Case Studies in Retro Computing Repair #16: Diagnosing and Fixing an Atari 800XL Booting to the RAM Test

Hardware, Repair

Introduction

I recently received a nonworking Atari 800XL that would boot straight to the built-in RAM test instead of the Ready prompt. It failed the RAM test almost completely with a grade of “F”. I discovered when I cracked it open that it was loaded with cheap Micron Technology (MT) DRAM 64Kx1 RAM chips that are notoriously unreliable (see below).

Unreliable MT RAM chips from Micron Technology
Unreliable MT RAM chips from Micron Technology. These were pulled from a socketed board.

Case Study

Unfortunately, the MT RAM chips were soldered straight on the board. Thus, I first had to desolder the chips and install new 16-pin sockets (see two photos below). I used my Hakko FR-301 desoldering gun to remove the solder underneath the board and then used my Yihua hot air rework station to safely heat the chips on top for removal without lifting any traces dues to residual solder. I swear by both methods and tools. I then populated the sockets with 256Kx1 DRAM chips (100ns) I purchased from eBay. Note prices are higher now. This brough the machine back to life!

Bad MT RAM desoldered out
Bad MT RAM desoldered out.
New 16-pin sockets
New 16-pin sockets.
NEC 256Kx1 DRAM chips from eBay
NEC 256Kx1 DRAM chips from eBay
NEC 256Kx1 DRAM chips from eBay arrived
NEC 256Kx1 DRAM chips from eBay
New 256Kx1 NEC DRAM installed and working in an Atari 800XL
New 256Kx1 NEC DRAM installed and working in an Atari 800XL

Comments

I have previously done the same repair for failed MT RAM chips on a Commodore 64. Note that Atari 8-bit computers are much more reliable that their C64 cousins. MT RAM is a common point of failure for both machines.

This is reposted from my Atari Projects blog.