I don't have a dedicated workspace for troubleshooting this so I have the motherboard stay in its "base" (lower part of the computer casing) which allows me to safely secure the PSU whenever I apply power, and adding support to the PCB so it won't be under any strain). But I will pay extra attention to whenever I need to move the PSU around.
Regarding the recapping issue I've posted a schematic with the replacement/new values as well as a complete BOM (which might be of interest for anyone else needing to perform the operation), posted here
, in that other recapping thread.
Regarding my comment/question about those low ESR Panasonic FR-series capacitors being "too good".... I got that cleared up in a different thread where this was regarding the 400V capacitors before the high frequency part of the PSU. So I've added a note about that in the Atari recapping thread I just mentioned. Your suggestion about marking each PSU capacitor one by one when I remove them is an excellent idea! I'll be sure to do that in case I mess up.
The only questions left surrounding this power supply are:
is changing the values of some capacitors as Exxos has done OK and electrically safe?
(as opposed to replacing the exact same values, but with low ESR caps -except for the two 400V ones that is)
is keeping the same value as before for C6 (120uF/400V) OK (now that many other capacitor values have been changed and thus might interact with each other in a different way from before), or is it essential that I also replace C6 with the Exxos' new value (150uF/400V)?
A final question about recapping the Mega STe (and STe as well actually): there are several electrolytics on the motherboard of these 25-30 year old computers and I'm sure they could need recapping as well. Given what I've now learnt about "too good" capacitors, should these be replaced only
with "normal" (but high quality/renowned brand) capacitors (and NOT low-ESR types)? And does that include the big one (C227: 470uF electrolytic) near the power supply connector which I assume are there to further stabilise the +5V power line? See image below (centre senction of page 2 (of 11) from the Mega STe schematic) where I also shouldn't use a low ESR type?.
The resistance measure tip without powering on is indeed useful. I wasn't entirely sure what the test was about so reminders like that are always welcome! And yes, having sourced the 7406 I should be fine in any case.
On a slightly different note, I took a look at the PC900 opto isolator (U302) inside the computer and it's actually labelled something entirely different: "HIL3 048J" with an "H" logo that I don't recognize from any other semiconductor. The exact same one is used in my STe as well, so I was hoping it could be easier to source that part, but so far nothing pops up when doing any online searching. Perhaps a proprietary part ordered by Atari at the time, but compatible with the PC-900 (it says "PC-900" in the schematics).
I don't know how that "Sound" CPX works. I don't think it's Mega STe-specific because as far as I can remember it's also used with my STe. Hopefully replacing that 7406 will fix a number of things....
Glad you've found the thread interesting. I'm very grateful for your and others' help I've received here and aim for a fully working computer in the not too distant future (the next weeks will be quite busy, but I'll be sure to post here once I get to try out the new parts). Also I'm learning a lot!
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