Quote:
Originally Posted by 3pinplug
Checked Pins 15, 17, 13 and 18 on the Logic board on my oscilloscope looking for pulses, assuming thats the correct way to do it?
Results were
Pin 15 - Pulse (waveform?)- pic attached
Pin 17 - nothing
Pin 13 - Nothing
Pin 18 - Brighter pulse (waveform?) than Pin 15 but looked the same waveform.pic attached.
Didn't change the pins round as 2 had nothing and one (Pin 18) was working as it should.
Mark
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Mark
As I suggested the signal generator is essentially working, but the band edge steering is driving the signal generator to the maximum edges.
On the logic board disconnect wire on pin 15. This should also stop the pulses on pin 18. If not there is a fault on the logic board, which is oscilating.
Now turn spinwheel one direction, then the other. You should see the logic at pin 13 change state depending on the direction of rotation.
If you do not see it change state, then you have a fault with UP/Down detection on the logic board.
What I suspect is happening is the band edge detector circuit (Around the PROM) has detected the frequency is out of band, and firing pulses to lower the frequency. It appears to be doing this (as the frequency is not going any higher, (it will eventually try to go so high that it stops the main oscilator and out put drops to zero) but as soon as the frequency comes back into range (by a few Hz) the Band edge detector turns off its control, but the output of the generator continues to go up, triggering the band edge detector again
Its a little complicated to describe as it is a closed loop system controlling the band edges.
Frequency goes 1 Hz over band edge, then control logic sends down pulses to pin 15 which lowers the output frequency by a few Hz
As soon as output goes 1Hz below band edge (due to down pulses) the band edge control stops, but something is then driving the output frequency up again, so the band edge control kicks in.
I suspect everything is working well (Counters, dividers, phase comparitor and reference oscilators, but the issue looks like it an oscilation on the logic board, but do the checks described to confirm it.