new PSUs in my Falcon causes video output to fail

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kodak80
Posts: 81
Joined: Sat Oct 21, 2017 1:14 am
Location: Brisbane, Australia

Re: new PSUs in my Falcon causes video output to fail

Post by kodak80 » Wed Aug 22, 2018 10:55 pm

From what Paul identified, the C7 capacitor controls the delay in the reset process. When you power on, this delay needs to match the delay in 5v rail supply to the board. My PSU had a delay of around 22-25ms before 5v was supplied to board and the C7 capacitor was starting the reset process before all compenents had received 5v and so boot failed.

I am not so sure that the level of the 5v was as important but we did see that my Falcon would not power on when we were seeing less than 4.9v. This may depend on the state of capacitors and other components in the system and so not all systems would be the same.

I would say that ensuring that the C7 capacitor was large enough to match the PSU 5v rail supply to the board was the fix and my Falcon is still working fine. I have Exxos PSU (with 5v modification by Paul), Exxos clock patch and Exxos RTC module installed.
Atari Falcon 030 | Atari 1040 STE | Atari 1040 STFM | Atari 1040 STF | Kryoflux & Supercard Pro Flux boards
Admin of Atari ST Review Magazine Archive: http://www.ataristreview.com

mikro
Posts: 125
Joined: Mon Aug 28, 2017 11:22 pm

Re: new PSUs in my Falcon causes video output to fail

Post by mikro » Thu Aug 23, 2018 8:24 am

kodak80 wrote:
Wed Aug 22, 2018 10:55 pm
From what Paul identified, the C7 capacitor controls the delay in the reset process.
Yes but in your first attempt you didn't solder the 22uF cap on C7 but C2 instead (I'm assuming that it's not a coincidence and you had been trying to install Czuba's reset fix as well). So I'm wondering whether that couldn't be one of the reasons it didn't work straight away (apart from the voltage).

kodak80
Posts: 81
Joined: Sat Oct 21, 2017 1:14 am
Location: Brisbane, Australia

Re: new PSUs in my Falcon causes video output to fail

Post by kodak80 » Thu Aug 23, 2018 9:00 am

mikro wrote:
Thu Aug 23, 2018 8:24 am
kodak80 wrote:
Wed Aug 22, 2018 10:55 pm
From what Paul identified, the C7 capacitor controls the delay in the reset process.
Yes but in your first attempt you didn't solder the 22uF cap on C7 but C2 instead (I'm assuming that it's not a coincidence and you had been trying to install Czuba's reset fix as well). So I'm wondering whether that couldn't be one of the reasons it didn't work straight away (apart from the voltage).
Hi Miro
The first capacitor was actual connected in parallel with C1 capacitor and has been removed when we did the C7 change. We were looking in the wrong place in the reset circuit initially and whilst it seemed to initially work, the booting issue came back when I got home from Paul's. C2 doesn't appear in the circuit diagram Paul drew for me showing the reset circuit.
Atari Falcon 030 | Atari 1040 STE | Atari 1040 STFM | Atari 1040 STF | Kryoflux & Supercard Pro Flux boards
Admin of Atari ST Review Magazine Archive: http://www.ataristreview.com

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