HOW TO MAKE A POWER SUPPLY CABLE FOR APPLE-1

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HOW TO MAKE A POWER SUPPLY CABLE FOR APPLE-1

This technical note for Apple-1 builders deals with making the power supply cable from the transformer(s) to the J1 pin header using easily obtained connectors I prefer to call "CFH" but known in the industry as "IDT", "IDC" or "MTA" connectors shown in this photo:

 

 

"CFH" stands for "Connector From Hell", my term for them, because over my professional career they did cause me lots of grief and trouble and wasted time, and IMHO they are no good but evil, hence, the "CFH". But with a little bit of out-of-the-box thinking, hobbyists like us can exorcise their demons and then use them successfully in homemade Apple-1 power supply cables, a feat which is all but impossible with the real "Molex" brand connectors, which can't be crimped properly by hobbyists. Don't even think a "crimp tool" like this:

 

 

 

could ever make a reliable crimp for Molex pins. If you try, you are likely to create a fire hazard lurking in your Apple-1 build. Just don't do it ! Leave Molex connectors to the industry which uses fully automatic or semi-automatic crimping machines costing five figures, and only those do consistently produce gas-tight and reliable crimps that can carry the full specified current without getting hot and hotter. Understand now where the fire hazard comes in ? It lurks in the J1 connector, pins 1 and 2, which carry more than 2 Amperes. Close to the 2.5A maximum rating for these Molex pins. Which requires perfect crimps a hobbyist can't possibly make. So don't try that. I will show you an alternative.

 

Uncle Bernies foul trick disclosed in this post misuses the easily procured and abundant CFH in a way never imagined by their manufacturers, but if done with some skill the outcome is a neat and reliable, homemade cable that stands up to the typical use in Apple-1 systems well. No special tools are required, which is good.

 

Core idea of the trick is to gently push pre-tinned stranded wires into the connector using punches and a small hammer and then solder them in place:

 

 

A more detailed writeup will be published on this site if you respond to this post and tell me you want to know more. I just don't want do spend my valuable RQLT on writing up stuff that nobody reads. (RQLT = Residual Quality Life Time).

 

As an appetizer, here is a photo of the resulting cable:

 

 

 

Which costs almost nothing to make, except for some time.

 

 

(To prevent questions why I don't connect pin #5, it's not needed. This "ground" carries only a low current. And if pin 5 of J1 is snipped off, which I recommend, there won't be a short of the 10Vac transformer secondary winding if the connector is put in wrongly, that is, turned 180 degrees from the photo. Which may happen as the CFH here is used already turned by 180 degrees to avoid the locking tabs to engage. A convenience to make disconnections easier without breaking off fingernails, and it also looks better: otherwise the wires would run over the PCB. But it sets a trap for those who insist to put in this connector into J1 in the orientation originally intended by its manufacturer, where the locking tabs would engage. So take care and stay safe !)