Hello, first time poster here! I had a stash of Disk II Drives that I have been fixing up and am down to one more, but cannot figure out the issue. The Disk II Analog Card had a faulty 74LS125 which has been changed out, but it will still not read any disks. However, when I insert a different, known working analog card, it reads fine, so I know the head is okay. I have tested each resistor, transistor, diode, and capacitor but still cannot figure it out. I have also changed out each IC chip with working ones with no avail. Only issue I have noticed is that for TP1 on the analog card, it is roughly 0.371 volts, while my other cards are at 0.741 volts. I plan on pulling out my oscilloscope sometime this week to do more troubleshooting, but wanted to see any insight anyone has.
Anonymous
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Since it is not reading with the bad analog card, I checked out the MC3470 IC chip. The IC chip is good, so I checked around each pin, and noticed something about R33; the ohm readings were off. I unsoldered it and messed around with it, and then when I reinstalled it, the card works now. I am not sure if it was just dirty or a bad solder joint, but the problem is now resolved!
Good job !
Can you please tell us the correct value of that resistor ?
IT was unreadable, wasn't it ?
Thanks
Julian
Cold solder joints - or solder joints that have failed over time thrhough heat cycling - do exist in old electronics.
Might be a good idea to replace that resistor ourtight with a new one, just in case.
By the way, I looked at several analog cards and none of them have R33. Have you got some odd revision, or are you talking about R3?