• Please review our updated Terms and Rules here

Atari 400 black screen and two click noises on start up Problem

Nrittich

New Member
Joined
Jun 13, 2023
Messages
2
Hello I am new to this forum, but I have stumbled across many helpful tips here and I was wondering about my seemingly dis functional Atari 400 computer. When I power it on, the power light comes on, the internal speaker makes two clicks (sometimes fast and sometimes more delayed), and displays a black screen. I am using the built in ref output connected to a tested ref modulator, connected to a tested TV. Everything seems like it should work, but all I get when I turn the power on is a black screen with no sign of input. I have tried to start the computer with a game cartridge already inside, but to no avail. I have also tried my basic cartridge, but still a black screen. I have seen on this forum that re-socketing the chips and cpu and rom/ram boards usually fixes this problem, but after I re-socketed every chip, but nothing changed. If there are any suggestions, I will be happy to try anything to save this old machine.
 

oldpcguy

Experienced Member
Joined
Sep 23, 2021
Messages
359
It sounds as if you have performed all the basic troubleshooting that one can do without actually getting into swapping parts or component level troubleshooting. I assume you do not have the skills necessary to perform the latter?
 

Nrittich

New Member
Joined
Jun 13, 2023
Messages
2
It sounds as if you have performed all the basic troubleshooting that one can do without actually getting into swapping parts or component level troubleshooting. I assume you do not have the skills necessary to perform the latter?
Yeah I don’t have any special tools, the only diagnostic tool I own is a multimeter, but that doesn’t really tell me much. I am ordering a logic probe to help run more diagnostics.
 

Bob-O-Rama

Experienced Member
Joined
Jan 11, 2022
Messages
95
Location
Allentown, PA, USA, Earth, ...
As you have gleaned from the service manual, Black screen is the CPU is not able to execute the reset code - for a number of reasons. I would ensure the gold pads on the CPU and RAM cards are clean. Use a piece of kraft paper ( from a brown paper shopping bag ) to polish them. Make sure the edge connector sockets are free of debris and the pins look good. Insert and remove the cards a few time and make sure you see tooling marks on the pads indicating a solid contact. Most of my black screen issues go away having done this.

As a jokey and also serious suggestion: Make an "audio monitor," which is akin to a stethoscope, it picks up local EMI from components and makes it audible. This can tell you a alot about what is / isn't happening. I use mine on a weekly basis. Watch this, with audio on...


The above is an old Radio Shack phone pickup and audio amp. Its ideal for this purpose. You can also use an old AM transistor radio, though its harder to pinpoint. Its easy to detect if oscillators are operating or if the CPU is in a tight loop or not doing anything. Its also just fun to eavesdrop if you like "computer noises"
 
Top