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#4638465 - 01/18/18 07:37 AM Electronics savvy, please comment....
daves66nova Offline


Registered: 04/11/04
Posts: 3652
Loc: los angeles
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?
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#4638517 - 01/18/18 08:17 AM Re: Electronics savvy, please comment.... [Re: daves66nova]
Virtus_Probi Offline


Registered: 06/25/15
Posts: 3966
Loc: New England
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.
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#4638518 - 01/18/18 08:17 AM Re: Electronics savvy, please comment.... [Re: daves66nova]
oldoak2000 Offline


Registered: 07/23/14
Posts: 119
Loc: North TEXAS
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).

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#4638551 - 01/18/18 08:53 AM Re: Electronics savvy, please comment.... [Re: daves66nova]
ARCOgraphite Offline


Registered: 05/17/09
Posts: 11963
Loc: N.H, U.S.A.
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.


Edited by ARCOgraphite (01/18/18 09:05 AM)
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#4638567 - 01/18/18 09:07 AM Re: Electronics savvy, please comment.... [Re: daves66nova]
daves66nova Offline


Registered: 04/11/04
Posts: 3652
Loc: los angeles
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.


Edited by daves66nova (01/18/18 09:09 AM)
Edit Reason: added on
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#4638635 - 01/18/18 10:10 AM Re: Electronics savvy, please comment.... [Re: daves66nova]
CT8 Offline


Registered: 10/09/14
Posts: 10925
Loc: Idaho
Contact MSD.
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#4638667 - 01/18/18 10:55 AM Re: Electronics savvy, please comment.... [Re: daves66nova]
Virtus_Probi Offline


Registered: 06/25/15
Posts: 3966
Loc: New England
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).
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#4638671 - 01/18/18 10:57 AM Re: Electronics savvy, please comment.... [Re: CT8]
daves66nova Offline


Registered: 04/11/04
Posts: 3652
Loc: los angeles
Originally Posted By: CT8
Contact MSD.
Their tech support and online forum is WORTHLESS.
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#4638676 - 01/18/18 11:03 AM Re: Electronics savvy, please comment.... [Re: Virtus_Probi]
daves66nova Offline


Registered: 04/11/04
Posts: 3652
Loc: los angeles
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.
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#4638689 - 01/18/18 11:16 AM Re: Electronics savvy, please comment.... [Re: daves66nova]
ARCOgraphite Offline


Registered: 05/17/09
Posts: 11963
Loc: N.H, U.S.A.
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.


Edited by ARCOgraphite (01/18/18 11:19 AM)
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#4638695 - 01/18/18 11:19 AM Re: Electronics savvy, please comment.... [Re: daves66nova]
user52165 Offline


Registered: 10/21/11
Posts: 1331
Loc: CA
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??



Edited by user52165 (01/18/18 11:29 AM)

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#4638697 - 01/18/18 11:23 AM Re: Electronics savvy, please comment.... [Re: ARCOgraphite]
daves66nova Offline


Registered: 04/11/04
Posts: 3652
Loc: los angeles
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.
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#4638722 - 01/18/18 11:57 AM Re: Electronics savvy, please comment.... [Re: user52165]
daves66nova Offline


Registered: 04/11/04
Posts: 3652
Loc: los angeles
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
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#4638723 - 01/18/18 11:59 AM Re: Electronics savvy, please comment.... [Re: ARCOgraphite]
daves66nova Offline


Registered: 04/11/04
Posts: 3652
Loc: los angeles
Originally Posted By: ARCOgraphite


I'm sorry, overall but Looks like junk from a distance.
It works is what counts, not "looks"
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#4638735 - 01/18/18 12:12 PM Re: Electronics savvy, please comment.... [Re: daves66nova]
Virtus_Probi Offline


Registered: 06/25/15
Posts: 3966
Loc: New England
Is it possible that one of the wires crossing over the lower left edge of the xtor is missing insulation on the bottom?
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