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| Click here to select a new forum. | | SCSI resistor packs | Posted by: jake18125 on 2020-11-29 04:56:23
I've recently acquired a pair of 1gb scsi drives which work absolutely fine... so long as the system has an external scsi terminator installed. As it turns out they are both missing the resistor termination packs, which I only now realise are a bit more complex than a SIL resistor pack. Does anyone know where I could possibly find replacements or a suitable alternative?
| Posted by: max1zzz on 2020-11-29 05:59:27
There are two types used as far as I know, the first is a simple SIL resistor pack, typically 9 elements with a value of 110 ohms. Drives using this arrangement typically have two resistor packs
The second has two elements per pin, one pulling up to TERMPWR and one pulling down to GND, typically the pull up element is 220ohm and the pull down one is 330 ohm. Drives using this arrangement typically have 3 resistor packs
It's pretty easy to work out what kind the drive expects, you just need to test for continuity at the ends of each resistor pack to ground, if one end is grounded you need the second type, if neither ends is grounded you need the first type.
As for replacements, I believe the second type is actually still made (Or at least NOS ones are easy to find one eBay) the first type I actually found to be really hard to get hold of in the past (At least in the UK, it might be different elsewhere) you can substitute 150ohm resistor packs (which are easier to find) in place of the 110ohm ones and it will normally work fine but keep in mind this is not in spec so might cause issues in some circumstances.
| Posted by: jake18125 on 2020-11-29 09:04:09
There are two types used as far as I know, the first is a simple SIL resistor pack, typically 9 elements with a value of 110 ohms. Drives using this arrangement typically have two resistor packs
The second has two elements per pin, one pulling up to TERMPWR and one pulling down to GND, typically the pull up element is 220ohm and the pull down one is 330 ohm. Drives using this arrangement typically have 3 resistor packs
It's pretty easy to work out what kind the drive expects, you just need to test for continuity at the ends of each resistor pack to ground, if one end is grounded you need the second type, if neither ends is grounded you need the first type.
As for replacements, I believe the second type is actually still made (Or at least NOS ones are easy to find one eBay) the first type I actually found to be really hard to get hold of in the past (At least in the UK, it might be different elsewhere) you can substitute 150ohm resistor packs (which are easier to find) in place of the 110ohm ones and it will normally work fine but keep in mind this is not in spec so might cause issues in some circumstances.
Yep it needs three resistor packs.
so they are literally just SIL resistor packs?
| Posted by: max1zzz on 2020-11-29 09:14:47
If it needs three I would expect them to be the split packs with two resistors per pin, I can't be 100% on that but all the drives I have had with 3 packs have used the split packs, if you have continuity form one end of where the resistor packs go ground you need the split packs
Something like this is likely what you need: https://uk.farnell.com/bourns/4610x-104-221-331l/res-n-w-dual-terminator-330r-0/dp/2908124
| Posted by: jake18125 on 2020-11-29 09:19:35
Just checked, pin ones goes to ground on all three of the packs, and pin 8 goes to termpower
| Posted by: jake18125 on 2020-11-29 09:39:31
Hang on I think I just found suitable replacements
Does this look right?
https://www.mouser.co.uk/ProductDetail/Bourns/4608X-104-221-331LF?qs=zRaq9JBfD9%2B12SkSx27ilw%3D%3D
| Posted by: max1zzz on 2020-11-29 09:44:36
Yep, they look like the ones!
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