Hey everybody.
So I recently acquired a Commodore 64, for those of you that don't know a while back I was looking for SID chips because I'm interested in building a MidiBox SID V2... So the C64 I got came with the power supply but no video cable. I brought it home, plugged it in, turned in on, power LED came on, I think to myself 'Well that's at least a good sign.' It sits for about a month till I get around to getting a video cable together and ... no output, whatsoever.
So, as Dave says, golden rule of troubleshooting is Thou Shalt Check Voltages. So I checked the voltages directly out of the brick. There's supposed to be 2 pins that have 9VAC and one pin with 5VDC, plus a ground pin.
Get this. I'm told that usually it's the 5VDC regulator (which is literally coated in a block of epoxy, making replacement impossible) that starts to go. The voltage creeps up towards 6, 7 V and it fries your C64, as there's no internal regulation. However, my 5VDC checks in at about 5.12V. Not bad, really.
One 9VAC pin is giving me about 2-3VAC. The other --- 20VAC!!! TWENTY volts for chrissake!! I double and triple checked this and was quite surprised as I can't even imagine a scenario where the brick is that #%@&ed up as to give out such wonky AC.
So -- now I need to build a simple 9VAC/5VDC power supply. Obviously I need to buy a 120VAC--> 9VAC transformer, a bridge rectifier, and a 5V regulator. I was thinking, to give the best performance, get a double-tapped 9V transformer so each pin has it's own tap (I'm not exactly a power supply aficionado, so I'm just guessing here). However, clearly I need some line filtering/regulation of some point. This is where I need help/guidance. I found one video on YouTube where this guy has re-built his own C64 power supply but I want to do this as simply as possible.
5V rail needs to handle ~1.5-2A max. 9V @ 1A (or so I've been told).
I was thinking a) common mode choke (or are they for after DC rectification?), and b) filter caps for both before and after transformer/regulation stages. Plus fuses, and any other obvious safety related stuff. Anything else obvious I'm missing? I want to put 2 analog meters on the front of the box, for voltage and current output. (On that note, would it be more important to have the voltage meter reading the 9VAC or the 5VDC? I was thinking the 5V, because the regulator seems more likely to fail than the transformer -- but then again, my screwed-up PSU seems to shoot that in the foot. Or I suppose I could find a meter that does AC/DC and install a switch).
Any advice for a first-time PSU builder is much appreciated! I've already looked at transformers on element14/Newark and I'm leaning towards this one:
http://canada.newark.com/block/fl30-9/transformer-2-x-9v-30va/dp/23M6267Actually, that's basically the only one they have that meets the VA requirements, and is available without shipping from the UK. Plus it's on sale which is great.
All help and advice is MUCH appreciated! Thanks a million guys.