exxos's Atari, Amiga & retro forum

exxos wrote: 01 Oct 2017 18:31 Lift one end of R470 and see if GCLK comes back up ? Also check CCLK both sides of C427.. and R489.

Number_Nine wrote: 01 Oct 2017 19:52 I've tried removing R470, and after removing - input of R489 (it's R469, I believe though) 4.6V, after R469 - 2.6V, on input of C427 it's 2.6V and on the side connected to pin 17 of 1377 it's same 5V.

exxos wrote: 01 Oct 2017 21:36

Number_Nine wrote: 01 Oct 2017 19:52 I've tried removing R470, and after removing - input of R489 (it's R469, I believe though) 4.6V, after R469 - 2.6V, on input of C427 it's 2.6V and on the side connected to pin 17 of 1377 it's same 5V.

So just a flat DC voltage there, no signal ?

So to recap, input to R469 has the clock, but the output does not ?

Also with the IC end of R469 lifted, do you still see CCLK on both sides of the resistor ?

Number_Nine wrote: 01 Oct 2017 22:00
Yep, no signal, I was blaming that from the beginning, but then I've checked on a good Atari and that was the same flat signal.
Both input and output of R469 have clock, output has it much weaker (~300mV), though, regardless of the IC side soldered or desoldered.
On schematics R469 is 5.0K, but on the board it's almost 6K, but I don't think that matters as I've tried shorting it out and got no difference.

And what's more interesting - it's all absolutely the same on my second Atari.

exxos wrote: 01 Oct 2017 21:53 This is what I get "left side input" of R469..

c1.png

3V p-p. Bias 0v.

Output side of R469 (IC side).

c2.png

about 0.2V p-p (200mV) with 0.4V (400mv ). DC offset.

Number_Nine wrote: 01 Oct 2017 22:09 Output C427:

exxos wrote: 01 Oct 2017 22:07

Number_Nine wrote: 01 Oct 2017 22:00
Yep, no signal, I was blaming that from the beginning, but then I've checked on a good Atari and that was the same flat signal.
Both input and output of R469 have clock, output has it much weaker (~300mV), though, regardless of the IC side soldered or desoldered.
On schematics R469 is 5.0K, but on the board it's almost 6K, but I don't think that matters as I've tried shorting it out and got no difference.

And what's more interesting - it's all absolutely the same on my second Atari.

I think you need to switch to 100mV on your scope and re-check, as you probably won't see the signal else. See my previous images, if I use 5V/div It would appear flat also on my scope.

exxos wrote: 01 Oct 2017 22:18

Number_Nine wrote: 01 Oct 2017 22:09 Output C427:

You need to be in x10 mode with your probe, and 100mV/div on scope...


c3.png

I don't think you will see it with the modes you are using.