How to Test Toro Interlock Module / Circuit - Snowblower Forum : Snow Blower Forums
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post #1 of 29 Old 02-08-2020, 02:40 PM Thread Starter
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How to Test Toro Interlock Module / Circuit

This hopefully takes some of the mystery out of testing the interlock / safety circuit on Toro snowblowers starting around the 1981 model year.

You shouldn't hook-up a voltmeter to the interlock modules...it could burn-out the internal circuit.

Tools you'll need:
  • Spark tester
  • 2 jumper clips
  • continuity meter (for the interlock circuit only...not the interlock module itself)

If the module itself fails, good luck finding one; they're NLA but do show up occasionally on eBay.

If the module passes however the interlock circuit (consisting of harness, handlebar switches, auger limit switch, gear-select limit switch) has bad continuity. Start by cleaning all of the connections and testing individual components. Use dielectric grease on the contacts to preserve them for years to come!



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post #2 of 29 Old 02-08-2020, 06:31 PM
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Excellent explanation of how the safety switches work in relation to the infamous module. "I" still want to dissect a failed unit to see what is inside and possibly duplicate the mystery electronics. Thanks Buddy.

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post #3 of 29 Old 02-08-2020, 07:57 PM Thread Starter
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Quote:
Originally Posted by Grunt View Post
Excellent explanation of how the safety switches work in relation to the infamous module. "I" still want to dissect a failed unit to see what is inside and possibly duplicate the mystery electronics. Thanks Buddy.
No problem Grunt! I know this mystery has been plaguing you more than anyone!

A dremel is probably the best tool for the bulk delayering and a chemical approach for touching down.

This circuit is tricky b/c you don't want it interfering with the normal ignition; If you don't have that sharp change in the primary current that this circuit is stealing from, the secondary charge will be weak.

My gut is telling me that since it's a current-driven circuit, it's feeding into the base of a BJT...and one of the 2 n/p junctions of that device gets roasted killing that isolation.

Darn it Grunt, now I'm curious!


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post #4 of 29 Old 02-08-2020, 09:08 PM
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Quote:
Originally Posted by classiccat View Post
Darn it Grunt, now I'm curious!
My interest is in the "Survival of the species" ideology. If people junk their machines because they won't start, won't operate with the few safety protections there are, an inexpensive way to reproduce the module might keep these old monsters alive for another 30-40 years.


I just thought of an old saying, "Curiosity Killed the Cat". Maybe you shouldn't get involved in this any further. I'd like to keep you around.

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post #5 of 29 Old 02-12-2020, 06:38 AM
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Excellent for Safety and will forward in the contact to keep care of these steps.
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post #6 of 29 Old 02-12-2020, 11:20 AM
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Grunt & 'Cat:

Gentlemen...you've piqued my curiosity about this, mostly because, even though I have heard of some snowblowers having safety interlock circuitry, I've never acutally worked on one that did.

Not sure I understand what the manufacturer's philosophy was here, but looking at the schematic, is it nothing more than they were trying to insure that you couldn't start the machine if the auger lever or drive lever were set to the engage position? Or is there more to it?

At any rate, it would seem to me that a solid state relay of the type that we used to see frequently in old computer equipment, could probably be used as a substitute. There used to be tons of these around from the surplus electronics vendors inventories, of varying voltages and currents.

Typically, these modules would be completely sealed in an epoxy cube or rectangular shaped pack, which would pretty much assure that they were impervious to moisture issues. The only caveat in trying to use one of these for a snowblower, that I would offer, is the question of reliable operation through a range of typically cold temperatures, but I would guess they would be o.k. It'd certainly be cheap enough to try.


Many of these modules have quite a range of "control" or "trigger" voltages. For example, you can easily find ones that have trigger voltage of 5-40 vdc, so you don't have to rely on a perfectly stable voltage. You could even run one of these using AC as a trigger, if you first run the trigger voltage through a full-wave bridge rectifier.

Though the plentiful and varied supply of these seems to be drying up from the surplus electronic dealers, the market has shifted to Ebay, where there are still plenty of them to choose from. I would guess that even if you had to add a bridge rectifier, you could get out of the whole deal for less than 15 bucks.


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Quote:
Originally Posted by SayItAintSnow View Post
Grunt & 'Cat:

Gentlemen...you've piqued my curiosity about this, mostly because, even though I have heard of some snowblowers having safety interlock circuitry, I've never acutally worked on one that did.

Not sure I understand what the manufacturer's philosophy was here, but looking at the schematic, is it nothing more than they were trying to insure that you couldn't start the machine if the auger lever or drive lever were set to the engage position? Or is there more to it?

At any rate, it would seem to me that a solid state relay of the type that we used to see frequently in old computer equipment, could probably be used as a substitute. There used to be tons of these around from the surplus electronics vendors inventories, of varying voltages and currents.

Typically, these modules would be completely sealed in an epoxy cube or rectangular shaped pack, which would pretty much assure that they were impervious to moisture issues. The only caveat in trying to use one of these for a snowblower, that I would offer, is the question of reliable operation through a range of typically cold temperatures, but I would guess they would be o.k. It'd certainly be cheap enough to try.


Many of these modules have quite a range of "control" or "trigger" voltages. For example, you can easily find ones that have trigger voltage of 5-40 vdc, so you don't have to rely on a perfectly stable voltage. You could even run one of these using AC as a trigger, if you first run the trigger voltage through a full-wave bridge rectifier.

Though the plentiful and varied supply of these seems to be drying up from the surplus electronic dealers, the market has shifted to Ebay, where there are still plenty of them to choose from. I would guess that even if you had to add a bridge rectifier, you could get out of the whole deal for less than 15 bucks.


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I’m afraid that this circuit is not going to be as simple as folks hope (a simple relay is a convenient analogy for explaining operation however they don’t work for starting and killing).
- a NC relay for killing won’t start
- a NO relay for starting won’t kill

The voltage on the primary wire is going to be quite high (several hundred volts).

My guess based on when this technology was implemented (early-80’s) is that it’s borrowing ideas from CDI. It will have standard diodes, zeniers, caps and resistors and then the magic will be possibly from one or more of the the following: SCRs, BJTs, Triacs or even an old school FET for switching.

Probably similar to the patent 3,726,265 by William A. Howard for magneto ignitions.





We’ll see, I have a failed unit soaking in solvent to try and loosen-up the potting.


^^^ that's the ground plane connection peaking out already


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post #8 of 29 Old 02-13-2020, 09:54 AM
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I've never have come across one.

Can they be disconnected and bypassed?

I've bypass my JD1032.

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post #9 of 29 Old 02-13-2020, 02:47 PM
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Quote:
Originally Posted by classiccat View Post
Iím afraid that this circuit is not going to be as simple as folks hope (a simple relay is a convenient analogy for explaining operation however they donít work for starting and killing).
- a NC relay for killing wonít start
- a NO relay for starting wonít kill

The voltage on the primary wire is going to be quite high (several hundred volts).


Classiccat:


My impression as to how this worked was based solely on the simple schematic that appears at the end of that video. My assumption was that the circuit allows one of two conditions:
1) allow voltage to feed the ignition module
2) cut off voltage to the ignition module

So, is there more to this than simply preventing the engine from starting when either the auger or drive is engaged?

So the stator on this engine is producing a voltage of several hundred volts? Obviously it's not the voltage going to the spark plug as that would be several thousand, not several hundred volts. Why is it so high?

Pondering this in real time here.......

Wait......Is this setup from before the days of solid state ignition modules?

Lol....and I thought I was confused before.....

Sorry for all the silly questions, and I hope you don't mind, but I am curious about its purpose and how this is supposed to work when everything is fully operational. .


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post #10 of 29 Old 02-13-2020, 05:39 PM
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Quote:
Originally Posted by classiccat View Post
Iím afraid that this circuit is not going to be as simple as folks hope
It looks to me that your second image, along with reading the patent, provides enough detail to almost copy it.


Quote:
Originally Posted by classiccat View Post
(a simple relay is a convenient analogy for explaining operation however they donít work for starting and killing).
- a NC relay for killing wonít start
- a NO relay for starting wonít kill

Right, but the patent does overcome those problems.


From the blue box at the upper right in the Google web page you linked to, you can download or view the full .pdf (it's easier to read than the Google web page).



Quote:
Originally Posted by classiccat View Post
My guess based on when this technology was implemented (early-80ís) is that itís borrowing ideas from CDI. It will have standard diodes, zeniers, caps and resistors and then the magic will be possibly from one or more of the the following: SCRs, BJTs, Triacs or even an old school FET for switching.

No magic (your second image explains it) and Toro may have licensed the technology from the patent holder. Or maybe Toro broke the patent and has or had its own patent.


Quote:
Originally Posted by classiccat View Post
Probably similar to the patent 3,726,265 by William A. Howard for magneto ignitions.




I was going to suggest that you might want to build upon that patent in an attempt to break it but, curiously enough, it looks like the patent expired today.


I'm in no way an expert and these are just my random thoughts.
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