Re: Checking X/Lisa Voltages

As I'm new to a voltmeter, I'm confused as to what to ground to when I'm checking these items.

The C21 gave me the correct reading when I grounded to the case. The rest are way off using this method. Is my power supply suspect or my voltmeter
skills ?

thanks !

James MacPhail wrote:
> >Did you check the voltages on the power supply? i have no idea to check
> >those under load though... the power supply is difficult to reach
>
> I agree that checking the power supply voltages is an important first step
> for most troubleshooting.
>
> You can access almost all of the voltages via the I/O board, which is
> relatively safe to do (no need to be near the high voltage in the power
> supply or video circuitry).
>
> In particular, on the I/O board you can find:
>
> +12 at the positive side of capacitor C21
>
> -5 at pin 8 of U10E (26LS30)
>
> -12 at the negative side of capacitor C9
>
> +5 at the maximum pin number of most TTL ICs or the adjacent bypass capacitor
>
> +5-Standby ( ~5.7 V ) at the anode of diode D9 (present if Lisa is
> plugged in, even if turned off)
>
> From the I/O board, you cannot access the +33 volts used by the analog
> video card, or the high voltages generated by it, but you can usually tell
> if the video card is working by the presence of something on the screen
> (even if it is random).
>
> If you have an internal hard drive that is not working properly, checking
> the voltages at the hard drive would be appropriate as it may see lower
> voltages compared to those appearing at the I/O board. (Due to the higher
> current drawn by the hard drive, and the different wiring path.)
>
> HTH,
>
> James

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. Received on 2015-07-15 16:36:32