Mac SE 800k with very strange startup screen (no chessboard but strange intensiv activity)

[stansteph54]

Dear all,

I’m the happy owner of a Macintosh SE M5011 first version with the 800k floppy and internal 20SC which luckily badged as well at its back.

Unfortunately I’m not able to have it booting despite of trying different ram simms combinations that were tested well on my other SE Fdhd.
Also different Analog board were tried including the working one the FDHD
No chime at startup unfortunately.




Here are 2 videos of that startup screen which is anyway changing when I push the reset button on the side of the motherboard.

The screen isn’t frozen compared to chessboard issues, there are kind of speedy activities.

Here is the 2nd video with reset button effect. it also makes a slight tic sound in the speaker when pushed (see also last 2nd picture which is with button pushed ).

R35 was cut, R36 is empty.
I did resolder R35 in order to try some 4*256ko configuration but anyway.. same startup screen.
Yesterday, I re socketed the Rom and IWM chips and deOxited all socketed chips without any positive effect, unfortunately

Any idea what could be the issue ?



Many thanks beforehand for your time spent in reading and helping me.





PS : Also, I found this link which is interesting relatively to HALT and RESET mistakes/short on the cPU caused by a wrong sound chip ?

Mac SE Checkerboard pattern after cleaning battery leak​

Hi, Just bought Macintosh Plus and Macintosh SE 1/40 on local market. Plus works (but I need a keyboard ), SE was known to be broken / showing only horizontal dotted line (not solid). After disassembly I saw this mess: After touching battery it got even worse it was still half-full of it's...

What I found is that both RESET and HALT lines are driven LOW (active) and for some reason they are both short. On working computer I applied 5V to them... and got sad mac face!

So I desoldered audio chip again, and tried resetting CPU by hand (this time on correct connector). And I got usual background!
After soldering ADB chip, got mouse and no system disk indicator, with disk connected it was hanging somewhere during MacOS boot - I added SCC back and it booted.

Sound UC is broken, at least RESET line part. It's LOW all the time. I isolated this single pin and after resetting CPU everything boots, and works, including sound.
I checked whole reset and power circuit, everything seems to be right. Schematics of this part is 1:1 from Mac Plus, just elements IDs are different.

 

[GiGaBiTe]

If you swapped the analog board, did you also swap the power supply? Those PSUs are notorious for capacitor leakage that cause voltage issues. I would verify all of the voltages are correct.

As for the memory, are you installing the modules correctly? The 68000 bus is 16 bits, and requires two 30 pin SIMMs to make up the bus. The memory modules need to be side by side to make up a single bank, not up and down. The jumpers also need to be correct as you've surmised.

With the jail bars on the screen, it almost looks like you have bus issues, like one of the data lines has a problem. You may have to break out the scope or logic analyzer.