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Breaking into an SLT-286

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tezza

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Yesterday I disassembled my unit to get at the floppy drive. I think it's faulty as it doesn't spin on boot-up. It could be a CMOS problem, but I wanted to check cables and replace the drive first then try to boot, just to eliminate the broken drive theory.

nige the hippy said:
if you can, get a set of "tamper-proof" torx bits, they are more universal.
If you ever need to fix a compaq, you'll DEFINITELY need them then ;-)
Click to expand...

Boy were these ever needed! I had to use at least three different sizes.

With no manuals or guides, getting into the machine was a bit of an adventure. I took it slowly, and step by step figured out how to do it. The hardest bit was getting the plastic plates off the rear end so I could pull the main assembly out of the case. I now understand another person's reference to needing a flat-blade screwdriver. You need this to prise the plastic cover off...carefully, without breaking the plastic snap-clips holding it on. It wasn't easy. Maybe there is a technique to it I don't know about?

Anyway, it survived my ham-fisted efforts and eventually I managed to remove the case, then the drive.

I then discovered that the drive wasn't your standard PC 3.5 inch drive. The connector at the back was a 26 pin one as opposed to the standard 34 pin one! (see pic...slt-286 drive on the bottom).

Oh well, so much for replacing the drive. As I said, I'm not convinced it's the drive (If I'm honest with myself, I really just wanted to see what was inside the machine). It might be the controller itself or a CMOS problem caused by a flat internal battery as discussed in another thread. The error at the beginning mentions the floppy controller. When I boot it up again I'll post the exact error. Hopefully, someone can throw some light on the problem.
 

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I'd seriously start by looking at the NVR, they do have a habit of setting impossible states.

I've just repaired the power supply connector on the SLT I picked up from the dump. (flat blade under the side opposite the notch releases the molex connector ;)) Rather frustratingly it booted to hard disk the first time, entered word perfect and announced it was called Rebeccah! But subsequently it tried to boot from floppy & failed. Will have to run the 720K setup utility, then probably STRIP-AARRRGGHH!!!!

It's a shame you're not this side of the planet, as I could probably help you with the chip, but Dallas semicon's sample department can be very helpful when sweet talked :D

consider the battery-crystal-less version of the RTC (can't remember the number-too sloshed! (11:30 PM Saturday!) with a home built battery & crystal added, then it will last for ever, or at least till it's tantalum capacitors die (another story), not 10 years max.
 
nige the hippy said:
I'd seriously start by looking at the NVR, they do have a habit of setting impossible states.
Click to expand...

Will do, if you could just tell me what NVR actually stands for :) . I'm a newbie at all of this hardware stuff.

nige the hippy said:
It's a shame you're not this side of the planet, as I could probably help you with the chip....
Click to expand...

Thanks. In some ways I wish I was too... you seem to have great dumps there to source stuff from! :)

nige the hippy said:
consider the battery-crystal-less version of the RTC (can't remember the number-too sloshed! (11:30 PM Saturday!) with a home built battery & crystal added, then it will last for ever, or at least till it's tantalum capacitors die (another story), not 10 years max.
Click to expand...

Yea, if it's what I think it is, I read up on that. Its a homebrew job, right? Given my still fumbling efforts with soldering iron and blades it looks a litte too scary to attempt just yet!

I'm suprised Compaq didn't use a more conventional battery. I mean, batteries DO run down right, and need to be replaced eventually. Why did they make it so hard? A little 3V battery holder on the board would have done the trick surely?
 
Sorry, too many TLAs ;)
The "Dallas Real Time Clock" DS1287 is what it's all about, it's the 24 pin cuboidal chip with an alarm clock on the top, it contains Non-Volatile-Ram, and a Real-Time-Clock).
They were originally supposed to have a battery life of 10 years, after which the computer was supposedly obsolete anyway. Many ran down after 3 or 4 years.
as far as I know (because the first SLT I replaced one in was a bit pre-chewed) there's room to put a socket in for the chip. then when you replace the chip (with the 12887 because any 1287's your likely to buy will have pre-flattened batteries!) hold it in with a bit of hot melt glue.
Alternatively use a DS12885 a 32Khz watch crystal, a separate lithium battery holder, some epoxy, and make up your own everlasting 12887.
Have a look at the data sheet!
 
Ok, I've dragged the SLT-268 out of storage again to try to get to the bottom of this problem. On booting after the memory check the screen says...

601-Diskette Controller Error
162-System Options Not Set - (Run Setup)

Insert Diagnostic Diskette in Drive A

(RESUME = "F1" KEY)

When I do resume, it tries to read the floppy drive, then eventually gives up and goes successfully to MSDOS on the hard drive.

As it's trying to read the drive the drive light is alternating green and orange (as I understand, one colour is for double density, the other for high density) and the drive doesn't seem to even spin any disk that's in it. I can't hear any signs of anything turning.

The question is...IS the dead drive because the floppy controller is faulty, or can this symptom (and the above message) be caused by a flat "Dallas" battery chip?

Hopefully it's the latter?
 
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