68kMLA Classic Interface

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SE/30 Diagnosis
Posted by: Jon183 on 2018-03-03 05:37:51 Hi everyone, I have an SE/30 which was reported to have a working PSU and the logic board had its caps pulled off ready for new ones. The board has had its video ROM chip, RAM and ROM SIMM reseated, board was washed and new caps have been installed. I have checked the continuity of all the caps and they appear to be connected to the board properly. Also checked Fuse 1-3 and they are OK. When turned on, fan runs, HDD seems to make a starting noise but screen stays off and chime doesn't happen. The machine does appear to react to the reset button though, and when turned on, the connected keyboard LEDs flash once. PSU cable on the logic board end was used to test PSU, 5v, 12v, -12v and -5v tested fine. Wondering what I should do, I dont know what chips and traces need testing for this sort of issue.
Posted by: beachycove on 2018-03-10 07:03:14 Do you have other RAM to try in the machine? I don't think it will take 2mb cards, for instance. There is also need to have it in specific RAM banks, depending on the configuration. Other than that, the symptoms are pretty much consistent with bad caps, or an improperly terminated hard drive, or a short in something like the floppy. You could try disconnecting the HD cable and see if you get a screen, recheck termination and reconnect, change the scsi cable, and definitely check the RAM. I had the floppy short one time; turns out the drive must have been dropped, as once removed, I could see that the cage was dented and the lower circuit board was cracked -- the upshot being that the machine (an SE?) would not boot. Took me a while to figure that one out, as the crack was well hidden when the machine was assembled, and as you tend not to see things you aren't looking for.
Posted by: Jon183 on 2018-03-12 01:51:25 Do you have other RAM to try in the machine? I don't think it will take 2mb cards, for instance. There is also need to have it in specific RAM banks, depending on the configuration. Other than that, the symptoms are pretty much consistent with bad caps, or an improperly terminated hard drive, or a short in something like the floppy. You could try disconnecting the HD cable and see if you get a screen, recheck termination and reconnect, change the scsi cable, and definitely check the RAM. I had the floppy short one time; turns out the drive must have been dropped, as once removed, I could see that the cage was dented and the lower circuit board was cracked -- the upshot being that the machine (an SE?) would not boot. Took me a while to figure that one out, as the crack was well hidden when the machine was assembled, and as you tend not to see things you aren't looking for. Thanks for the reply, sadly, the machine with working sticks and no floppy/hdd plugged in still gives the same blank screen and no chime.
Posted by: Jon183 on 2018-05-30 18:33:32 UD8 and UE8 have been replaced and still nothing. Planning to try and repair it in late June. Currently have an iron, oscilloscope, some chips like UD8 and UE8 and will get logic probes. Where should I start?
Posted by: superjer2000 on 2018-05-30 20:03:23 I know you said you washed the board but from the pictures the legs of the ics by many of the caps still seem really dirty. Might be worth bathing the board in isopropyl and cleaning the board and the ic pins with a soft bristle toothbrush.
Posted by: MikeatOSX on 2018-05-31 01:28:22 Are you sure you installed new caps? I see many old caps.
Posted by: Jon183 on 2018-05-31 01:31:00 The picture is old, also, the caps are new, board came with no caps at all, I used cheap nichicon ones that look a lot like the originals.
Posted by: Bolle on 2018-05-31 01:40:57 The Sony soundchips look like they got hit by a lot of cap goo. Can see corrosion on both of them I think. If they are bad the SE/30 will never come out of reset when powered on. From the top of my head I am not sure which one of the two is controlling the bus reset. Get the schematics and check what the /BRST line is doing.
Posted by: trag on 2018-05-31 15:05:29 Are those sound chips custom to Apple or are they something purchasable in disguise?
Posted by: Bolle on 2018-05-31 22:14:24 They are custom Apple parts.
Posted by: trag on 2018-06-01 16:07:21 Thanks. I wanted to know because they seem to often take the brunt of capacitor leakage. At heart, they're just D->A converters aren't they? With some extra logic...
Posted by: Bolle on 2018-06-02 00:48:04 Correct. The extra logic does all the reset stuff. One probably could implement standard DACs and some extra logic to handle the reset on a little board that installs instead of the two Sony chips if sources of donor boards have dried up somewhere in the future.
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