-
Hello MLAers! We've re-enabled auto-approval for accounts. If you are still waiting on account approval, please check this thread for more information.
SE/30 Not Recognizing Disks In Internally-Connected Drives
- Thread starter Turaiel
- Start date
When you own another Mac SE you could try to compare the resistance of each FDD connector pin to the ground between the good and the faulty boards.
If you multimeter has a diode test mode: red probe on ground, black probe on each pin of the FDD connector joints. Otherwise, test in resistance mode.
If there is a problem in the logic board's the circuitry you'll get a notable difference...
That will only tell you so much, of actually very little.
Only thing that is good for is finding huge discrepancies and/or direct shorts.
Problem is, the semiconductors are never the same from chip to chip, transistor to transistor. There are manufacturing variances, die variances, etc.
Thats why one transistor might read .561 but the next one reads .512 and another one reads .608 But they are all 2N3904s from the same batch.
This is a small trap to look out for.
Only thing that is good for is finding huge discrepancies and/or direct shorts.
Problem is, the semiconductors are never the same from chip to chip, transistor to transistor. There are manufacturing variances, die variances, etc.
Thats why one transistor might read .561 but the next one reads .512 and another one reads .608 But they are all 2N3904s from the same batch.
This is a small trap to look out for.
Last edited by a moderator:
I agree with you that this kind of measure is very coarse. Anyway, it's one of those quick troubleshooting techniques helping to rule out reasonably simple issues like missing contacts or shorted traces. Any other issues would require attaching an oscilloscope to the board and do a complex logic analysis in order to identify failing circuitry components. That's clearly beyond the skills of the average DIY Macintosh hobbyist...
I'd also check the voltages on the drive board for sure, both +5V and +12V rails. It should be definitely done under load, i.e. the drive need to be connected to the logic board.
For pin position and numbering, you can refer to this page.
+5V rail -- pin 11
+12V rail -- pins 13,15,17 and 19
GND -- pins 1,3,5 and 7
For pin position and numbering, you can refer to this page.
+5V rail -- pin 11
+12V rail -- pins 13,15,17 and 19
GND -- pins 1,3,5 and 7
Last edited by a moderator:
Oops! It looks like I've posted a link to the wrong page. Sorry!
This link shows a pin diagram for the IDC 20 male connector.
I just got a chance to check the voltages here. On both my SE/30 (issues) and SE (known good), pins 13, 15, 17, and 19 are measuring around -12V with pin 11 measuring between -7 and -7.6. You mentioned they should be +12 and +5, so the reversed polarity seems a bit weird to me.
Last edited by a moderator:
13, 15, 17, 19 are all +12V
9, 11 is 5V
Not sure how your getting negative voltages unless you have your meter wired wrong.
9, 11 is 5V
Not sure how your getting negative voltages unless you have your meter wired wrong.
The voltages are definitely reading negative, unless for some reason the red probe is supposed to go on the ground pins. Pin 9 is measuring around -7.5V. Something of note: pin 11, which was reading -7ish V yesterday is now 0V (on both machines). The machine which was previously working can no longer read disks. The SE/30 also powered off unexpectedly while I was testing and refused to turn back on until I removed the power from the PSU for a few seconds.
Last edited by a moderator:
As an update, neither floppy drive on my SE/30 is functioning now, including the external. The external now will not even power on. On top of that, I now get a "bus error" when I try to shut down the machine. The restart button on the dialog just causes it to do the same thing, and the interrupt button on the programmer's key just cases an "unserviceable interrupt" error.
These symptoms were not present prior to my voltage testing. I hope I didn't fry anything...
These symptoms were not present prior to my voltage testing. I hope I didn't fry anything...
Last edited by a moderator:
Hello again,
It's been a while since I updated this thread. I've decided to pick up this project again but I'm still stuck in the same place I was in September. That is, the machine bombs if I try to shut down, restart, or press the interrupt button. No floppy port is functioning either, including external. It's possible that back when I was testing voltages out of the floppy connector, I touched the data and power leads together with my probe. Is my SWIM perhaps damaged, and more importantly, is this recoverable? Also, any ideas on the wrong voltages appearing on the board?
At this point I've put so much time and money into reviving the machine that I don't want to give up on it, but the issues may have exceeded my skill level at this point.
Thanks.
It's been a while since I updated this thread. I've decided to pick up this project again but I'm still stuck in the same place I was in September. That is, the machine bombs if I try to shut down, restart, or press the interrupt button. No floppy port is functioning either, including external. It's possible that back when I was testing voltages out of the floppy connector, I touched the data and power leads together with my probe. Is my SWIM perhaps damaged, and more importantly, is this recoverable? Also, any ideas on the wrong voltages appearing on the board?
At this point I've put so much time and money into reviving the machine that I don't want to give up on it, but the issues may have exceeded my skill level at this point.
Thanks.
