Trying to fix Mikro's wrecked TT board

[mikro]

I wouldn't worry about such stuff right now. If you see a whatever crash due to whatever chips missing, that's already a huge win. One of the first things is video init.

[dml]

I wouldn't worry about such stuff right now. If you see a whatever crash due to whatever chips missing, that's already a huge win. One of the first things is video init.

Yeah you're right - I can make progress without most of this. I was mainly just being patient to not get bogged down in some strangely specific bad luck, such as the initial stack pointer being placed on a faulty RAM chip :) that's exactly the kind of thing that would happen to me and send me in circles for a week :)

(I'm also busy with a few things at once so I'm not quite ready for another deep dive on the board until probably the coming weekend)

[dml]

Quick update on this.

All the DRAM chips test ok, have installed them back on the board.

Have also put most of the 'likely essential' chips back on the board, leaving a few out for now.

Will find a 68030 I can maybe afford to burn (not one of the 50MHz rated ones! :p ) from my boxes of old stuff, which I'm hoping to test directly in the mainboard CPU socket, instead of the daughterboard. Still thinking about this one... if I find a reason in the schematics this could be bad, I'll back away from that idea. It would be nice to confirm the mainboard though before introducing that other board.

Anyway while putting the ICs back, I noticed another socket with a squashed pin - the RTC chip. It probably would have worked but I think I'll change it at the weekend before trying any tests.

Screenshot 2025-04-23 at 20.41.43.png

The DMA and FDC sockets also looked a bit corroded but I'll try cleaning them first.

[dml]

So after going through some boxes of stuff, I found a 68030RC33 with a small dent in the gold cap which works fine at 40MHz in a DFB1X booster.

I think I'll use this one for TT testing.

[rubber_jonnie]

Quick update on this.

All the DRAM chips test ok, have installed them back on the board.

Have also put most of the 'likely essential' chips back on the board, leaving a few out for now.

Will find a 68030 I can maybe afford to burn (not one of the 50MHz rated ones! :p ) from my boxes of old stuff, which I'm hoping to test directly in the mainboard CPU socket, instead of the daughterboard. Still thinking about this one... if I find a reason in the schematics this could be bad, I'll back away from that idea. It would be nice to confirm the mainboard though before introducing that other board.

Anyway while putting the ICs back, I noticed another socket with a squashed pin - the RTC chip. It probably would have worked but I think I'll change it at the weekend before trying any tests.


Screenshot 2025-04-23 at 20.41.43.png

The DMA and FDC sockets also looked a bit corroded but I'll try cleaning them first.

If you have spare sockets it is possible to just replace that one squashed pin, I've done it several times and it saves removing a whole socket.

Just desolder the bad one and make sure it is properly loose, then push it through from the bottom. Drop a new one in, solder it up. Saves a lot of time and reduces the risk of board damage.

[dml]

If you have spare sockets it is possible to just replace that one squashed pin, I've done it several times and it saves removing a whole socket.

I do have spare sockets so I'll probably go that route first. The other pins look ok.

[dml]

Today the TT adventure will resume! :D

I have replaced the bad pin on that socket and added back a known-good RTC for now. Will put the original back later if I get any life out of the main core components.

Leaving the Floppy controller, SCSI controller and SCC out for the first tests.

[dml]

The RTC mini sub-saga...

Lifted out the bad pin....

Screenshot 2025-04-26 at 12.26.50.png

Screenshot 2025-04-26 at 12.27.04.png

Fitted a new pin. Like nothing was ever wrong :) not suspicious at all!

Screenshot 2025-04-26 at 12.27.35.png

Helping out as always...

Screenshot 2025-04-26 at 12.27.58.png

New RTC in the socket.

Screenshot 2025-04-26 at 12.28.30.png

Next is the fun part - testing!

[dml]

So I have repopulated the board with a mixture of original ICs (which I marked) and some known-good ones, for things like the MFPs, which I have here and would be extra annoying to trace if they were faulty.

That's another reason I wanted to be sure the DRAMs were good enough to not be pulling bus lines down when reinserted.

Screenshot 2025-04-26 at 12.34.52.png

A few secondary ICs were left out for now. Will focus on trying to get a video signal at least and then move to the secondary bits and pieces.

I decided to go ahead and fit a known-good 030 CPU directly onto the mainboard. A slightly dented, suspicious looking one I had in a junk box - but which worked fine when tested in a Falcon last week.

In order to avoid that thing getting permanently wedged into the PGA socket, I raised it slightly on cocktail sticks. The fit wasn't firm enough so I swapped those for slightly thinner pieces of PLA filament. It's firmly on the board now and shouldn't be a nightmare to get back out later on.

Screenshot 2025-04-26 at 12.41.05.png

[dml]

Well, with 5V applied to the main rail and current-limited to 1.6A I get a black screen ...but it's dropping to 4V so I'll raise it to 2.1A. Any more than that seems unlikely to be ok.

.......


.....it's now drawing about 1.8-2A and is self-limiting and I still have a black screen - but the monitor did glitch briefly this time and seemingly detected a refresh signal. Chips are cool or just warmish, seems normal.

......

Will try messing with the reset & reset circuit next - then time for diagnostics.