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Old 2nd Jan 2018, 8:57 am   #18
cmjones01
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Join Date: Oct 2008
Location: Warsaw, Poland and Cambridge, UK
Posts: 2,669
Default Re: 8085 processor questions

The CPU clock not running could certainly cause these symptoms. Check with your scope on pin 37 which is the clock output: that doesn't run the risk of the probe capacitance affecting the crystal oscillator. Another likely possibility is the reset or interrupt lines being stuck. Check those with a multimeter or logic probe.

RAM faults are also common. There's a bank of 16 chips on the left hand side of the board which looks like RAM to me, though I can't read their part numbers. They have 18 pins which makes me think they might be 2114 static RAMs, which are amongst the most unreliable chips ever made! Check what part they actually are.

Chris
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