Model 1 Help

[ldkraemer]

DIP Shunt installed or removed?


Larry

 

[joeatact]

z21 pin 12 gets that wave form with and without shunt installed

 

[joeatact]

I am thinking z36?

 

[ldkraemer]

See what you have on Pins 15 & 1 of Z21.
Also see what you have on Pin 4 of Z36. (It should be the same as Z21 Pin 12.

Z36 doesn't look to be the issue, as it has a resistor R48 tied to +5 as a PULLUP resistor.
This means there is +5 volts on the (INPUT) Pin of Z36 unless something is making it LOW.

Larry.

 

[joeatact]

Seens like a bus problem
heres whats on z21 15 & 1

 

[joeatact]

I was looking around and saw you had mention pin 26 of the z80
well I checked mine it goes high when turned on and when you press reset it stays high.
Joe

 

[ldkraemer]

Pin26 of the Z80 should be HIGH all the time unless you depress the RESET button,
which will make it pulse LOW for a short duration.

Larry