Need help fixing a 464 with a potentially dead CPU

[thesmiler37]

Thanks for the info! I feel like a bit of an idiot now. 

At least i have a spare CPU, i'll get out the logic probe in a bit and check IC 115 and the RAM, although i might just socket it all anyway for easier access in the future.

I was planning on getting a switchable EPROM with Amstrad diagnostics on it, does anyone know if that's a good diagnostic ROM and i noticed the 464 ROM comes in 2 parts, the OS and BASIC, do i need to send both to be burned onto the EPROM or is there a combined version?

[thesmiler37]

I've got my culprits!

I tested the RAM chips and IC 115, pin 3 top and pin 2 bottom are the ones that stuck out to me, the chips in green tested high and the ones in red tested low on those pins, seems like i've got the dead chips right?

IC 115 checked out aswell although if that was dead none of the RAM chips would test high.

[SerErris]

Thanks for the info! I feel like a bit of an idiot now.

At least i have a spare CPU, i'll get out the logic probe in a bit and check IC 115 and the RAM, although i might just socket it all anyway for easier access in the future.

I was planning on getting a switchable EPROM with Amstrad diagnostics on it, does anyone know if that's a good diagnostic ROM and i noticed the 464 ROM comes in 2 parts, the OS and BASIC, do i need to send both to be burned onto the EPROM or is there a combined version?

You only need the lower ROM as the diagnostic. 

[SerErris]

It is a little bit difficutly to understand.

There is no pin 3 on top ... RAM chip top pins are 9-16.

Ram In is 2 Ram Out is 14. 

And it does not tell you anything if some are high and some are low. That changes actually every ram access. If it is stable highor low on the output or input then there is a problem.

[thesmiler37]

I was just counting from the left side of the chip to make it easier for myself, so pin 3 top would be pin 14 and pin 2 bottom would be pin 2, the chips in red would oscillate mostly towards low and after a minute or 2 of being turned on would go completely low, the chips in green would oscillate towards high and didn't change.

[SerErris]

You may want to try to put one working ram chip on another and then give it a try. However the best thing is still diagnostic rom for now, as it indicates which RAM chip(s) is/are bad.