348 348 Speedo trouble

It was ///Mike who had the "kits", but he's no longer active here. Last post was June or July of last year and last visit was March 16, 2019. I tried reaching out awhile back... but no response.

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Here's the deep dive into the speedo.

https://www.ferrarichat.com/forum/threads/348-speedo-burned-internals.503511/

 

Good find. Very interesting to see..Hope you can get it repaired.

 

Reading though the deep dive thread you'll find a "lessons learned". In other words, fixing the damaged item didn't fix the problem. As such, my newly repaired speedo got fried after I reinstalled it. Might have caused a dash fire as well if I wasn't watching it at the time. Turns out, there was a short in the system that was feeding voltage to the wrong circuit.

Hence my warnings about trouble-shooting the wiring first.

Good luck, hope your adventure is less dramatic.


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Here's the "before the repair" and the damage "after the repair and testing".


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Details are in the thread, but it was related to the seat belt system ECU. So your "cause" may be elsewhere since, I assume, you have no mouse motor seat belts - passive restraint system (= active belts with manual lap belts).

 

If you do have an unexpected voltage on R/B, it may be possible that your car did, originally, have a passive seat belt system and that not all the components have been deactivated.

Because R/B is connected to R/N from the speed sensor, you might also expect an unexpected voltage at pin 2 on connector 115. If you do find an unexpected voltage at pin 2, also check pin 5 (male side). Anyway, simply disconnect plugs on the R/B & R/N line until you lose the unexpected voltage at the speedometer.

Do you know how to access connectors "D" and "A" on the passenger footwell relay panel? and where to find the passive seat belt ECUs?

 

Unfortunately, these connectors are on the back of the relay panel. You have to fold down the relay panel to see them. The 348 panel is probably similar to the 355's panel. There is only one bolt holding the relay panel in, but you have to know which bolt. It is on the outboard side of the panel (half way up). After you have removed the bolt, slide the panel outboard a few centimeters. There are two locating pins on the inboard side which keep the panel in place. Then carefully fold down the panel.

There are lots of interesting things behind this panel that you probably didn't know existed

On the left hand side of my diagram is a coloured graphic of the relay panel which shows the connector and pin numbering. Connector "D" is the larger yellow one. You can check voltages on the pins without removing the connectors, but for proper fault isolation, you may need to remove them. They can be very tight.

Connector 115 has a few other wires going through it, but none seem to carry live battery power, so I don't know why you would get voltage on the RN wire (unless you have a faulty passive seat belt system). This rectangular connector will carry the same information as the circular one. Here is Miroljub's famous graphic:

https://www.ferrarichat.com/forum/posts/146734949/

 

Wade will be the better guy to ask about that. He took these photos of the mousetrack ECUs

348 Speedo Burned Internals

I couldn't be 100% sure. The presence of no unusual voltages is only half the equation. You could have a short on the output side of the speedometer. As mentioned before, the speedometer feeds the Motronics ECU. You might also have incorrect voltages on the RB/RN line with the key in the RUN/ON position

Note that if you are checking for improper live power at connector 115, be sure to check for voltages on the pins and the sockets. Note also that on the F355, there is a live wire from the battery going through connector 115. Perhaps the new type plug does have a pin with voltage on it at all times.

 

Correct

You should only get voltage on one of the other pins if the F348 is like the F355, but you are correct, there should be no voltage on 2 or 5 with the key OFF.

 

As your transistor BDB02C seems to have blown, you should, while investigating the wiring get a replacement for it (as well as the other components listed below). Once you have completed the investigation (whether found anything or not), you should first replace the BDB02C and give it a try. However, the BDB02C seems no longer available (unless someone here knows where to get it). If you cannot find this transistor, you can try with 2SA1315 which is easily available (Ebay or radio shacks in your area, get a few pieces). This transistor is very similar to BDB02C.

If replacing the only the BDB02C transistor does not solve the problem, you should then replace it again together with the other components as follows:

Large Chip: HCF4024BE or MC14024BCP - easily available.

Small Chip: 92693 (by Harris) - hard to get but you can try at https://www.jotrin.com/product/parts/92693 or at http://www.gpecsrl.net/componenti-elettronici/integrato/92693.html?id=28066 (Italian website). NOTE: the Italian website offers the chip as 92693/CA3140 and they actually send you the CA3140 (I know as I have ordered it from them). However, it seems that the CA3140, although it may electronically be equivalent to the 92693, has different pinout so it cannot be just soldered in. Perhaps you can give this company a call and ask whether they can supply the 92693. Otherwise, don't order from them.

Smaller Transistor: BC237B - easily available.

 

Where did you find BDB02C, I would like to order a few.

 

On plug D, pin 7 (GV wire), you should have battery voltage (around 12 volts) with the key on. Also 12V on plug A, pin 5 (VB wires). On plug D pin 12 (RB wire) and plug A pin 12 (RN wire), the voltage will be dependent on the position of the sensor head in relation to the gearbox reluctor. Here's the tutorial on testing the voltage output from the sensors:

http://www.dinoplex.org/instruments/vegliaspeedosensor/