Randolph wrote:
> jim beam wrote:
>
> <snip>
>
>>>Voltage signals are the wrong concept since the devices work
>>>by current like 74 series TTL does. If you uncouple the signal]
>>>wire to measure it on voltage alone, the lack of current may lead
>>>you astray!
>
>
> 74 series TTL came with totem-pole output and open collector output.
> 7400 is an example of the former, 7401 of the latter. I gather you mean
> the ECU output is open collector.
>
> <snip>
>
>>hence now i want to
>>dry test the igniter. and i want to try this without stripping the
>>working car back down again because i have a broken finger which makes
>>for a little bit of a dexterity problem!
>>
>>any thoughts?
>
>
> I would hook it up as follows (terminal numbers pr.
> http://www.gcw.org.uk/rover/igncloseup1.jpg):
>
> 0V: = 0V (ground)
> T1: = leave open
> T2: = 1 k ohm resistor to +12V
> T3: = +12V
> T4: = Leave open for now.
>
> Then measure the voltage at T4. If the ECU is open collector (or likely
> open drain) the ignitor would need to have a pull-up device. You should
> see either about 12V or about 5V with T4 left open. If you have a
> function generator, set it to a square wave, 25 Hz, negative peak to 0V,
> positive peak to whatever you measured at T4 when it was left floating.
> Hook the function generator to T4. This simulates the engine running at
> 750 RPM.
>
> Now you should see square waves at both T1 and T2. You can also hook up
> the coil (short the secondary to avoid painful surprises!) and measure
> if you still get a square wave at T2 with the actual coil in the system
> instead of the 1 k resistor. The resistor is a much lighter load than
> the coil.

perfect - can measure t4 open & use that. thank you!