VOGONS


First post, by Intel486dx33

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Hi, I have a DELL Optiplex 433/L with 486dx-33
I am trying to fix.
What happened is that I was fooling around with it out side on the patio table trying to add a CDROM drive and I must have shorted something out. From what I remember the computer was turned on when I was connecting the CDROM drive. The power supply fan is so quiet I did not realize the computer was turn on.
Previously it was working.

So now I get NO video
I checked the power supply and it tested good.
Power supply Fan spins up too.
I took a multimeter to the motherboard and some capacitors report 12v
Some 5v.

The PC Diagnostics card reports nothing. No beeps and no error codes.
No blinking of lights either.

I tried a different video card but no success
Anyone have a motherboard schematic or diagram for this computer ?

Any Ideas on how to go about fixing this ?

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Last edited by Intel486dx33 on 2019-10-10, 21:55. Edited 4 times in total.

Reply 2 of 19, by quicknick

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Nice computer, I like Headland chipsets and had no idea they had one for the 486. Must be their last, I think.
The Reset LED on your POST card is lit at all times, it seems. It should be just for a brief moment at power on, or when you press the Reset button. Check the connections that go to your front panel.

Reply 3 of 19, by Intel486dx33

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I put a new CPU with no success
I replaced the power supply with No success
I removed the ram with No success
If I connect the hard-drive to the IDE controller on the motherboard the hard-drive will not spin up.
If I remove the IDE connection from the motherboard the hard-drive spins up.
I get no activity from the floppy drive.
Front panel power LED lights up okay.

I get NO post
No error code
No flashing lights
No drive seeks.
No beep errors
Nothing !.....

Reply 5 of 19, by Intel486dx33

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Predator99 wrote:

Key is indeed the always-on RESET-LED. It should be off most time, also with CPU, RAM and all cards removed. Something is blown on your board...

I figured that. So where should I test on the motherboard to see what is blown ?
Anyone have a Schematic or diagram for this motherboard ?

If I hit the reset switch on the computer nothing happens.
Now all the lights on the PC Diagnostic card stay alway on.

From what I remember I think I was connecting and disconnecting the hard-drive and CD-ROM drive from the motherboard when it stoped working.

The power supply fan is really quiet I did not realize it was turned on.

Reply 6 of 19, by pentiumspeed

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Two ways this is asserting reset low stuck is from power supply is partially bad, (one wire is "Power GOOD" which is a reset held low for a few millisecond while the power voltages settles out at instant of power up or found internal problem with power supply and is not letting it de asserting low to high.
Try another AT power supply first.

The other one is reset circuit in the motherboard itself stuck low that take some troubleshooting to find.

Cheers,

Reply 7 of 19, by Caluser2000

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May I suggest getting a copy of this

20191011_132044[1].jpg
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It's very good and covers 486s.

There's a glitch in the matrix.

Reply 8 of 19, by Intel486dx33

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pentiumspeed wrote:
Two ways this is asserting reset low stuck is from power supply is partially bad, (one wire is "Power GOOD" which is a reset hel […]
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Two ways this is asserting reset low stuck is from power supply is partially bad, (one wire is "Power GOOD" which is a reset held low for a few millisecond while the power voltages settles out at instant of power up or found internal problem with power supply and is not letting it de asserting low to high.
Try another AT power supply first.

The other one is reset circuit in the motherboard itself stuck low that take some troubleshooting to find.

Cheers,

I tried another power supply already. And the motherboard reset switch will not reboot the computer.
The power switch does work however.

Reply 9 of 19, by Intel486dx33

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Caluser2000 wrote:

May I suggest getting a copy of this

20191011_132044[1].jpg

It's very good and covers 486s.

Those SAM’s books are for beginners. I need a Schematic of the motherboard form DELL.

Reply 11 of 19, by Caluser2000

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Intel486dx33 wrote:
Caluser2000 wrote:

May I suggest getting a copy of this

20191011_132044[1].jpg

It's very good and covers 486s.

Those SAM’s books are for beginners. I need a Schematic of the motherboard form DELL.

Well it does mention things about powering down, unplugging and wearing a static strap which you obviously weren't aware of. Some times when we get older we do tend to forget things. I know I do. I turned 60 last Sunday. Thought reading the guide would assist you in doing things correctly.

There's a glitch in the matrix.

Reply 12 of 19, by Intel486dx33

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The power supply does have a fuse. I checked it and it tested okay but it does look blown.
The tube is all white as if the fuse blew.
So maybe it is not fully functioning.
I am going to replace the fuse and test again.

Reply 14 of 19, by gca

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Board looks identical to my 466L (I think its was used in several models differentiated by different model numbers based on CPU).

Sadly mine is also dead(ish) but I did manage to coax it into running an on board diagnostic which provided pointers towards my problem. Not sure what the correct procedure is to get into that on board diagnostic (I have no manual and on-line detail appears to be scarce) but it must be stored in BIOS. The diagnostic started after multiple reboot attempts pressing the reset switch.

So, yeah, I need a schematic as well (good luck finding one but if you do please share).

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Reply 15 of 19, by Intel486dx33

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Intel486dx33 wrote:
The power supply does have a fuse. I checked it and it tested okay but it does look blown. The tube is all white as if the fuse […]
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The power supply does have a fuse. I checked it and it tested okay but it does look blown.
The tube is all white as if the fuse blew.
So maybe it is not fully functioning.
I am going to replace the fuse and test again.

Well, I replaced the fuse but still nothing.
So the problem must be in the motherboard.
Maybe a blown controller module for the IDE ?

Reply 16 of 19, by Caluser2000

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Intel486dx33 wrote:
I put a new CPU with no success I replaced the power supply with No success I removed the ram with No success If I connect the h […]
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I put a new CPU with no success
I replaced the power supply with No success

I removed the ram with No success
If I connect the hard-drive to the IDE controller on the motherboard the hard-drive will not spin up.
If I remove the IDE connection from the motherboard the hard-drive spins up.
I get no activity from the floppy drive.
Front panel power LED lights up okay.

I get NO post
No error code
No flashing lights
No drive seeks.
No beep errors
Nothing !.....

We kinda figured it wasn't the fuse.

There's a glitch in the matrix.

Reply 18 of 19, by Vynix

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I heavily doubt Dell has kept the schematics for such an 1ncient machine, and even if they kept it, I don't think they'd just give 'em like that.

Proud owner of a Shuttle HOT-555A 430VX motherboard and two wonderful retro laptops, namely a Compaq Armada 1700 [nonfunctional] and a HP Omnibook XE3-GC [fully working :p]

Reply 19 of 19, by AvalonH

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First rule out if the motherboard has become shorted. Power off the board and unplug everything (including CPU). Use this diagram of the standard AT power pins and locate your board. (I think this Dell model uses standard AT pinout)
ATConnector3.jpg

With a multimeter on continuity mode (beep) put one probe on any of the ground pins (4 are in the middle) and the other probe on +5. It should not beep indicating no short. Do the same for the -5, -12, +12 pins. If any of them do beep you have a short somewhere.