Dell System 310

RetroViator

Tinkerer
Oct 30, 2021
129
159
43
retroviator.com

Righting a Wrong​

My company was cleaning out an old telecom closet when they decided to get rid of the "door stop" they had been using to prop open the door when working in the tight space. It was a Dell System 310, or so it seemed. The IT guys knew of my interest in old computers, and I was delighted when one day I walked into my office and found it sitting on my desk.

IMG_2370.jpeg


My excitement held until I got it home and discovered that its motherboard had been replaced. The original 1989 Dell motherboard with its 386DX was gone, replaced by an Amptron PM-8600 with a 233MHz AMD K6. I should have known something was up when I saw a 36x CD-ROM had replaced the original 5.25 floppy.

IMG_2386.jpeg

I thought about making it into a sleeper system, but instead I set out to find the original motherboard. A year later, I was blessed with a fruitful eBay alert, and the original board was mine.

Now, I'm going to restore the computer to its proper configuration. The original motherboard looks good, though with plenty of tantalum caps waiting to pop. Its RAM is missing, but it should use standard 30-pin SIMMs — a real plus, considering many systems of this era used custom memory cards (it also has a custom memory expansion connector). One wrinkle is that the system lacks an onboard keyboard jack. The jack is supposed to be mounted in the case above the motherboard and connected using a 4-pin header. I'll have to figure that out.

IMG_2389.jpeg

This will be my first 386DX system. I longed for a 386DX system back in the day, but I could only swing an SX. And thus far, all the 386s in my collection are of the SX variety.

I've been looking forward to working on this one for a while.
 

RetroViator

Tinkerer
Oct 30, 2021
129
159
43
retroviator.com
I did more research on the motherboard, and realized that I won't be restoring the System 310 to its original condition because I have the motherboard for its big sibling, the Dell System 325. The 310 is a 20MHz 386DX and the 325 runs at 25MHz. When released, the System 325 was Dell's flagship computer.

Luckily, I was able to find the original installation and troubleshooting manual on Archive.org. After uploading a high-resolution photo and other information to The Retro Web Discord, I sat down and studied the motherboard. It looks good, but when checking the AT power supply connector, I see the following:


JPS1 ConnectorPower SignalOhms to Ground
Pin 1Ground0 Ω
Pin 2Ground0 Ω
Pin 3-5 V+ MΩ
Pin 4+5 V+ MΩ
Pin 5+5 V0 Ω
Pin 6+5 V+ MΩ


JPS2 ConnectorPower SignalOhms to Ground
Pin 1Power Good0 Ω
Pin 2+5 V0 Ω
Pin 3+12 V0 Ω
Pin 4-12 V+ MΩ
Pin 5Ground0 Ω
Pin 6Ground0 Ω

So, I have shorts on two of the +5V lines and the +12V line. I count more than 50 dipped tantalum caps and even more axial ceramic caps. Any cap I check is a dead short back to the power connector, so I don't have a good place to start. I tried removing a few of the caps nearest the power connector, and I found the ground plane makes it very challenging to get caps off the board, but when I lifted the positive leg, nothing changed.

Unless someone has a better idea, I may start with removing all the socketed chips, and see if that makes a difference.
 
Last edited: