Mac SE FDHD issue

[Borgmac]

Hi all of you,
I am new here. Tinker Different was suggested by Bruce Rayne in a Facebook group as a good place to meet people working on vintage Mac, so here I am!
Need help for a Mac SE!
My Mac SE does not want to start anymore. Everything was OK a month ago. I got the startup sound and the fan runs. SCSI drive is rotating. Voltages at the motherboard are OK but it get stuck on this display.

Tried reseating RAM and ROM, same.
According to "Trouble shooting your Macintosh 1992", that means hardware intialization (RAM and ROM I guess) is ok.
I have a lot of corrosion at the connectors, but nothing on the motherboard. I live for a few years next to the sea, very hot & humid environment. I think it is external corrosion.

Caps look ok, no leakage on the board.
Any hint of what to look for?

 

[Branchus]

@Kai Robinson, any ideas? It looks like he's getting the initial grey screen, but not advancing to the cursor.

 

[Kai Robinson]

@Branchus - is this the same problem you had with the ADB controller basically dying and hanging up the machine?

 

[Branchus]

@Kai Robinson, no I was still able to see the cursor, I just couldn't move it.

 

[RetroTheory]

Just wondering, if you turn it on without any scsi drives connected do you eventually get a flashing floppy question mark?

 

[Borgmac]

@Branchus - is this the same problem you had with the ADB controller basically dying and hanging up the machine?

Hi Kay, no, this is another computer

 

[Borgmac]

Just wondering, if you turn it on without any scsi drives connected do you eventually get a flashing floppy question mark?

Thanks for the suggestion but I tried it already without any cable connected except the floppy drive, no floppy question mark. I also tried with hard drive and/or SCSI2SD, internal and external, same issue

 

[Borgmac]

Hi Kay, no, this is another computer

How to check if there is any issue with the ADB?

 

[Kai Robinson]

I've just spotted something in the image you've uploaded - the system has passed all the diagnostics and the low-level initialization (VIA's, SCC) - however, it's not drawing the rounded corners, or showing the pointer.

So, you're getting to at least this line in the ROM's boot sequence:

40048C: PEA $FFE8(A2) ; push gray

But not getting this far:

400490: ToolBox $A8B4 ; _FillRoundRect

My guess would be a problem with ADB controller. In the SE, the ADB controller is a bit-banged implementation derived from the IIgs - based on a PIC 16CR54 MCU. These can go wrong, as @Branchus has discovered previously.

Pull the logic board and double check all the connections from the ADB chip - i'd bet there's a damaged trace, dry joint or something around the ADB MCU.

 

[Borgmac]

I've just spotted something in the image you've uploaded - the system has passed all the diagnostics and the low-level initialization (VIA's, SCC) - however, it's not drawing the rounded corners, or showing the pointer.

So, you're getting to at least this line in the ROM's boot sequence:

40048C: PEA $FFE8(A2) ; push gray

But not getting this far:

400490: ToolBox $A8B4 ; _FillRoundRect

My guess would be a problem with ADB controller. In the SE, the ADB controller is a bit-banged implementation derived from the IIgs - based on a PIC 16CR54 MCU. These can go wrong, as @Branchus has discovered previously.

Pull the logic board and double check all the connections from the ADB chip - i'd bet there's a damaged trace, dry joint or something around the ADB MCU.

Thanks a lot for this detailed information Kai, impressive!
I started already to reflow some solders that I found suspect on the back side of the board. I am going to check tomorrow more carefully everything around ADB chip and traces.

 

[Borgmac]

@Kai Robinson, tested all joints and traces between ADB connector and ADB MCU, cannot find anything suspect but I reflow a couple of them to be sure.
Tested the bus filter, looks ok. I measure the same amount that for a LC which is working properly (0.5 ohms ...)

Made another test, but still the same issue. Voltages around ADB filter looks ok.

I tested also the Q3 transistor. I am not sure if all the data are OK, but the gain is close to 300, the maximum of the 2N9304.

Tomorrow I am going to put back the Q3 and reflow again a couple of things around the ADB chip.
Any other suggestion?
@Branchus how did you realize that your ADB chip was KO?
Thanks for your help.

 

[Branchus]

@Branchus how did you realize that your ADB chip was KO?
Thanks for your help.

I got a little further into the boot sequence and the cursor was actually on the screen, but I couldn't move it and it would hang during startup. I replaced the ADB chip and that fixed it.

 

[Borgmac]

I got a little further into the boot sequence and the cursor was actually on the screen, but I couldn't move it and it would hang during startup. I replaced the ADB chip and that fixed it.

@Branchus Thanks. I guess the only way to replace the ADB chip is to take one from another board?

 

[Branchus]

There are 2 options (that I know of). Either grab one from another SE board, or you can use a 342S0440-B PLCC ADB chip from a Mac Classic, and use this nifty little adapter created by @Kai Robinson.

 

[Borgmac]

Got some progress!
After reflowing again and putting Q3 back, startup with a mouse and only floppy drive connected, I went until floppy with question mark.
I recorded in BLUE voltages values.
Then restart, no more ? floppy.
Voltages changes are in pencil black, in a square.
Restart a few time, no success and then ? floppy again.
I will analyze results of BLUE and BLACK value tomorrow.
If anybody has a an idea, here are the data