switch box rebuild ?

[pepper]

yes, I have a dumb question and i cant find any information on the net so i thought i would ask some smart people. can a switch box be rebuilt , can you get the resin epoxy out or what ever that stuff is , can any one help please?

 

[Barnacle_Bill]

Re: switch box rebuild ?

No, you would never get it apart without damaging a lot more components.

 

[Jim662]

Re: switch box rebuild ?

I've thought about this myself. That switch box has to have discrete componnents in it that are obtainable at far less cost than a new one. What we need is the schematic for the internal parts of the switchbox. I've never seen it. Given the fact that it is heat-synced, I'm assuming there's some big wire-wound resistor. There has also got to be a capacitore in there too, and that's probably the part that fails most often. What's on the box? Seven terminals? I'm guessing that there's less than 7 componnents inside and that their cost is under $10.

Also, I don't think that it is epoxy resin that the parts are set in. I think its a heat-based material. Wnen mine goes, I'm popping it in the oven at 450 deg and see if the stuff doesn't pour off.

 

[sschefer]

Re: switch box rebuild ?

I've thought about this myself. That switch box has to have discrete componnents in it that are obtainable at far less cost than a new one. What we need is the schematic for the internal parts of the switchbox. I've never seen it. Given the fact that it is heat-synced, I'm assuming there's some big wire-wound resistor. There has also got to be a capacitore in there too, and that's probably the part that fails most often. What's on the box? Seven terminals? I'm guessing that there's less than 7 componnents inside and that their cost is under $10.

Also, I don't think that it is epoxy resin that the parts are set in. I think its a heat-based material. Wnen mine goes, I'm popping it in the oven at 450 deg and see if the stuff doesn't pour off.

They are Capcitive Discharge ignition systems so yes capactor(s) do play a role. There is also a SCR (Thyristor) and from what I've seen, a second full wave bridge rectifer that uses diodes. Both are rectifiers but the SCR is what most call the bias circuit. Find out the P/N on that and you might just be able to build your own switch box.

 

[7920hpMercury]

Re: switch box rebuild ?

If you soak the late seventies switchboxes in acetone a couple of days, the goop will curdle and will come right off. Then you can see what all is inside.

For me, it was a situation of "what next?" Unless you have a schematic and troubleshooting info for the electronic circuit, I could not do much. For the late seventies 2 cylinder switchboxes, there was a circuit board with quite a few parts in there.

Good luck!

 

[Karl_Childers]

Re: switch box rebuild ?

I am gonna start a new thresd on this one but I wonder if there's a better way?

 

[pepper]

Re: switch box rebuild ?

mabe it's not such a dumb question after all,the way i look at it is : some one dont want us to look in side because it's simple,because if it's electronics i can just about fix it, like you said probley not over ten bucks worth of parts in side , we just need 2 know what this stuff is and how 2 disove it.

 

[Chris1956]

Re: switch box rebuild ?

Pepper, Merc and CDI do not pot their switch boxes to keep you out. They pot them to protect the components from moisture, vibration and heat. It is not a conspiracy to keep a secret.

There are a lot of aftermarket CDI ignition systems available. You might do some research and see if one meets the ign needs of the Merc Outboards. Figure out how to time it and power it and then report back on price and work involved. Newer Mercs have gone to the CDM-style ignition.

 

[sschefer]

Re: switch box rebuild ?

I agree, there's really no secret here. You might find one in the aftermarket motorcycle world that would work just fine.

You can pay 350.00 for a Merc part or 175.00 for the same part from CDI. If you want to build your own just take one apart, read the values on the caps, resistors, inductors, diodes, SCR, etc. Trace out the circuit board and build one. You could probably save some time by just going to Sam's and buying a schematic.

 

[Laddies]

Re: switch box rebuild ?

Just to disprove the secrecy theory, here is a symantec right from Mercury on a 6 cyl. ADI system so it very plain to see how on functions and another for battery CD.

Sorry no part numbers.

 

[Jim662]

Re: switch box rebuild ?

For the Thunderbot system, which is what I have, there's a capacitor, resistor, diode a mystery "trigger circuits" and another mystery "converter". That's not much. The trick will be to figure out what the part values are and what the "trigger ciucuit" and "converter" are. I doubt either are a microprocessor. If you could get all of the poured plastic off the parts without ruining the painted-on numbers on the parts you'd just about have it.

Does anyone have access to the Sam's folders? It should give the part values and a better explanation of what the trigger circuit an the converter are.

 

[pepper]

Re: switch box rebuild ?

Laddies do u have a symantec for 1981 mariner 4 cl. switchbox ? thanks.

 

[sschefer]

Re: switch box rebuild ?

Thanks Ladies, imagine how many sb's you could resurect if you could just replace the bias cap. Looks to me like that is the most likely component to fail if a battery is hooked up backwards.

 

[j_martin]

Re: switch box rebuild ?

A symbolic diagram is called a schematic.

The "switch" symbols would include an ignition capacitor for each cylinder, an isolation and charging circuit for that capacitor, a comparator to compare trigger voltage to bias, a pulse shaper to create the firing signal to fire the last circuit, a transistor or scr coil firing circuit.

That's a bunch of discreet components for all that functionality.

The diode steering bias circuit shown in the schematic is deceptive. It shows functionality, but not the voltage divider components that would be required. Looking at it with instruments, it is obviously a rectified, voltage divided, and integrated voltage. The bias cap in the diagram is the capacitor part of the integrator circuit.

I've gained all that description from actively monitoring the operation of switchboxes while playing with timing circuits. (Picture a bass boat with precision recording voltmeters and an oscilloscope on it.)

hope it helps
John

 

[pepper]

Re: switch box rebuild ?

Thanks a bunch Laddies, and yes it does help , now i can understand this box a little more and how it works inside. now 2 just get inside for part numbers.