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Integrator
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Discussion Starter #5
Esprit Headlight Lift Module Failure

Preventing headlight lift motor current sensing module failure.

There are two bidirectional triode thyristors, which may overheat and fail.

As a countermeasure, add heat sinks to both triacs. Apply heat conductive white goo before tightening screws.

Add two strips of closed cell foam over the terminal blades to seal off the box against water intrusion.

??? Anyone has a x-reference for this component???
I know it has been used on GM cars in the 80-s.

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Wingless Wonder
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Hey! Can't you read? :facepalm

The sticker in your photo says "REPLACE DO NOT REPAIR" :no:


rotfl rotfl rotfl



More seriously:
Add two strips of closed cell foam over the terminal blades to seal off the box against water intrusion.
Where is this located again...and why would it get wet? :scratchhead:

(Yes, I DO see water stains in the first pic)

You should post this in a separate Topic since it applies to ALL Stevens Esprits, BTW.)
 

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Those are MOSFETs, not thyristors. I have a spare good module if anyone needs one, to replace, not repair :)
 

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Those are MOSFETs, not thyristors. I have a spare good module if anyone needs one, to replace, not repair :)
I also have a spare (that's not for sale :D) but note that its the same module fitted to the M100 Elan and over on the LEC forum somewhere it was discovered that this was fitted to several GM cars of the period (85 to 95) so they are still available, should you want to replace not repair:D
 

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Wingless Wonder
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So...tell me where the module located in the in M100, too (in case I want to grab it while no one is looking). >:)

JUST KIDDING... (maybe) :p
 

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Integrator
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Discussion Starter #12 (Edited)
Blinking Econ Light = Speed Sensing Module failure

Thank you Van for this insightful investigation and a repair procedure.


Fri Mar 17, 2017 7:36 am (PDT) .
Posted by:
"Van Overhouse" van_overhouse

For 86-88 MY cars with the Bosch CIS system the green ECON light should come on steady while off throttle and in overrun condition. In two cases now I've seen that the light blinks rather than remain on. I traced this back to a bad "Speed Sensing Module" which I replaced the first time. Now that I've seen the problem a second time I decided to try and fix the Module rather than buying a new one. The first step was to do some reverse engineering and generate a schematic for the Module. I've posted the schematic at Turbo List files/tech/electric .

What I found was that either the Module design has an error or the Lotus application is incorrect. Within the module there is a 750 ohm 1/4W resistor connected between pin #15 (V+ from RPM Relay) and terminal #31b going to the Thermal Time Switch. During warm up, terminal #31b is grounded by the Thermal Time Switch until the water temperature reaches 35C. During this period the 750 resistor has 14.5V across it which generates (14.5*14.5/750= 0.3W) watts which is greater than the resistor specification allows. Once up to temperature the ground is removed and the power drops to about .13 watts. This extra stress on the resistor eventually causes it to fail.
In addition, the 750 ohms is too large a resistor and current flowing through it and out to the thermal time switch is causing too much voltage drop. The voltage at the node with the 750 ohm (?), 27K and ITT diode is too low to turn on the BC547 transistor. Making the resistor smaller will raise this voltage to the acceptable level.
?What would be the smallest 1/4W resistor you could use to replace the 750 ohm (R= E*E/P). At 14.7V that would be 865 ohms.
So if you put in a 1W resistor that would be 316 ohms. I'd replace it with a 330 ohm, 1W resistor.

After replacing the resistor, the should not fail again.

If you have a blinking Econ light and want to quickly test if you have the same problem just disconnect the Thermal Time Switch connector once the engine is up to temperature. If the Econ light no longer blinks you most likely have the same problem. If you do have this problem you should fix it as it is also pulsing the air bypass valve which will wear it out prematurely. Don't throw away your old Speed Sensing Modules they are repairable and we may need them some day.

Module: It's the one with the black base and you should see the Bosch part number 0 280 230 103 on the case [back wall, above the coil]. I didn't replace the Ecap on the PC board since I tested the module on the bench. Probably should have replaced it with 35V or 50V cap. Hopefully, it doesn't come back to bite me.

After thinking about the error I believe it must be the Lotus application of the module that is incorrect. Also, I believe that pretty much every Lotus module out there has a "750 resistor problem".
The original resistor looks to be a ceramic thin film resistor and the failure mechanism for this type of resistor is when it overheats is for the resistance to increase (if it doesn't fail outright like a fuse).
Once the resistance becomes high enough, it will no longer overheat. In some cases the higher resistance is not sufficient to cause the circuit not to work. In other cases it is too high and the module fails with the blinking ECON light syndrome.
 

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Here ya
go, NOTE: the sunbird/Fiero modules are NOT the ones you want, you want the 92/93 Firebird modules:

Lotus Elan Central
The other GM modules do NOT work in the Esprit. The look identical and they plug in but they will not function properly. You're throwing money away if you buy one. I have been down this path and tested out a bunch of them. If you need a module contact Sanj. He can repair them if the MOSFET is bad.
 

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Integrator
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Discussion Starter #15
Overspeed Module Problem

Hi John:

Yes, I believe there is an error in the [Overspeed Module] design. There is a "B" revision (B082M6374) which may correct the problem but I'm not sure since I dissected the "A" rev part.

The failure symptom is after driving the car and you park it hot and leave it for 10-20 minutes it will not start. If you wait for an hour or so and it cools down it will start.
The problem, I believe, is that humidity is collecting around R6 (2.2Meg ohms) and lowering its resistance. The specification for the TC4538 says that the maximum resistor value allowed is 1Meg (!). If you look at the bottom of the schematics you can see a note where I changed the value of R6 to 220K ohms and C4 to 1uf. Other values which result in the same time constant (R6 X C4=220ms) would also be OK. After replacing these parts I've never had the problem reoccur.

Van
 

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Integrator
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Discussion Starter #16 (Edited)
C4 and R6 are soldered directly to the pins of the IC! Yikes!
If I try to de-solder them, I'm running a possibility of overheating the IC.

My solution:
Crush C4 to expose its conductors above the board and and solder the new cap to them? Resistor can be dealt with in the same way.

Note: Tantalum caps have polarity! The + leg is always longer.
"While you're there", replace the 22uF electrolytic cap (large, blue) with a fresh 50V rated part
.
 

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Integrator
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Discussion Starter #17 (Edited)
Re: posting #5 of this thread.

Preventing headlight lift motor current sensing module failure.

There are two MOSFETs, which often overheat and fail.

As a countermeasure, add heat sinks to both semiconductors. Apply heat conductive white goo before tightening screws.

Add two strips of closed cell foam over the terminal blades to seal off the box against water intrusion.

.
This mod applies to ALL Esprits/all model years.

If you need a help with yours, talk to Sanj on this forum.
 
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