Need help with c64 psu

Question

I know I need a 9vac for part of this but I only have a 110 to 15vdc brick is there a way to transform to 9vac, or can i trick with 9vdc and a 555 timer so the board thinks it is ac?

Any help would be appreciated! Thank you in advance!

baldengineer · Answer

This is not the case in the C64. The 9VAC supply is needed to generate a higher voltage necessary for the 12V rail, which drives the SID (sound) chip. The on-board power supply uses a capacitor voltage doubler to step the 9 VAC to 18 volts. A DC supply will not work. It also feeds directly to the cassette drive to power the motors. [Edit: Actually, I think the rectified, unregulated voltage is used to drive the cassette drive.) The C64 needs a 9-12 VAC supply to operate correctly.

baldengineer · Answer

No, you cannot bypass.

The 9VAC supply is needed to generate a higher voltage necessary for the 12V rail, which drives the SID (sound) chip. The on-board power supply uses a capacitor voltage doubler to step the 9 VAC to 18 volts. A DC supply will not work.

It is also feed directly to the cassette drive to power the motors. The C64 needs a 9-12 VAC supply to operate correctly.

You need to use a 120 to 9 V AC transformer.

Gough Lui · Answer

This is not always true. You need to be familiar with the circuit diagram for the equipment you're using to know for sure. Some pieces of equipment NEED a 9V AC supply as they use the AC to generate a positive and negative rail internally. Many older computer-based equipment such as modems rely on this technique because the connectivity (e.g. RS-232 RS-232 ) also requires negative signalling voltage or they're using older CMOS logic which requires negative voltage rails. The easy way to get 9V AC from the mains is to use a 9V AC brick. Having a 15V DC brick is not particularly handy - it's the wrong voltage and the wrong type of current. It is dangerous and inadvisable, but removing the rectifier from such a brick will give you 15V AC. Perhaps by modifying the secondary winding of the transformer, you can unwind almost half the turns to get down to 9V AC but that's very much an impractical way to do things. Likewise, a 555 will only generate a square wave - while you can make pulsed DC with it, it is still not truly AC and will have a square waveform which is high in harmonics which is likely to upset sensitive devices. Just get a proper 9V AC adapter, especially if you care about safety or the reliability of the device. - Gough

ldeevans · Answer

This maybe is the wrong forum for this question, however I think you will find that a 9vac piece of equipment will work fine with a 9vdc supply, your just "by-passing" the input rectifier (and adding a small volt drop).

Need help with c64 psu

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