Rebuilding early GM circuit board

[bazthespazz]

I've got a simple circuit board in my '84 El Camino that controls the Check Engine light that's got problems and I'd like to try to rebuild it. I've found a replacement already so this is just a "let's try it for fun" project. From what I can tell it consists of 3 resistors, 1 transistor a capacitor and diode but I don't know enough to recognize the markings and was hoping somebody could tell me the exact replacement parts I'd need. All of the resistors have the color code bands on them but I don't see any markings on the rest of the components. I just took another look at it with a jewelers loupe and all the components have numbers on them. The black thing in the upper left is labeled 345 7594 and has the markings shown in the image below, black upper right is 194 SC834 and the lower right is G 270K Y5S 100V if that helps. Could somebody also give me the values of the resistors.

 

[rjenkinsgb]

The transistor and diode numbers appear to be "in house" codes - specially numbered for the equipment maker.

They are often a standard or generic part, and with small transistors can frequently be substituted by numerous common types, as long as you can identify the pinout and whether it is a PNP or NPN device.

A photo of the board underside and any wiring diagram info showing the connections to it would be useful!

The capacitor is most likely 270pF

The resistors appear to be:
10K (brown black orange; 1 0 3)
15K (brown green orange; 1 5 3)
3.5K (orange green red; 3 5 2)
The first two bands/digits are literal numbers, the third is how many zeros to add.

If the middle band on the lower two is actually blue rather than green, then that digit is a six rather than five.

 

[shokjok]

The transistor markings appear to be from National Semiconductor. The part number isn't found as an N.S. device at www.datasheet4u.com . As rjenkinsgb suggests, a PCB photo would help us help you.

 

[bazthespazz]

Here's a picture of the back side of the board along with a flipped version of the top side so you can see the placement of the components and the circuit.

 

[rjenkinsgb]

Sorry, that photo is just not quite clear enough to be certain of all the PCB traces and it's not high enough resolution to blow it up or do any filtering.

Does the top resistor connect to the top trace that goes to the test point pad at the top right?

This is my best guess for the diagram, based on what I can make out; connection numbers are top to bottom, for the photo above. The transistor and diode type numbers are just random one to create the schematic:

 

[ronsimpson]

When I saw the transistor I thought: 2SC634a 50V 200mA NPN transistor.

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[Pommie]

What does the circuit do? What's connected to each pin?

Mike.