View Full Version : Troubleshooting a non-responsive C128

January 31st, 2010, 08:06 PM
I recently acquired a Commodore 128 in its original box from a collector. I plugged in the power supply and flipped it on, but I get no response whatsoever. The power light does not come on, and I can hear no signs of life from the unit.

I'm very unfamiliar with the C128, so I'm wondering if there's something obvious I'm missing or if the hardware is actually dead. Is there perhaps some sort of mainboard battery I could replace? Would cleaning some dust out of it help? Are there any troubleshooting tasks I could go through to confirm that it is really, truly dead?

January 31st, 2010, 08:39 PM
I would start first with the power supply, making sure there's power coming out of the unit. After that (this is where I get experimenting) I would open the unit up and look for a fuse, or broken connections from the PSU or the power switch.

February 6th, 2010, 11:17 AM
I agree with Dreadstorm. I would wager that the power supply is the problem. The PS fuse is accessible from the outside of the unit (push in and twist). However, only the 9VAC is fused and if you have no power light on the 128, the fuse probably isn't the problem. Who knows... From your description, it could just be that the power LED is unplugged from the mainboard! A "dead" computer is usually the easiest to fix, IMHO. It is generally indicative of a power problem.

So start with the basics.

Do you have a monitor attached? Is it attached correctly? The rf plug in the back of the unit does not send a signal that is recognized by the RCA jacks by modern televisions and monitors. If you are using the rf line, the signal must be fed in to an antennae / cable input on a television.

Does the monitor at least flicker at all when you power up? Anything on the display at all? If you are using a television, does the screen show static when you power the 128 on?

Okay... Disk drive time. Plug the disk drive in to the 128's serial port and turn the disk drive on (do this with the 128 OFF). Now with the disk drive ON and the 128 OFF, flip the on switch of the 128 on. Does the floppy drive react (it should spin for a second or two).

Remember- The 128 does not have a fan or anything... so it will run silent all the time.

If none of that helps, I'd dig out the multimeter and start checking your voltages where the power plug meets the 128. You will have two 9VAC and one 5VDC pins. http://pinouts.ru/Power/c128power_pinout.shtml Here is a pinout. But this pinout shows the female side (the pins on the 128 itself) so if you check the pins on the plug, the pinout will be flipped. Be careful if you get your voltages from the PS cord. If you short anything out, you'll most likely blow the fuse on the PS.

If you aren't getting your voltages and the fuse is okay, it's time to crack open the power supply and look for burned and bulged components. If the caps (those cylindrical doodads) are bulged or leaking, that's probably the problem. If you see any components that look like they have been tried for heresy in the Spanish Inquisition, that's probably your problem.

If you aren't an electronics guy, perhaps you might want to replace the power supply (perhaps offer to trade your broken one in order to keep these in circulation and out of a landfill).

If you have any more questions, don't hesitate to ask. The 128 is a fun machine with an enormous library of software, so your troubleshooting efforts should pay off. Good luck!