K66 Transistor Ignition - Delco Circuit Module Failure, Diagnosis and Repair

[Richard M.]

I'd like to share with you a recent experience relative to a interesting TI failure that occurred to me. As usual, this will be long and detailed but may be worthwhile "bath-room" reading for you in the future......

The other day after doing some finishing touches and wheel/tire work on this '67 with K66 TI Ignition, I went for a test drive. Everything was running great. Engine strong, car feeling tight, brakes responsive, etc. I needed to test the 3x2 secondaries a bit, so I gave it a little quick burst between gears. All good. Then all of a sudden the engine started to miss and stumble. Rats, what the heck happened?

Stopped, and the engine was feeling like a V-Seven and not a 427 V-Eight. Decided to get it trailered back for fear of making things worse. Winched him up in the trailer and got him back okay. Tested briefly again after the usual electrical connections checks but still sounded like the right bank was not running good while listening through the N14 Side exhaust. I pulled the 4 Spark plugs, and there it was, the #2 plug had black soot all over the end and the sign of the trouble. I cleaned the sooty plug for reuse later.

The plug tested open/short as good with a quick ohmmeter test, so then I checked the plug wire. Bingo. Instead of about 15k ohms or so, I'm getting about 50k ohms. I then wiggled the plug end with the meter attached....no change. Then wiggled the end removed from the distributor cap......Yup, anywhere from 50K to 500K to over a Megohm. Intermittent wire at the terminal. I was glad I found it, but then I was angry at myself for not getting a new spark plug wire set. As usual, what we do not change in a restoration of 50 year old cars......usually fails soon afterward! This would have been bad during a OPs or a PV test for sure.

These wires were on the engine before rebuild for some time but appeared fine. In the process of reinstalling them after engine rebuild, something obviously got loose at the #2 terminal end. I was unsure how old they were, but looked good and I reused them as they were dated. These are the U69 Radio shielded type, with those braided cable covers and terminal ends that get grounded to engine metal. We ALL know that there have been continual problems with these wires and deemed unreliable at times. This certainly adds to the list of those that are unhappy with them. I know some folks here have made there own with solid core wire. I may visit that arena at another time.

Ref photo of the wires before body-on and completion....
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So I went ahead and found the intermittent end, removed the brass end, cleaned, and got a fresh strand of wire, re-crimped it to the terminal and all good. I decided to buy a new wire set and placed the order. I'd get them in a few days.

I put everything back together, and so very confidently went to do a startup and be happy.........Not! The engine sounded like before, and now even seemed to sputter and run rough in the Left Bank also. So I then pulled the Left bank apart, checked all plugs and tested those wires, all good. Hmmmm, what's going on here?

After putting it aside for a while to take care of non-Corvette tasks, the next morning it hit me. I felt I knew what had happened.....the TI module was damaged from the intermittent open in the single spark plug connection. This TI Module was a restored original Delco unit that was on the car from new. Even the power transistors were date coded to the car build. I had restored the outer case and kept the original dated module inside for the sake of originality. After all, it was good for 49 years, why not keep it in there? (note smart-aleck face)
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I had acquired a upgraded replacement from K & B and was planning to keep it as a spare. I previously tested it in another spare module case I had and it was fine, so I wrapped it all up and was planning to keep it as the extra in a box in the Jack-Well for safe keeping.
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The original Delco Circuit board was the type prone to problems if there were multiple open spark plug wires. It is stated directly in the CSM to never pull more than one spark plug wire to test for spark or damage to the TI Module Circuit Board could result. The intermittent high current connection may have caused a feedback through the ignition coil and toasted one of the output transistors in the module. Probably just one of the 2 transistors as the engine could still run but a weak spark.

So I swapped out the suspect TI module with the new K & B module...........The engine fired right up, ran good with all eight cylinders firing away correctly. All fixed. Perfect. Done.

I decided I will dissect the Delco circuit and remove the 2 transistors and test them separately to try to find root cause. I have some spare transistors and may give it a try after diagnosis. I also want to do some experimental analysis tests using my oscilloscope to show some waveform differences during operation for future reference. This for comparison of the old Delco type to the newer and more reliable replacement units.

Rich

[Joe R.]

Re: K66 Transistor Ignition - Delco Circuit Module Failure, Diagnosis and Repair

Hi Rich,

More strong work from you as I've come to expect!!! I was blissfully unaware that open plug wire(s) could damage the Delco TI module. As a fellow EE (and TI owner), I'm very interested to see your oscilloscope analysis of the TI circuit.


Keep up the good work!!!
Joe

[Ken A.]

Re: K66 Transistor Ignition - Delco Circuit Module Failure, Diagnosis and Repair

Rich, There is no long term repair for on OE board and there are no germanium transistors sold anymore, i.e., you're wasting your time.

[Leif A.]

Re: K66 Transistor Ignition - Delco Circuit Module Failure, Diagnosis and Repair

Rich, There is no long term repair for on OE board and there are no germanium transistors sold anymore, i.e., you're wasting your time.

Ah, but Ken, Rich said he had some extra transistors laying around. Carry on, Rich...truly enjoy your comprehensive threads...always enlightening.

[Richard M.]

Re: K66 Transistor Ignition - Delco Circuit Module Failure, Diagnosis and Repair

Rich, There is no long term repair for on OE board and there are no germanium transistors sold anymore, i.e., you're wasting your time.

Sorry Ken, I'm "goin' all in" when I get a chance.

I have several original transistors and a few NOS. Even though they may be good, the age is the issue. I have seen strange unexpected things happen with old electronics. I'm going to start by finding which of the pair(or both) is at fault. Then experiment with some tests.

It's really more of a curiosity and a learning thing.

Rich

[Gene M.]

Re: K66 Transistor Ignition - Delco Circuit Module Failure, Diagnosis and Repair

Rich
I would suggest solid strand copper Packard 440 wires, BUT I do not know if the low resistance would "blow out" the TI.

I recall years ago Charlie Stewart (now not with us, RIP) had been redesigning a solid state circuit to fit inside the original housing that eliminated the original units short falls. Their must be somebody out there doing the same today.

[Richard M.]

Re: K66 Transistor Ignition - Delco Circuit Module Failure, Diagnosis and Repair

Rich
I would suggest solid strand copper Packard 440 wires, BUT I do not know if the low resistance would "blow out" the TI.

I recall years ago Charlie Stewart (now not with us, RIP) had been redesigning a solid state circuit to fit inside the original housing that eliminated the original units short falls. Their must be somebody out there doing the same today.

Gene, The only issue is that this one is Radio equipped and needs the shielded wires as all of the 427's with RPO U69 in 1967 were equipped with. I have seen some folks remove the wires from the shielded sheathing and made their own with the solid Packard wires. I may look into that but unsure if it's a issue with TI. Maybe Ken could answer that.

As far as the TI circuit modules......Presently there are 2 manufacturers of the upgraded circuit board. K & B in Georgia and M & H in California. When the original Delco unit failed recently, I removed it and replaced it with the K & B module I purchased some time ago as it's replacement. I just hadn't changed it over before Lakeland. Thankfully, that original module, and the intermittent wire that caused the failure had not surfaced then. It ran fine in the SnF area before the event, fine through OPs, and fine on a short drive after the event Saturday. It wasn't until I got it back and some additional test drives did it fail hard. Just shear luck.

Rich

[Richard M.]

Re: K66 Transistor Ignition - Delco Circuit Module Failure, Diagnosis and Repair

I've been diagnosing some TI troubles remotely on a '67 L71. Since there is no easy method to test the TI modules without a car, I have devised a bench test. I have 2 old original Delco TI Modules. Using a borrowed TI distributor as a "test generator", I am now able to test the modules. One was unknown given to me from a friend. He had it for nearly 50 years. Datecodes on the Power Transistors are 1966. The other module was a suspect in some on-car troubleshooting a while ago. I diagnosed it as failed, with NO spark from the Ign coil. However, recently I suspected it may actually be good as I may have misdiagnosed the fault.

First I disassembled both modules and tested the transistors and discrete components separately before proceeding with the operational tests. Both modules' transistors tested good using a simple ohm meter, and the other components tested fine as well and within tolerances. I had to remove some devices from the circuit to test them. This is actually outlined in the 1967 CSM.

I don't have a TI harness so I created my own. It's not a pretty setup, but it allowed me to test the 2 modules for basic operation. By manually rotating the TI distributor I can then see if the module generates spark at the test-sparkplug.

I promised you folks some waveforms and will post a video later today. Here are a few shots of the setup.

My test results on both modules was conclusive. BOTH modules Pass and generate Spark. My hunch was right about the suspect which failed in the car. It Passed the bench test. I was chasing a ghost then.

I will also try to acquire some suspect returned failed "upgraded" Modules to verify them.

Rich

[Ken A.]

Re: K66 Transistor Ignition - Delco Circuit Module Failure, Diagnosis and Repair

Rich,
If the stator & PU ring are not in the same horizontal plane, and change during operation, then all of your problems will exist. I still believe your distributor is at fault.
Ken

[Richard M.]

Re: K66 Transistor Ignition - Delco Circuit Module Failure, Diagnosis and Repair

Rich,
If the stator & PU ring are not in the same horizontal plane, and change during operation, then all of your problems will exist. I still believe your distributor is at fault.
Ken

Yes. A new shaft is en-route to replace the modified shaft. This should alleviate any issues with it as it will be checked again for proper assembly.

Rich

[Richard M.]

Re: K66 Transistor Ignition - Delco Circuit Module Failure, Diagnosis and Repair

Bench test video now available with some waveform analysis.

https://youtu.be/9wYtu32Fx00

Unfortunately, while doing some further testing today, my Tektronix Model 455 Oscilloscope malfunctioned. I spent a while diagnosing it. A blown internal 32V DC fuse. All DC voltages dead. It lost it's main power supply transformer. I looked around the internet for a replacement, but none found. It's a Tek 120-1188-00 transformer, if anyone has one lying around I'll take it off your hands.

No more waveforms until I get it fixed.

[Thomas B.]

Re: K66 Transistor Ignition - Delco Circuit Module Failure, Diagnosis and Repair

The upper scope trace - the trigger transistor - appears that stays "high" for quite a while (can't read the time base), even though the output transistor seems to be edge triggered on the positive, if the trigger transistor doesn't go "low" (at max Engine RPM / 2 ) then the output transistor will not trigger? Spinning the distributor by hand the frequency is low enough that this is not an issue - how about when it is sped up?

[Richard M.]

Re: K66 Transistor Ignition - Delco Circuit Module Failure, Diagnosis and Repair

Tom, I didn't record the waveform timebase but if you look at apx time 6:00 in the clip I sped up the rotation to see the multiple traces. I'll look at the circuit again to verify I was on the output of the trigger.

I'm uncertain if the output transistor switches to positive on another transition of the trigger. You can see a small transistion on the upper waveform at the time the lower trace switches back to high again.

I'd like to experiment more and get some additional waveforms, but my scope is now unusable. Very frustrating.

My main objective was to do a basic spark test using the 2 old Delco boards and other new boards on the way, but it's interesting to see the circuit work on a scope. Additionally, I wanted to take some snapshot traces of the old versus new boards to see a better quality waveform on the newer technology. This will have to wait.

Just for fun.

Rich

[Dan D.]

Re: K66 Transistor Ignition - Delco Circuit Module Failure, Diagnosis and Repair

Bench test video now available with some waveform analysis.

https://youtu.be/9wYtu32Fx00

Unfortunately, while doing some further testing today, my Tektronix Model 455 Oscilloscope malfunctioned. I spent a while diagnosing it. A blown internal 32V DC fuse. All DC voltages dead. It lost it's main power supply transformer. I looked around the internet for a replacement, but none found. It's a Tek 120-1188-00 transformer, if anyone has one lying around I'll take it off your hands.

No more waveforms until I get it fixed.

Hi Rich,

I find it very unusual that a Tek transformer went bad. Those old Tektronix scopes are very good units. I know you are a very good troubleshooter, but I don't see how a bad transformer can a blow a DC fuse.

I Googled on several versions of your part number, but I got no hits, which kind of tells me that that part has never had any activity. I have a Tek 454 scope (dated 1969) that I do all my work with and I don't believe it has ever had a part replaced. I also have a junk 454 that I am saving for parts just in case it should ever need something. I checked the transformer part number, but it is 120-0470-00, so I am sure it will not work. If it was the same number, I would give it to you. So I think your best and only hope will be to find a junk 455 somewhere.

Rich, this is a very interesting science project you have going - this is the kind of stuff I like doing in my old age now. I might add that Joe Randolph (NCRS member in Massachusetts) is/was building a modern day Sun machine replacement. He was doing some very interesting work on this project - in part a simple setup to mount a distributor and drive it using a heater motor. He designed a simple electronic circuit that will turn a distributor from a low RPM up to 3500 RPM.

I would only suggest that you make sure that you do not have a DC short someplace that blew the fuse. Possibly a bad capacitor or something. But still, when I read your writings and see what you do, well, you are my hero.

-Dan-

[Richard M.]

Re: K66 Transistor Ignition - Delco Circuit Module Failure, Diagnosis and Repair

Dan, Thanks. I know you like these experiments too.

Transformer definitely bad, smoking, smelly, making crackling noises. I checked the AC output at the +5. -5, +32 volt inputs to the PS board and all are about 1 to 2 volts. I think the DC fuse may have blown as the xformer voltage dropped, causing higher current from the load circuit.

Regardless, it's definitely "at least" the xformer. I found a supplier online, and emailed them but no luck. I also found a site which discussed that the old age causes a breakdown of the internal winding insulation and potting and they eventually fail. I stunk up the entire shop yesterday when I had it apart and testing voltages, etc.

This site has many 120 series, but not the 1188.....http://www.sphere.bc.ca/test/tek-transformers.html
I emailed them and a very nice quick reply, but none available.

This has lots of info but nothing on the 1188...http://www.pmillett.com/tek_xfmrs.htm

I found a great site with the manual here....http://exodus.poly.edu/~kurt/manuals/manuals/Tektronix/ so I'll have my work cut out for myself when I get time.

Rich