The 8207 coil looks to be a CD type coil, given the low turns ratio in it. This low turns ratio beats the hell out of the switching transistor every time the plug fires.

TI modules are about the simplest ignition module out there, and easy to fix. It shouldn't be that expensive to repair, given the minimal number of parts in it.

 

The modules that no longer work are sealed. I still have the original GM module, but being almost 50 years old, I went with the aftermarket solid state version. I ordered another module, this being module #3. I also ordered another pair of distributor box mounting brackets. I'm going to lengthen them and mount the original t.i. coil inside the box. Maybe by next weekend I'll have it back together. Thanks again for all your help.

 

How sealed are they?

 

It looks like some kind of epoxy potting. Basically an aluminum case with the 3 terminals sticking out of the potting. It's not like a circuit board with traces and components soldered onto it. I attached a picture.

 

if the module is junk try dissolving the potting material with MEK and see what is in there.

 

Thanks for the suggestion. I was trying to figure out what might dissolve that potting material, but was drawing a blank. Unless the manufacturer gives a decent "core charge" credit for the old "broken" part, it seems worth the time for the OP to see if that potting crap can be removed to look at or repair the damaged components.

 

back in the 70s when electronic ignitions came out in dirt bikes and snowmobiles I repaired these units by dissolving the potting material and MEK worked the best. I also repaired TI boards. here is my test setup. the aluminum box contains wire wound resistors and a DPDT relay that is used as the make and break the circuit like the dist pole pieces do on the engine

 

I'm going to see if the seller will take them back first. Prob;y not being an electrical part even though the instructions says it will work with any points type and high performance coil.

 

Interestingly that the MSD coil burned the module.
Because the MSD coil has ~1ohm resistance, double the value of the TI coil.
Standard coil has 1,5ohms.

 

There's more to a coil's construction than just the primary winding resistance. The primary inductance has a great effect on the current risetime, which affects the average current level that the switching transistor has to conduct, and the average wattage dissipated by that transistor. The turns ratio also has a significant impact on the stresses seen by the module. A typical points coil has a turns ratio of about 100:1, the TI coil is about 135:1 IIRC, and the MSD coil mentioned has a turns ratio of 70:1.

Assume for discussion that the plug arcing voltage is 20 kV (at some gap size and cylinder pressure). Obviously the secondary windings are also at 20 kV at that moment. Because the primary windings are immersed in the same collapsing magnetic field as the secondary windings, there's going to be a similar flyback/spike voltage induced on the primary windings, except at a smaller level due to the smaller number of primary windings. This voltage spike isn't a big deal for the coil because a coil is designed to deal with high voltages, but this high voltage is also connected to some semiconductor circuitry (the module switching transistor). Notice the math: At 20kV secondary voltage the primary voltages of the different coils mentioned in the previous paragraph are:

TI coil: 20kV/135=148 volts.
Points coil: 20kv/100= 200 volts
MSD coil: 20kV/70= 285 volts

There's a lot of claims that the TI coil has a large turns ratio to produce higher voltage to the plug. That's incorrect/backwards. The TI coil has a large turns ratio to produce smaller primary winding voltage spikes so that damage to the TI module switching transistor is minimized. As you can see from the three calculations above, there are three different stresses imposed on the primary circuit/transistor depending on which coil is hooked to the module.

Either way, it's still speculation what actually failed in the module. IIRC the manufacturer stated that the module is designed to operate properly with most any coil. Unless the defective module is examined to find out what actually failed, we're left guessing whether the manufacturer's claim is accurate.

 

69427, if you want I can send you a module. Maybe you can determine what failed. The oem t.i coil is mounted and module #3 should be here Thursday. Maybe by Saturady I'll have it running.

 

I'll take a look at it. I'll need your permission though to use some chemicals to try to dissolve the epoxy covering everything.

I'll PM my address to you.

 

Not a problem. It is not worth anything to me. I'll get it to you. Thanks.
Mark

 

Finally got a break from a bunch of life-sapping activities and hooked the TI board up to my distributor machine. I started with a light resistive load on the module output (the transistor output that drives the coil primary circuit) to see if there's any activity at all in the board. There is current coming out of the transistor, with the "key" on, and no RPM (normal for a TI design), but after spinning the distributor I noticed that the output doesn't shut off on the negative transitions of the distributor pickup coil. I manually triggered the input line to confirm things, and the transistor output continued to be non-responsive to the input waveform. I ohmed out the output transistor (the stock TI design has a protective zener diode across the transistor, but I don't see any large diode in the epoxy topography that covers the large parts), and I'm getting a near dead short across the switching transistor (emitter to collector), explaining why there's continuous current coming out of the board when it's powered up.

If there's still no objections, I'll try the MEK on the output transistor section to see if I can clean it enough to possibly unsolder and replace the failed transistor. I don't expect to be able to read the part number on the transistor, but that won't hold up ordering another transistor just by looking up the required specs for the replacement.

Wish me luck on the chemical part of this endeavor.

 

Go ahead and see what it is. I don't need it. if you can use it if fixed, it's yours.