ericpskl Posted January 27, 2021 Share Posted January 27, 2021 I have an Atari 2600 (Darth Vader, CX2600A) that I've been trying to repair. Symptoms: With a known good cartridge inserted, I get a good RF signal on the TV, but only have a black screen. Logic probe shows pulsing on the clock pins, but no pulsing on any address or data lines. Clock frequency matches that of a good 2600. All three major chips check out okay -- they are socketed and work fine when installed in another 2600. Good +5V coming out of the voltage regulator. Known good external power supply. All contacts cleaned multiple times. Any recommendations on what to check next would be appreciated! Quote Link to comment Share on other sites More sharing options...
Stephen Moss Posted January 28, 2021 Share Posted January 28, 2021 If you perform a search of the internet or the 2600 forum you should be able to find a copy of the 2600 field service manual which may help you to diagnose the problem. Did you check for the clock on all the relevant pins, TIA pins 4, 11 & 26, 6507 pins 26 & 27 and pin39 of the RIOT? Also check that pin 32 of the TIA is taken to ground and that the reset pins of the 6507 and the RIOT (1 & 34 respectively) are pulled high to 5V. 1 Quote Link to comment Share on other sites More sharing options...
ericpskl Posted January 29, 2021 Author Share Posted January 29, 2021 Stephen, I owe you a pint! Followed your instructions and found that the RIOT reset pin (PIN 34) was at 0.4 volts. Pin 34 connects through a 22K (R227) pullup to +5V with a 0.1uF bypass cap (C238) to ground. Pulled and tested both components and found the cap was bad. Replaced the cap and she booted right up! 1 1 Quote Link to comment Share on other sites More sharing options...
Stephen Moss Posted February 1, 2021 Share Posted February 1, 2021 Another Atari lives again. You did most of the work, with the information you provided, for me a missing clock or reset issue seemed the mostly likely explanation and thus the next things to check. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.