Hi everyone, I have a strange problem with the Apple II floppy drive unit, considering that I have another working floppy disk, I cleaned the lens, straightened the blade where the spiral wheel is and calibrated the motor to 300 rpm so on a mechanical level the unit also works because I swapped the analog board and it works perfectly, I tried to replace all 4 chips ULN2003, 74LS125, CA3146 and 3470 but without any change, it doesn't read. Note that the 3470 chip is definitely faulty because by putting it alone on the working unit it no longer reads, does anyone have any suggestions?
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I'm confused by your post. Your event timeline is unclear.
Did you replace the analog board with a known-good board in the suspect drive? And it worked with the replacement analog board?
Did you put a suspected-bad 3470 into a good analog board on a good drive and it did not work?
Did you put a known-good 3470 in the suspected bad analog board and did it work or not?
Sorry, I certainly made a bit of confusion in writing, I have 2 floppies, one works and the other doesn't, the problem is definitely the board because by exchanging the boards the other one also works, it's not an IC problem because I tried to replace them all
You can check whether all cables are safe or not. And clean the dust and test with other disks.
changing analog card works, I wrote it above :) the floppy has already been cleaned
I have to fix the broken analog but I have already changed all the chips and the 3 axial capacitors
Suspect Q1. The power transistor. I've blown one once and it didn't read properly.
Have you got a transistor tester?
Yes, I have the ESR meter that also tests transistor, but when I measured the voltage it it seemed good, I'll try to desolder it and test it
Q1 and Q2 are good
the problem is that the floppy always seems to be in waiting mode, or rather I tried with the thermal imager to check the components that heat compared to the other working floppy, the components that heat are exactly the same if I don't insert a floppy disk inside , when I insert a floppy into the working one, a switch occurs and the floppy starts to heat up other components, so this switching phase on the other one doesn't happen, maybe someone who knows how it works well can explain why?
This is a long shot, but I remember reading about someone who found a bad read-write head.
As unlikely as it seems, that might be the cause here.
Measure the resistance across the two coils in the read-write head. If one of them is open then you've found your issue. And if it is bad, you should (a) buy a lottery ticket and (b) take the drive apart for spare parts because it's nearly impossible to find that particular replacement part.
Spare parts of anything but a few of the cable, ICs and the belt are basically unavailable for either the Shugart or Alps mechanisms Apple sold in Disk ][ drives. So even a non-working drive is valueable to someone who has a drive that has failed in a different way.
My original Disk ][ drive (Shugart mechanism) I bought new back in 1981 I had already worn out and had to replace the drive door due to it having been opened and closed so many times. I've replaced a few broken cables, a lot of 74LS125 and a few of the other chips over the years. These days a lot of belts need changing because they turn hard or rot eventually.
A broken drive would also be a good candidate for holding a FloppyEMU -- that project has gotten a lot of attention here on AppleFritter...
But swapping with another board works, how can the head be bad?
So it is....I had forgotten.
If you've swapped out all the logic and amplifier chips, then let's see where else the issue could be.
Here's the schematic for the analog board.
disk001_1.jpeg
disk002.jpeg
The R/W head is connected via two 1N4148 diodes to the CA3146 chip (for writing) and the MC3470 chip (for reading).
Maybe check first that there are no cold solder joints on the read/write head connector. Next maybe check the circuitry around the MC3470.
Just a thought...better to look at the schematic than to brute-force the repair by replacing everything on the board.
You said that the 3470 chip was bad - something killed it.
Was it damaged because you connected the ribbon cable off by one pin? If so can you recreate that connection to see where the +5V and +12V may have been directed? And then let's see what else may have been killed in the process.