Macintosh SE/30 Vertical & Horizontal Bars on Display "Simasima" Repair Guide

[GreenBar0n]

S1 is perfect everywhere else and throughout the Simasima Repair Guide, everything works except the Sony Sound chips Pin6.

Just so there is no confusion I made this video:

Pin5 is 0 - 0.80mV
Pin6 never goes much below 3.9, for both UB10 and UB11.

Thanks for the help!

 

[David Cook]

S1 is perfect everywhere else and throughout the Simasima Repair Guide, everything works except the Sony Sound chips Pin6.

Just so there is no confusion I made this video:

Pin5 is 0 - 0.80Mv
Pin6 never goes much below 3.9, for both UB10 and UB11.

Thanks for the help!

Actually, that looks good. The computer is in reset when when pin 5 of each of those chips is low (0V). The computer runs when pin 5 of each of those chips is high (5V). So, that looks to be working (don't worry about the voltage of the reset button -- it's correct and functioning.)

 

[GreenBar0n]

So when the Repair guide says Pin6 should be 0V, this is an error in the guide?

 

[David Cook]

Typo regarding pin 6 on the table, IMHO.

When the computer first powers up, all the chips will be held in reset (frozen state) by the Sony sound chips by outputting a low (0V) on pin 5. In schematics, the little bar above the word "reset" or the little circle next to the pin indicates the function is activated on low. So, ~reset means a low resets the computer. Below, see ARST and BRST have lines above them.

When the Sony chips think the power supply voltage has reached a stable 5V (or more likely 4.75 or something near enough), they will turn off ~reset by outputting 5V. That allows all the chips connected to that line to begin operating. Monitoring voltage at power up is really important, as different chips will start working at slightly different voltages. The ~reset line makes sure they all can run at the same time.

Now, a smart engineer reuses these parts to implement a reset button for the user. This reset button makes the Sony chips think that the power supply voltage has dropped down to 3.6 volts. That causes the Sony chips to ~reset all the chips until the voltage climbs back up through R11.