EEPROM Programmer

Matthew — Tue, 25 Aug 2009 22:42:49 +0000

My first attempt at building an EEPROM programmer around the KM2865A/AH EEPROM chip. This circuit connects directly to the 40-pin card edge connector on the Color Computer, and is entirely powered by the machines bus. No 12 volt supply is needed for this EEPROM, which simplifies the circuit. 8K x 8bit should be enough for anybody.

EEPROM Proto board

I completed the proto type the other night and tested a few writes. Not sure what the eventual usage of this is, but I’ll probably use it as a capturing tool for the CoCo3 ROMs, or saving data while I try to bootstrap some programs between the assembler and BASIC (which don’t run at the same time).

Electrolytic Capacitor Failure

Matthew — Tue, 25 Aug 2009 22:40:35 +0000

There are two reasons I like to roll my sleeves up and try to fix something instead of just buying a replacement item: 1), it’s fun and 2), it’s a whole lot cheaper! Case in point… the audio amplifier I have in my car died not too long ago. Not a horrible death with smoke and fire like some electronic parts, but a slow gasping drowning death. When the car would hit a bump, the stereo would thump. Then, it started vibrating the speakers in sympathy with any vibration the car felt. Now, it won’t turn on without a sufficient whack to the heat sink and it won’t stay on if it’s vibrated. Most of the problems started after one of the super hot and humid days we had this year. After lots of checking the circuit board for breaks and bad solder joints, and carefully inspecting each part, I finally found the problem: The main power capacitors seem to have dried up or lost their electrolytic fluid. When you tap them very lightly the amp goes hay wire. Some of them are very sensitive, some are not. Seems that they’ve lost their electrolytic fluid. I’m guessing that most of the damage was done that July afternoon and the sealant on the capacitors just evaporated through fatigued seals. Here’s a great article describing the issue:

http://sci.tech-archive.net/Archive/sci.electronics.basics/2005-04/msg00118.html

It’ll cost around $20 to replace all the main capacitors (parts + shipping). Thanks to great online retailers like Jameco. Or I could have shelled out another $150 for a new amplifier and re-wired the speaker, remote turn on and possibly power wiring. Plus the amp has really good sound quality!

Code and more » electronics

EEPROM Programmer

Electrolytic Capacitor Failure