348 Speedo Burned Internals

That transistor (CQ949) is much more powerful than the BDB02 in your old circuit board. Also, it is NPN type as compared to old PNP. However, there is no datasheet for CQ949. It could be again an automotive application code or it could be same as BD949. If this is the case, it is a 40W transistor as compared to just 1W of BDB02. In any case, just comparing the sizes and shapes of the two, the difference in power is certainly significant. Also, the change from PNP to NPN means that there was some re-design (recall?) of the circuit.

 

Miroljub, that causes me to wonder if there is a relatively easy way to find an updated replacement for the original ODB02...

 

Thanks for the pics, Wade! I was hoping you'd take some for comparison purposes.

Any chance of some overall pics of the board? And what is the number on the board?

 

BTW, the suffix (or whatever you call it) on the 8 pin DIP is different, but the part number is the main number is the same.

 

The numbers on our original boards are 29002 610.001 and they're supposedly interchangeable. Miroljub, are you certain that the transistor on the new board is an NPN? I can't help but think that the boards/circuits are functionally the same.

 

Wade, I forgot to follow up, but I did look at the harness going to the instrument pod (which is removed, allowing for good visibility all the way to the center of the dash) and there are no Scotchlocks visible in the entire area.

Have you removed one or both sides of the center tunnel? I'm curious how the stereo wiring ties into the car wiring.

Also, have you checked the voltage on the red wire at each of the connectors with them disconnected? That should at least help isolate the section of the harness where the voltage is being introduced.

 

Assuming that CQ949 is same as BD949, it is an NPN transistor. If they went from PNP to NPN, the circuit change would have been only within the circuit board with the inputs and outputs remaining the same. It would have involved changes to some of the polarities and, in the case of the Op-Amp (92693) it would have been just moving from its inverting to non-inverting input (or vice versa).

Whatever the change, the new transistor CQ949 is certainly much more powerful. It has a heat sink tab but it was cut-off for this application as not necessary as it looks like a big overdesign, possibly because there were many cases of failure of the small BDB02.

 

My voltage measurements on the red/black wire at the (working) speedo connector:

Sensor connected, Key off: 0.00 Volt
Sensor connected, Key on: 11.5 Volt
Sensor disconnected (at 115), Key on/off: 0.00 Volt

Wade, looks like you have something wrongly connected to the R/B wire (or wires upstream of it). Based on the diagram that we got recently, there should be nothing connected to the line from the speed sensor to the R/B wire at the speedo.

 

To test whether the voltage you are getting has any substance or whether it is just some "shadow" voltage, connect a 100 Kohm resistor from the red/black wire to the ground and see whether the voltage drops. Perhaps you have a very sensitive multimeter. Another way is to measure the voltage with an analogue voltmeter.

 

Not even at the R/W wire that presumably comes from the speed sensor?!?!?

 

Pin 2 is the top center pin in the 115 connector?

 

I just retraced the diagram now that I know we're supposed to be using the first one. Either my memory was playing tricks or I had traced it incorrectly before, but I now see what you mean-- the R/W wire is shown as having a straight shot from the sensor to the speedo, changing to R/B at some point (connector A?). There is no second R/W wire shown in the diagram and no connection between that wire and an engine ECU. Apparently it is the G/W wire that connects to the bank 5-8 ECU, but I can't find how that wire connects to the speedometer in the diagram. Can you?

Anyway, the second R/W is indeed a mystery. It appears to be stock, yet it's not shown on the diagram. How far can you chase it to determine which direction it goes in the chassis?

I hope I'll remember to measure the voltage at pin 2 late tonight when I'm with the car, but it's safe to assume it'll be ~0 since the rest of that line is ~0 in my car under your proposed conditions. If I get ambitious I'll pull the fuse box cover and check for a second R/W wire. Should I be able to see it just by pulling the cover itself?

 

Cool. I could not tell from the other pic. From this one it's clear that Pin 2 is the frontmost of the center row of pins. You might add this pic to your other post.