[Guv Bob]

This not a lot of detailed info about these old 1G's out there, so I'm having to do a lot of guessing...

My problem is the Check Engine light does not illuminate. The bulb and all circuits external to the ECU board are fine. The board is also good between the 12VDC into the board from the bulb and ground. I suspect the trouble is the transistor, resistor or any associated capacitor, but the board has been worked on before and the markings on these parts are no longer readable.

Without a schematic, I wonder if someone more familiar with this type of circuit could guess at a possible replacement for the transistor and capacitor.

I know this is not the "proper" way to do it, but the alternative is buying a new ECU - several hundred $$. So I'd like to try a few things that might have a chance of working before doing that.

Here's the only schematic I can find that shows the transistor and resistor on the board, but no info as to what the parts are. Also, can't find what is connected to the base, and can't get in to check the base signal. I can swap out the parts from the component side of the board OK, but can't trace the leads without damaging something else on the board -- due to the condition of the board.

Probably sounds goofy to you guys, but until I can get that light to work and the car to pass smog, I can't justify spend much cash on restoring the car.

http://img823.imageshack.us/img823/7787/pdv.gif

Thanks in advance!

Bob

[Scromlette]

On 17/09/2013 11:47 AM, Guv Bob wrote:
This not a lot of detailed info about these old 1G's out there, so I'm having to do a lot of guessing...

My problem is the Check Engine light does not illuminate. The bulb and all circuits external to the ECU board are fine. The board is also good between the 12VDC into the board from the bulb and ground. I suspect the trouble is the transistor, resistor or any associated capacitor, but the board has been worked on before and the markings on these parts are no longer readable.

Without a schematic, I wonder if someone more familiar with this type of circuit could guess at a possible replacement for the transistor and capacitor.

I know this is not the "proper" way to do it, but the alternative is buying a new ECU - several hundred $$. So I'd like to try a few things that might have a chance of working before doing that.

Here's the only schematic I can find that shows the transistor and resistor on the board, but no info as to what the parts are. Also, can't find what is connected to the base, and can't get in to check the base signal. I can swap out the parts from the component side of the board OK, but can't trace the leads without damaging something else on the board -- due to the condition of the board.

Probably sounds goofy to you guys, but until I can get that light to work and the car to pass smog, I can't justify spend much cash on restoring the car.

http://img823.imageshack.us/img823/7787/pdv.gif

Thanks in advance!

Bob



What about throwing together a little monostable using a 555. Turn key
on == check eng light on == times out & light goes off???

[Guv Bob]

"Scromlette" wrote in message ...
On 17/09/2013 11:47 AM, Guv Bob wrote:
This not a lot of detailed info about these old 1G's out there, so I'm having to do a lot of guessing...

My problem is the Check Engine light does not illuminate. The bulb and all circuits external to the ECU board are fine. The board is also good between the 12VDC into the board from the bulb and ground. I suspect the trouble is the transistor, resistor or any associated capacitor, but the board has been worked on before and the markings on these parts are no longer readable.

Without a schematic, I wonder if someone more familiar with this type of circuit could guess at a possible replacement for the transistor and capacitor.

I know this is not the "proper" way to do it, but the alternative is buying a new ECU - several hundred $$. So I'd like to try a few things that might have a chance of working before doing that.

Here's the only schematic I can find that shows the transistor and resistor on the board, but no info as to what the parts are. Also, can't find what is connected to the base, and can't get in to check the base signal. I can swap out the parts from the component side of the board OK, but can't trace the leads without damaging something else on the board -- due to the condition of the board.

Probably sounds goofy to you guys, but until I can get that light to work and the car to pass smog, I can't justify spend much cash on restoring the car.

http://img823.imageshack.us/img823/7787/pdv.gif

Thanks in advance!

Bob



What about throwing together a little monostable using a 555. Turn key
on == check eng light on == times out & light goes off???

Yeah, that's basically the same circuit I was putting together for a different application, but it would not indicate a real fault.

[dave]

On 09/16/2013 08:47 PM, Guv Bob wrote:
This not a lot of detailed info about these old 1G's out there, so I'm having to do a lot of guessing...

My problem is the Check Engine light does not illuminate. The bulb and all circuits external to the ECU board are fine. The board is also good between the 12VDC into the board from the bulb and ground. I suspect the trouble is the transistor, resistor or any associated capacitor, but the board has been worked on before and the markings on these parts are no longer readable.

Without a schematic, I wonder if someone more familiar with this type of circuit could guess at a possible replacement for the transistor and capacitor.

I know this is not the "proper" way to do it, but the alternative is buying a new ECU - several hundred $$. So I'd like to try a few things that might have a chance of working before doing that.

Here's the only schematic I can find that shows the transistor and resistor on the board, but no info as to what the parts are. Also, can't find what is connected to the base, and can't get in to check the base signal. I can swap out the parts from the component side of the board OK, but can't trace the leads without damaging something else on the board -- due to the condition of the board.

Probably sounds goofy to you guys, but until I can get that light to work and the car to pass smog, I can't justify spend much cash on restoring the car.

http://img823.imageshack.us/img823/7787/pdv.gif

Thanks in advance!

Bob


I'd try a wrecking yard for a salvage ECU.

[Guv Bob]

"dave" wrote in message m...
On 09/16/2013 08:47 PM, Guv Bob wrote:
This not a lot of detailed info about these old 1G's out there, so I'm having to do a lot of guessing...

My problem is the Check Engine light does not illuminate. The bulb and all circuits external to the ECU board are fine. The board is also good between the 12VDC into the board from the bulb and ground. I suspect the trouble is the transistor, resistor or any associated capacitor, but the board has been worked on before and the markings on these parts are no longer readable.

Without a schematic, I wonder if someone more familiar with this type of circuit could guess at a possible replacement for the transistor and capacitor.

I know this is not the "proper" way to do it, but the alternative is buying a new ECU - several hundred $$. So I'd like to try a few things that might have a chance of working before doing that.

Here's the only schematic I can find that shows the transistor and resistor on the board, but no info as to what the parts are. Also, can't find what is connected to the base, and can't get in to check the base signal. I can swap out the parts from the component side of the board OK, but can't trace the leads without damaging something else on the board -- due to the condition of the board.

Probably sounds goofy to you guys, but until I can get that light to work and the car to pass smog, I can't justify spend much cash on restoring the car.

http://img823.imageshack.us/img823/7787/pdv.gif

Thanks in advance!

Bob


I'd try a wrecking yard for a salvage ECU.

Thanks, struck out with that -- or finding someone to repair this one.

[ehsjr[_3_]]

On 9/16/2013 11:47 PM, Guv Bob wrote:
This not a lot of detailed info about these old 1G's out there, so I'm having to do a lot of guessing...

My problem is the Check Engine light does not illuminate. The bulb and all circuits external to the ECU board are fine. The board is also good between the 12VDC into the board from the bulb and ground. I suspect the trouble is the transistor, resistor or any associated capacitor, but the board has been worked on before and the markings on these parts are no longer readable.

Without a schematic, I wonder if someone more familiar with this type of circuit could guess at a possible replacement for the transistor and capacitor.

I know this is not the "proper" way to do it, but the alternative is buying a new ECU - several hundred $$. So I'd like to try a few things that might have a chance of working before doing that.

Here's the only schematic I can find that shows the transistor and resistor on the board, but no info as to what the parts are. Also, can't find what is connected to the base, and can't get in to check the base signal. I can swap out the parts from the component side of the board OK, but can't trace the leads without damaging something else on the board -- due to the condition of the board.

Probably sounds goofy to you guys, but until I can get that light to work and the car to pass smog, I can't justify spend much cash on restoring the car.

http://img823.imageshack.us/img823/7787/pdv.gif

Thanks in advance!

Bob


If you can get to the trace connected to the base of the
transistor and solder a wire to it, you can connect a
meter and measure the voltage there. It needs to go to
about .6 volts above the emitter to turn on the light.
You could also connect a 2.2 K resistor to that wire.
When the other end of the resistor is connected to +12,
the bulb should light. If it does, the failure is
in the base circuit and you'll have to pull the board
to diagnose further. If it doesn't light, then replacing
the transistor or resistor or repairing traces on the board
is indicated, and you can read the rest of this long post
for more information on how to figure out the part values.

The transistor is an NPN. Get an NPN of the same physical
size, with the highest current rating (see the datasheet)
you can find. Even better, determine the current rating of
the check engine lite bulb, and get a transistor rated
for at least that current. The resistor between the
collector of the transistor and the bulb limits the current
available to the bulb. The value of that resistor can
be determined by measuring it with an ohmmeter, unless it
is burned up/damaged/cracked etc.

If the resistor value can't be measured, you can figure it
out mathematically or by experiment. Here's an example
using math:

Lets say the bulb is rated at 12 volts and 800 mA current.
That means that when the bulb is hot, it has a resistance
of 12/.8 or 15 ohms. Now an auto can provide say 14.5 volts
when the engine is running, so we want to drop that down to
no more than 12 volts. And to lengthen the life of the
bulb, dropping down to 11.5 volts would be better. So, if the
target voltage is 11.5, we want to add a resistor that will
drop 3 volts. The circuit would look like this:

+12 ---[Bulb]---[Resistor]---[Transistor]---Gnd

That's what you have in the schematic you provided.

When the transistor is switched on, it will drop a small amount
of voltage, but for this example we'll ignore that.

So our circuit is the bulb, which is 15 ohms when hot, in
series with an unknown resistor that we want to drop 3
volts. That means there will be 9 volts across the 15 ohm
resistance of the bulb, and 3 volts across the unknown
resistance when 12 volts is applied to the circuit.
We can solve for Ru (the unknown resistance) using ohm's
law: Voltage (E) = Current (I) * Resistance (R)
We know the voltage across the bulb's 15 ohm resistance is
9 volts, so 9 = 15 * I. That means I = 9/15 or .6 amps

That same .6 amps flows through Ru, dropping 3 volts, so
3 = Ru * .6 and therefore Ru = 3/.6 or 5 ohms. That 5 ohm
resistor will heat when .6 amps flows through it. The power
dissipated will be 1.8 watts, and it makes sense to use a
higher wattage resistor. So in this hypothetical example,
a 5 ohm 5 watt resistor would be a good choice.

Here's how to do it experimentally:
Connect the bulb to a variable voltage supply. Gradually
increase the voltage until the bulb is bright enough.
Note that "bright enough" means less than full brightness.
Measure the voltage and the current. Call that the target
current. The unknown resistor needs to drop the difference
in voltage between bright enough and 13.8 volts, at the
target current. At this point you can determine the
value of the resistor you need to add mathematically as
follows, or continue experimentally as in the next paragraph.
Vdrop = 13.8 - measured voltage; I = target current, so
13.8 = R * I, therefore R = 13.8/I. R is rated in ohms.
The power dissipated (rated in watts) by that resistor must
be at least Vdrop * I You want a standard wattage resistor
that is at least 50% higher wattage than computed, and double
is better.

Continuing with the experimental method:
Now add a 1 ohm 1 watt** resistor in series with the bulb,
and raise the voltage until you get the target current
again. Repeat the process of adding 1 ohm resistors
until you reach the target current at 13.8 volts.
** = the wattage presumes that the target current is
1 ampere or less. If higher than one ampere, use 2 watt
resistors, if higher than 2 amperes you would need 5
watt resistors - but it is highly doubtful that dashboard
bulbs would draw current that high.

Ed

[Guv Bob]

"ehsjr" wrote in message ...
On 9/16/2013 11:47 PM, Guv Bob wrote:
This not a lot of detailed info about these old 1G's out there, so I'm having to do a lot of guessing...

My problem is the Check Engine light does not illuminate. The bulb and all circuits external to the ECU board are fine. The board is also good between the 12VDC into the board from the bulb and ground. I suspect the trouble is the transistor, resistor or any associated capacitor, but the board has been worked on before and the markings on these parts are no longer readable.

Without a schematic, I wonder if someone more familiar with this type of circuit could guess at a possible replacement for the transistor and capacitor.

I know this is not the "proper" way to do it, but the alternative is buying a new ECU - several hundred $$. So I'd like to try a few things that might have a chance of working before doing that.

Here's the only schematic I can find that shows the transistor and resistor on the board, but no info as to what the parts are. Also, can't find what is connected to the base, and can't get in to check the base signal. I can swap out the parts from the component side of the board OK, but can't trace the leads without damaging something else on the board -- due to the condition of the board.

Probably sounds goofy to you guys, but until I can get that light to work and the car to pass smog, I can't justify spend much cash on restoring the car.

http://img823.imageshack.us/img823/7787/pdv.gif

Thanks in advance!

Bob


If you can get to the trace connected to the base of the
transistor and solder a wire to it, you can connect a
meter and measure the voltage there. It needs to go to
about .6 volts above the emitter to turn on the light.
You could also connect a 2.2 K resistor to that wire.
When the other end of the resistor is connected to +12,
the bulb should light. If it does, the failure is
in the base circuit and you'll have to pull the board
to diagnose further. If it doesn't light, then replacing
the transistor or resistor or repairing traces on the board
is indicated, and you can read the rest of this long post
for more information on how to figure out the part values.

The transistor is an NPN. Get an NPN of the same physical
size, with the highest current rating (see the datasheet)
you can find. Even better, determine the current rating of
the check engine lite bulb, and get a transistor rated
for at least that current. The resistor between the
collector of the transistor and the bulb limits the current
available to the bulb. The value of that resistor can
be determined by measuring it with an ohmmeter, unless it
is burned up/damaged/cracked etc.

If the resistor value can't be measured, you can figure it
out mathematically or by experiment. Here's an example
using math:

Lets say the bulb is rated at 12 volts and 800 mA current.
That means that when the bulb is hot, it has a resistance
of 12/.8 or 15 ohms. Now an auto can provide say 14.5 volts
when the engine is running, so we want to drop that down to
no more than 12 volts. And to lengthen the life of the
bulb, dropping down to 11.5 volts would be better. So, if the
target voltage is 11.5, we want to add a resistor that will
drop 3 volts. The circuit would look like this:

+12 ---[Bulb]---[Resistor]---[Transistor]---Gnd

That's what you have in the schematic you provided.

When the transistor is switched on, it will drop a small amount
of voltage, but for this example we'll ignore that.

So our circuit is the bulb, which is 15 ohms when hot, in
series with an unknown resistor that we want to drop 3
volts. That means there will be 9 volts across the 15 ohm
resistance of the bulb, and 3 volts across the unknown
resistance when 12 volts is applied to the circuit.
We can solve for Ru (the unknown resistance) using ohm's
law: Voltage (E) = Current (I) * Resistance (R)
We know the voltage across the bulb's 15 ohm resistance is
9 volts, so 9 = 15 * I. That means I = 9/15 or .6 amps

That same .6 amps flows through Ru, dropping 3 volts, so
3 = Ru * .6 and therefore Ru = 3/.6 or 5 ohms. That 5 ohm
resistor will heat when .6 amps flows through it. The power
dissipated will be 1.8 watts, and it makes sense to use a
higher wattage resistor. So in this hypothetical example,
a 5 ohm 5 watt resistor would be a good choice.

Here's how to do it experimentally:
Connect the bulb to a variable voltage supply. Gradually
increase the voltage until the bulb is bright enough.
Note that "bright enough" means less than full brightness.
Measure the voltage and the current. Call that the target
current. The unknown resistor needs to drop the difference
in voltage between bright enough and 13.8 volts, at the
target current. At this point you can determine the
value of the resistor you need to add mathematically as
follows, or continue experimentally as in the next paragraph.
Vdrop = 13.8 - measured voltage; I = target current, so
13.8 = R * I, therefore R = 13.8/I. R is rated in ohms.
The power dissipated (rated in watts) by that resistor must
be at least Vdrop * I You want a standard wattage resistor
that is at least 50% higher wattage than computed, and double
is better.

Continuing with the experimental method:
Now add a 1 ohm 1 watt** resistor in series with the bulb,
and raise the voltage until you get the target current
again. Repeat the process of adding 1 ohm resistors
until you reach the target current at 13.8 volts.
** = the wattage presumes that the target current is
1 ampere or less. If higher than one ampere, use 2 watt
resistors, if higher than 2 amperes you would need 5
watt resistors - but it is highly doubtful that dashboard
bulbs would draw current that high.

Ed

Thanks a lot Ed. It's been a long time since I dug into components. I will post any progress I make with this.

[Guv Bob]

The +12 from the LED connects to this component unfamiliar to me. Anyone recognize it? It is labeled CM104. Can't get a clear view for a photo. Rough sketch....

http://img18.imageshack.us/img18/9116/h3yu.gif

Most connections on this part of the board are underneath parts I can't get to. No markings on it that I can see. There are 7 of these on the board, all packed close together under a metal piece which is not practical to remove.

[Leif Neland]

Guv Bob forklarede den 22/09/2013:
The +12 from the LED connects to this component unfamiliar to me. Anyone
recognize it? It is labeled CM104. Can't get a clear view for a photo.
Rough sketch....

http://img18.imageshack.us/img18/9116/h3yu.gif

Most connections on this part of the board are underneath parts I can't get
to. No markings on it that I can see. There are 7 of these on the board,
all packed close together under a metal piece which is not practical to
remove.

Could it be a resistor array?

http://sell.bizrice.com/selling-lead...-Resistor.html

Does the name suggest their workers are paid in rice?

I can't crosspost to all your groups, as at least one of them is
missing on my newsserver, so I hopeyou get it.

--
Husk kørelys bagpå, hvis din bilfabrikant har taget den idiotiske
beslutning at undlade det.

[Guv Bob]

"Leif Neland" wrote in message ...
Guv Bob forklarede den 22/09/2013:
The +12 from the LED connects to this component unfamiliar to me. Anyone
recognize it? It is labeled CM104. Can't get a clear view for a photo.
Rough sketch....

http://img18.imageshack.us/img18/9116/h3yu.gif

Most connections on this part of the board are underneath parts I can't get
to. No markings on it that I can see. There are 7 of these on the board,
all packed close together under a metal piece which is not practical to
remove.

Could it be a resistor array?

http://sell.bizrice.com/selling-lead...-Resistor.html

Does the name suggest their workers are paid in rice?

I can't crosspost to all your groups, as at least one of them is
missing on my newsserver, so I hopeyou get it.

--
Husk kørelys bagpå, hvis din bilfabrikant har taget den idiotiske
beslutning at undlade det.

Thanks, LN, that's pretty close. I'll get to work checking and see...

I was having trouble focusing, but these are somewhat clear...

http://imageshack.us/a/img706/7599/6r3.gif
http://imageshack.us/a/img33/5871/wyu.gif
http://imageshack.us/a/img196/4357/4hvy.gif
http://imageshack.us/a/img27/1993/5ol.gif
http://imageshack.us/a/img713/6607/1qt.gif
http://imageshack.us/a/img708/1773/id9g.gif

[Guv Bob]

"Guv Bob" wrote in message m...
"Leif Neland" wrote in message ...
Guv Bob forklarede den 22/09/2013:
The +12 from the LED connects to this component unfamiliar to me. Anyone
recognize it? It is labeled CM104. Can't get a clear view for a photo.
Rough sketch....

http://img18.imageshack.us/img18/9116/h3yu.gif

Most connections on this part of the board are underneath parts I can't get
to. No markings on it that I can see. There are 7 of these on the board,
all packed close together under a metal piece which is not practical to
remove.

Could it be a resistor array?

http://sell.bizrice.com/selling-lead...-Resistor.html

Does the name suggest their workers are paid in rice?

I can't crosspost to all your groups, as at least one of them is
missing on my newsserver, so I hopeyou get it.

--
Husk kørelys bagpå, hvis din bilfabrikant har taget den idiotiske
beslutning at undlade det.

Thanks, LN, that's pretty close. I'll get to work checking and see...

I was having trouble focusing, but these are somewhat clear...

http://imageshack.us/a/img706/7599/6r3.gif
http://imageshack.us/a/img33/5871/wyu.gif
http://imageshack.us/a/img196/4357/4hvy.gif
http://imageshack.us/a/img27/1993/5ol.gif
http://imageshack.us/a/img713/6607/1qt.gif
http://imageshack.us/a/img708/1773/id9g.gif

PS -- Yes, they evidently were paid in rice.... see the speckles on this one? LOL!!
http://imageshack.us/a/img196/4357/4hvy.gif

[Leif Neland]

Guv Bob sendte dette med sin computer:
"Leif Neland" wrote in message
...
Guv Bob forklarede den 22/09/2013:
The +12 from the LED connects to this component unfamiliar to me. Anyone
recognize it? It is labeled CM104. Can't get a clear view for a photo.
Rough sketch....

http://img18.imageshack.us/img18/9116/h3yu.gif

Most connections on this part of the board are underneath parts I can't get
to. No markings on it that I can see. There are 7 of these on the board,
all packed close together under a metal piece which is not practical to
remove.

Could it be a resistor array?

http://sell.bizrice.com/selling-lead...-Resistor.html

Does the name suggest their workers are paid in rice?

I can't crosspost to all your groups, as at least one of them is
missing on my newsserver, so I hopeyou get it.



Thanks, LN, that's pretty close. I'll get to work checking and see...

I was having trouble focusing, but these are somewhat clear...

http://imageshack.us/a/img706/7599/6r3.gif
http://imageshack.us/a/img33/5871/wyu.gif
http://imageshack.us/a/img196/4357/4hvy.gif
http://imageshack.us/a/img27/1993/5ol.gif
http://imageshack.us/a/img713/6607/1qt.gif
http://imageshack.us/a/img708/1773/id9g.gif

Yes, that definetly look like an array of resistors pulling inputs to
12v when they are not grounded by a switch.

Leif

--
Husk kørelys bagpå, hvis din bilfabrikant har taget den idiotiske
beslutning at undlade det.

[ehsjr[_3_]]

On 9/21/2013 7:46 PM, Guv Bob wrote:
The +12 from the LED connects to this component unfamiliar to me.

In your earlier post you talked about the check engine _bulb_

Now you mention an LED. Is the check engine light an LED rather
than a bulb? It makes a big difference.

Ed

[Guv Bob]

"ehsjr" wrote in message ...
On 9/21/2013 7:46 PM, Guv Bob wrote:
The +12 from the LED connects to this component unfamiliar to me.

In your earlier post you talked about the check engine _bulb_

Now you mention an LED. Is the check engine light an LED rather
than a bulb? It makes a big difference.

Ed

Sorry about that. It's a bulb....
Wagner Lighting PC74 Miniature Bulb
1 Watts, 6 Voltage, 140ma Current Draw

[Guv Bob]

"Guv Bob" wrote in message m...
"ehsjr" wrote in message ...
On 9/21/2013 7:46 PM, Guv Bob wrote:
The +12 from the LED connects to this component unfamiliar to me.

In your earlier post you talked about the check engine _bulb_

Now you mention an LED. Is the check engine light an LED rather
than a bulb? It makes a big difference.

Ed

Correction....
GE LIGHTING 74 LIGHT BULB
14 volts; 1 watt

[ehsjr[_3_]]

On 9/22/2013 11:43 AM, Guv Bob wrote:
"Guv Bob" wrote in message m...
"ehsjr" wrote in message ...
On 9/21/2013 7:46 PM, Guv Bob wrote:
The +12 from the LED connects to this component unfamiliar to me.

In your earlier post you talked about the check engine _bulb_

Now you mention an LED. Is the check engine light an LED rather
than a bulb? It makes a big difference.

Ed

Correction....
GE LIGHTING 74 LIGHT BULB
14 volts; 1 watt



Ok. That means the bulb draws about 71 mA and provides
about 200 ohms resistance when hot. If the schematic is
correct, then you can use a 22 ohm 1 watt resistor between
the transistor's collector and the bulb to replace the
existing resistor, if it's bad.

Ed