128k MoBo, garbled video and chime with Sad Mac

[Macdrone]

I put good roms on the board and it didn't change anything, but that was before the chips were changed.

 

[TheMacGuy]

Ok, I'll have to try that out either tomorrow or over the weekend. I should have time this weekend so I can do some diagnosing.

 

[TheMacGuy]

I made a video of the problem which can be viewed

.
When I had the 128k ROM in, it threw an error of 04E925. I slapped the 512kE (Plus) ROMs in, and the error code changed; 03E925. The second digit changed, the others stayed the same.

04=failed Mod3

03=failed byte write

And all of the times I rebooted it, the last 4 digits always stayed the same, E925. Could this mean there is a problem with the ROM and the RAM (or RAM decoder chip)?

 

[uniserver]

i guess is the ram its self.

 

[Macdrone]

I had the same outcome you did with swapping roms. That's why I thought some other chip bit the dust. Interesting, maybe we are getting somewhere with this idea. if its not the roms, and not the ram what else is at boot? VLSI chip? Ram decoder?

McD any way to swap one of those off a plus board to try?

 

[mcdermd]

I have replaced half the chips on the board with no change. Coincidentally, I did not swap the ROMs. I have another 128 K/512 K ROM set I could stick in there for giggles.

 

[uniserver]

really would be nice to find a common denominator!

 

[Macdrone]

plus roms from a plus board I gave you should work, or were they all SE boards? When I did it just the number changed like the other person with the 128 issue. It changed the 4 to a 3. 3 still listed as a memory issue. So whatever other chip is a memory checker or video ram deal is what I am suggesting. Whatever those two chips are.

 

[techknight]

Or one of the custom ICs is bad. Or, eroded trace.

 

[TheMacGuy]

So I was looking at uniserver's thread about un-upgrading a Plus upgraded 128k when I noticed something different between his board and mine:

[attachment=0]IMG_0284.jpg[/attachment]

On his board, spot D-14 is empty, mine however does with the markings of:

TRW

8413

810-1-222G

Could this mean anything? I know this board was a NOS service part, maybe something was supposed to be removed before usage?

 

[Macdrone]

On all my 128 boards have that bridged piece at D14 like your talking about. Only the original board that McD is attempting to do something with has the same problem as you. My other boards are "upgraded" to 512 but still have that TRW part.

I still have a hunch its the video chip, as it accesses ram and probably wont/cant boot if its rotted. That would explain the video and the fact it reports ram errors. Just a hunch, its beyond me that's why I gave it to someone wayyyyyyy better than me.