Re: CD-Burn: Not as green as a Brussels Sprout!
- From: Andrew Hill <user@xxxxxxxxxxx>
- Date: Sun, 08 Jan 2006 15:57:43 +0000
Steve Fryatt wrote:
On 8 Jan, Wendy Gray wrote in message <6df0fde54d.Wendy@xxxxxxxxxxxx>:
In message <43c070d7$0$82661$ed2619ec@xxxxxxxxxxxxxxxxxxxxxxxxxx> Andrew Hill <user@xxxxxxxxxxx> wrote:
That's a good point Steve. I found my SCSI setup was unreliable when my PSU was struggling - in fact the SCSI termination is the only thing that struggled (it was otherwise asymptomatic). Eventually I swapped it out for a 105W PSU.
Jutst in case you're not sure (or can't remember your GCSE physics) - take the lid of the RISC PC. On the PSU is a yellow sticker. It's got
a number of voltages and currents. Multiply each voltage by each
current, and make the results positive. Now sum the results. It
should be either 70 or 105.
Ah, thanks for that, Drew. In my ignorance I thought it was a PSU in the CD-writer we were talking about.
No problem. The PSUs really should just state '70W' or '105W', but sadly they don't, and it does tend to cause confusion :o(.
We were, sort of. I had assumed (possibly through not reading the thread fully enough) that the CD Writer was in the RiscPC case and powered off the RiscPC PSU. From what you've just posted, I assume that isn't correct.
Yeah, I'd assumed that too.
Now, I need husband's help; the 17" Iiyama monitor is too heavy for me to safely lift off on my own. Means moving other stuff around too. In fact as a retired head of maths, he can do the calculations whilst he's at it :-) Neither of us ar physicists. If it is 70, I take it we need to upgrade (cue Chris Evans?).
It's probably not a relevant question, given that the CD Writer is in an external box (it is, isn't it?). The PSU in the SCSI box may still be an issue, of course; that's a lot harder to make suggestions about, though, as there are many different types of box and as many different types of PSU in them.
Actually - the PSU output would still be an issue even if the CD writer is external.
Firstly, since I was also under the presumption that this was an internal drive, let's just revisit your SCSI setup again.
SCSI requires termination on each end of a chain of devices. A SCSI card is a device like any other SCSI device. However, normally a SCSI card usually has equipment to double as a terminator if it is at the end of the chain, which is why it's always positioned at one end of the chain where possible.
So, in a situation where all the devices are internal, or they're all external, the SCSI card can act as a terminator. In many cases you have to switch this on or off (either using software or physically adding or removing the terminator packs from the card, depending upon what it is.) You then need a single terminator at the end of your chain of internal or external devices.
When you've got internal AND external devices, the SCSI card is really sitting in the middle of a chain. The terminator should therefore be OFF on the card (because it's a middle device.) There should be TWO terminators, one at the end of the internal device chain and one at the end of the external device chain.
It is well worth thoroughly checking this. It would be easy to have the SCSI card termination on or off inappropriately, or have an internal terminator but not an external one when you have both internal and external devices, etc.
All things considered - IDE CD writers are extremely cheap these days, and it may be easier just to put an IDE writer in since CDBurn accepts them. SCSI's great when it works, but it's a beast to set up correctly.
Going back to the PSU issue, the problem comes with the podule bus. If your machine has a PC card (in particular,) a couple of podules, and one or two hard drives, it can easily exceed the 70W PSU's output. In these situations, every device has to make do with less. The thing that suffers first is usually the SCSI card, which doesn't have enough current to put through the SCSI cable. As a result, the cable often looks to the SCSI card as though it's terminated (intermittently) when it isn't - so you get sporadic errors or problems. Even if you found an alternative drive, if this IS the problem, then you'll still find the machine unreliable unless this is solved.
THe reason that the PSUs are a problem are that Acorn underestimated just how much most people would expand their RISC PCs. Or, cynically, you could look at it that they wanted to sell second PSUs ;oD.
Let us know what equipment you have in your RISC PC, and then some of the eagle-eyed here can probably work out whether a 70W PSU is adequate.
Best wishes,
Drew .
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