I bought my Atari 400 in February 1983. I thought it had been thrown out many years ago, but I recently found it in my mother's cupboards!
I tried powering it up, but it won't work. I tried a known-good 16K RAM card from my old Atari 800 and Star Raiders plays fine.
I remember spending every cent on upgrading the RAM from 16K to 48K back in '83, which worked fine up until I last used it, which was probably around 1989/90.
The odd thing is that the motherboard needed no mod wires to make it work. I've looked at many threads on here and on other sites and all upgrade kits seem to have needed the 4 mod wires from the RAM connector to the ROM cartridge connector.
My board is a 'Mapsoft' one, so I'm wondering if anyone else has seen one, and perhaps they can advise me as to how to go about troubleshooting faults on it. I've socketed every IC, and have replaced all 74LSxxx ICs, followed by the RAM ICs themselves. I substituted the Mostek 4564-20 ones for 4164-15 chips, which I'm told will work. The originals were 200mS, but the new ones are 150mS. All chips replaced are known-good and I've tried more than one of each just in case. I even tried the 4-wire mod in case I was going mad!
Any help would be greatly appreciated. I have an oscillocope and a multimeter!
Edited by davemac, Thu Jul 13, 2017 5:23 PM.