Atari 1400XL debugging

[electronizer]

My garage sale 1400XL decided to stop working sometime between VCF West 2018 and now. When I turn it on, all I get is a black screen. No luck on video or RF, and nothing with Star Raiders inserted either. I also tried booting with OPTION held down and seeing if I could start the audio test, but that didn’t work.

 

So far I’ve swapped Sally, GTIA, ANTIC, and POKEY into a good 800XL, and they all work fine. I’ll need to dig out my 130XE so I can test FREDDIE. Nothing is burning up, though two of the PAL chips seem to be getting pretty hot.

 

Any suggestions on what else to try? I have an oscilloscope if it would help to look at clock signals, etc.

[AtariGeezer]

Have you checked the 3 voltages (+5, +12 and -5) on your power supply?

[xrbrevin]

would the sys-check device by @tf_hh work on the 1400XL? if so its a worthwhile purchase

[+kheller2]

1 hour ago, electronizer said:

My garage sale 1400XL decided to stop working sometime between VCF West 2018 and now. When I turn it on, all I get is a black screen. No luck on video or RF, and nothing with Star Raiders inserted either. I also tried booting with OPTION held down and seeing if I could start the audio test, but that didn’t work.

 

So far I’ve swapped Sally, GTIA, ANTIC, and POKEY into a good 800XL, and they all work fine. I’ll need to dig out my 130XE so I can test FREDDIE. Nothing is burning up, though two of the PAL chips seem to be getting pretty hot.

 

Any suggestions on what else to try? I have an oscilloscope if it would help to look at clock signals, etc.

Not that there is much difference, but do you have a 1400 or 1450 motherboard in there?  You could also try remove the V:T: ROM and the Voice chip.  Just guesses at this point.

[electronizer]

Thanks for the input everyone! AtariGeezer, good point about checking the basics first. All three voltages are present and correct on the board. Also, the sys-check device definitely looks like it would be worth it for fast diagnostics if I were going through lots of machines.

I have a 1450 board. I’ll keep swapping parts and see if I come up with anything. 

 

[electronizer]

Well, my 130XE isn’t socketed so I decided to test everything else first and FREDDIE last. Found the problem: one of the Intel 2164 RAM chips is bad. The 1400XL is happy once again with an 8264 subbed in from my 800XL.

 

I’m looking around for a place to buy a replacement chip. All the RAM chips in my 1400XL and 800XL are 150ns but I’ve heard 200ns will work as well, is that correct?

 

Also, it looks like 2164, 4164, and 8264 RAM chips are all compatible, and you can even use a 41256 (256k) RAM chip, since the extra address bit is just tied to Vcc through a pull-up resistor.

[xrbrevin]

glad you got the thing sorted! ?

people obtain DRAMs from ebay and aliexpress

[Rybags]

Supposedly 250ns is the upper limit as I'd read in a Ram expansion article for the 400 in the day - 200ns should be fine (250ns equates to a bit under half a 1.79 MHz cycle)