Atari 400 - no sign of life - black screen

[TheDash]

Hello folks

 

I recently had a 'dead' Atari 800, which I posted here, and thanks to your help I got working.

 

Now it's the turn of the Atari 400.. I could have sworn this worked, albeit many years ago I guess. When I power on I get just a black screen.

 

Is there a step thru diagnosis I could follow to find the fault? I get the feeling this will be something at chip level and not as easy as my 800, but any pointers / help greatly appreciated. Detailed photos will follow for those interested

[ACML]

You may want to try the "low hanging fruit" checks first, but I've revived a few 800 and 400 black screen issues by simply removing and reinserting the the RAM and CPU boards. I think they oxidize and lose continuity. It's an easy solution, but in the case of the 400, it requires significant disassembly.

[TheDash]

but in the case of the 400, it requires significant disassembly.

 

You're absolutely right there - I'm a bit stumped already trying to carefully open the thing up. I have the bottom chassis off, but can't seem to get further ... any advice on how to disassemble the thing?

[ACML]

Steps to disassemble a 400:

 

1) Remove the four screws that hold the top shell from the bottom.

2) Open cartridge door and lift the top cover over the cartridge door.

3) Disconnect the keyboard ribbon from the mainboard and remove the cover over the open cartridge door.

4) Disconnect the RF video from the PWR board.

5) Remove entire assembly from bottom base and set on something that does not conduct electricity.

6) Remove the external speaker connector from the mainboard.

7) Remove the two screws that hold the PWR board to the metal case shield. Be careful, those two screws come with a washer (don't lose).

Separate the PWR board from the mainboard.

9) Turn the mainboard/case assembly over and remove the ~8 screws that hold the bottom metal case to top metal case.

10) Pull metal case shield off mainboard.

 

Now you can pull the RAM and CPU boards out, clean connections and reinsert. I suggest testing before reassembly. Remember to put something that does not conduct electricity under the PWR board to prop it up since the metal case shelf is not there to support it. During reassembly, make sure the plastic "hangman" cartridge door closed switch thingy is plugged into the case before you try to attach the PWR board back to the mainboard.

 

Good luck!

Edited March 31, 2018 by ACML

[TheDash]

Absolute top notch - thanks so much for the step by step instructions, really appreciated. I'm very impressed by the overall help offered on this website! You do it a great credit.

 

So, I carefully followed them. I had to laugh a little at step 2 - that was what had me stumped earlier. That cartridge door ...

 

I'm going to attach some pics (as promised, pics fans), but there seems to be something maybe a little unusual about the RAM board. It has soldered wires going to another IC on the board, and to the underside of the cartridge connector. Is this normal? The underside of the chassis has a red label saying '16k RAM', but also a hand written label saying '48k'. Inside there's what looks like an engineers label stating 'A400 48k' - could it have been upgraded? Pics to follow.

[TheDash]

Pic 1. The RAM board contacts were clean, but the CPU ones very dirty - as you can see.

 

 

 

This is the RAM board. Do the chips look normal? As in standard 16k setup?

 

 

 

The reverse side of the RAM board, with 4 wires connecting to an IC board on the motherboard

 

 

 

And the yellow / green pair of wires connecting to the underside of the cartridge connector.

 

 

Lastly, what looks like an engineers label stating, possibly, that the machine is 48k? The label is a little cryptic - I'm assuming A400 is Atari 400, and 7/84 the date? Has anyone seen this before?

 

[ACML]

Wow! Certainly looks like a 48K since the board has 4564 (64Kx1) DRAMs. I have never seen that version of an upgrade board. I've seen several Atari 48K and Intec 48K boards, but never that one. When you get the chance to test, let us know if it just needed the boards to be reseated. If you use isopropyl alcohol to clean the card edges, make sure it's at least 90%. Don't use the 70% "rubbing alcohol" (too much water content).

[TheDash]

Well holy Donkey Kong - it works! That was really quite a nerve wracking experience, putting the connectors back together. Yeah, I know it's old, but - so fragile? Well phew anyway.

 

Thanks a whole stack for your help there Dragonstomper - really appreciate it.

 

So I'm not sure what fixed it exactly - but I cleaned the contacts (95% alcohol), pressed down on the chips a little (one of which clicked), and that was it really. Now to reassemble the thing properly. More nerve wracking coming up.

 

I can't tell you much about that RAM board - it would have been done back when I was more interested in playing with Star Wars toys and reading comics, and getting to school on time. But I'll bet it wasn't cheap for sure.

 

The picture is snowy as expected - but pretty badly so. Was it always that bad?

 

 

Donkey Kong lives on. Now I'm thinking AV mod .. the picture is dreadful!

 

[Nukey Shay]

Wouldn't all the interference be expected if on of these is out of it's shell? That metal case has a purpose.

[TheDash]

It made very little difference sadly. I replaced the Astec modulator with a newer one, just as an experiment, and there was a slight improvement - but I think I'll go the composite mod at some point in the future if I'm going to keep using it.