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SCSI2SD V5.5 on Mac 512k


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I have a 512k with a Dove MacSnap SCSI add-on and was interested in using a SCSI2SD V5.5 as an internal HDD. Instead of routing the 25 pin SCSI connector through the battery cover, I would just keep it inside and connect it to the SCSI2SD and make a bracket for it on top of the floppy drive. As for power, could I power it up a similar way I have my piezoelectric fan hooked up? Right now I have it wired to the CR23 and CR24 capacitors as recommended in Macintosh Repair & Upgrade Secrets by Larry Pina. I realize the fan isn't on 5V like the SCSI2SD needs, but I was wondering if there was something along the same lines. And if so, would it put a strain on the power supply? Or, is one of the other SCSI2SD versions a better idea for this for some reason?

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On 3/17/2021 at 8:02 PM, Stillwell said:

I have a 512k with a Dove MacSnap SCSI add-on and was interested in using a SCSI2SD V5.5 as an internal HDD. Instead of routing the 25 pin SCSI connector through the battery cover, I would just keep it inside and connect it to the SCSI2SD and make a bracket for it on top of the floppy drive. As for power, could I power it up a similar way I have my piezoelectric fan hooked up? Right now I have it wired to the CR23 and CR24 capacitors as recommended in Macintosh Repair & Upgrade Secrets by Larry Pina. I realize the fan isn't on 5V like the SCSI2SD needs, but I was wondering if there was something along the same lines. And if so, would it put a strain on the power supply? Or, is one of the other SCSI2SD versions a better idea for this for some reason?

Yes, if you feed 12 volts DC to pin 25 of a SCSI2SD V5.5, you will release the magic smoke. There's probably a place you can pick off 5 volts DC from the Dove board itself.

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Posted (edited)
20 hours ago, aperezbios said:

Yes, if you feed 12 volts DC to pin 25 of a SCSI2SD V5.5, you will release the magic smoke. There's probably a place you can pick off 5 volts DC from the Dove board itself.

 

Yup haha, the fan is actually connected to 120V, so the SCSI2SD definitely wouldn't like it. I don't think the Dove board has 5V on it, but not sure. I know the floppy drive has 5V going to it, but probably isn't a good spot to tap into because I will use my floppy emu now and then and I could see that causing some issues trying to power both at the same time. I actually just ordered a BlueSCSI and am going to go that route, but it still requires 5V power. 

 

I tested the power output from the floppy drive and got 4.9V, +12.4V, and -13.3V, so I need to adjust the voltage up a bit too before I go adding more load. I'm also not sure why my -12V is so far out when the 5V and +12V are close to where they should be. Larry Pina's book shows they should be 5.0V, 12.45V, -12.15V. Classic Mac Repair Notes goes into more detail on adjusting/fixing power problems, so I'll just follow the advice in that and see how it goes.

Edited by Stillwell
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Doesn’t that Dove board provide 5V term power on the add-on SCSI port?  Mine is on a high shelf at the moment so I can’t easily check but ... from memory I think it does.  I think you can just plug in your SCSI2SD and be good to go.

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20 hours ago, Crutch said:

Doesn’t that Dove board provide 5V term power on the add-on SCSI port?  Mine is on a high shelf at the moment so I can’t easily check but ... from memory I think it does.  I think you can just plug in your SCSI2SD and be good to go.

That would be best case scenario, I hope it does. I just assumed that since the Mac Plus didn't, that the Dove didn't. I couldn't find anything saying that it did have it. I also don't have any SCSI devices to test it, yet. I'll report back when I get my BlueSCSI and put it together.

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Yeah most of the (good) SCSI add-one had term power. The Plus was an outlier. I know my Levco MonsterMac add-on to a 512k has it and I’m pretty sure the Dove does also. I don’t think you’ll need separate power. 

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Those diodes must have cost at least $0.30 including the labor for installation.  ‘80s Apple had to keep those margins up, couldn’t afford extravagances like that. :) 

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