Electronics savvy, please comment....

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I have an MSD box, which is an ignition box for a vehicle. This transistor seems to intermittently spark a little around the edge when engine is running. I can see it at night when I block the light around the box. Now, Is this due to that piece not being grounded properly with the screws holding it down tight enough , or would it be something else? It has 2 and only one does this and it does get a little warmer than the other one that doesn't spark. I don't know anything about electronics to troubleshoot. Thanks!! Also, has anyone here ever repaired MSD boxes?
 
Can you see the markings on the problem transistor so we can figure out what node the tab is connected to?
I don't deal an awful lot with discrete power xtors, but I looked a random bipolar family in a TO220 package and the tab was the collector whether the device was a PNP or NPN. The collector is unlikely to be ground for an NPN, but it's quite possible for a PNP. You could also have a FET that might have totally different connections, really would be good to get the part ID if possible.
 
Insofar as electronics, Careful, the case of the transistor is 'part' of the circuit, and should not be 'grounded' to anything that it isn't already connected to. Its normal for them to get warm during operation. 'Grounding' it may cause it to short-out and overload, thereby burning it out.

I'm not a 'msd' expert, but it shouldn't be sparking around the transistor; however, the transistor itself only switches LOW voltages (under a hundred volts) - probably energizing/switching (on/off) the 'bat' side of a coil (much like points would on a classic engine). If there is sparking, it's being leaked from somewhere else in the circuit on the HV side, or maybe even bad spark-plug wires or plugs with too much gap (worn).
 
Regular iggy coils resonate so they are "multiple spark" also.

This on a high comp race engine? If not get rid of it.

____________________

If yoyu wish to ftry to fix it:


You make be getting leak back from the high tension side. Check for cracks and bad secondary lead.

Open the unit and look for traces on the boards if its not potted.
OTW most power transistors should have thermal compound or film
under the semiconductor switch. It get dried up. Maybe remove and re compound.
 
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I hope this pic downloaded.
Yes it did. The area where it sparks is at the lower left edge of the transistor. The car just a 22R Toyota engine, daily driver.
 
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That is a power PNP and the case is the collector, so it is possible the case is tied to ground.
Is there a screw head sheared off in the upper right or is that just a different type of component holding the case down?
If it's sparking near the screw, I can't see any harm in trying to tighten the screw to see if that helps (keep yourself isolated JIC).
 
Originally Posted By: Virtus_Probi
That is a power PNP and the case is the collector, so it is possible the case is tied to ground.
Is there a screw head sheared off in the upper right or is that just a different type of component holding the case down?
Missing screw there. I installed one recently.
 
was the switch previously blind riveted to the case/heatsink? Maybe your screw went too deep and is near a B+ trace underneath.

I'm sorry, overall but Looks like junk from a distance.

I would Remove it, go back to stock, but use IR plugs if single coil ignition.
 
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MSD = May Self Destuct

I've seen so many problems with MSD. How do they even still survive as a business?

What possible reason for this box on this engine??
 
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Originally Posted By: ARCOgraphite
was the switch previously blind riveted to the case/heatsink? Maybe your screw went too deep and is near a B+ trace underneath.

I'm sorry, overall but Looks like junk from a distance.

I would Remove it, go back to stock, but use IR plugs if single coil ignition.
I believe it previously had screws on each end. Im running the box. Does run better, smoother with it.
 
Originally Posted By: user52165
MSD = May Self Destuct



What possible reason for this box on this engine??

Easier starting hot or cold, smoother running, possible mpg gain, spare box just laying around, easy to install,etc,etc
 
Originally Posted By: ARCOgraphite


I'm sorry, overall but Looks like junk from a distance.
It works is what counts, not "looks"
 
Originally Posted By: daves66nova
Originally Posted By: ARCOgraphite


I'm sorry, overall but Looks like junk from a distance.
It works is what counts, not "looks"
Where is the case for that unit? Have to agree with ARCO. If an electronic unit looks that neglected, how are the mechanicals?
 
I use an MSD box on a 1949 Farmall "C" tractor (points triggered, white wire)

Anytime it rained or was humid, I would have to mess with the points.

Now...... it just works. Always. No hassle.
 
Originally Posted By: HosteenJorje
Originally Posted By: daves66nova
Originally Posted By: ARCOgraphite


I'm sorry, overall but Looks like junk from a distance.
It works is what counts, not "looks"
Where is the case for that unit? Have to agree with ARCO. If an electronic unit looks that neglected, how are the mechanicals?
Who ever said it was out of the case???he circuit's in the case still, the cover was removed and i took a picture of it. I don't go into the circuitry and try to make it look "nice" Mechanicals are great, by the way.
 
Really, it needs to be pulled and troubleshoot'ed. Way too many things that could be wrong, especially if there was a fastener failure on a transistor. Solder joints can't be assumed to be good if it was moving at all with heat/cooling cycles with that missing fastener. But that's just one thing.

Even though it may seem to be working now, failure with electronics never really just goes away. It just prolongs the ultimate failure point. If you don't want to replace it, pull it and get a competent tech to have a look while it's still possible to be put back to 100%. If something fails, it tends to take other stuff out with it, making the repair all that more expensive or impossible.
 
I've repaired an MSD box before. They are essentially a power supply that is turned on by the trigger. As has been stated, the case of the transistor is the collector and it should have a solid electrical connection. If it does and it still sparks then you have another problem. Take it apart and examine the circuit board and components for defects using a strong light and magnifier.

The 22R should have electronic ignition as standard. Are you triggering the MSD box with the magnetic pickup? If so, and you want a more reliable ignition system that makes very good sparks get a GM, not aftermarket, 4-pin HEI module and use that.
 
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