exxos's Atari, Amiga & retro forum

stween wrote: 18 Dec 2022 20:27 A quick check between festive tasks: with no glue, no CPU, address fc0000: DTACK is low.

Check DTACK resistance to 0v (with power off of course) something doesn't seem right there.

exxos wrote: 18 Dec 2022 21:42

stween wrote: 18 Dec 2022 20:27 A quick check between festive tasks: with no glue, no CPU, address fc0000: DTACK is low.

Check DTACK resistance to 0v (with power off of course) something doesn't seem right there.

Looks like 1k resistance to ground.

stween wrote: 19 Dec 2022 03:47 Looks like 1k resistance to ground.

Doesn't sound right. Should be open circuit really.

Not sure without looking , but remove the other chips which have dtack on them. Likely MMU, MFP, etc

exxos wrote: 19 Dec 2022 04:32

stween wrote: 19 Dec 2022 03:47 Looks like 1k resistance to ground.

Doesn't sound right. Should be open circuit really.

Not sure without looking , but remove the other chips which have dtack on them. Likely MMU, MFP, etc

Mmm. Okay, I removed all chips I see DTACK on. I still see 1k to ground.

Not sure if this is relevant:

Decided to go fishing and look at resistance on adjacent pins to DTACK on each socket. Figured sharing the same path might be indicative of ... something. What I did so far is NOT AT ALL thorough because I didn't map the top of the socket to the grid layout on the back, but looking at immediately adjacent pins on the top of the sockets didn't show the same resistance as DTACK on any socket, except on the GLUE.

On GLUE: pins 28 through 33 show the same 1k resistance. That's: RDY, VPA, BERR, DTACK, IPL1, IPL2.

What does DTACK measure to 5v then ?

EDIT

With no chips on the board and unrelated signals.. I wonder if your aware of this fix ? viewtopic.php?f=89&t=5256

You could remove the inductors and see if those pins go high then...


There should be noting at all on DTACK.. Basically blitter, CPU, MMu,GLUE,68K sockets, MFP. 3.3V buffers.


Aside from RDY which isn't on the CPU.. The others are unrelated aside from the 3.3V buffers. and even then different ones!

exxos wrote: 20 Dec 2022 05:07 What does DTACK measure to 5v then ?

Just under 1k to 5V. (To ground is actually just over, like 1.1k. To 5V, it's 0.9k.)

DTACK is open circuit to ground from the 3.3V expansion slots; I figured those are separated off from the rest of the board anyway so forgot to mention.

With no chips on the board and unrelated signals.. I wonder if your aware of this fix ? viewtopic.php?f=89&t=5256

I have definitely never seen this page before :) Replacing those might be beyond me and my tools though!

stween wrote: 20 Dec 2022 13:38 I have definitely never seen this page before :) Replacing those might be beyond me and my tools though!

Just blob them with a solder blob and they will ease off.. clean off the pads with braid. Not sure how the buffers will react, but cant make things any worse. In theory just the 3.3V bus won't work, but that's not important right now anyway.

exxos wrote: 20 Dec 2022 13:50

stween wrote: 20 Dec 2022 13:38 I have definitely never seen this page before :) Replacing those might be beyond me and my tools though!

Just blob them with a solder blob and they will ease off.. clean off the pads with braid. Not sure how the buffers will react, but cant make things any worse. In theory just the 3.3V bus won't work, but that's not important right now anyway.

Okay. Specifically, just the highlighted resistor-shaped packages to the top left of each of the larger chips? (the bus converters?)

I can futz with it this evening. If not this evening ... then I'll probably have to park it until mid January/early February!

stween wrote: 20 Dec 2022 15:06 Okay. Specifically, just the highlighted resistor-shaped packages to the top left of each of the larger chips? (the bus converters?)

I removed them in this post.

viewtopic.php?p=87527#p87527

stween wrote: 20 Dec 2022 15:06 I can futz with it this evening. If not this evening ... then I'll probably have to park it until mid January/early February!

You cannot keep us in suspense that long :lol: :chairsmack:

Though if it is not those bus converters then I give up :lol: :roll:

exxos wrote: 20 Dec 2022 15:17

stween wrote: 20 Dec 2022 15:06 Okay. Specifically, just the highlighted resistor-shaped packages to the top left of each of the larger chips? (the bus converters?)

I removed them in this post.

viewtopic.php?p=87527#p87527

Useful, thanks!

stween wrote: 20 Dec 2022 15:06 I can futz with it this evening. If not this evening ... then I'll probably have to park it until mid January/early February!

You cannot keep us in suspense that long :lol: :chairsmack:

Though if it is not those bus converters then I give up :lol: :roll:

haha I'll be away from home, that's the real problem! I probably have time tonight. I've just got the fear about components so small!