OT Identify electrical component

I have a Deere 425 with Kawasaki 2 twin. It's got ignition problems when it warms up after 5 min of mowing the left cylinder stops firing. I've read many threads that say it's corrosion inside this igniter module, but I don't see corrosion and It's all got a conformal coating. I do see one hot component in the lower left corner with some slightly cooked looking board around it. After I removed the housing and had the board in free air I never had a cylinder drop out. It ran all afternoon.

I'm not sure what the component is exactly to replace it. the markings are not clear to me. Zener diode? can I determine what one I need through testing voltage with multimeter?

a new module is about $200.

thanks

Definitely looks like a diode, but unless you can determine the markings you're going to have a hard time determining exactly what it is.

The bad component is likely the switching transistor that controls spark to the cylinder that is dropping out. The diode is just passing extra current.

If the diode were bad, both cylinders would go dead. Since it is only one, has to be the switching transistor or in the driver circuit for it.

You might want to try ebay. There are vendors there that sell JD parts for reasonable prices.



This stuff gets time consuming, you will have to order components and likely not get it repaired on the first attempt. You likely have no schematics so you will need to reverse engineer the thing and on top of this you have to mess with the encapsulation coating before and after repair.

Yes the module is almost $200 but do you want to mow the grass or be an electronics repair technician?

Maybe they got the heat dissipation wrong in the design, run it as is,
with it open to free air.

I hope someday, somehow, they invent a way to make an engine run without a computer board. Just think of how awesome that would be! Shit would just run without all the glitches and wallet-wounding exercises. I bet if Tesla were alive he could figure it out, maybe.

According to Murphy's law the component markings are likely facing the PCB and you would have to unsolder it to read them.

I would suggest heating the tip of an old screwdriver and see if the coating melts. If so it might be possible to remove it.

Generally, with no schematic and either lacking in diagnostic skills or the time to do so your best course of action might be to "Shotgun" it. What that entails is carefully identifying the markings on each component, buying replacements from some place like Digi-Key and replacing everything you can. Probably under fifty bucks.

One hint - if that diode is very small it's likely a small signal diode like a 1N914 and if it's larger it's probably a zener. My guess is it's a small signal diode used as a snubber to protect a transistor from reverse bias.

If you are certain that this module is your problem buy the new one. The zener diode will also have a line around it at one end like the line you see around an ordinary diode they usually fail short or open. A zener diode has a voltage value eg 3.3v,5.7v etc and a wattage value you need to know the voltage value. I know the board is small but if you spend a day working on it you need to allow a dollar value for your time. By all means work on it but do not be disappointed if this is not the problem with it.

dsergison said:

can I determine what one I need through testing voltage with multimeter?

thanks

View attachment 262035View attachment 262036View attachment 262037

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Yes

step 1, set your multimeter to the diode scale. take a reading, write down the reading and how the leads (red/black) were connected, reverse the leads and repeat.
step 2, run the engine, set the multimeter to the voltage scale, measure the voltage across the diode.

Report back.

CarlBoyd

TeaJunky said:

If you are certain that this module is your problem buy the new one. The zener diode will have a black line around it at one end like the white line you see around an ordinary diode they usually fail short or open. A zener diode has a voltage value eg 3.3v,5.7v etc and a wattage value you need to know the voltage value. I know the board is small but if you spend a day working on it you need to allow a dollar value for your time. By all means work on it but do not be disappointed if this is not the problem with it.

Click to expand...

The root cause issue is likely a bad coil. The problem is that the bad coil takes out the switching transistor. All of this causes excessive current to flow through the diode that is over heated.

Replace the coil on the cylinder that drops out and the ignitor board.

The board issue is only a symptom of the root cause.

dsergison said:

I have a Deere 425 with Kawasaki 2 twin. It's got ignition problems when it warms up after 5 min of mowing the left cylinder stops firing. I've read many threads that say it's corrosion inside this igniter module, but I don't see corrosion and It's all got a conformal coating. I do see one hot component in the lower left corner with some slightly cooked looking board around it. After I removed the housing and had the board in free air I never had a cylinder drop out. It ran all afternoon.

I'm not sure what the component is exactly to replace it. the markings are not clear to me. Zener diode? can I determine what one I need through testing voltage with multimeter?

a new module is about $200.

thanks

View attachment 262035View attachment 262036View attachment 262037

Click to expand...

The module may cost $200.00, but considering you've gotten many years of service out of it the cost sounds more reasonable. JD made the 425 series tractors from 1992 to 2001. That means you've gotten a minimum of 18 years service or possibly up to 27 years service out of the board. That means the board has cost between $7.40 and $11.00 per year of service.

I have the next generation 445 tractor with the fuel injected version of the engine. Parts are a bit more expensive than those for a Murray or Craftsman, but the dependability is there. It may be difficult to spend the money, but given that the grass keeps growing how long can you try to save a buck before you have to pay someone more than the cost of the board to mow the lawn.

Been there done that with another brand tractor. I had an intermittent spark problem that took nearly a full summer to diagnose and repair. It would quit and I'd tow it back to the shop. By the time I got there it would sometimes start and run for an undetermined amount of time. Sometimes I could go back out and mow, while others I got to where it had stopped only to die again and have to back towed back to the shop. Every time it quit I'd spend an hour towing it and trying to diagnose the problem, then go cut the lawn with a hand mower.

I finally broke down and took it back to the dealer. It was expensive to repair, but I got back 4 hours a week of my life, and resolved an extremely frustrating problem

If you're feeling brave you could desolder the component from the right side igniter, then try to characterize it either though scope/DVM/other means reading or looking for data marks on it. Presumably it's not degraded, so why I suggest it for forensics and not the left side one.

Also check the left side board for excessive heat damage to laminate or traces, you may decide it's better to replace the entire unit.

That pictured component is most certainly a diode, and very unlikely to be failing intermittently. In my experience they're either dead or not. Most of the time they fail open, occasionally shorted. Follow Carl's advice and test it, then you'll know for sure.

And GregSY: Ha! You kill me!

Not much to lose, having at'er! Use a multi-meter to check the resistance values of the coils. They should match from side to side.

I picked up a 425 a couple years back. Compared to the die cast zinc crap the JD dealer wants nearly $10K for, now, they are a rock solid piece of gear, and worth sinking some time and money in to.

The problems I have had with mine, are that one cylinder will occasionally drop it's spark plug wire (I need to replace the cap), and I had to put a new time delay relay assembly on it ($50 Cdn, at the dealer) as it was refusing to start most of the time, while when it WOULD start, it would run for an indeterminate amount of time, then cut out and refuse to start again.

At some point, I soldered a separate start button on to the interlock safety board too. The key switch and board will get replaced together. Maybe. Someday.

You say it works OK in free air. That tells me that the board is OK or that some component is sensitive to temperature.

If that diode was bad, it would probably be bad all the time. I would not worry about it except to check the solder connections on it's leads on the bottom of the board. You may have to re-melt them or even replace that solder.

SOME OTHER component is causing the problem. A transistor, as others have mentioned, is a good candidate. Transistors can become damaged by excessive heat/current. If I were to replace anything on that board it would be those two transistors or FETs on the heat syncs.

AND when reinstalling the board or a new one, I would add some additional ventilation and/or larger heat syncs on those two transistors/FETs.

Have you tried asking Deere about what those parts are? Can't hurt to ask. They may even have some tips on the repair. But try to get past the PR people who usually answer the inquiries.

In another part of my life, I did board level repair. Some of the equipment I worked on either had bad or non existent schematics. If something had an intermittent problem, it was almost always due to heat unless there was something going on with a trace or cold solder joint. I will just say what I did and you can take it for what it's worth. Look at the solder side of the board very carefully under magnification for a cold solder joint. The joint will either have a tiny annular ring around it or it will be dull (more likely an annular ring). Look at the board like you were reading a book. Left to right and down the page so you don't miss any joints. Your best friend for finding a heat problem is a hair dryer and a can of freeze mist. Heat up the whole board until something craps out and it stops working. Cool the whole board down until it starts working again and reheat to verify that it is in fact heat related and not a fluke (if it unplugs easily then stick it in the freezer for a few minutes to cool it down and save a lot of mist). Shield half of the board with cardboard and heat only one half. If it doesn't crap out then do the same with the other half. Then quarter the board etc. Eventually you have narrowed the problem down to a small section. With the freeze mist and the spray tube that came with it, you can narrow it down to one component by alternating between the hair dryer and the freeze mist. As stated by someone else, it will probably be a semiconductor. Power resisters often look fried and even burn the board beneath them and they are often just fine. Diodes usually just go and are not heat sensitive. Transistors, FET's, Mosfets etc. are all subject to heat damage that causes them to work intermittently. Hence the heat sinks.

The mention of "free air" brought to mind an incident I had with an old (1950's era) Bolens Ride A Matic. It had a Kohler 8 hp single cylinder engine with a rope start. I had mowed about an acre of grass on a hot (90*+ day) and knew I was running low on fuel. I drove it back to the shop, shut it off, and refilled the tank.

I went to restart it and nothing. I probably rewound and pulled the rope 20 times without a single pop. I removed the plug and pulled the rope a few more times.. It had plenty of spark, but every time I reinstalled the plug nothing. I removed the carb to check the float level and jets. Everything seemed fine so I reassembled it and tried again. Once again nothing.

By now I had wasted a couple hours and no grass was being mowed. I tested the plug wire and coil and tried again. Nothing. Whenever I removed the plug there was plenty of fire, and plenty of fuel, but the engine still wouldn't run.

I was about to give up for the day when I decided to put in a new sparkplug. I had my doubts as to whether or not it would make a difference since the plug in it only had about 5 hours runtime. One pull on the rope and the engine jumped to life. I spent the entire afternoon sweating (without the aid of any beer) all because the sparkplug porcelain had cracked and the plug wouldn't fire under pressure.

Lesson learned. Check the easy stuff first, and don't take for granted just because a part is fairly new it won't fail.

I suppose with everything people try to repair we are trying to avoid buying expensive replacement parts that we then find that we didn't need, we all fall into that trap and often more than once. It is always a good idea to ask questions and try to diagnose a problem which is often easier said than done, and often getting the repair done without having made the problem worse first is an achievement in itself.

GregSY said:

I hope someday, somehow, they invent a way to make an engine run without a computer board. Just think of how awesome that would be! Shit would just run without all the glitches and wallet-wounding exercises. I bet if Tesla were alive he could figure it out, maybe.

Click to expand...

afraid it's already been done. 130 years or so ago. Magnetio, no battery to go dead, no starter motor or generator. Or, a hot bulb. Not diesel, uses kerosene. Was commonly used with oil well pump engines.

Tom

GregSY said:

I hope someday, somehow, they invent a way to make an engine run without a computer board. Just think of how awesome that would be! Shit would just run without all the glitches and wallet-wounding exercises. I bet if Tesla were alive he could figure it out, maybe.

Click to expand...

He did....got rid of all the recip parts too.
Made a turbine with no blades, just smooth disc's.

TeaJunky said:

If you are certain that this module is your problem buy the new one. The zener diode will have a black line around it at one end like the white line you see around an ordinary diode they usually fail short or open. A zener diode has a voltage value eg 3.3v,5.7v etc and a wattage value you need to know the voltage value. I know the board is small but if you spend a day working on it you need to allow a dollar value for your time. By all means work on it but do not be disappointed if this is not the problem with it.

Click to expand...

The color of the line really has nothing to do with whether it is a zener diode or not.

Most glass-cased diodes will have a black line(though I have seen some with a white line).

Most epoxy-cased diodes will have a white line, since the epoxy case is black.