The purpose of this report is to document the repair of Vance's 610906 Solid State Ignition, SSI on his Miller Blue Star 2E welder with a Tecumseh OH 160 engines.
When I received the unit, I ran it on the engine simulator. It put out about three sparks and then none. This indicates to me that the problem is the main capacitor. The repair is to disconnect one end of the capacitor, C1 , abandon it in place and replace it with a new one outside the shell. To do this we need to remove the epoxy from the Printed Circuit Board, PCB to make the disconnect and new connections.
I first tried to remove the epoxy in area A, but could not find the PCB because there was none there. So I went to the other end. I removed the epoxy in strips by prying it up with a small screw driver. The epoxy lets go of the PCB fairly easily. But, the first strip by the input power connector and ground screw was very difficult and a lot of time. Next time I will leave it there and start with the second strip. I drilled a hole at the end of each strip to make it easy to separate. With the second strip, I cut it on both sides and gently pried it up. I cut one strip at a time because I use the adjoining strip to pry on.
With the the epoxy removed and circuit diagram, we can locate the components and connections.
It looks easiest to disconnect the grounded end of the capacitor. When making a change to the PCB, I try to make it reversible so I can go back if I need to. I removed the foil around the grounded end of C1 and left the lead wire sticking up. This allowed me to make some low voltage test measurements on directly on C1. The measurements are not totally accurate in indicating a good capacitor, but the indication of a failure is accurate. In this case, the measurements indicated that C1 is good. Reference: www.enginesandmagnets.com, Att 1, How it Works / Schematics
When disconnecting C1, I noticed that the solder connections might be cold solder joints. So I reconnected the C1 ground and re-soldered the other end and ran the unit on the simulator. Walla, the ignition ran fine for an extended period.
3 February 2022
I am wondering what percentage of the 610906 failures are the main capacitor. I tested another unit on the simulator and it had no spark. Testing just the capacitor with the capacitance meter indicated that capacitor had failed, so I ordered some new capacitors. www.mouser.com; 598-936C4W4P7K-F; 4.7uF 400V 10%
5 February 2022
See Miller Tecumseh Ignition Repair https://youtu.be/bCEzLarsAuY
New Replacement Ignition, Part1, General
Dave Cave has an article “Buzz Coil-How To” in February/ March issue of Gas Engine Magazine, see
He uses a GM LS2 Ignition Coil, and a simple trigger circuit suitable for the low and constant RPM hit miss type engines. The spark timing would be fixed and after TDC, but instead of just one spark, it puts out a burst of sparks. The LS2 is very small, includes the electronics that was in earlier decades in a separate box and costs only $18. I got to thinking about trying the LS2 Ignition Coil triggered by the induction type of trigger that I have used for many years with the Chrysler Control Module. See GM LS2.jpg.
Most small engines have only two levels of spark advance; no spark from zero to a few hundreds RPM and then an advance spark starting at a RPM where the engine won't kick back. This is simple, least expensive, but makes a compromise on timing. With the induction type trigger we have an added level of spark advance for much easier starting. It provides a spark starting at about 100 RPM that is timed at Top Dead Center, TDC for no kickback and is easier on the battery and starter motor. I chose to try the GM PC2 Crank Sensor for the trigger because I had them, but some signal conditioning is required to have them work with the LS2 Ignition Coil.
GM PC2 Modification:
The LS2 Ignition Coil is triggered by a signal form a computer. This signal is at Zero Volts until a 5 Volt pulse comes along and triggers the spark. The PC2 Crank Trigger puts out more like an AC type signal with a negative and a positive pulse. The LS2 won't like this negative pulse. This is easily fixed by routing the PC2 output thru a bridge rectifier like those used for converting the AC from the Stater to DC for charging the battery. This gives us a trigger pulse that is a doublet of two pulses.
The induction coil, PC2, has an output voltage that increases with RPM which we need for RPM control of spark timing. Voltages much higher than 5 Volts would not compatible with the LS2. So we just clip the top off the trigger signal at 5.1 Volts which is above the trigger level of the LS2. This requires a 5.1 Volt Zener diode . I am using small components so I can fit them in the PC2 connector, but have an alternative of a small box. See GMPC2Mod.jpg
The result wave form looks like this:
Note that both the Advanced and the TDC trigger pulses are firing sparks at this RPM.
The complete ignition is shown in PC2LS2Sys.jpg.
The wiring is very simple. The Black wires go to ground. The Red wire provides power from the battery and the Green wire from the PS2 provides the trigger signal to the Green wire on the LS2.
The PC2 needs to be mounted with .024” initial air gap to the tallest trigger pin on the flywheel. This is important because this air gap sets the voltage output thus the transition points between the three levels of spark advance. A wider air gap will increase the RPM for the first spark for both the TDC and advanced. A non-magnetic feeler gauge is shown for setting the initial air gap.
For all my testing here I used my Tecumseh HH 120 engine simulator (which is driven by a tread mill motor) since it already has the trigger pins installed. The PC2 trigger is installed on a bracket mounted where the original Solid State Ignition was and is adjusted to be aligned with the tall trigger pin on the flywheel at an air gap of .024 inches.
The amount of spark advance is determined by the physical location of the trigger pin on the flywheel. To the best of my knowledge, the Tecumseh HH and OH series of engines were the first to use the Trigger Pin concept for switching between levels of spark advance. The Onan NB engine uses this concept too, but with only one trigger pin since I believe it has a compression relief .
If you are using a different engine and there is no room for the PC2 , I am working on an alternate bobbin type trigger like that I used on the Briggs and Stratton ignition replacement. https://youtu.be/VS_HKaXx9JY.
In New Replacement Ignition, Part 2, Details, I plan to be addressing:
- PC2 Modification, fabrication of the connections to the LS2.
- Parts List
- Tecumseh Installation and initial testing
- Onan NB Installation
- Briggs and Stratton Installation
- Kohler Installation