1983 Suzuki GS 1100 ESD Tach

[reddirtrider]

You test a zener for opens and shorts the same way as you do a regular diode.

It could be a zener of 17 volts, however, I wouldn't know what it's function would be. Possibly more weight to keep the front end down?

[rustybronco]

You test a zener for opens and shorts the same way as you do a regular diode.

I removed the diode and it read ~0.2 ohms in both directions so i'm trying to find a replacement for it.

would indicate its bad.

It could be a zener of 17 volts, however, I wouldn't know what it's function would be.

redundency, to protect the tach and SM014, because of a non regulating R/R?

[posplayr]

d'Arsonval Movement

Rusty

The only things I have questions about, are his resistance reading of .2 ohms in both directions, does the tach indicate voltage or current and at what voltage is the "diode" set to regulate. because of this information I believe it to be higher than 5 volts, more on the order of 17? ish.

Most all meters are basically a needle connected to a light spring and a current creates a magnetic Field to pull on the needle. The more current the further the deflection. So it is a current sensor. You make a volt meter out of it by putting a resistor across it so that you limit the current through the movement to something it can handle.

see references.

http://notes.ump.edu.my/fkee/1313/Lecture%20Notes%2005.ppt#256,1,DC Voltmeters

http://www.tpub.com/neets/book3/7j.htm

I'm in the process of redwaring the schematic now.

Pos

[reddirtrider]

would indicate its bad.
redundency, to protect the tach and SM014, because of a non regulating R/R?

Could be, but I doubt it. I've been wrong before, so I'm just giving my opinion.

Modern digital multimeters are basically current sources with a voltage measurement circuit.

I have a GS750ES tach in the garage that I can look at to make some measurements later. It's off the bike but it's a simple process to connect that board to a battery and measure the voltage across the zener.

I'm not sure the darn thing worked prior, so I'll have to check with my son. He 'lets' me work on his motorcycles. Actually to be fair, it's a restoration that's going to be a wedding present, so I have no idea what works and what doesn't until I go over the entire bike.

[reddirtrider]

Well, it appears that the 33 ohm resistor on this tach is open. I can't make a voltage measurement until I replace it. My wife is in town today so I'll give her a call and see if she can pick up one.

[posplayr]

ESD Tach Schematic

OK here is a schematic that I redrew based on the hand drawn version. I did not check all of it against the layout except to make sure that everything connected to the tach movement was correct. I also conferred with one of the guys here to see what he thought.


The diode is most likely a zener to provide a stable voltage reference to the ND SM014 as well as to the + side of the tach movement. This provides power to the part as well as an actively controlled reference. The 33 ohm, 33 uF paid also provide filtering. The zener is most likely 5 volts as Red suggested before.

The way this appears to work is when RPM is zero, the output on pin #2 (starting from the right) floats high to the +5V supply rail. In this way no current flow through the movement. As the RPM pulses occur, the voltage at pin #2 drops to toward ground causing current to flow and the RPM needle to deflect.

The rest of the circuitry depend on what is in the SM014, but none of that will change how the movement is controlled.

Pos

[reddirtrider]

The 33 ohm resistor is not 27 watts as was posted earlier. It appears to be a 2 watt part (again just a guess as the markings on these parts are pretty cryptic). This is possibly why it fails. If the assumption is made that the zener is 5 volts and the battery power is 12 volts then 2 watts is enough, as the power dissipation is 1.5 watts. It easy to exceed this rating if the battery power to this unit is above 13.1 volts.

I would suggest that those replacing this resistor upgrade to a 3 watt unit. I'm going to go that route and then try to measure the zener voltage so we can be sure it's a 5 volt device.

[posplayr]

Red

using the Suzuki manual standard changing range upper limit of 15.5V I get about 3.3 watts (10.5V drop). I guess that explains it's size.

Jim

[Nicholaschase29]

Hey guys,

Looks like you've been working hard on my problem and i appreciate your help.

Posplayer - The plus and minus were fed into the meter, the wires off the board were red and black. As far as the polarity of the diode goes, I just copied the symbol off the back of the board, oriented how it was shown. I don't know how to determine which side is the anode and which is the cathode on the part itself.

Reddirtrider - I haven't powered it up since it has been apart.

I was looking over the diagram that posplayer drew up, it looks good, thanks for taking this seriously for me I'm lost on my own. I was looking at the input 12V wire though and found that where I have the voltage branching in your diagram all the voltage is fed through the 33 ohm resistor. I drew up a new diagram, it is the best i could do, and the 9th pin on the IC is the top pin on my drawing. It might still be hard to read though.

I made this diagram based on my hand-drawn diagram, I did not check it against the back of the board.

Once Reddirtrider has a chance to verify that diode on his board I'll go get a replacement for mine and keep my fingers crossed.

Thanks again guys.

[posplayr]

CAD teeth cutting

Nicholas,
I looked at the change. The diode is still probably a zener 5V device. I hope Red can confirm when he gets his working.

Pos

[reddirtrider]

using the Suzuki manual standard changing range upper limit of 15.5V I get about 3.3 watts (10.5V drop). I guess that explains it's size.

Jim

True enough, but for power dissipation we use average power, not instantaneous. Voltage ratings are different, they go with instantaneous.

My wife just returned. I'll try to make time for this tonight. My fingers are sore from sanding rims, so it will be a welcome change.

[posplayr]

15.5v

True enough, but for power dissipation we use average power, not instantaneous. Voltage ratings are different, they go with instantaneous.

Is the upper limit at 4000 RPM so in one hour of riding at 4000 I'm sure you will reach thermal equilibrium or run away which ever applies.

[reddirtrider]

Well, I ganged seven 220 ohm 1/2 watt resistors together and gave it a try (radio shack is all we have within 40 minutes driving time) and the voltage reading was 2 volts. Unfortunately, I think there is something else wrong as the makeshift resistor was very hot to the touch. When I say very hot, I mean burning hot.

I didn't expect to dig into this right now with the rest of the bike still in pieces, so I'm not prepared to do much else as my bench space is gone. I'm rigging this up on the seat of the ATV and using its' battery.

If all else fails it wouldn't be difficult to design a circuit that does the conversion necessary to drive this tach. The unknowns at this moment are what is the input and what is the necessary output for any given input. Since I don't have a running bike, it's hard to determine either.

Sorry for the bad news, but such is life. This bike has given me problems every step of the way. If it wasn't my sons' I'd seriously think of parting it out.

[reddirtrider]

Is the upper limit at 4000 RPM so in one hour of riding at 4000 I'm sure you will reach thermal equilibrium or run away which ever applies.

If we ever figure out what the components are on this board we can work the numbers. Right now we're ****in' in the wind. Frustrating my friend.

[posplayr]

Red

Regardless of the components on the board, Power ratings should be based on the steady state maximum voltage available from the charging system.

The manual states that 15.5V is an acceptability state maximum at 4000 RPM (you brought up the terms instantaneous which do not apply to these numbers).

Considering there are plenty of GS's running around Even above this (one recently at 18.5V ).

Any power calculation should at least use 15.5v if not something higher like 16.5v to provide some margin. Otherwise with certainty if the R/R were to stop regulating the Tach components will soon go into thermal overload and fry.

Using a upper voltage like 16.5V for thermal calculation is a good idea and I know that now and that is NOT"****in' in the wind".

Pos