mondial 8 impulse generator

is there anybody out there in the know that can tell / guide me through a test and repair procedure on the impulse generator on my 81 mondial 8, i have enclosed pictures of it below
this is what i have done so far, stripped the pc board out the housing , found 2 wires at the bottom of unit had come loose , replaced them, still got no ohm reading on the muli meter, more testing revealed a resistor was open, replaced resistor and got an ohm reading through the 2 wires on top of unit. replaced the unit in the car, and with the car on blocks started an ran the car in gear , speedo still not working. disconected the sensor and connected to multi meter , getting the same ohm reading but no pulse when car is running in gear,
have shopped around, found a couple new ones available, however when i change pounds, dollars,or euros into south african currency ....... well i could probaly buy a small car here for that price, so i realy have to fix this thing
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It should Not be that expensive.
Try Ferrparts here in California.
The 1981 unit is not the Ultra rare,, 1975 unit.
Get a used unit.

Good luck.
Edwardo

 

thanks for the reply, i have been on there site and have e mailed them, but like a lot of other spares places around the globe , they do not reply, prehaps you could give me another contact email adress for them,
thanks
george

 

It's hard to tell from the photos, but how are the solder joints? Are they still smooth and shiny, or are they grainy and coarse looking?

Do you have a DMM with a forward bias setting? If so, you should be able to check the junctions on those transistors. Also check the diode's junction. Not sure what your electronics skill level is, but that's a pretty simple looking circuit. Like a basic emitter follower with a diode clamp?

Sorry if my post is too complex or unhelpful.

 

There is a stunning repair thread on the 308 section from a guy in Germany, I'll try and find it and get back to you.
Nick

 

Can you post a picture of the open-circuit resistor you replaced? As I do not see a magnetic sensitive element in that circuitry, it could have been a (broken?) coil.
(coils and also capacitors do sometimes come in a form that very closely resembles a resistor)

Or is the magnetic sensor coupled to the board with the wires you had to replace, and not in any of the pictures?

 

thanks for the replys, my skill level on electronics is very basic, i have enclosed 2 more detailed pics of what i have done, unfortunitly i cant find the resistor i took out, but i replaced it with one that has the same amount of rings and same colour rings as the one that came out. on the pic i have marked it A. ...... B and C are the 2 wires i replaced [ they had come loose of the board ] the bit that has me puzzled is that there is no magnet type coil bit on the board[ not that i can identify ] and there is no magnet in the base of the unit. the board slots into the base of the unit which is plastic,
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Has the unit been apart before, before you got to it?
It looks likely to me there was a magnetic sensor (Hall pickup or coil) and that that sensor it now missing. Either that, or that the resistor was really a (broken) coil. Any idea what the wires on the back were for (or do you mean tracks on the printed circuit board that you replaced with wires?)
Can you read what is on the transistors?
These sensors are available. 116987 so it seems?? Not cheap for a sensor but then again I have seen Ferrari parts more outrageously priced.

 

I think there may have been a sensor in the central cavity of the plastic piece where the slot is for the circuit board. The broken leads may have been connected to it. It may still be in there.

Also, the plastic piece may have an embedded magnet, or it might contain ferrite (a so-called plastic-bonded magnet). I would inspect that cavity to see if there's anything in there, and also use a strong magnet to see if the plastic part has any magnetic properties.

I think this would be the case whether it used a coil (variable reluctance), Hall-effect or a magnetoresistive device as the sensor.

 

thanks for all the input, im begining to get an understanding as to how this works, i got hold of a microscope and had a look at the plastic end capsule that the board slots into, there is what appears to be a disc moulded into the capsule [ it is not picked up with a magnet though ] and looking down the slot on the side of the capsule i can see now that those 2 wires that appeared to have come of the board actualy need to be attached to the disc inside the capsule and not on the board. there appears to be a realy small locating pin in the brass barrel , that will line up and fit into the slot on the plastic capsule , i assume one of the 2 wires that go into the capsule would need to make contact with that locating pin to create an earth. does this make sense or sound like im on the right track, im going to split the capsule carefully [ so that i can rejoin it again, i need to get the disc out to reattach the 2 wires ] the slot on the side of the capsule is only 1mm wide and 5mm deep meaning 2 wires fit into a 1mm slot and they appear to attach 5mm down, what stills concerns me though is that the disc inside there is not atracted to a magnet .

 

I wouldn't be too worried about the lack of attraction to a magnet. I think the key issue now is to reattach the sensor to the wires while avoiding damage. Once we know what the disc looks like, we can probably infer what type of sensor it is, and if a replacement part might be had.

 

ok, i have managed to split the plastic capsule with out any damage, i have enclosed one pic below taken through a magnifing glass,the left unit holds the coil which the 2 wires have to be attached to, the right unit shows the slot which the 2 wires have to go up, one wire appears to go half way up the slot and is fastened to near the outside edge i assume to make contact with the pin in the brass barrel, the other wire appears to go through the slot and connect on a point on the pc board , i dont know on which point it connects to yet, im going to atempt to repair the wires tomorrow, however this stuff is realy small and at this point im not sure im going to win, is there anything else i can replace the part in the pic shown with.
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So it's an inductive sensor. From the picture it looks like the coil is wound on a plastic bobbin, and that's probably a small ferrite magnet in the center of the coil. I would certainly give the repair a try.

I think polarity shouldn't matter when reattaching the coil leads, as this sensor only needs to generate pulses in relation to speed, as opposed to, say, a crank position sensor where the rising or falling edge of the pulse is used to determine timing information.

If the repair is impossible, and a replacement part is unavailable, then I'd look into transplanting the guts of another inductive speed sensor into the housing. This will require a bit of reverse engineering and an understanding of the properties of the output signal. Not impossible, but it might take a bit of electrical engineering background.

BTW, I think the sensor is made by Veglia, though it may have been sold by Magneti Marelli. I'd certainly do a web search for "Veglia speed sensor" or the like to see what else is out there. Searching for other Italian cars of the era might turn up something. You might find that this part is used in other applications (with a different part number). I think it's also likely that this same basic circuit was used in a number of Veglia parts of that era, with the differences being in the housing and electrical connections.

 

took the unit to a mate of mine who runs a radio repair shop in a neibouring town , whilst he didnot know how the circuit worked, he managed to put all the wires back as i asked him to [ he got a magnifying glass that makes the unit look like the size of the bottom of a coffee mug and the tools to replace the wires neatly ] before i reassemble the the whole sensor id like to confirm , that small coil in the middle of the unit, would it only have two wires comming of the coil, [ one from the top of coil and one from the bottom of the coil ] would there need to be an earth of some sort to the coil unit,im quite to put it back in the car this weekend an try it out

 

i also just noticed this morning im getting magnetic action on the sensor now, but not the way i expected to see it, when placing a small magnet at the pick up side of sensor it repels , i was expecting it to attract, have i got wires crossed.

 

pic taken through magnifying glass of unit assembled
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I think you should be fine with it, assuming the rest of the circuitry is ok. It is most likely just a two wire connection to the coil, without the need for anything to be separately earthed. Also, the polarity of the coil wiring should not matter, as the the rate at which the impulses occur is the only thing that needs to be measured. (This would not be true in other applications where the precise time of impulse occurrence needs to be known.)

If it works, you saved yourself some expense. Let us know the results. Assuming it works, I think the biggest remaining risk would be environmental exposure... that sensor lives in a inhospitable place.

It might be possible to trace out a schematic from the photos of the circuit board. If I find the leisure time I will try to do this as it would be helpful for the Mondi community in general. I don't know if these are truly NLA, or if they're being newly manufactured, but as time goes on we will need information like this.

 

before i glued the unit together last night i was running through the whole system with my limmited knowlege on this unit ensuring that i havnt missed anything [ i want to have the best possible chance of this thing working again ] when i reliesed the 2 wires comming up threw the slot on the side from the coil were touching each other, not sure what this may have caused but decided to insulate them with silicon, however at the end of the operation one wire came of the coil, so its back to my mate at the radio shop this comming friday afternoon, what can i use to clear a bit of epoxy of the coil wire to at least get a bit of wire bare to attach the broken wire to, iv scraped it down to the bare wire and can see the complete wire in the epoxy , i somehow need to lift about 3mm of it out the epoxy to ensure a decent connection this time

 

well, after much more headscratching and research , it works

 

Hey, I'm currently doing the same procedure with my speedo sensor. How did you manage to open it up? Do you have to unscrew the white part with the cables out of the metal shield?

 

hi, the brass body [ housing ] has a lip that is pressed over the white plastic part [ looking at the sensor from the top ] i held the brass body in a lathe and carefully machined the lip away , the next step is very important [ i didnot know what the unit looked like inside and i pulled the white plastic part out from the top and did more damage to the internals then what was already blown ] DO NOT PULL THE WHITE PLASTIC PART OUT FROM THE TOP, push the internals out from the bottom by pressing on the round brown plastic part on the bottom of the unit [ see last pic in above posts . titled pic taken threw magnifying glass of unit assembled the brown part on right hand side is where you need to press on the bottom, there are two very very very small wires that connect the bottom brown part [ which is an inductive magnet ] to the pc board and when they brake of as mine did they are extremly difficult to replace, and they will brake of if you pull the plastic part from the top. the problem i found on mine [ apart from the damage i caused by pulling it out from the top ] was a resistor [ labled A in one of the above pics ] was blown wich i replaced i hope the above helps you
george

 

Thanks for your answer, I will try to open it up.

 

Pushing out the internals is considerably easier if you heat up the brass body with a heat gun first.

Some more infos about the type 2 sender (116987 impulse generator):

Sender repair, type 2 sender described on page 4
http://www.ferrarichat.com/forum/308-328/416720-308-early-speedo-drive-sensor-repair.html

New exchange circuit board project for type 2 sender
http://www.ferrarichat.com/forum/308-328/464677-need-failed-speed-sensors.html