troed wrote:Replacing TOS with known good chips is always an easy start. Verify the jumpers are in the correct position for the chips used.
czietz wrote:No, the ROMs from an STF will not work in an STE.
There is not that much you can do without measuring instruments. You could try to carefully remove and reinsert socketed ICs in case the contacts are bad due to corrosion. You could try replacing the power supply (e.g. by one from the STF, they are compatible). Other than that you'll quickly end up in a situation where a multimeter or even an oscilloscope is required, I'm afraid.
Which kind of monitor are you using? Is it some kind of modern LCD / TV that will show you whether a video signal is present? Iirc, right after power-up you should see a 60 Hz color mode.
mlynn1974 wrote:What are the states of the following pins?
HALT: pin 17
BERR (Bus error): pin 22
I am thinking that HALT will be low and BERR may be high.
As mpattonm says it would be wise to check the clock signal first.
mlynn1974 wrote:I would suspect that the ROMs are at fault. I am not familiar with the STs physical ROM chips but I have seen arcade guys on YouTube with hardware to calculate checksums for EPROMs. That would tell you if they are bad or not. If either of them are bad then you should replace them with known working TOS 1.06 or 1.62 ROM Chips as stated.
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