Keith Matthews  wrote:
> Hi All,
>
> I have a breadbox style C-64 that has stopped working.
> I connected my 1501 Power Monitor to the Power Supply and it
> seems fine for both 5v and 9v (well it shows 10v)
>
> The Power Supply work fine with my C64C machine.
>
> I connect the 1501 Power Monitor to the User Port and I
> only get the 5v indication
>
> There does not seem to be 9v at the user port.
> I have pressed in all the chips and checked the internal fuse on the C-64.

If the power supply 9V voltages are alright when used with your C64C, but
drop when used with this one, it could be due to a short in the computer
causing excessive load and in turn the 9V voltage to drop below that
required by the computer. That could be due to a failed capator or other
component connected to the 9V supply.

Also use a multimeter in its lowest resistance mode to check that there
is very low resistace between the 9V pins of the power plug at the back
of the computer, and the 9V pins of the User Port.

There are a pair of pins to check for this:
Power pin 7 to User Port pin 11
Power pin 6 to user Port pin 10

If there is more than a few ohms resistance, there could be a partial
or complete break in the circuit board, or in the connection for the
power plug.

If it is a low resistance, but the 9V voltage reading is low when the
computer is on, then a component failure or other short inside the
computer is likely.

If the 9V fuse in the computer hasn't blown, you might try removing it
and connecting your multimeter in its highest current measureing range
across the fuse terminals. With the computer breifly switched on, you
may observe the current above or near the 1A maximum rating which would
indicate a short or component failure. This test should be breif, as the
excessive load does risk overheating the transformer in the power
supply.

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