SE/SE/30 Power on without logic board?

[sam1729]

Hi all, I'm currently trying to fix up an SE/30, and could do with some help diagnosing the problem.

This machine came to me with simasimac, and a burst Maxell PRAM battery, but after a thorough clean and recap, and a couple of repaired traces, I put the board back in the SE/30, powered it on, and got... nothing. No bong, no image, no fan, no disk activity. 

The behaviour is exactly the same whether the logic board is connected or not, and therein lies my question - is that normal?

I cleaned, and recapped the power supply although admittedly, I made no effort to replace the largest cap (I'd heard they're much less likely to fail, and couldn't find a replacement). Same result. Then, I re-soldered a few joints on the analogue board that looked slightly suspicious under the microscope. No change.

 Am I on a wild-goose chase here, and the problem is still the logic board, or is there also something wrong with the PSU/Analogue board?

What should happen when the SE or SE/30 is powered on without a logic board? 

I haven't been able to find any definitive answer on this, although I feel like there's sometimes an implication that the fan would run, even without the logic board.

Any information, or anecdotes would be welcome.

 

[LaPorta]

This might sound totally absurd, but is the PSU plugged back into the AB? I’ve done that before and was scratching my head for a while.

Also, when you say it came with simasimac, was it doing that when you received it and you were able to power it on at that time, or you never tried to power it on before now? That part I wasn’t clear on.

 

[sam1729]

Yeah, I've plugged the PSU back into the analogue board. Re-soldered the joints for that connector, for good measure.

I was able to see the simasimac with my own eyes after receiving it, although it might be worth noting that the first time I plugged it in, it displayed the simasimac pattern for about 10 seconds, before powering off completely.

I put it down to the corrosion on the board at the time, but I guess that might indicate that there was some analogue board/psu problem from the outset.

 

[LaPorta]

A few photos would be helpful as well. What does the inside of the plastic sheet covering the analog board look like? If there is a burn mark, that could be a clue.

 

[sam1729]

Oh yeah, the logic board was in bad shape, no doubt about it

https://imgur.com/a/iQuuWPT (Pictures are before any cleaning/repair)

To be honest, I've almost resigned myself to trying to get another board, and using this one for parts, but I'd like to chase down the issue (if any?) with the PSU/AB first. 

 

[LaPorta]

Wow, that is sad...not sure if you can come back from a hold basically burned through the thing. I was luckier with my SE in the sense of that the battery literally exploded and showered the frame and the board, but it didn't sit in the one spot like yours. I'm sorry to see that.

As far as the AB, I'd like to see pictures of that to see what is going on.

 

[sam1729]

Ah, sorry, I read 'plastic sheet' and 'burn mark' and went straight to the burn mark I did have!

https://imgur.com/a/y1JFfDJ
Analogue Board looks decent, no tell-tale residue on front, or back. No real scorching on the shield, the dark marks that are there rub away easily with a finger. 

Flyback has seen better days, though. 

 

[LaPorta]

First thing I’d do then is switch on the PSU with its end disconnected. Use your multimeter to probe out and see if the pin that should supply 12V supplies 12V, etc. if not, it’s your PSU and you can narrow down the problem to there

 

[sam1729]

Yeah, looks like it must be the PSU, unless I need to bridge anything on the connector to get it pumping.

Measured between Yellow, and Black per the schematics, and got something that read about as high as 6V before sliding down. Guess I'll need to do a bit more digging there.

As I was doing this, though, I noticed something I hadn't seen before, the PSU connector seems to have a bit of corrosion - but only on the ground pins?
https://imgur.com/a/6Utat7e
It's so distinct, that I can't help but think it's not a coincidence.