Falcon NVRAM / no post issues

[paj777]

Hi All,

I've been struggling intermittently with my Falcon being able to post since I got it back in July. I assumed it was part of the whole NVRAM / RTC battery debacle that every Falcon owner seems to have struggled with.

Anyway, to cut to the chase - no amount of different clock/NVRAM (including the Exxos one) seems to have cured the issue - the machine will work fine for a while until I get no video output after resetting. There seems to be no pattern other than things 'warming up' and there being a manual reset (CTRL+ALT+DEL / Reset button or full power off/on). At one time I thought a screen resolution change followed by a reboot would cause this but the results are still patchy. Sometimes several resets and the ALT+SHIFT+LSHIFT+UNDO trick will work, but often it is unsalvageable unless I leave it for a few days with everything unplugged and the RTC removed. I've done a partial re-cap including changing C7 to a 47uF but this doesn't appear to have changed anything.

So there's the general gist, now my particular question: In the schematics, it looks like (and *is*, according to other posts) PIN 17 on U64 should go to pin 55 on the Combel, but the scans are pretty unclear. On my board, pin 17 ends up at pin 86 on the combel. This is the RTCDS line so I thought it might be contributing to my issue. Can anyone else with a REV A motherboard (or otherwise!) confirm what happens with their pin 17??

Many thanks in advance!

Paul

[exxos]

If after powering up ( turning on) machine and it does not reset, but pressing the reset button solves the problem, then there is a reset circuit issue.

Also bear in mind when the RTC settings as not everything is compatible.. This caught a lot of people out back in the beginning.

You may have one or two problems, but you need to focus on one problem at a time..

[paj777]

I would definitely like to rule out the reset circuit being an issue. The results are not reliable enough to say whether this is definitely faulty though as there is no solid pattern either in the events leading up to or recovering from the crash.

Is there a guide to overhauling / testing the reset circuit? Naively I thought this might just be replacement of a couple of caps which I think I may have done through recapping most of that part of the board.

[exxos]

Have you seen this page ? https://www.exxosforum.co.uk/forum/viewt ... =17&t=2175

[paj777]

I hadn't seen that post but having read it through it seems I may have already done something resembling that fix.. So I'm looking at this part of the schematics:

Screenshot 2021-09-16 at 15.13.58.png

I changed C7 to 47uF, and C1 / C3 swapped like for like.

[exxos]

Have you noticed I said swapped the values ?

There is something like a 10uf and 22uf ( where I say change to 47uf ) but also those 10uf and 47uf need to be swapped around..

[paj777]

Ah no - I missed that part! :D Great thanks; will check the values in a bit. Fingers crossed that will fix at least one of the issues!