EMAX 1 No Boot

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MIPS
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Joined: Sun Nov 10, 2013 4:24 am
Gear: Emax I, Yamaha FB-01, Yamaha DX7, 1040ST + Notator
Location: Kamloops, Canada
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EMAX 1 No Boot

Post by MIPS » Tue May 24, 2016 9:35 pm

I've had this thing langusihing for a while. I originally got it PACKED with dead roaches and a dead floppy drive. I have since cleaned it out and replaced the floppy drive with another (Teac FD-235HF 4240) and generated a new EmaxOS 3.2 disk but it's still not behaving.
Also before someone asks, no, I do not have the budget at this time for a floppy emulator.

So I write the DS/DD disk using EMX or EMXP. It formats, writes and verifies fine between two machines so while I don't know for certain that the disk is good, both utilities mutually agree that data is where it should be.

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I turn the EMAX on, it prompts for the disk, I pop it in and the display says it's loading, I hear the drive step three times, the status LED's on the controls blink and seems to step back to track 00 and start over with three steps followed by a blink f the LED's. Rinse and repeat. Tested the floppy drive on another machine and confirmed it was able to read and write DOS formatted disks, regenerated the floppy again and still no go on that either.

Pulled the digital board and reseated all the socketed IC's (found more dead roaches hiding under two of them! GROSS!) Also went through the RAM and swapped out both 256K banks with good chips. No change.

(I removed VR1 for testing)
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Do not have an EPROM image I can compare with and no spare 64k RAM chips to test with either.
Then I probed the voltage rails. +12 and +5 seem fine however +5 has a 22 ohm resistance to ground on this particular board. With all the socketed chips pulled, VR1 removed and the board washed even when given a regulated 5V supply from the bench the board has a 22 0hm resistance to ground and chews up just over an amp of power but nothing gets hot from that low a resistance. Last two things I can personally think of is one or more shorted tantalums or a short between layers which means the board is dead.

Any ideas?

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