5V supplied by FD-1 - can this fry the CPC?

[eto]

Do all FD-1 put 5V on some unused lines of the drive cable or just those, that were sold together with the DDI-1?

Since its so easy to connect the drive in the wrong way, I would see this a major risk to fry your CPC when connecting a drive. Or is that not a problem because the relevant pins are not connected?

[Bryce]

It shouldn't be possible to connect the drive connector the wrong way on an original DDI-1 as the connectors had a key-way to stop this. Either way, it wouldn't fry anything as the "wrong" pins are connected to GND, so at most it would fry the FD-1.

Bryce.

[eto]

Sorry, I didn't mean the DDI-1, I meant a 664 or 6128:  

On the CPC the edge connectors could be upside down and on FD-1 side, the cables also can be connected in both directions. There is nothing on the FD-1 or the cable that prevents this.  If I understand correctly, the 5V are on pins, that are N/C in the 664 or 6128. But once I accidentally turn the cable on one end, the 5V should end up on some pins, where they do not belong. 

[Bryce]

Yes, if you put the connector the wrong way around in this case, you would be shorting the 5V ouput of the FD-1 to GND which would most likely damage the FD-1.

Bryce.

[eto]

OK, thanks a lot. 

I am surprised this doesn't happen regularly and that there is almost no warning anywhere. I know that the cables usually have a "this side up" sticker (or similar) but I would not bet that they are present on all cables and except for that, there is nothing that would prevent me from putting it the wrong way into the Fd-1.

[Bryce]

The 5V rail in the FD-1 is regulated with a 7805 linear regulator. These are extremely robust, with built-in over-temp and over-current protection and additionally, the flat cable would offer a certain amount of current limiting, so the FD-1 would most likely survive a short if it only occurs for a very short time (no pun intended).

Bryce.

[SerErris]

For a 6128 you can put in larger resistor to minimize the risk or cut the line in the cable... 


However both methods will turn the cable useless for a DDI-1 interface as it is getting powered from the drive and not from the CPC.

[Bryce]

The DDI-1 has its own fixed (non-removable) cable, so you would never be using the 6128 cable on a DDI-1 anyway.

Bryce.

[SerErris]

I totally forgot about that ... funny ...

Thanks for correcting me.