Troubleshooting Compaq Portable I

[SteveHere]

Hi All,

I've been working on restoring an early Compaq Portable I from 1983. I've replaced the foam pads, serviced the floppy drives, upgraded the BIOS from Rev. B to Rev. C, installed a Lo-Tech XT to CF, as well as a through cleaning. I'm really enjoying the green screen and experiencing what early PCs were like before I was involved with the PC scene.

There is one remaining problem with my Compaq Portable. It has an intermittent startup problem. About 1/2 of the time when I start, I hear a single click sound and the cursor appears and it boots normally. About 1/2 of the time, I see this...



No matter how long this is up on the screen the computer won't boot. Power Cycling the system (sometime repeatedly) fixed the issue. Once the cursor appears on the monitor, it boots every time.

Is this an issue with the CRT or the Power Supply? I don't really know where to start with troubleshooting this problem.

Thanks,
Steve

 

[SteveHere]

Following up to close out this thread in case anyone else ever encounters this. I did finally determine the root cause of this failure, and unfortunately like so many this one was self-inflicted.

Since I don't have an EEPROM programmer, the way I upgraded the BIOS ROM in this PC was by using the Lo-Tech XT to IDE board to write the Compaq BIOS onto an SST 39SF010A. Then, partially following Adrian Black's suggestion, I built a 32 pin to 28 pin adapter using a Socket to fit this part into the ROM socket on the motherboard. I tried to shortcut this operation and left the two high address bits floating, and this caused the PC to enter an indeterminate location in the EEPROM on power up. When I finally realized what might be going on, I pulled the ROM socket adapter out and tied the high address bits to ground. The problem immediately went away and the PC has booted the first time, every time for many months now.

 

[Andrettigto]

Thanks for the follow up post