Hello, people. I opened my real MC-1000 to know what are the resistors that are linked to the NE555 astable circuit.

Then I used this online toot to interpret the color codes:
  • R16 = brown, black, red, gold = 1000 ohms
  • R17 = orange, white, yellow, gold = 390 Kohms

Then I could reconstitute the NE555 part of MC-1000's awfully blurred schematics:
Code
 +---------*---*---o V+
 |         |   |
+-+        |   |
| |309K    |   |
| |R17     |8  |4
+-+      +-------+
 |      7|       |3
 *-------|       |-------> /INT (Z80)
 |       |       |
 |       |       |
+-+R16  2| IC 28 |
| |1K +--|       |
| |   |  |  555  |
+-+   |  |       |
 |    | 6|       |5
 *----*�-|       |---+
 |       |       |   |
---C30   +-------+  ---C29
---103       |1     ---103
_|_         _|_     _|_
///         ///     ///
Then I used this other online tool to calculate the square wave produced by NE555.

I filled the fields with:
  • 0.00000001 farads (C = C30; "103" = 10 x 10� pF = 0.01 �F)
  • 390000 ohms (resistor 1 = R17)
  • 1000 ohms (resistor 2 = R16)

...and got:
  • 99.74489795918367 Duty Cycle Percentage
  • 368.1126130105722 Frequency in Hertz
  • 0.00000693 Seconds Low
  • 0.0027096299999999998 Seconds High

368Hz?! What do you say? I know nothing of electronics. Did I use the right values? Are this results correct?

Last edited by Ensjo; 10/30/10 07:52 PM.