Stacy repair

[Bikerbob]

Hello all,

Trying to get a Stacy up and running for a friend.

Have it apart.

I can power, but all I am getting is a white screen nothing more, no disk access. The battery light on the screen flashes when I turn it off. I hear a positive click as things get power.

The internal PSU above the cpu is putting out 5v and 12v

I have pulled the daughter cards, deoxit the pins, pulled and pushed down the TOS chips again. I have pushed on all the socketed chips.

I assume this is no different than any ST as far as the startup goes. Anyone have a ideas that might be specific to the STacy that I have not looked at?

All caps LOOK ok.. but I have not pulled anything or gotten in with a SCOPE or anthing yet.

James

[derkom]

Any serial port output from the diagnostic cart (set it to regular ST mode)?

There's nothing special about Stacy startup.

[Bikerbob]

I will give that a try next. I do have the exxos diag cart.

James

[Bikerbob]

So the screen went from white to having a yellow box filling the screen.. a few flashes I think.

What is the baud rate for the serial output?

James

[PaulJ]

9600 8N1

[derkom]

So the screen went from white to having a yellow box filling the screen.. a few flashes I think.

FWIW, I had some yellow box output when I was working on tracking down which signals needed switching to build my CPU switcher board for my own Stacy project. Maybe just coincidence, but something to bear in mind if you find yourself scoping out signals down the road. Possibly you've got something not connected up on the CPU properly. Probably it is something different, but maybe just maybe this post will come back in the future and prove handy. ;)

[Bikerbob]

Well the one thing I changed on this machine was how the power switch was wired. I went to JP15 instead of wiring to the DC<>DC board and J2 on the board. The solder joint was breaking and it seemed better to have the switch removable.

now I found I had the wrong cable ( not null) found a converter got it working.

20210412_142305.jpg

no menu just right to this.. so having issues. But at least I am getting output.

I do have a working Stacy that is apart. So I think since the memory is on the daughter card, I will swap the daughter board and see if that helps. If I can at least isolate to the daughter board that would help.

James

[Darklord]

Yep. Those boards can be tricky.

I ordered the 2 megs for 4 megs upgrade swap from Best Electonics at one time and
actually received a 4 meg board that would not show up as anything but 2 megs. I
returned it and Brad sent me a different one that worked fine since.

I also had to do some RAM swapping on one board. I had 80ns and 120ns speeds
mixed.

Very *bad* for the Pak 68/3. :)

[derkom]

Well the one thing I changed on this machine was how the power switch was wired. I went to JP15 instead of wiring to the DC<>DC board and J2 on the board. The solder joint was breaking and it seemed better to have the switch removable.

The power switch should be connected to J15. J2 is the alkaline battery connector.

I do have a working Stacy that is apart. So I think since the memory is on the daughter card, I will swap the daughter board and see if that helps. If I can at least isolate to the daughter board that would help.

Yup, that seems the right move. If the problem doesn't go away, check/reflow the solder connections on U33 (just left of the MMU). I saw very similar diag errors on a Stacy board I was working on last year, and the problem turned out to be a dodgy factory solder job on U33 that had eventually broken under stress.

Other ICs of interest are U21, U22, U23, U24, near the CPU. You can pretty easily trace all of the RAM lines through these, the MMU, and U33, and find any problems. But have a look at U33 first, in case you are seeing the same failure.

[rubber_jonnie]

now I found I had the wrong cable ( not null) found a converter got it working.

no menu just right to this.. so having issues. But at least I am getting output.

I think I replied to this on FB, but the diag cart will behave this way if it can't start, otherwise you'll get the on screen menu for the diagnostics.