Hardware Rescue 101 (Part II)
by Coral1
Ahhhhh! I see you came back. That means you are either brave or crazy. I hope it is a little of both ... it will help.
Today I think we will strip a system down to bare metal. Just to brag a little, I now average about 20 minutes to do one of these (longer if is something new to me). And I once won a bet I could do it in 10 minutes or less. Of course I quit counting how many of these I have done when I ran out of fingers and toes to count with. If you take less than 30 minutes on the first dozen or so that you do, you are not giving yourself a chance to learn anything. So take your time and really pay attention to what you are doing.
Before we even start, make a habit of this: ALWAYS ground yourself to something before working on ANY hardware. Touching the metal part of a plugged in system works. It does not have to be turned on, just plugged into the A/C outlet. Anything that gives you a static shock is also good. Static will kill your top dollar "whatever" before it even gets close to the computer. Or you could move to Florida. There are only about a dozen days a year when the humidity is low enough for this to be a problem.
Eanie, Meanie, Minnie ....
Since I took a pass on the mini-tower that was networked to the 486 last time, I think it's time to find out what's in there. On the front there is:
- • 1 CDRom
- • 1 Floppy.
- • 2 switches.
- • 3 LEDs
• Soundcard • svga • lan
• 9 pin and 25 pin serial ports (I haven't see a 25 in awhile)
• ps/2 and parallel port (aka - printer port).
[Although these and the serial ports are probably cabled to header pins on the mobo (motherboard)]
Treasure Hunt
First undo all the screws holding the cards in the slot bay. Let's see what kind of goodies we got here:
OK, the PS/2-game ports and 9-25 serial ports are ribbon cables connected to header pins on the mobo. Check for pin 1; make a note of it for later. I know. I hate taking notes also. But the first time you run into an mobo where the header pins are not marked with a number, a thick line, a little triangle (usually), or are keyed (a missing header pin and a plugged cable end), you WILL be glad. As an added note, different mobos count #1 in the header blocks different ways
First up, the soundcard. It an ISA card and it says it's an OPTi OP931. It goes in the ISA box for later testing.
Next is a PCI NIC card
Time for the video card. Again, not too shabby. A S3 Virge DX. Also PCI. 4 soldered on ram chips with 4 upgrade sockets already loaded. Let's see... chip number AS4C256K16EO-50JC. If the numbers are not "coded" (some chip numbers are straight forward, some you need a listing to find out what they are), this seems to have 4megs of ram on it. It needs to be tested to be sure. Well... if you wait a second I'll tell you how I got 4megs.
Minor Detour
In this case, the numbers that count are: 256K16. So it becomes 256 kilobits X 16.
Now it takes 8 bits to make a Byte. So 16 bits divide by 8 bits equals 2 Bytes. Still with me?
Good. Now... 256kb
Tthis number: TC59S1608AFT-12A doesn't give a clue. You need to go to Toshiba to track it down. But since this chip is on a marked 16Meg SDRam stick
Back to business
I noticed that this case has a removable mobo mount tray. Pull the lever down 
But first all the cables and connectors have to be unhooked. Make a note of the red stripes on the cables to know where #1 is. Make a diagram of the Front Panel connectors and wire colors. Unplug the front panel connector, IDE cables, floppy cable, CPU fan, and power connectors. And anything else that is plugged in to the mobo. Undo the clips holding the ram sticks in. These are the older 72-pin SIMM
The 168 pin SDRam
Everything off but the CPU? Good. Now we pull down the lever and take the mobo and mounting plate off. I like to leave them together when possible as it helps protect the mobo. Otherwise you have to find and undo the mounting screws. Usually between 6 and 9 per mobo. Check around the edges and for 1 hiding in the middle somewhere. Make a note of how many and where they are. You usually DO NOT want to put a screw into a hole that DOES NOT have a metal ring around it. Things are more standard now, but there have been times I had to get.. err.. creative when installing a mobo in a case where the case standoffs and mobo holes didn't match up. Ahhh! Good times. WooHoo! A couple of plastic standoff on this one. These are great for those times when you need to get creative. 5 screws in this mobo. I don't see any surprises. Just a basic Baby AT mobo.
Break Time
I see you are yawning, so go get some INE and stretch your legs, while I reload my coffee cup. 
You know! INE. CaffeINE, nicotINE, legal amphelamINEs. But stay away from the codeINE. Why? Because you will Not enjoy the way I wake you up. Although I will.
Coffee pot is over there. Help yourself. If you can find where the cups are hiding.
Front Cover
Feel better now? Time to take this beast down to bare metal. As long as the mobo is out, let's see what it is. Hmmmmm... says P5BTX7L rev.B. Has a max of 66MHz with a 3.5 multiplier. Yes! CPU core voltage settings, so it will take up to a 233MHz. Let's see what's in here now: a Pentium 200 MMX. Like I need another one of those. Anyway, on to the fun part. The front cover.
The 3 main ways they attach these are:
- Snap on - These are usually just some kind of pressure clip. Just grab a handy spot and pull firmly. If they are real tight, a slot screwdriver pries them off nicely. Normally 4 clip points.
- Clip on - These are barbed plastic tabs that have to be spread so the tab will go back out of the slot. Again, 4 is the magic number.
- Screws - Thought they couldn't find a place for more screws, didn't you? Well... they did. The easy ones are screwed into the side of the metal case where they are easy to see and get at. But mostly they are hiding on the inside of the cover, around the outside edge. Almost need a special tool to take them out, but a long thin phillips head screwdriver works. These go through a metal edge into the front cover. You guessed it. 4 of them.
Ahhh... we lucked out. A snap on. Even better the LEDs and Reset Switch are in a separate do-hicky instead of hot glued to the cover. The do-hicky is a clip on. Undo the barbs, slide the wires through the case hole, and plug the wires back in to the mobo ... Presto! All you have to do is plug in the PSU and instant test bed. Whoops... forgot the speaker. This one is held in place by small metal tabs to the front of the chassis. Bend them up, and the speaker comes right out. Plug it into the mobo and Presto! Instant test bed. Complete with lights and sound.
Locate the screws holding the drives in place. Take them out, and remove the drives. Some systems have the drives on rails that slide in and click into place. In that case you have to find the tab to "unclick it" and slide them out.
Lose the Juice
Almost there. All that's left is the PSU (power supply unit).
This is an AT PSU. That means it has a real ON/OFF switch that carries 110/220 volts. It's a big black cable that runs from the PSU to the front of the chassis. Where the power switch on the ATX PSU is just 2 small colored wires that run from the front panel to the mobo, and let a small voltage go back to the PSU when pressed. Inside of which is where the real ON/OFF switch is.
This one is a push button type of switch. That means there are 2 small - dare I say it? - screws that have to come out. If it is a rocker type switch, it should have 2 tabs that need to be squeezed together to get it loose.
If the switch will not go through the case hole, you will have to unplug the 4 wires (sometimes only 2) to get it free.
WARNING!! Make A Note Of The Wire Colors And Where They Plug In!! If you get these wires plugged in wrong, 1 of 2 things will happen when you throw the power to it:
- Nothing. I mean nothing, nada, zip. Count yourself lucky and unplug it from the wall and try again.
- FIREWORKS everywhere! Pull the power cord out of the wall or whatever it is plugged into ASAP
! If not sooner. Pray to your favorite deity of choice that the worst thing that happened is that only the PSU is fried. And not the mobo and everything hooked up to it. In the other direction, the surge suppressor, power strip, UPS , all the way back to the circuit breaker (in whatever hard to get at place they put it). What blows depends on what/how you have things connected. As a matter of fact, having any hardware you are testing plug into a power strip first is a good idea. The breakers in them will usually trip before any thing else.
With the switch undone, we can now go to the back of the case and take out the 3-4 screws (the last ones. Finally!) that hold the PSU in place. There are a couple of ways they mount PSUs, but this is the most common. You need to hold the PSU with one hand while you take the screws out, and then it will just slide out of the case.
Finally
Since I said we were going down to bare metal, there is one thing left to remove. The rubber feet on the bottom of the case. Most of the time these are round but I have seen rectangles also. Some are flat pads. These are glued on. They can be pried off with your fingers, but using a slot head screwdriver is easier. The others have a split stem that fit into a hole in the bottom of the case. From inside the case you have to push out the center rod that keeps the stem spread apart and then push the stem out the hole. Most of the newer, fancier cases now have a base on them instead. These can be quite interesting to figure out.
Quitting Time
While systems as old as this one are getting less and less worth the effort to strip, they are still a good source for odds and ends. Like LEDs, wires, jumper caps, cmos batteries, cases, cables, etc. Mobos, Harddrives, CDRoms and even floppies are useful in testing and setting up test beds. They are also good to practice on. Things like OverClocking, (if you toast it, who cares? You just know not to do THAT again), how to swap parts in systems, tracking down manuals and info on the Web, and general hands on experience.
What's a test bed? A test bed is usually a motherboard and power supply that is not in a case. You also need a video card, and ram. And a Floppy, CDRom and a hard drive with some kind of OS on it (I use W98SE), for running diagnostic programs. The hard drive is not as important as it used to be, as they now have CD disks that will boot that have these programs on them. My current weapon of choice is UBCD (Ultimate Boot CD).
With a working system on the bench, you can test pieces and parts to see if they are good by swapping stuff in and out. My current primary test bed is a AMD Socket A (462) rig with a 750 MHz Duron and 64meg of PC-100. It's good for testing PC100/133 SDRam, DDR 200/266, hard drives up to 200gig ATA-133 (well that's the largest I have had plugged into it), CDRoms, up to AGP 4X video cards, and AMD Athlons up to 1800+. I also have rigs for 386, 486, Socket7, Super7, SlotA, Slot1, and Socket370
That's it for today. It's time to scratch up some supper and zone out in front of the TV.
NS! NR!
