Please help with weird short simasimac problem

[tjempeng]

Hi All,

I hope someone can help me with a weird issue that I have with my Mac SE/30.
I am having this mac for about 30 years (but not used for 30 years, it has been in the addict all that time) and I just recapped the Analog board, Power Supply and Logic board.
But with the logic board I made a terrible mistake by soldering the tantalum caps the wrong way and so when I tested the Mac, it turned on and chimed immediatly which is normal, and then the screen showed normal with the arrow pointer so I was waiting for the question mark icon and at the time it should apear a small explosion and smoke came from the logic board.
I immedately turned the Mac off and saw that C7 was exploded. A search on google I learned that all the tantalum caps where soldered in the opposite way, because I thaught the stripe on it was the marker for the - pole, but it turned out that for tantalum it is the mark for the +.
I ordered some new 47uF tantalum, this time from AliExpress and surpisingly these where delivired faster then the ones I got from the US (I'm in Europe).
So I replaced the exploded cap and resoldered the rest of the tantalum caps in their correct possition this time.
But when I turn on the Mac now, there is no chime it shows me first the screen as you would see with the simasimac issue, and when I wait for about 10 seconds, the chime sounds come and the screen turns normal with the arrow pointer and later with the question mark.
When connecting the blue scsi I can even boot from it.
But the startup is not normal anymore like it was before. Every time it shows the simasimac first for about 10 seconds then the chime and normal boot.

Anyone any ideas what might causing this ? Could this be caused by the cheap AliExpress caps ? Thats the first thing that comes to my mind.
Or is some other component probably damaged by the first mistake placing the tantalums in the wrong possition ?
I hope someone has encountered this weird behaviour before and can point me in the right directions.

 

[smrieck511]

I haven't had a similar experience, but the first things to check would be to make sure all of your solder connections are clean and you aren't possibly bridging anything on any capacitor.

sounds like something is delaying 10 seconds to address something else on the board… once it finds it, things are OK but for those 10 seconds, simasimac.

on my se/30, on a reboot, I sometimes see a simasimac for a split second before it chimes and boots. Always assumed that this is the time it takes for the processor to see the ram. If I had to guess, and believe me, it's a guess, I'm not an expert, I would say that there is something delaying the processor seeing the ram.

Since C7 exploded, there could be residual stuff on the board. I assume you cleaned it very carefully after but maybe something got between a couple pins. Since that is the cap that is near the graphics chips, be especially careful and certain that those look good.

Also, it's usually a good idea to try different ram configuarations and or swap out the rom if you have another. at least to make sure there's no issue there.

Good luck.

 

[tjempeng]

Thank you for the feedback.
I figured out what was wrong and fixed it !
It was another booboo from my side offcourse, here is what happened.
Like I said after the blown out cap, I reseated all the tantalum caps in the correct position again, but then I remembered while doing that I also checked and measured the caps with my multimeter to see if they where ok.
And then I found one that showed (what I thought) with an odd value. I was expecting around th 47uF. So I replaced that cap as well together with the blown one, both 47uF.
It turned out this cap should be 1uF, it is C6.
So after putting back the 1uF and testing, the SE/30 turns on and chimed immediately again and showed the correct display and all is working fine.

Thinking of this, it is obvious that the start-up was slowed because of the bigger capacitor. But I am also thinking that the simasimac pattern is then actually pretty normal but we don't see it, and maybe this pattern is some sort of POST or something ?

Anyways I am very glad this is fixed, now I want to do some more upgrades, the bluescsi v2 is awesome, I wish we had this back in those days

 

[mousehouse]

I think the pattern comes from the display chip reading from uninitialized video memory. How I remember it is that as soon as your hear the chime it means the CPU is running ROM code.

Glad you got it sorted! Enjoy the “second coming of your SE/30” !

 

[halkyardo]

Yes, that's right. If you switch your Mac off and back on quickly enough that the tube doesn't cool down, it'll show a Simasimac-like corrupted version of what it was last displaying for a moment before the CPU comes out of reset and initializes the video RAM.

Glad it's working now! It's an easy mistake to make with those capacitors.