Unusual SE/30 problem

[MacGyver]

Hi there,

I got an SE/30 which behaves weird.

On Power up I get the normal gong, black screen, no signs of drive activity on the internal HD, on an inserted boot floppy or an (known good) external floppy.

The CRT doesn't heat and the high voltage to the CRT is missing.

Okay, swap the PSU or analog board, you might say. Guess what I did - I swapped a known good logic board into this SE/30 and the PSU and analog board work just fine, so the problem must be with the logic board. Then I swapped all user changeable parts (ROM etc) of the broken logic board with known-good parts, still no success. Then I washed the board (the way it brought many Classics back to life) but I still have the symptoms mentioned above.

Since there is no high voltage and no CRT heating when the bad logic board is inserted, I believe that this logic board generates no horizontal sweep signal to the analog board. And it seems that it hangs somewhere in the ROM process, since it would boot otherwise or show any signs of drive activity.

I'd really like to rescue this SE/30. Tools for soldering SMT components are available to me, the only question is: What component is likely to be bad? Tough question. Maybe I could find the bad component if I had a schematic of the logic board at hand, but it seems there is no schematic of the SE/30 logic board available on the net.

Any ideas?

Thanks a lot,

MacGuyver

 

[MacGyver]

Oh, i have to correct myself.

I do get CRT heating with the broken logic board, but the high voltage is missing.

I also just tried the reset button, which gives me a nice gong everytime I push it. I also get the usual sad mac sound if I push the NMI button directly after pushing the reset button.

Does anybody have experience with this kind of fault? Could it still be bad caps and the dishwasher trick just didn't do it this time?

 

[tt]

Oh MacGyver, we're sure you'll find a solution in your usual bag of tricks, such as using an egg, a shoelace or a toothpick to fix that logic board... your against using guns, but you aren't adverse to using rocket launchers...why MacGyver, why?

 

[MacGyver]

Ah, that's it... I forgot to try bubblegum. The only question is - where should I stick it to? By the way, eggs won't work. The CPU doesn't get hot enough to fry an egg. This trick is reserved for modern CPUs. }

I fact I'm not even a fan of MacGuyver. Maybe I watched about 5 episodes when I was a kid, but that's it. It was simply the first nickname that came to mind when I registered myself in this forum

And there's one more thing (no pun intended)... This is my first thread in this forum and I forgot to introduce myself. I'm from central Germany (please excuse my bad English... ), 24 years old. My computer carreer began with an //e I acquired when I was 12. I got my first Macintosh, a Macintosh Classic, around 2001. Since then I started collecting vintage Macs 'unintentionally' by always searching for newer, faster Macs I could afford (remember my age back then, so they were usually pretty old). My upgrade path looked like this: LC, IIci, Performa 6100, 5200, 8600 with G3 Upgrade, G4 Quicksilver, G4 MDD. About in 2007 I started to collect Macs intentionally .

I like the early and/or less common Apple computers the most, for example the Apple /// or the Lisa. Especially I'm interested in repairing broken machines - There's hardly anything more satisfying than getting a vintage piece of technology running again, so I spend a great amount of time fixing broken machines. I also collect and save rare pieces of software and documentation for Apple machines. Apart from collecting vintage Apple equipment I spend a lot of time driving, repairing and restoring vintage cars and motorcycles. It all boils down to vintage technology.

Now you know a little bit more about me. Any ideas regarding my half-dead SE/30 are highly appreciated ;D

Thanks a lot!

 

[beachycove]

The obvious thing would be to replace the logic board's capacitors. Washing a board (I do this too) can enable a machine to boot by removing electrolytic residue, but it cannot resolve the underlying electrical problems caused by original parts that just no longer work.

The next thing would be to experiment with different RAM, and in the first instance, I think I would try just one bank, as the problem could be something like a bad memory slot. I also find my SE/30s to be very sensitive about RAM.

 

[wally]

Make sure no capacitor goo leakage from C7, C8, C9, C10 has spread and caused corrosion or shorts. If 20 pin PAL UI6 is socketed, note its direction, carefully remove it, and inspect all pins and socket metal for corrosion under magnification. Especially pin 18. Clean as required. Carefully replace. You may wish to do same for all other 20 pin PALs as sockets do become intermittent.

Turn board over. Look for R24 near J12 pin 10. Verify 75 ohms and continuity to UI6 pin 18, J12 pin 10. Locate all long black bar shaped parts designated by L followed by one or two digits. Using an ohmmeter, verify all these individual ferrite decoupling chokes have end to end continuity, and are not cracked.

 

[MacGyver]

Good morning! (8 AM over here)

I tried every combination of RAM, RAM sockets etc. that made any sense and also swapped the RAM with known-good modules from a working SE/30. No success.

Wally:

Sadly, only the CPU is socketed (and the video rom etc. of course). I already thoroughly cleaned all contacts when I washed the board.

It seems that there has been minor leakage from various caps (including C7, C8, C9, C10). You can tell by looking at the solder points surrounding the caps, they appear slightly dull. However, there is no serious corrosion and it doesn't look nearly as bad as some other logic boards I was able to bring back to life by washing/recapping them.

R24 has 75 Ohms, continuity to UI6 Pin 18 and J12 Pin 10 is there. The decoupling chokes are all fine

Do you have an opinion on this specific problem possibly being caused by the old caps? Every mac with bad logic board caps I've seen before at least displayed anything (horizontal/vertical bars, sad mac, etc.) and didn't chime or had the sad chime, so I'm afraid that swapping caps will not resolve the problem here.

If there's no other option, I'll see if I still have enough caps in stock to fully recap the board. Maybe it will magically come back to life...

Thanks a lot

 

[wally]

UI6 produces the missing signal, and also the main clock to the 68030. Either it is faulty, or missing an input signal, or the output is shorted (possibly by corrosion, but it is far from the capacitors). A scope or even better a logic analyzer would tell the story. The solder pads being dull but no serious corrosion makes shorts seem less likely, unless there are some directly under a cap causing unseen evil. I'm feeling like you-capacitor problems are possible here, but a long shot for taking out horizontal sync. Capacitor goo might be taking out some other signals and inhibiting proper booting, however. Especially if corrosion has added or deleted some connections under the SCSI and/or floppy controllers UI12, UJ11.

If you have a parts donor board you could replace UI6. Or there's also a trick test where before replacing, you carefully piggyback a good chip over the suspected bad one and compare outputs. In the case of piggybacking UI6, all pins need to touch except lift all outputs 12 thru 19 inclusive (bend them out to slightly clear or use tape on the lower DIP) and use a scope to see if there is identical output activity on most and in particular look for horizontal sync output on pin 18.

 

[MacGyver]

Hey,

I just desoldered all the electrolytic caps with a hot air reflow tool. No lifted pads, everything looks good. I'm quite sure that there's no damage to the copper traces and interlayer connections surrounding the caps. The board has been washed and dried twice now, one run with a mild alkaline (?) cleaning agent followed by tap water, second run with isopropanol to draw out any moisture left.

I found out that I just ran out of "classic mac recapping tantalums". Then I was about to solder in the tantalum caps I still had in stock from a camcorder repair, when I suddenly noticed that they were 47µF, but only 10V

. I'll order the correct tantalum caps tomorrow, so recapping has to wait .

When the caps have arrived, I'll warm up my trusty old Tektronix scope and I'll poke around the UI6 IC. But let's keep our fingers crossed that the SE/30 will fire right up with new caps and further troubleshooting won't be necessary. I don't think so, but we'll see .

Wally, thanks a lot for your very detailled support so far! Sadly (or not so sadly), my other SE/30s are alive and kicking, thanks to recapping, so I'll have trouble finding a replacement part if UI6 is the root of all evil. But knowing the fault would give me the opportunity to fix the fault in the future when I get my hands on a replacement part.

Greetings from Germany!

 

[JDW]

I just desoldered all the electrolytic caps with a hot air reflow tool. No lifted pads...

Please show us a photo of your hot air reflow tool.

 

[MacGyver]

Hi,

to be correct, it is a simple and cheap hot air rework tool made by "Aoyue", but does an surprisingly excellent job. I practiced using it with a IIci board which was beyond repair (exploded PRAM battery) and had no problem removing even big PLCC ICs with the included special jets. For the SMD capacitors I use an ordinary small size straight jet which you can see on the photo:

I bought it used (maybe once? there was no discoloration of the jets) for 30€ if I remember correctly. As I understand, you can get these new for around 80€ with only 2 or 3 simple jets. Mine came with a whole bunch of jets for various IC sizes.

 

[techknight]

This EXACT thing is what ive been harping about all along. I have a similar rework station that i use to remove caps.