6 Al No Tach Reading When Cold?

[bobrey]

I have several MSD boxes and am extremely satisfied with performance and reliability.
This problem has me confused! It's an SBC S-10 with MSD 6AL, MSD distributor, Sunpro tach. Tach doesn't work on start up. After 3-5 minutes of engine running everything is fine! I've tried 3 tachs including 2 that I removed from cars with 6A boxes that worked fine before and after. Same cold no tach problem when connected to 6AL. Engine runs fine.

Solutions???

Thanks for the assist.
Bob

PS: I forgot to mention, my MSD shift light, connected to the same tach terminal on the 6AL displays the same symptoms. It works when the tach does and doesn't work when the tach doesn't. Power and ground for both are good. I even tried direct battery connections for both. Same sympoms!

[msdtech2]

If you have access to a voltmeter that has a low voltage scale Probe the tach output with the voltmeter in a 5-volt scale and it should read about 1.5 to 3 volts with it running, if you get a different reading, I would recommend sending it in for repair. This test will only give you an indication that there is a signal output, but an accurate test is by using an oscilloscope, which should read a 12 volts square wave. This can only be done if you send it in for testing.
Thanks,
msdtech2

[bobrey]

Thanks for the info.

I do have a volt meter and even an oscilloscope! I'll check it out tomorow AM.


Thanks again,

Bob

[msdtech1]

Let us know what you find. I have listed the shiiping address to MSD in case you need to send it in.

MSD Tech1

Send the MSD component prepaid to the attention of:

Customer Service Department
Autotronic Controls Corporation
12120 Esther Lama, Dock 5
El Paso, Texas 79936