Salvation Army find - whew the mess

[@iguanac6466]

You should get a dead test cart and an inexpensive oscilloscope. Dead test will allow you to do a test without the ROMs (in case those are bad) and will also let you know if you have one more more bad DRAM chips (or a memory related LS logic chip). Oscilloscope will let you check the reset pin on the CPU and check data and address lines for correct voltages. Black screen with a white line means you're generating a good clock signal. Clock circuitry and VicII are probably good. PLA tested and good. Feel the chips to see if any are getting very hot...Esp those DRAM chips with the red dots. Your kernel ROM has a red dot, too. Looked like the LS logic chip next to the top row of DRAM to the right of the resistor pack has a red dot, too.

[@highshelfrich]

Great comments!!!! Thanks and going to check into this dead cart. I just put an order in for an oscilloscope based on watching some folks do just what you said. Thanks !

[@RayBellis]

*Always* test (and if necessary fix) the power rails first. Not days later...

[@chubbyadler3276]

Do you have some sort of oscilloscope? Either a used analog unit from the 1980s or one of the modern things off Amazon would help, so long as it gives you a couple megaherz of bandwidth. Most I have seen go to 10MHz. Also, if you haven't done so, Adrian's Digital Basement here on KZbin may be worth checking out for getting some ideas on what to look for. Every so often, he'll do a vintage computer repair, often a C64, and in those he talks about how to troubleshoot.

[@highshelfrich]

Scope is on order! Really enjoy ADB I learned the touch for hot chips from him need to dig in his older videos now that you mention it. Thanks for the ideas.

[@chubbyadler3276]

@@highshelfrich I'm sure checking for activity will tell you a lot once you get to looking at it.