Topic: Starter motor safety Unit-whats inside?

[lucky]

OK....
I wanted to find out what was in the starter motor safety unit and why all of the used ones had cracks and shrinkage on the outside case.
So I took one of the ones I had and decided to sacrifice it.
First I tried using a small exacto saw and started removing the outside case.
You can see in the photo the typical cracks and shrinkage. I wanted to know why.
I Started to remove the case and you can see the line between the case and the potting material.
I removed the potting material as carefully as possible with a small hammer and chisel.
In one photo you can see the large aluminum heat sink that caused all of the shrinking and cracking of the outside case.
I did accidentally damage one component during the removal of the potting compound.

I am wondering why this component cannot be reproduced since it seems like a simple construction. I have looked on the internet and cannot see to find any for sale.
I did see one Facebook account holder that was restoring a Honda CB750 and he had a new one that had a light grey case. He did not say where he got it.
I would ask but I do not want to become a Facebook member now that they share info with all the other social networking sites.

I do not know enough about electronics to make a new unit. I cannot identify some of the parts on the circuit board.

[lucky]

Any comments from the electronic experts?
I did the work(damage) now lets hear what you know about it.
What can you tell us?

They made this part for so many years of CB750 but no replacement is available.
Ant thoughts about why it cannot be reproduced? Non legal.

Thanks.

[HondaMan]

I usually bypass the whole thing by grounding the Green/Red wire from the starter solenoid to the spare Green wire under the left side cover.

Honda replaced it all with a simple diode: see the 1976 F bike wiring diagrams for examples.

[lucky]

I usually bypass the whole thing by grounding the Green/Red wire from the starter solenoid to the spare Green wire under the left side cover.

Honda replaced it all with a simple diode: see the 1976 F bike wiring diagrams for examples.

But then can you start the motorcycle in gear with the clutch pulled in, in any gear? And what year were you talking about? Kind of a murky piece of advice.

[CycleRanger]

From the Honda Update '74 dealer info.
Now anyone can build their own!

[LesterPiglet]

Useless device IMHO.

[lucky]

This information and diagram is still not useful.
We already know what the SMSU is supposed to do and then Hondaman says the "diode" will replace it. But  the SMSU  had more that two wires going to it ,
so my question is if you have the diode unit do you still need the left handlebar
switch? On my 1975 wiring aftermarket harness I could not get a
Correct solenoid. I could only get the one with the red/yellow wire and the green red wire. Right now I have the green red wire connected to the black wire coming out of the harness now. I am afraid if I plug the green /red wire into the green wire it would be a direct short circuit.

[CycleRanger]

The diagram shows the wire colors and function.

[lucky]

The diagram shows the wire colors and function.

Unclear.....Which diagram, the one in the workshop manual
or the one shown on this thread?

[lucky]

I have a 1975 wiring harness aftermarket.
My bike is wired as a 1975. Problem is if I order a solenoid new(which I did)
It does not match the 1975 wiring diagram because it was superseded.
The solenoid I get has a red/yellow and a green wire with red stripe.
It is supposed to be red/yellow with black wire.

I have the green/red wire from the solenoid, connected to the black wire from the harness the starter works. If I unplug the green red wire from the solenoid going to the black wire from the harness  it will NOT start. When it is connected it starts.
That tells me that when the key is ON that the green /red wire from the solenoid is getting 12V when the key is ON. If I hooked the green wire from the harness to the green/red wire from the solenoid like HONDAMAN says it would be a direct short to ground!!  NO GOOD. El fry-o grande.

[lucky]

I usually bypass the whole thing by grounding the Green/Red wire from the starter solenoid to the spare Green wire under the left side cover.

Honda replaced it all with a simple diode: see the 1976 F bike wiring diagrams for examples.

Only the 1978 bike had a green/red wire and a yellow/red wire coming from the solenoid. All the previous bikes, K3-K7s' had a solenoid with a black wire and a yellow /red wire.

[CycleRanger]

The diagram shows the wire colors and function.

Unclear.....Which diagram, the one in the workshop manual
or the one shown on this thread?

Both. 

[Fritz]

I usually bypass the whole thing by grounding the Green/Red wire from the starter solenoid to the spare Green wire under the left side cover.

Honda replaced it all with a simple diode: see the 1976 F bike wiring diagrams for examples.

Only the 1978 bike had a green/red wire and a yellow/red wire coming from the solenoid. All the previous bikes, K3-K7s' had a solenoid with a black wire and a yellow /red wire.

The way the starter button has been wired differs from the early and the later models.
The later models have the starter button connected to ignition (black) and the solenoid (yellow/red) while earlier models have the button connected between the clutch switch (green/red) and the starter solenoid (yellow/red).
The ealier button connected the solenoid indirectly to ground (via clutch and neutral switch), the later to +12V.
The earlier type connected the solenoid's other pole to +12V (black), the later indirectly to ground(via clutch and neutral switch, green/red).

Now, if you have an earlier type harness and a later type solenoid, just connect the solenoid's Green/Red wire to black, throw away the SMSU and connect a diode (e.g. 1n5008) between LightGreen/Red and Green/Red at the SMSU connector. The negative pole of the diode (ring on casing) should point to LightGreen/Red. The Yellow/Red wire of the solenoid connects to Yellow/Red in the harness.

The green wire that had been connected to the SMSU is not required any more. The SMSU needed it to power the transistors.

[CycleRanger]

Thank you for supplying the missing bit there Fritz!