Wait, is that a real book?
-
Hello MLAers! We've re-enabled auto-approval for accounts. If you are still waiting on account approval, please check this thread for more information.
LCIII+ SCSI2SD + external BlueSCSI DB25 (termination issue?)
- Thread starter ToneMalone
- Start date
Lmao perfect for the ADD brain!!! I've always wanted to achieve legendary status with Mac SCSI and now I can!! I don't know whether to call you Mr. Fahrenheit or Mr. Warmth
You’re Canadian, so the book is $49.95. Mr Fahrenheit is fine. I’m 200 degrees, which is more than “warm”.
Lol I appreaciate a little roast! Snowing at my house today; I don't know if I should just burn my cash for heat or turn on the furnace, will probably cost the sameYou’re Canadian, so the book is $49.95. Mr Fahrenheit is fine. I’m 200 degrees, which is more than “warm”.
The same page also says 'These switchboxes may not look like the one pictured, but they are very similar and do the exact same thing. All units have a 1-year warranty.'
Could be that what they are selling is different to what you have. I agree with the others, I wouldn't use it with SCSI devices.
That is hilarious.
I still am unaware of the risks involved, so in the spirit of ingorance and negligance I will continue to guinea pig this switch. I do have a cpl battery bombed boards and a hot air rework station... Call me stupid but I can't see this destroying my mobos or devices. Being as they do the 'exact same thing' internally, I don't see the difference. I also do not run an HDD of any kind in my Macs, I feel I'd be more weary if I was using an old SCSI HDD. However if I show up complaining that it's ruining my devices then I don't expect any sympathy!! lol
The list of risks for this is on page 42 of my book. You’ll have to order it to find out.
Seriously though, I agree with what others say (not to use it), mostly because I wouldn’t take that risk myself either.
But at the end of the day, it’s yours and being told it could cause issues, it’s your own decision to make. Reliability could to beyond ruining something and instead cools involve system instability or data corruption.
Similarly to how using an inferior scsi cable, or bad (poor quality) terminator, could cause issues and data loss. Questions I would think about are whether the switch changes any electrical values (resistance, etc) as they pass through it. SCSI is very sensitive to slight changes.
Back in the day, some problems were solved by not using that generic SCSI cable and instead using a good quality more expensive one, or not using the $10 terminator and instead using the $60 Granite Digital active terminator.
Do you have a way to measure the lines going through the switch box to ensure nothing is interfering with it from end to end? To be honest I don’t know what tools you’d use or what you’d be looking for specifically, but I’m sure there’s a way to verify nothing is happening with the switch in the line.
OKAY, warn me thrice AND tell me the risks I guess this is not an experiment and just an exercise in Tom foolery to keep using it blindly! Let's see what's inside. 
So here we can confirm it is a pin to pin configuration, 0 resistance between pins when set to the 10ohm scale. I checked all the pins on both settings to be extra sure. I also checked to see if there's any connection bleeding through to the inactive port and I could not detect a connection on any pins.
I believe this confirms that it's safe to use, but I will use my discretion next time before jumping in with both feet!
So here we can confirm it is a pin to pin configuration, 0 resistance between pins when set to the 10ohm scale. I checked all the pins on both settings to be extra sure. I also checked to see if there's any connection bleeding through to the inactive port and I could not detect a connection on any pins.
I believe this confirms that it's safe to use, but I will use my discretion next time before jumping in with both feet!
That’s a bit more comforting, but I’d still be a bit concerned looking at the rats nest of cables in there.
Reason being, SCSI cables were all shielded. Using unshielded cables creates electromagnetic interference. How much or how it affects the data being transferred, I don’t know.
Whether it’s truly a requirement for proper data or whether it was a “just in case” thing I can’t answer. Not experienced in that regard.
Example, some Macs had electromagnetic shielding covers that were just for FCC compliance as far as I know. Is that the case with SCSI cables?
What’s interesting is that SCSI cables were required to be shielded externally, but everything used ribbon cables internally. So is this any different than an internal ribbon cable?
Thoughts to ponder.
Yes indeed!
I can only speculate but what comes to mind is internally the ribbon cables are sheilded by the case of the computer itself, like how your microwave has those small holes to see through; the waves of radiation are larger than the diametre of the holes, so they stay inside the nuker. With scsi I think we're talking 10mhz - 320mhz, or 100ft - 3ft wavelengths. So I think any sheilding should solve EMI issues.
I'm in way over my head, I don't even know if those numbers translate correctly but it was fun to ponder on. Seems like our whole existence is built on frequencies, but that's another conversation lol
FYI on a 50 pin SCSI ribbon cable, every other wire Is connected to ground to maintain signal integrity
Good luck on using the switch with your devices. You may not be so lucky in 3 years at 1:00 am, when you switch with all devices powered up and see a small puff of smoke emerge from your drive…
Good luck on using the switch with your devices. You may not be so lucky in 3 years at 1:00 am, when you switch with all devices powered up and see a small puff of smoke emerge from your drive…
Let's keep it realistic Forrest.
You may suffer extra crashes, and your data might get corrupted.
You could run a hard disk test in MTP for a few hours and if you don't have read / write errors, you could conclude that the risk isn't huge. But like the others, I'd not use one. Those things are designed for parallel and serial devices, not SCSI. Parallel and serial are much slower.
Please add me to the list for the first printing of the @MrFahrenheit book!
Last edited:
For what it's worth, I've used those switch boxes for D-Cinema audio in the past and honestly they're pretty terrible - you'd get audio dropouts at best. Especially for older stock. If you can get into the switch itself some contact cleaner works wonders, but only for a while.
This is before you get into the "unsheilded rats nest" discussion.
Personally I'd stay on the lookout for a second zip drive, or get both of your Macs networked!
This is before you get into the "unsheilded rats nest" discussion.
Personally I'd stay on the lookout for a second zip drive, or get both of your Macs networked!
