Author Topic: Automotive relay help  (Read 3014 times)

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Offline dbert

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Automotive relay help
« on: October 17, 2022, 04:17:52 am »
Hello Brain Trust, newbie here.  I have only enough electronics knowledge to cause a lot of damage, so I've come here to see if I can find an answer to a question about the function of an automotive relay I'm having trouble with.

The relay in question came out of a 1989 Ferrari 328.  It is not functioning correctly, and it was made 33 years ago in VERY small quantities.  I have several parts suppliers looking around the world for a replacement, but no one is hopeful that once can be found.  So I'm forced to devise an alternative.  This relay drives a brake pressure pump and is critical to the operation of the braking system.

Most automotive relays are very simple.  A typical one is supplied with battery power on a high current circuit.  Inside the relay is a coil that is energized by an incoming trigger voltage (usually switched).  The coil's magnetic field causes a high current switch to close, which connects the battery power to whatever device is controlled by the relay, like a motor or a lamp.

Usually the relay  coil only has a resistor across it, but the one I'm dealing with has a PCB inside the relay with a PNP transistor and 5 resistors.  It looks like this:

[attachimg=1][attachimg=2][attachimg=3]

I know this isn't much to go on, but I'm trying to understand the purpose of the transistor in this thing.  If it matters, it's a B327-25.  All that the relay needs to do is close the contact and connect pin 30 to pin 87 when a trigger voltage (12V) comes in on pin 85 (from the car's ignition switch).  As you can see, the emitter is connected to the coil and the collector connects to battery supplied power.

Before I try using a generic $5 relay and possibly damaging something else in the car, can anyone take a guess at what that transistor's purpose is?

Hope I posted in the right place.  None of the Ferrari techs I've talked to have an answer.  TIA.
 

Offline dbert

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Re: Automotive relay help
« Reply #1 on: October 17, 2022, 04:28:42 am »
I forgot to mention...the part of the relay that has failed is the coil.  It no longer switches in response to the trigger input.  If I press it closed with my finger, I get continuity between 30 and 87 as I should.
« Last Edit: October 17, 2022, 04:30:15 am by dbert »
 

Offline floobydust

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Re: Automotive relay help
« Reply #2 on: October 17, 2022, 04:46:58 am »
The PNP transistor is likely BC327-25 CBE pinout.
That schematic is wrong and the 5 extra parts are important to know. I think the glass diode with 3 yellow stripes is a zener diode and it would take a test to see what its value is or perhaps people here know the markings.
I can't see the three parts stashed under the relay coil. A black diode, a resistor and something else.

Wild guess is this relay activates when a control voltage is at a certain level or lower, and it requires very low control current to activate, as if from a small switch contacts.

Sometimes with an open relay coil you can do surgery as the break is likely at the winding's end connection points. I would remove the relay from the pc board to find the open connection point.
 
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Offline geggi1

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Re: Automotive relay help
« Reply #3 on: October 17, 2022, 04:49:13 am »
have you tried to measure the resistancen through the coil?
 
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Online Haenk

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Re: Automotive relay help
« Reply #4 on: October 17, 2022, 09:38:18 am »
I assume this is just to reduce the load on the ignition switch to a minimum.
Maybe a solid state relay DC/DC would be a great alternative.
 
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Offline BradC

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Re: Automotive relay help
« Reply #5 on: October 17, 2022, 01:41:24 pm »
I forgot to mention...the part of the relay that has failed is the coil.

Have you actually tested the coil? A failure of the transistor would exhibit the same symptom.
 
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Offline PaulAm

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Re: Automotive relay help
« Reply #6 on: October 17, 2022, 01:54:22 pm »
You should draw out the circuit or at least give us a couple of better pictures so it becomes obvious. I agree that it is quite possible the transistor is at fault and is more likely than the relay coil burning out.

My guess is this was used to use a very low current from the driving module.  Was that an ABS system in 89?  I would strongly suspect the control signal does not come directly from the ignition switch.  Not even Ferarri would do that.  Since it controls the brake pressure pump, it probably comes from the brake control module.

What you do not want to do is replace that with a normal relay without a full understanding of why they used that design.  In any event, that should be repairable or a replacement can be made.
 
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Offline dbert

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Re: Automotive relay help
« Reply #7 on: October 17, 2022, 05:21:00 pm »
The PNP transistor is likely BC327-25 CBE pinout.
That schematic is wrong and the 5 extra parts are important to know. I think the glass diode with 3 yellow stripes is a zener diode and it would take a test to see what its value is or perhaps people here know the markings.
I can't see the three parts stashed under the relay coil. A black diode, a resistor and something else.

Wild guess is this relay activates when a control voltage is at a certain level or lower, and it requires very low control current to activate, as if from a small switch contacts.

Sometimes with an open relay coil you can do surgery as the break is likely at the winding's end connection points. I would remove the relay from the pc board to find the open connection point.

Unfortunately, the only schematic available is what is shown in the car's wiring diagram.  I just drew it out because the wiring diagram is  fuzzy.  I've taken some more pictures that hopefully will be helpful.  I can't tell what the resistor values are under the coil.  I'd have to remove the coil from the board and I'd rather not do that unless necessary.

have you tried to measure the resistancen through the coil?

I did, but I'm not certain I did it the right way.  I did it by putting my test leads on the 85 and 86 pins of the relay with no voltage present on any pin, and it read something in the 20M-ohm range.  I would have expected something like 100 ohms.

I assume this is just to reduce the load on the ignition switch to a minimum.
Maybe a solid state relay DC/DC would be a great alternative.

You may on to something.  See my note at the end of this post regarding voltage spikes and diode protection in relays.

You should draw out the circuit or at least give us a couple of better pictures so it becomes obvious. I agree that it is quite possible the transistor is at fault and is more likely than the relay coil burning out.

My guess is this was used to use a very low current from the driving module.  Was that an ABS system in 89?  I would strongly suspect the control signal does not come directly from the ignition switch.  Not even Ferarri would do that.  Since it controls the brake pressure pump, it probably comes from the brake control module.

What you do not want to do is replace that with a normal relay without a full understanding of why they used that design.  In any event, that should be repairable or a replacement can be made.

Well, you'd be surprised what Italian engineers in the 80's would do.  Indeed, the control voltage comes directly from the ignition switch to this relay when the key is in the "run" position.  It's a continuous wire from the switch to the relay socket 85.  Voltage is interrupted by the switch during engine cranking.  This is supposed to prevent the pump (yes, it's an ABS system) from running when the starter is engaged to allow more current to the starter.

You're right, I don't want to just try another relay without knowing what I'm doing.  Being an old Ferrari, parts are scarce and ridiculously expensive and I don't want to damage anything.  A replacement (used) ignition switch, for instance is $2k plus another 500 or so for professional installation.

I removed the transistor and tested it.  I'm getting the following diode voltage drops:

left leg - 974
right leg - 977

when I reverse the test leads, I get nothing on either leg with respect to the base, so I assume that's normal.  Are those numbers too high?  The Youtube videos I've seen say that something in the .600-.700 range should be expected.

Now then...about an hour ago someone on another board pointed me to this link - https://www.truckelectrics.com/blogs/news/automotive-relay-guide-what-is-a-relay

I draw your attention to this portion:

"Some automotive relays are designed with diodes or resistors built in. These devices help suppress coil voltage spikes and protect the electronic circuit.

DIODE RELAY PROTECTION:
When the voltage is removed and a relay is de-energized the magnetic field collapses.  This can result in a voltage surge in the opposite direction.  These low current surges can have significantly high voltages, often up to 100 volts.  To prevent the damage of sensitive upstream electronic circuitry a diode can be installed across the coil.  The diode absorbs and dissipates the momentary voltage spike and protects upstream damage. "

So now I'm wondering if the transistor is just there to provide the same protection to the ignition switch that a diode would (but then why not just use a diode?)  There IS a diode on the board as floobydust noticed.

Pictures to come in my next post.
 

Offline dbert

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Re: Automotive relay help
« Reply #8 on: October 17, 2022, 05:40:47 pm »
Here are more pics.  Does the symbol circled in red in the picture of the relay's outer case mean anything to you?  It may just be a company logo but  I think I've seen it before somewhere.
 

Offline dbert

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Re: Automotive relay help
« Reply #9 on: October 17, 2022, 05:42:57 pm »
More pics
 

Offline dbert

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Re: Automotive relay help
« Reply #10 on: October 17, 2022, 05:45:57 pm »
More pics
 

Offline dbert

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Re: Automotive relay help
« Reply #11 on: October 17, 2022, 05:46:39 pm »
Last one.
 

Online bdunham7

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Re: Automotive relay help
« Reply #12 on: October 17, 2022, 06:06:54 pm »
What ABS system is used in this model?  I'm thinking that the relay is not driven directly by the ignition switch, but rather is actuated by the pressure switch on the brake accumulator.  The purpose of a transistorized relay would be to reduce the current across the contacts of that switch.  It is possible that it is driven by the ABS module, but if that system is one of the ones I'm familiar with, they need the pump to function even if the ABS system fails entirely as the pump and accumulator are required for even normal braking.  Does that all seem right or is there a vacuum booster?

Edit: I looked it up, apparently it is Teves Mk 2, same as Jaguars, TCxMaserati and some other models of that era with early ABS systems.  Every implementation has the possibility to be a bit different, but I think that relay is driven directly by the pressure switch as I said.  You aren't measuring the coil properly, you need to figure out which solder pads on your board correspond with the coil wires and I can't see that in your photos.

Quote
It's a continuous wire from the switch to the relay socket 85

If that is true, then the control circuit is likely on the ground side, which is a fairly common way of doing it.

« Last Edit: October 17, 2022, 06:45:02 pm by bdunham7 »
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 
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Offline floobydust

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Re: Automotive relay help
« Reply #13 on: October 17, 2022, 06:22:53 pm »
It's easy to conquer this relay design, I can draw a schematic for it later this aft.
The complexity is the two glass diodes with yellow stripes, I think they are zeners.
It might actually have an analog signal coming in for pressure and the relay switches the pump on and off based on that. So the relay is on when pressure is low.

edit: Teves Mk 2 appears to be purely mechanical pressure switches
« Last Edit: October 17, 2022, 06:27:29 pm by floobydust »
 
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Offline strawberry

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Re: Automotive relay help
« Reply #14 on: October 17, 2022, 06:23:34 pm »
relay circuit
pull control input to 12V to activate relay
diode voltage drop on silicon BJT must be 0.6..0.7V but some weird multimeters that share ohms and diode might be exception

you think it is hard, try finding intermittent fault between 100 transistors and 100 resistors and no schematics at all
« Last Edit: October 17, 2022, 07:02:43 pm by strawberry »
 
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Offline floobydust

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Re: Automotive relay help
« Reply #15 on: October 17, 2022, 06:28:10 pm »
It's PNP and three diodes
 
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Offline strawberry

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Re: Automotive relay help
« Reply #16 on: October 17, 2022, 07:03:04 pm »
fixed
 
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Offline dbert

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Re: Automotive relay help
« Reply #17 on: October 17, 2022, 08:28:41 pm »
What ABS system is used in this model?  I'm thinking that the relay is not driven directly by the ignition switch, but rather is actuated by the pressure switch on the brake accumulator.  The purpose of a transistorized relay would be to reduce the current across the contacts of that switch.  It is possible that it is driven by the ABS module, but if that system is one of the ones I'm familiar with, they need the pump to function even if the ABS system fails entirely as the pump and accumulator are required for even normal braking.  Does that all seem right or is there a vacuum booster?

Edit: I looked it up, apparently it is Teves Mk 2, same as Jaguars, TCxMaserati and some other models of that era with early ABS systems.  Every implementation has the possibility to be a bit different, but I think that relay is driven directly by the pressure switch as I said.  You aren't measuring the coil properly, you need to figure out which solder pads on your board correspond with the coil wires and I can't see that in your photos.

Quote
It's a continuous wire from the switch to the relay socket 85

If that is true, then the control circuit is likely on the ground side, which is a fairly common way of doing it.

I'm impressed!  I wasn't expecting anyone here to know about ABS or other automotive systems.  What you wrote is mostly correct.  Yes the 1989 328, which is the last year it was produced (a total of about 1200 worldwide), was the only year that had ABS.  And, this Italian relay we're talking about was ONLY used on this model, so you can understand how scarce it is.

I have to confess that I fibbed a bit in my first post.  This relay doesn't power the brake fluid pump directly.  Instead, it feeds power to another relay, which in turn feeds power to the actual pump relay.  Ferrari calls this first relay the "ABS Control Relay".  Electrically, everything else is downstream from it.

I'm attaching the complete ABS system wiring diagram, which includes all the relays, the pump, the mechanical pressure switch, the ABS ECU, the battery and the ignition switch.  In Ferrari's implementation of Teves Mk 2, The ABS system and regular braking system share most of the components.  In the case of ABS system failure (wheel speed sensor or even the brain itself), the pump, accumulator and pressure switch still maintain boost pressure to the regular braking system.  Sadly, in the case any of the relays go bad, both systems are broken.  Yep, this model doesn't use vacuum boost.  Just the ABS pump.

In addition to the wiring diagram, I've attached a spreadsheet with a summary of what I've learned from studying the wiring diagram and poking around with a test light.  Maybe it will save you some time.
 

Offline floobydust

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Re: Automotive relay help
« Reply #18 on: October 18, 2022, 12:47:04 am »
Uh, I followed the Ferrari wiring diagram and find my head hurts so I put it on one page. Sorta figured it out.
Relay  75 "ABS system control relay" fed from battery (with no fuse) yet control connects to the ignition/anti-theft switch. No idea what "R, 30, P, 15, 50" mean wrt to the ignition switch 88.
Relay 182 "Control relay for the ABS system during cranking" connects to the ABS system module. So I think the manual has flipped the descriptions?

Note this relay defaults to always on (for safety) and the control line shuts it OFF when +12V power is applied to 85.
So on a workbench connecting 12V power across 30(+) and 86(-) the relay should always clank and pull in. Then connecting (+) power to 85 should make the coil release. The extra transistor and all the drama is to invert the relay's operation.

OP, the 30/51 and maybe 86 terminal at the PC board looks like a cracked/fractured solder joint in the pictures. You can use a magnifier and look at it while wiggling the terminal. It's a very common failure in automotive modules. When re-doing solder joints, don't wreck it with too much heat - only need a couple seconds max. and add a bit of fresh solder.
Can you give us any markings on the black diode, right now it's the only puzzle. Like 1N5xxx etc.

fixed
Not quite, the oddball black diode is not across the coil and there is an orange+red stripe on the resistor so likely a 3k3. I'll post what I drew in a bit, it's still not making sense though.
 

Offline PaulAm

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Re: Automotive relay help
« Reply #19 on: October 18, 2022, 02:15:46 am »
You should be glad it's not a Teves Mk3
 

Offline floobydust

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Re: Automotive relay help
« Reply #20 on: October 18, 2022, 04:15:55 am »
This is what I think is the relay module's schematic. Ferrari 62567200 Control Relay for ABS system, Italamec 493.

The choice of diodes seems weird, three different types it appears. My concern is the battery (30) and control input (85) can have different voltages due to voltage drops in the car's wiring so it should tolerate that and I expected a (glass) zener. That diode has three yellow stripes and a grey one which is not the cathode?

edit: updated schematic with ref. designators
« Last Edit: October 18, 2022, 06:50:55 pm by floobydust »
 
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Online bdunham7

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Re: Automotive relay help
« Reply #21 on: October 18, 2022, 04:39:05 am »
OK, so I've uncrossed my eyes and followed the diagram around a bit, so a few questions.  I also looked at your notes and they look right as far as I can tell at a quick glance.

What is the part called out as '181' ?

What are the exact symptoms observed with the car?  Are you actually seeing the +12V on pin 85 of relay 75e when cranking?  If you jump pins 30 and 87 does the ABS system then function normally?

A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 
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Offline dbert

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Re: Automotive relay help
« Reply #22 on: October 18, 2022, 05:07:41 am »
No idea what "R, 30, P, 15, 50" mean wrt to the ignition switch 88.

They're the male spade terminals on the back of the ignition switch.
30 - constant hot from battery
15 - accessories, hot when key in run position
50 - connected to the starter, hot when key in start position
P - not used in the 1989 model year
R - supplies the ABS system, hot with key in run position only

Note this relay defaults to always on (for safety) and the control line shuts it OFF when +12V power is applied to 85.
So on a workbench connecting 12V power across 30(+) and 86(-) the relay should always clank and pull in. Then connecting (+) power to 85 should make the coil release. The extra transistor and all the drama is to invert the relay's operation.

I'm confused by this.  Are you talking about the relay I'm having trouble with, 75e?  Are you saying that this thing is supposed to have the contact normally closed, and opens up when it receives voltage from the ignition switch on 85?  That would seem backward to me.  It would mean power is supplied downstream only when the key is off, right?
 

Offline dbert

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Re: Automotive relay help
« Reply #23 on: October 18, 2022, 05:09:07 am »
I'll reflow the joints.  I also have some new transistors arriving in another day or two so I'll pop one in when I can and see if it works again.

By the way, thanks for combining the two halves of the diagram.  I'm curious how you did that while also making the whole thing a little less fuzzy.  That helps a lot!
 

Offline dbert

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Re: Automotive relay help
« Reply #24 on: October 18, 2022, 05:12:24 am »
You should be glad it's not a Teves Mk3

At the moment I'm kind of wishing it didn't even have Mk 2! |O
 


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