Trying to fix Mikro's wrecked TT board

[HigashiJun]

Love it !

:D

[rubber_jonnie]

hmm.png


:coffee:

Fantastic scope, would love a small CRT type scope 😁

Great work on the TT BTW 👍

[dml]

(thanks!)

Good news.... the least-dead of my faulty scopes - the Philips/Fluke PM3392 - is working again from this morning.

Interesting CPU/ASIC/FPGA blob inside that thing - has passives on top of the ceramic? Anyway the trigger level can be moved now so I can investigate things properly again.

trig.png

inside.png

[stephen_usher]

:dualthumbup:

[dml]

Quck update on stuffs...

I had recently been quite busy building/repairing machines for some forum members and did not make any progress on my own things for a while. That and a ton of work stuff going on and family birthdays coming up soon.

This is how the repair-conveyor-belt was looking in my kitchen area around easter time! (no empty cases there!)

repairs.jpg

(that didn't quite upload in the same orientation it views here :/ )

...anyway I'm nearly done with all of that for now and my scope is back up and running so I'm hoping to return to this in the next week or two and figure out what's going on with the CPU board.

I also need to do some work on three or four of my own machines, somewhere in between :roll:


...I should add that Exxos shop has been a [MegaS]ignifica[T] source for needed bits and pieces in repair-a-thons!

[exxos]

(that didn't quite upload in the same orientation it views here :/ )

There's a rotate icon that hen you upload images with precise to get them in the right orientation :)

viewtopic.php?p=86684#p86684

[CiH]

I think the third from the right (top - edited,) might well be my CT60 :D

I spotted the CF card.

[dml]

I think the third from the right might well be my CT60 :D

eagle eyes :p

[dml]

There's a rotate icon that hen you upload images with precise to get them in the right orientation :)

I was wondering about that but couldn't see it - thanks!

[dml]

So I came back to this today with the scope and had a poke around.

First I made sure the machine boots @16MHz without the CPU board, just a 68030 plugged into the mainboard.

With the CPU board installed, black screen.

So I scoped out the oscillator wire & pinheader on the CPU board to find the correct orientation and plugged it all together. I see 32MHz on the pinheader on the back of the CPU board (back facing upwards, when installed).

Traced this to a 7404 buffer, still seeing 32MHz on the output from the buffer. After that it gets lost in a maze of 7474 flip-flops which I have no plans to manually debug right now (!) I did scope out all 4 of the 7404 buffers being used and they are all inverting something (the last two are unused).

I noticed from the Atari service info, a version of this CPU board circuit is visible on the main schematic for rev1. It shows pin 12 on the second custom PAL goes to the CPU CLK-in pin and nowhere else. Confirmed 32MHz on that output, at least. The other PAL is outputting 16MHz from the same pin 12, which I guess is for the mainboard.

One of the PALs is managing a lot of bus signals so while its a good thing to be seeing 32MHz to the CPU and 16MHz divided for other bits, it doesn't necessarily mean the PALs are ok...

So... hmmmm. :shrug:

I'm not really sure how the 16MHz clock is being managed - if its being taken from the mainboard and just known to line up with the 32MHz clock on the CPU board (since the mainboard clock was divided from that) or if the CPU board is dividing it and shoving it back to the mainboard - which would suggest maybe a jumper somewhere would need moved... which could explain something like this.

Not sure what to do next - don't really want to remove the CPU and put a socket because it makes the board higher and it's going to be difficult getting a memory board on top of it even without that. Removing the socket again after testing will damage the socket. Also don't want to change the PALs without more evidence they are damaged.

The 7474s could be swapped but they are SMD and close together. Also no evidence yet any of them are damaged.

Will think about it a bit more, maybe find something else to probe, maybe with 2 channels. Maybe look at the HALT/BERR signals etc....