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VFR400 tacho does not proper work on mod VF500


RalfR

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Hi all togehter,

 

this winter I have started a little modification project on my VF500 dated from late 85.  My intention is to give the bike a more modern look and ride.

It should get the look Honda would create for a VF600F instead of launching the CB600F. But they did not so somebody has to do it.

 

Beside changing the wheels, the fork and brakes I have converted the instruments to the VFR400R NC30 clocks.

The speedodrive sprocket cover and drive was a mechanical job to do and works fine now.

The temperature gauge works as well but the tacho does not. It acts but shows only readings up to 2000 rpm, even when the engine is defintily reving much higher.

It seem that the tacho signal from the ignition box is different to the from the VFR400R....

Does anybody have an idea or a solution for this conversion?

I think I have seen this kind of conversions on earlier threads but could not find it.

 

Greetings from Germany´s Corona hotspot......

Cockpit fertig.jpg

Lenkeransicht.jpg

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The first thing I would do is replace the 4ea Electrolytic Capacitors on the board, C2, C6, C7 and whatever the large one is, especially the low valued ones like C6 which is a 2.2ufd 50v.

Being a 1985 device these capacitors are at least 35 years old, they tend to internally dry out and loose their capacitance and can become resistive, in other words, stuffed!

 Their values will be printed on them as per C6. Make sure your new ones are all 105degC temperature rated and the same capacitance value, you may probably be supplied with higher working voltage ones but that's fine, but NOT lower. 

Before removing the capacitors MAKE SURE you note where the negative leg of the capacitor goes as they are polarity sensitive.

Any good Electronics Parts supplier will have these capacitors.

Also make sure there are no cracked or poor looking solder joints on the other side of the board. Good Luck, hope this helps.

 

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16 hours ago, GreginDenver said:

And what is the letter designation above the kinda transparent-looking item above R3?  I can guess the function of most of the other components but that one is a mystery to me.

Hi Greg.

The device is a potentiometer or variable resistor. I'm guessing it would be used to calibrate the instrument, it's possibly labeled as VR1.

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4 hours ago, Grum said:

Hi Greg.

The device is a potentiometer or variable resistor. I'm guessing it would be used to calibrate the instrument, it's possibly labeled as VR1.

Thanks Grum, now that you say it I can easily see the "V" in "VR1" in the picture.  

 

I was thinking there would have to be a potentiometer included in this circuit board as there would be the need to do a bench-calibration of the completely assembled tachometer circuit board.  This post-assembly calibration would be necessary for quality control (with pass-fail evaluation criteria) and a fine-tuning calibration effect for the circuit boards that fall within the "pass" level of quality control.  This would compensate for small variations in the resistors, capacitors and such.

 

I can imagine the technician, sitting there with a pile of these circuit boards, hooking one-after-another into to a purpose-built bench testing unit that puts a set of controlled inputs into the circuit board and shows the results on something like an oscilloscope and/or voltage meter.

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I am back from my first motorcycle run out this year. Because of the beautifull weather I could do a trip to the Nürburgring and back home again.

Due to Corona we are not allowed to gather or meet, but driving the VF with modern tires was a really nice experience.  

So sorry for the delay of my answer.

 

The pictures are only from the VF500 instrument but I will use the VFR400 clocks. The 400 tacho I will open when a solution is coming closer.....

Grum you are right that those capacitors are quite old, but this instrument was working fine before dismantling. But I will have think about your advice when working on the 400 tacho board....

 

Gregs suggestions are correct and there is a potentiometer in clear plastic.

 

I did (can) not read the resistors markings, I have simply measured the resitance with a multi meter.

 

The bottom picture shows the connections and it is only a one layer board. So no secrets in between layers. Tacho signal input is left side top.

 

circuit board left.jpg

circuit board conector.jpg

circuit board bottom.jpg

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I'm looking at that "R1" resistor and I can't tell which end is the gold band, so I can't tell which direction to read the colors, in the picture it isn't quite in focus and has some glare on it.  But if I read it right-to-left I get brown-violet-red-gold = 1.7kohms or if I read it left to right I get brown-red-violet-gold = 120Mohms.  So I'm guessing the gold band is at the left-hand end.

 

It would be informative to see the connecting traces on the back side of this circuit board.  I'm assuming the circuit board is probably a single-layer, but maybe a 2-layer board.  Is it possible to get a picture of the backside, or short of that maybe you could draw/diagram out what you see on the backside?

 

And what is the letter designation above the kinda transparent-looking item above R3?  I can guess the function of most of the other components but that one is a mystery to me.

 

And I'm guessing that the red and black wires at the left-hand side of the circuit board are marked M+ and M- (can't see the "-" below the lower M, but guessing it's there)?  Do these wires lead to and from the galvanometer (i.e. electromagnet) portion of the gauge?  And are they the only two wires that go there?

 

But yeah, very interesting just in this one picture.  For instance the resistor that is banded red-black-black-gold (I think it's marked "R5") is a 40 Ohm resistor which would be perfect for the job of reducing 12volt to 3volt in an application that is pulling about .25 amps.

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Perhaps the guts of the 500 tach can be transferred to that housing.

 

I don't have the answer, but I have questions about the rest of the bike.

 

 

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Ok I can show some more pictures but I would not deviate to much from my problem.....

 

What I have found so far is that Honda has different ratios for the tacho signal coming from the ignition unit. Similar to the mechanical speedodrives you find 1:2 and 1:4 ratios. No idea for the reason.....

For my problem it looks that the VF500 emits only a fourth signal of the VFR400 unit, or so.....?

And it looks not a good idea to transfer the internal from one casing to another. Does not look like a straight fit....

 

Seite vorne rechts.jpg

Seite rechts hinten.jpg

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I "think" the spark units on the VF500F are the same except one sends the signal for the tach.  Perhaps use two spark units each sending a tach signal?  I don't know.   just brainstorming.

 

Maybe contact these guys. 

 

http://www.v4spark.com/

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I'm interested in your tachometer swap problem.  I think you've got lots of room for experimentation here. 

 

These old-school motorcycle tachometers are always just a "galvanometer", which is a gauge that uses electrical inputs to induce an electromagnetic "pull" against a factory-calibrated spring.  And the tachometer's face-sweep needle is connected to this.

 

On Honda motorcycles it seems that their normal approach is to give the tachometer a positive input from the Ignition Module (12 volts, intermittent signal that is matched to crankshaft speed).  The only other connection the galvanometer-type tachometer needs is a Negative (ground) wire.  So, to recap, the Honda method: Intermittent 12 volt (positive) input, constant Negative (ground) connection.

 

Most other older motorcycles that I've worked on (that use this standard galvanometer-type tachometer) do it opposite of the Honda way.  My older Suzuki and Kawasaki use a constant 12 volt connection, and an intermittent path-to-ground by way of one of the coils (which means that every time the Ignition Control Module grounds that coil to charge it to saturation the tachometer's galvanometer will flow electrons through its electromagnet, which pulls the needle against the factory-calibrated return spring).

 

But either way you choose to do the positive and negative, it really doesn't matter.  All that matters is getting the correct amount of 12 volt power flow through the tachometer to register a correct needle indication.

 

One place to start out in exploring this situation would be to check what the voltage output is on the wire from your VF500F Ignition Control Module to the tachometer.  Maybe you'll find something like: The VF500F Ignition Control Module puts 5volt power down that line to the tachometer.  If the NC30's Ignition Control Module puts 12volt power on that line to the tachometer, then there you have an explanation for the low RPM reading on the swapped-in NC30 tachometer.

 

But, what If it turns out that the Ignition Control Modules on both of these motorcycles use 12volt power on that line to the tachometer?  In this case it might be true that the VF500F module produces a shorter 12volt pulse than the NC30 module does.  An oscilloscope can show you the length of the square-wave pulse (I know not everyone has access to this sort of equipment).

 

I'd say the next thing to look at would be the circuitry inside the tachometers (both the old VF500F tachometer and the new NC30 tachometer).  You'll probably find that both tachometers have a resistor installed on the line coming in from the Ignition Control Module.  It would be possible to de-solder and replace the resistor on the NC-30 tachometer with a lower-value resistor to let more voltage through which would swing the galvanometer's electromagnet more vigorously.  You could try different resistors until the correct value was discovered for accurate tachometer readings.

 

People who know more about electronics than I do can help if you explain this situation to them.

 

 

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It would certainly be a great start if you could see exactly what the Ignition Control Module (on both bikes) is doing. 

 

Obviously the Ignition Control Module output to the tachometer will be a square wave, a simple on-off-on-off, zero volts-then up to "X" number of volts, then back to zero, then again...  Nothing tricky about that.  The interesting questions to answer will be:  what is the amplitude (the voltage) of the square wave, is it just plain old 12volts or is it something else like 5volts or 3volts?  and what is the duration of the square wave (is the Ignition Control Module output to the tachometer the same exact period of milliseconds across the entire rev-range of the engine, or does it vary in length because it's paired up with something like the Ignition Control Module's pre-programmed spark dwell period)?

 

And as you mentioned, there's a question of: Does the Ignition Control Module send just 1 square wave pulse to the tachometer per 360 degrees of engine rotation, or is it sending 2 (or even 4, I think 4 would be unlikely, but 2 is possible)?

 

And, yeah, I understand about having limited electronics knowledge, I'm in the same boat there.  But there's a lot of what-if questions you can pose without knowing the exact electrical principles or "best practices".  Then you find somebody who does know all of that and they can steer the situation from there.

 

There are also ways you can "get around" the electronic education/knowledge needed to conceive and construct complex circuitry...

 

This whole thing could be as simple as: Get an Arduino Nano, solder on wires for power and ground, solder on the input wire from the bike's Ignition Control Module, and solder on an output wire to the Tachometer.  Then write up a very simple operating program for the Nano that says: every time you get a voltage input from the Ignition Control Module you will output "X" voltage on your output line to the Tachometer.  Then you could incrementally raise that output voltage until you get a tachometer sweep-needle result that is properly calibrated to actual engine RPM.  Or if the voltages are the same (for both the VF500F and the NC30 tachometer signal) but the duration of the square wave is different (either longer or shorter) you could command the Nano to change that duration of signal.

 

This solution could be used to tailor/correct either of the two most probable differences between the VF500F and the NC30 Ignition Control signals: either the two signals are of different voltage, or the signals are of the same voltage but the square wave is of different durations.  With data gathered from an oscilloscope you could correct either of these situations.

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Now its getting into details. I like it and will take up the challenge.

First I will measure the signals from the vf500 box with the oscilloscope and collect data.

After that I should see the number of signals per revolution and know the voltage and duration. Hopefully the signal is not dependant on the ignition advance setting or something like that.....

 

Meanwhile I opened the vf500 tacho to have a close look to the circuit board, see it on the picture.

1445486712_circuitboardvf500.thumb.jpg.4cff5685d55c5776f4538cb0085f8a76.jpgre.

The connector bottom right is the tacho input signal (yellow cable), R1 above is about 18 kOhm. Middle connector is ground (green cable) and left connector is 12V (black-brown).

Because of the 12 V source connector I would not expect a 5 V tacho input signal, but who knows.....?  The red and black cable go directly to the instrument coil.

 

The Arduino solution sounds easy but would take me to the next level. (I am still a mechanic related person).

But I can ask some colleagues in my office at work for support. They should know it when programming cnc controllers every day....    (o:
 

 

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Hi Greg,

thank you again for following my problem.

I defintly think that the old VF500 version uses the wasted spark logic and there is no camshaft sensor on board. I even can't remember a camshaft sensor with my VFR400 rebuild some years ago.

If I have to change the starter clutch hardware I think that I have to go to far for this tacho modification. But I will do a last step and ask the guys from v4-spark for some advice and support.

The next modification of the engine (rising to 600cc capacity) would need a modified ignition curve as well. So maybe their system is a good step forward to proceed. 

 

If I get a proper answer I will let you know. Thank you so far for your support !

 

And stay healthy........

 

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After looking at the traces on the backside and seeing how the components are placed on them I've learned a bit.  On this VF500F tachometer circuit board it's obvious that the input wire from the Ignition Control Module is used as nothing more than an input to the Integrated Chip, it only connects to the long black item labeled "I" in the middle of the circuit board after going through the 1.7K ohm resistor.  The 12volt connection wire is what's metered through to the galvanometer based on the frequency of the Ignition Control Module wire.

 

Will be interesting to see if the NC30 tachometer circuit board runs the same sort of setup. 

 

If it does use the same setup the only problem will be getting either: 1. a matching the voltage that an NC30 Ignition Control Module would put on the input line or, 2. If the VF500F and NC30 input line voltages are close together, simply change the resistor it's connected through in order to put through the proper voltage to the Integrated Chip.

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So if I understand you right  you think changing the bespoke resistor R1 could adjust the voltage input to the IC and then improve the magnification of the needle reading? As the simple solution......

To check the tacho signal voltage level of the vfr400 box is not that easy, because the bike is not running at all.  That means opening the vfr 400 instrument seems a must to shure about the internal board design. This might take a few days so be a bit patient with me.

 

Yesterday I had a look at the v4-spark website and the offered ignition modules are quite intersting. A free programmable ignition curve and a rev-limiter are good options for the next planned steps towards a VF600 engine......

 

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Hi thank you to both answers.

 

@ Captain 80s:  Using two ignition modules with each tacho signal output might be a solution. Only thing I am not shure about is the signal time delay from box one to two.

But yes it would double the signals anyway and should improve the reading. I will think about that, but have no second box to make an immediate check.

 

@GreginDenver: My idea, no my hope, was that Honda does not switch the logic or even the signals for the tacho drive. But unfortunatly they changed something 10 years after the VF500....

I will pick up your hints and look for an oscilloscope from work. Then I can check the signals from the vf500 ignition box (tension 5 or 12 V and how many pulse per revoluiton may appear). Normally I  have a VFR400 for comparison but the bike is not running yet.

To exchange any resistors it would be nice to have a detailed plan from the internals.  I can open both instruments and check the resistors on the incoming line, but shortly after that I will be lost. My electronic knowledge is not that deep......

 

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Happy Eastern weekend in thoses strange times....

 

I did an oscilloscope check of the tacho signal when the engine is running. The signal is generated from the vf500 ignition module while the vfr400 tacho is connected.

The oscilloscope pre-setting is something new to me, but I think I could achieve what I expected.

A stable tacho signal of 12V and 30µs duration (33.3kHz). But the signal frequency related to the engine turns is interesting. It shows about 50 Hz at normal idle speed (around 1200 1/min ) and 130 Hz at high idle (est. 3000 1/min.)

Normally I would expect 1200 / 60 = 20Hz in case of a wasted spark ignition. Or half the amount 10 Hz at exact iginition timing.

What I see is about 2,5 times more tacho signals than expected ??

It seems that the vfr 400 tacho is expecting even more signals/engine turn which results in a reading of very low numbers of revs./min.

Any ideas?

 

I am bit shy to open the vfr400 instrument because the bezel is curled to the instruments cup and might be destroyed when opened. That would solve my problem in different way....

Through the connection hole I can see the circuit board which is different to the vf500 board. There is a more modern IC and again some capacitors and restistor. But I can not identifiy anything inside. 

 

For me it looks as the only chance is to exchange the vf500 ignition module to a vfr400 module? Or ask at v4-spark.com for support......

 

Ideas are welcome.....(o:

 

 

idle reading vf500 ign.modul.jpg

high idle reading vf500 ign.modul.jpg

Tacho vfr400 circuit board through hole.jpg

Tacho vfr400 rear view.jpg

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7 hours ago, RalfR said:

For me it looks as the only chance is to exchange the vf500 ignition module to a vfr400 module? Or ask at v4-spark.com for support......

That's an interesting thought.  Both bikes have the same crankshaft design, a 360 degree crankshaft.  I'm guessing that Honda used camshafts that produced the same "big bang" style order: 1-4-0-0-3-2-0-0- 

 

The big question would be: What do the crankshaft trigger wheels look like on the two bikes?  Obviously, Honda incorporates the "trigger pattern" into the bike's starter clutch assembly.  Because of this your real question is: Can you substitute an NC30 starter clutch onto a VF500F engine?

 

Is there any hope that the starter clutch assemblies of both bikes have identical proportions (diameter, height, etc.) and have identical bolt-on pattern/spacing for the 3 bolts that secure it to the ?  And is the Variable Reluctor (Position Sensor) mounted/located in the exact same place on both bikes (so it "senses" the trigger wheel pattern "bumps" at the proper time during crankshaft rotation)?

 

I have to say that from a quick look at pictures of both items they do look like they're very similar.

 

 

Screen Shot 2020-04-13 at 11.41.05 AM.png

 

Screen Shot 2020-04-13 at 11.59.30 AM.png

 

Also, does the NC30 Ignition control Module require any inputs that the VF500F module did not require?  For example: I know that some of the more advanced '90s and 2000s carb bikes used a throttle position sensor input to the Ignition Control Module.  And I'm going to guess that the NC30 wasn't so advanced that it required a camshaft position sensor, right? 

 

(Actually, now that I think a little more about the engine architecture of both bikes I realize that the ignition is probably fired in "wasted spark" mode, which means that the spark plugs inside either head (1 and 3 in the rear head, and 2 and 4 in the front head) both fire on every 360 degree rotation of the crankshaft so there's no need for a camshaft sensor on the engine)

 

But if the "stars and planets line up perfectly" with both bikes having identically engineered clutch sprag wheels with identical bolt patterns and an identical placement/location of the Variable Reluctor pickup (position sensor) and no other mitigating conditions (like requirements for Ignition Control Module inputs that the VF500F did not provide)...  Then you're off to the races and it'll be just a question of matching up the necessary wiring to achieve success.

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