exxos's Atari, Amiga & retro forum

Hi there,
I got a PAL Atari 1040STE which has video sync problem, so I've been debugging it today and noticed that VSync and HSync are all right, but CCLK signal is suspiciously silent (both video connector pin #2 and U403 MC1377P pin 17).
According to MC1377 sheet it should be around 2-3 MHz, but on my machine it's just 4V all the time.
I've been scrolling through STE schematics many hours today and still I can't see where it comes from. I would imagine it comes either from MCU or maybe Shifter, or something like VSync gets mixed with HSync...
Any idea, please?

PS: Poked PSU with a scope - not much noise, levels seem OK too. Dully recapped C103, C415, C417, C423, C433.

CCLK goes U308B pin 12 and comes from a clock circuit only present on PAL machines (I put the signal in red bellow) : Rodolphe

Some monitors do not like st video modes.

You could try this fix where a couple people said it helped with sync issues also.

https://www.exxosforum.co.uk/forum/viewt ... f=17&t=135

rpineau wrote: 23 Sep 2017 23:47 CCLK goes U308B pin 12 and comes from a clock circuit only present on PAL machines (I put the signal in red bellow) :
Screen Shot 2017-09-23 at 15.45.00.png

Rodolphe

Much appreciated!

exxos wrote: 24 Sep 2017 00:11 Some monitors do not like st video modes.

You could try this fix where a couple people said it helped with sync issues also.

https://www.exxosforum.co.uk/forum/viewt ... f=17&t=135

I am using an old CRT Philips CM 8802 which works perfectly with my other STE.
Thanks for the link, I think that might be a bit different, but I'll try your fixes.

Number_Nine wrote: 24 Sep 2017 10:49 I am using an old CRT Philips CM 8802 which works perfectly with my other STE.
Thanks for the link, I think that might be a bit different, but I'll try your fixes.

Its easy to try, not exactly the same no, but its the regulator for the video circuit. So its a sensible place to start :)

Having changed U403 (MC1377P), still no idea why is there nothing (constant 6VDC) on the composite output (pin 9 of U403), still guessing it might be because something is wrong with the Osc In signal (pin 17) - I see CCLK on R469, but after R469 it's so weak so after C 427 U403 has +5V instead of CCLK on its own (I've tried 4 MC1377Ps - all the same, I have to check this pin on a good Atari, though), but bypassing composite sync to composite output seems to work for me, as anyway I am getting RGB right from U401, but yes modulator won't work like this...

Checked a working Atari STE - everything is just exactly the same, the only difference is that it has also composite out on pin 9.
I am out of ideas.

Number_Nine wrote: 30 Sep 2017 21:31 Checked a working Atari STE - everything is just exactly the same, the only difference is that it has also composite out on pin 9.
I am out of ideas.

What are you seeing on cclk on working and none working machines ? Can you post scope images?

Have you lifted pin 9 out of the socket and checked that way ?

What is on pin 2 of the 1377 ?

Check q404 and make sure you have 12v there.

exxos wrote: 01 Oct 2017 00:41

Number_Nine wrote: 30 Sep 2017 21:31 Checked a working Atari STE - everything is just exactly the same, the only difference is that it has also composite out on pin 9.
I am out of ideas.

What are you seeing on cclk on working and none working machines ? Can you post scope images?

Have you lifted pin 9 out of the socket and checked that way ?

What is on pin 2 of the 1377 ?

Check q404 and make sure you have 12v there.

Thanks for the reply.

I have already assembled the good Atari back together as I noticed no differences earlier.

12V on collector of Q404 is there.
With pin 9 of 1377 unconnected - all the same (no Composite off it).

CCLK: Pin 2 of 1377 (VSync + HSync -> XOR (U2009A) -> Invertor (U211C)): Pin 17 (Osc In) on 1377: