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Fairchild Channel F burned power supply


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#1 Alesmukler OFFLINE  


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Posted Tue May 1, 2012 10:16 PM

recently I got a Fairchild Channel F in working state, but in a oversight I connected the power supply to 220v instead 110v!
The PS was burned, so I opened the console to remove and replace the dead PS; but I am aware of the voltages used. Someone could help me with this issue? The power supply internal connector has three wires (Red, White, Red). Thank you very much!


#2 e5frog OFFLINE  



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Posted Sun Aug 26, 2012 7:43 AM

Found this while googling for pictures of the various models's PSU:s...

Just fixed one of these recently, it was the small one just like yours that only has three wires, the iron core is much too small to handle only our 50Hz in Europe so it will overheat, even if using a stepdown transformer and getting about 110V instead of the 230V we've had in Europe for several years now...

Anyway, when I finally found out that this PSU will overheat at 50Hz anyway I only fixed my American friends PSU which meant knocking it open with a knife and hammer and then tear the tape off the transformer and desolder the temperature fuse mounted there (no "real" fuse in the whole console) replacing it with a new one (96 degrees centigrades) - I managed to bust it again after the first swap before I found out about the relation between iron core sizes and frequencies...

Anyway, I decided to use a broken C64 transformer instead, I had already removed the PCB from one of those wedge shaped things Posted Image and found that the transformer part itself was OK but the DC PCB was not. So as the original Channel F PSU is an 18VAC transformer that is center tapped, I simply used the two coils of the C64 and soldered two ends together so I got the white wire of the Channel F in the common center of these two coils and 18VAC over both (each giving 9VAC and when soldering the right two ends together the phases are in the same direction and voltage peaks to the double) that's where I hooked the two red ones - problem solved.

So that means between either red wire and the white you have 9VAC and between the two red 18VAC.

The voltage is not crucial since there's a bridge with capacitors and two regulators that takes these down to 12VDC and 5VDC. You could just as well drive it directly with 5VDC and 12VDC for example from one of those external hard drive PSU:s if you hook it to the right spot of the mother board (out pin of the regulator for example, or a capacitor connected there). I was running the ones I mentioned with an old PC PSU I use as at the work bench.

So this would be more than enough (can't say anything about the quality at that price though)

Don't really know where you can find a center tapped 18VAC PSU, a double 9VAC is probably easier, depending on how important looks are you can also use two plain 9VAC transformers, cut the plugs, wire one wire from each PSU with the other and if you got your 50% right you'll have 18VAC on the non together twisted ends. If you have close to zero you need to use the other wire on one of them. Make sure you plug them the same into the power outlet later on or else you might invert one of them and get 0V on instead of 18VAC on the outer once. Best thing is probably to use an extension that you don't unplug them from.
This is probably the easiest way, red wires then go to one single wire each and the white goes to the two that are tied together as described earlier.

So two of these (I recommend at least 200mA):
and one of these with three hookups:
Posted Image

You can be up and gaming again in 10 minutes, requires pliers and a screwdriver as well, some wire peeling...

As I mentioned a C64 PSU works, possibly others as well, if you want to build your own then one of these 2x9VAC cores will be fine, this particular model might not be good enough.

There are many other models and ways this could be solved.
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#3 ball_master OFFLINE  


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Posted Fri Sep 19, 2014 11:45 AM

Hi e5frog! Since yesterday I have been trying to figure out how to plug the c64 power supply to my fairchild channel F. I have a 4 colour input (2 for each voltage). According to the original (burned) psu: RED/YEL == 15V AC 3.75VA and BLU/WHT == 10V AC 16.5VA.

At the c64 psu I have the transformer and 4 cables coming out. Two go directly to the cable (9VAC each) and two go to the board with the bridge and the regulator.


Can you give me a hand with this? I don't want to burn the c64 psu (which is working fine).




#4 e5frog OFFLINE  



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Posted Thu May 28, 2015 6:45 AM

Hadn't noticed this before.

You'll have to crack open the C64 PSU and rewire it to use just the outputs from the transformer. You just use the four wires directly from the epoxied transformer. PCB can be desoldered and saved for something else.

Any other kind of 2x9VAC transformer could be used - even two plain 9VAC transformers. Hooking up a switched PSU that gives 12V and 5V (like the ones to externally power a hard drive) is also possible, just hook power up after the regulators - where they usually spurt out these voltages.

#5 carlsson OFFLINE  


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Posted Thu May 28, 2015 3:53 PM

You might also want to look into an R-Core transformer, which outputs roughly the AC voltages you need.


Actually Doss in Australia used to manufacture an inexpensive power supply with roughly suitable voltages - the same combination of 9/10V AC + 15/16V AC seems to be common among Channel F, Interton VC4000, Spectravideo SVI-318/328/728, CreatiVision and probably a bunch more systems, but for some reason they quit making and selling it. Somewhere in China there ought to be someone who makes these custom transformers for small money, but I haven't found the distributor yet.

#6 pokemontrainer OFFLINE  


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Posted Thu Feb 28, 2019 3:56 AM

I'm thinking about replacing the original power supply with a switching one directly connected to the DC lines, as described above. Questions that came up by looking at the schematics of the model 1 (see bottom left corner of this schematic):

  • Can i connect the power supply directly to the output of each voltage regulator, or do I have to remove them to avoid strange behavior of the ac/dc circuitry that would get current in the other direction (some kind of back-flow)?
  • What about the negative voltage (-5V) for the RAM that is at the bottom of the power supply schematic, does it suffice to give the +12V and +5v to the voltage regulators output pins, or do I have to construct some kind of -5V supply for that point as well?

#7 pokemontrainer OFFLINE  


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Posted Thu Feb 28, 2019 8:43 AM

To add to the second question: If the -5V is needed, can I replace the entire internal power supply circuit with input from a -5V, 5V, 12V power supply likes this (Mean Well GP25A13A-R1B) ?

#8 e5frog OFFLINE  



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Posted Thu Feb 28, 2019 11:47 AM

Not sure about removing regulators. 5V and 12V is enough. -5V is made on the board and only used by RAM.

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