troubleshooting results for GMCTD

[mhagie]

jd, On 10/22 You wrote
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So.....troubleshooting -

Circuit connected and powered up, engine off, negative voltmeter lead to ground, tach signal lead disconnected from Collector -

Base = approx +0.8 volts bias
Collector\1k junction = +12.6 or battery volts
Emitter = 0 volts or ground
ESS\capacitor junction = 0 volts

Connect tach signal lead to Collector, previously-measured voltage should not drop appreciably - one volt = 1 milliamp would be greater than 10k tach input impedance
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OK, here be the results= Voltage at base terminal of transister or out of 220k ohm resister=.521vdc
1k resister at collector side 10.61vdc
Emitter and Ess/capaciter tests ok
connected tach,collector voltage 9.05 dropped 1.56v
So it would appear that my voltage is a tad low
it seems to me the output of the 220k resister is low,try different resister? same or different value?
Got a little fancy and connected Ess to drill press =1300 rpm equaled 600 rpm at tach
it would seem that I'm about a fourth what would be normal range.
That is using the 93 stub Ess sender I would doubt it but maybe it is only producing 1 impulse per revolution.
Back to troubleshooting would low voltage at base cause the low rpm at tach?
Will try your tricks w/scope later in week
Tach dip switches are set at 8cyl as per Dr. Lee article
Many thanks again for all your help......Merle

[gmctd]

Ok - I kludged this ckt up on my bench this am.
I get the same static voltages as your ckt. My previously stated values were doing the Ohm's Law calcs.

Connecting a 0.5v 4p\25ms signal resulted in 12v pulses on the collector.
Placed a 10k load on the output for no drop in drive signal.
'Course, when they state a 10k ohm input impedance for the tach, it does not necessarily imply 10k resistance. It would take 1kohm actual resistance to drop that drive signal by 50%.
You might measure the input with an ohmmeter for actual resistance, but I would suspect it's capacitively coupled, and would measure infinite impedance.
We need to observe the signals with a scope to get an idea of what's happening

The ball's in your court again, Merle. Keep up the good work. After this, you should be able to apply for electronic tech employment. ;)

jd

Later: Re-read your post, where you had given voltage drop before and after tach connected.
The transistor is turned on slightly by the 15k\220k bias voltage on the Base.
Parallel the transistor Emitter-Collector on- current with the 10k tach input resistance results in the additional 1 volt drop across the 1k Collector load resistor.
10 volt pulses should be sufficient to drive the tach, so we need to see what's happening with the scope.

jd again

[ 10-29-2003, 03:45 AM: Message edited by: gmctd ]