Heating Controls ECU

[jeboa]

Hi all,

Looking for some advice before I attempt a job next week.

My 94 Griffith is giving no response from the Heating contorls. The LEDs are illuminated, but with the ignition on (engine not running) I am getting nothing from any of the controls. I suspect it is the control unit (ECU) as I would be surprised if all servos and the fan unit were faulty.

I have checked the ribbon cable connection on the controls circuit board and this is in place.

My first question is - how do I get to the ECU? I have looked at a picture on www.ballisticbanana.co.uk and think that the arrowed item is the unit.
<img src="www.jeboa.com/images/heater_ecu.jpg" width="278" height="232">

Is it possible to access using the radio slot? If not I guess it is a dashboard removal?

Has anyone had any experience in repairing/diagnosing these devices. I am assuming the heatsink is for cooling the servo/fan power transistors?

Is the ECU controlled by a microproccesor or does it contain servo controller IC's?

Any help would be appreciated, once I have got inside I will take some pictures and write a page on fault finding it if possible.

Thanks in advance to anyone who has a bit of know-how!



>> Edited by jeboa on Friday 17th June 17:41

>> Edited by jeboa on Friday 17th June 17:43

[stringbag]

Hi Jeboa, dash out is the easiest way. Black box on the bottom left hand side of the dash hole. Not sure how it works, but it is a TVR specific part.
Look at thegriffithpages for instructions on how to get the dash out if you haven't got the bible.

[JoolzB]

This is probly total nonsense but how I understand it works (someone like David Beer would be able to give you a more detailed explanation)

The controls consist of 2 potentiometers with a bit of gigerypokery in the middle: the TVR environment processor attached to yer knobs and a black box which in my car was under the radio, I could access it by taking the radio and cage out.

As you twizzle your control pot the motor the other end moves the other pot until the resistance matches.

The problem my car had was one of the components had lost it's solder in the black box.

Hope that helps a bit

[jeboa]

Thanks guys.

I have found the offending box. It was connected by the main 10-way connector and the ribbon cable. This would explain why the LEDs were working.

The three servo motor controls were not connected - here's my first problem - they are labelled F, R & W. Do you know which way they conenct from?

Second problem - The controller uses op-amps to work the servos (LM324 & L272M I/C's). The op-amps are powered by a small regulator IC (TA78l008) which provides 8 volts. Examining the board this IC has overheated and is not providing power. I have ordered some replacement ICs from Radio Spares - so hopefully this will sort out that problem.

I suspect that the IC has burnt out because one of the servos has stuck - so once I have it running again I can get to grips with that.

The wiring for the main fan blower seems to be sound and I don't see any evidence of overheating so the MOSFET should be okay.

The 10 Way connector is the other thing that is stumping me.

Looking at the connector there are 8 wires:

They are:

1 - Black / Red (x2)
2 - White
3 - Pink / Black
4 - Black
5 - Blue / Orange (x2)
6 - Green
7 - Not Connected
8 - Not Connected
9 - Black / White
10 - Black

Black / Yellow and Black Spade connectors shorted together - Fan Works!!!

[jeboa]

Sorry back again....this one might be an easy one for David Beer.....

Still working on the TVR Environment Control, turning out to be a good electronics tutorial!!

I have connected it up and the majority of it seems to be working now, with just one problem.

When I connect the fan wires, they only work if the +12v (yellow/black) is connected to the Drain of the MOSFET, if I connect the other way round I just get constant fan speed. This is good ('cos it works) but bad because it puts the heatsink at +12v, which is a big chunk of metal to have knocking round behind the dashboard at a positive voltage!

David, when you replaced your MOSFET did you use a Mica insulator to isolate the heatsink from the Drain? I checked BB website and in his dashboard removal pics he has his +12v connected the same way as mine.

I first suspected the MOSFET to be damaged (especially if I connected it in reverse polarity), but I have removed it and it tests out no problems. My MOSFET is a discontinued item. What type did you replace yours with?

Just one more thing.... one of the resistors on my board seems to have been snipped off (R30). I think its a 670k one and would explain why the Fresh/Recirculate servo isn't functioning. Have you had any experience with these burning out - maybe a previous DIY'er snipped it out?

[david beer]

My car is away being Takara'd, what mosfet do you have, the ones i have replaced were easily available. As for the heat sink being 12v pos, must be wrong, sounds nasty !

[jeboa]

It seems like a strange one - the wiring inside is blue and red - which you would have thought was the +ve red, blue -ve?? But with the -ve connected to the drain, the fan doesn't work correctly.

My MOSFET is a SNP60N06, which is no longer available. The closest replacement is the RFP70N06. I think my best bet would be to mount it to the heatsink using a mica bush and wahsers, at least that will prevent the heatsink being live!

Next time anyone has a control unit out, could they take a photo of the wiring connections and the PCB please?

[jeboa]

On another sidenote, does anyone know what rating the varaible resistor on the servos are, and where you can source replacements at present?