exxos's Atari, Amiga & retro forum

I'm sourcing parts from aboard, which means 6 weeks on average....

Meanwhile, with all the experimentations it seems the PSU decided it wanted a break. I am not getting a stable 12V, rather it alternates between 6-9v with clocking sound. I took the PSU out to the bench and am trying to debug but have little clue as to how to approach it as there are no diagrams.

If anyone has a few idea what could be the cause of this, please drop a hint. I saw similar issues upon searching the web, but there was no clear direction.

The 5v was stable yesterday going by your scope readings.. 12v isn't normally regulated so the voltage is generally to low. Ticking means short circuit or not under load. But the 5v would also be malfunctioning..

I wonder if you should just stop investigating, as your piling up many faults faster than can be diagnosed. Even though it costs a lot postage, send me your motherboard to diagnose before things get any worse.

Update: The PSU issue is a non existent one as 12v needs load to work and I tested it disconnected and with no resistive load. My bad :oops:

I've installed back the legacy clock patch and can report the following behavior:
1. Installed legacy clock patch, no DFB1X, Cubase audio works ok with no clicking (for at least 30 min)
2. Installed DFB1X in disabled mode, Cubase audio working same as #1
3. Enabled DFB1X, no TTRam, Cubase audio does not work and there are audio clicking and distortion (see video). The DFB1X enters some sort of panic mode as can see towards the video end.
4. Enabled TTRam, Cubase audio works for about 6 min before audio clicking and distortion. Changing sample rate somehow resets everything and I'm getting more minutes until next distortion state.

For scenario #3 above, here's the video clip


Here are a few scoping images. I have clock patch Variant 1.1 as seen in https://mikrosk.github.io/clockpatch/.

1. Close to the DSP 2. D2A / Input 1 3. Q2 - Out to FPU and SDMA 4. D3A / Input 2 5. Q3 - Expansion slot

Its unclear if you removed the 100pf and 62R when you went back to original clock patch?

Also If this is v1.1 the one you have... OK so stupid svg format so can't attach :roll:

CPU gets original clock, bus masters and exp get inverted clock.

I'd remove that Q3 wire and connect the MB side of the wire to R222 bottom.. So exp clock gets same clock as CPU.. See if that changes anything..

exxos wrote: 10 Aug 2025 16:56 Its unclear if you removed the 100pf and 62R when you went back to original clock patch?

Did not remove either. The 62 ohm is bypassed using a short wire, 100pF still on the underside.

Do I need to?

whomper wrote: 10 Aug 2025 17:14 Did not remove either. The 62 ohm is bypassed using a short wire, 100pF still on the underside.
Do I need to?

You can leave 62R but maybe try and scope without the 100pf.. Then we can see if anything changes and what signals look like.

Took out 100pF from underneath the board, severe digital noise and often Cubase crashes. This is scenario #4 above, meaning DFB1X plus TTRam.

Attached scope of the DSP side of the signal (where wire patch). If you compare it with my previous DSP scope, you can see the signal is different.

I have reinstalled the 100pF cap and confirmed scenario #4 above still works now as before (i.e. a few good minutes of audio).

Thanks.

Please try this next viewtopic.php?p=132315#p132315

Also switch your scope probe to x1 and measure the left side of the 62R.. I don't need single.. Just see if audio gets better or worse when you're measuring.

Connected Exp clock to R222 bottom, instability came rushing in much faster than with it connected to Q3. Digital distortion and audio clicks started after a few seconds.