Re: Help needed with - Racal Dana 9081
Hello Mark,
Firstly, the waveform that I posted yesterday for TP16 was wrong. It should be a 12V positive pulse, every 400us. It just so happens that it was missing when you tested pin 1 of the ICs. It looks now like the fault is somewhere in the logic between the outputs of the counter ICs and TP16.
There are three test point to check. TP7, TP8 and TP15.
TP7 should show 10V positive going pulses, in a mix of single and double pulses.
TP15 should show something approaching a fairly wide pulse with a period of 3.3ms.
If TP15's waveform looks good, check at pin 12 of IC8. You should see an inverted version of the waveform there.
Check pin 2 of IC21, which you have seen working. Move to pin 10 of IC22. You should see a similar waveform there.
Check pin 11 of IC22. Assuming TP7 was as described, you should see a series of negative going pulses, rather irregularly spaced, about every 250us.
TP8 should show a single brief (600ns) pulse every 330us or so.
With these checks it should be possible to home in on the culprit.
Paula
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