing with an IR thermometer showed 65C max temp with no air flow (tested outside the housing) on a few fan speed settings.
I think this will last longer than the old ones... and thanks to the thread contributors for the help.
Andrew
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Thanks Mel, I'll see how it goes.
If it fails again, I'm sure there is a DC motor controller that can be adapted to make this work better.
This design cracks me up because the A/C at low fan speed is blowing air across a 65C+ heating plate.
I'm sure the original plate runs at over 80-90C but I didn't measure it.
Andrew

 

Hey All-

Bunping this thread bc I need to replace the same transistor in my ‘87 TR.

Anyone throw a 12v DC fan on their heat sink that runs at full speed anytime the air is turned on? I think this type of unit mounted to a heat sink should work pretty well.

Alternatively an electrically insulating but thermally conductive gasket between a heat sink and passenger kick panel should be perfect.

Thoughts?