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Has my PSU been recapped already?
Posted: 27 Mar 2023 22:25
by Slartibartfast
I’m currently trying to get a 520STFM working and one thing I was planning to do was recap the PSU as a matter of course.
None of the electrolytic are bulging but I thought it worthwhile preventative maintenance given that the PSU is obviously quite old. However, I noticed that the top of all the key electrolytic have a black dot marked on them (sharpie?) and wondered if this is where a previous owner has already done the swap and marked them to remind themselves.
Anybody got any thoughts on this or did the capacitors tend to have these marks from the factory?
Re: Has my PSU been recapped already?
Posted: 27 Mar 2023 23:50
by exxos
From factory
https://exxosforum.co.uk/atari/last/psu/index.htm if you look at the first image.
No idea why it was All done. All sorts have had pen or paint on them from factory. Some ICs have marker pen or painted dots on them.
Its possible someone just marked the negative side of the caps so the assembly monkeys didn't screw it up :shrug:
Though the TOKIN PSU had random red dots on them :shrug:
Re: Has my PSU been recapped already?
Posted: 28 Mar 2023 05:47
by Slartibartfast
Ahh, interesting thanks for the link.
So looks like there is no reason to think my unit has been recapped.
One reason I was considering doing it was that although none of the capacitors showed signs of stress or age, I was seeing around 100mV of noise on the 5V rail. Looking through the information you linked to, it seems this is actually quite reasonable for my unit so I may put the job on hold for now initial I get the rest of the machine sorted.
Re: Has my PSU been recapped already?
Posted: 28 Mar 2023 10:07
by rubber_jonnie
Slartibartfast wrote: 28 Mar 2023 05:47
Ahh, interesting thanks for the link.
So looks like there is no reason to think my unit has been recapped.
One reason I was considering doing it was that although none of the capacitors showed signs of stress or age, I was seeing around 100mV of noise on the 5V rail. Looking through the information you linked to, it seems this is actually quite reasonable for my unit so I may put the job on hold for now initial I get the rest of the machine sorted.
In instances like this, I'd recommend you post photos to help people understand just what you're looking at, as there can be quite a bit of variance as suggested by
@exxos
Re: Has my PSU been recapped already?
Posted: 28 Mar 2023 13:10
by Slartibartfast
Picture uploaded
Atari ST PSU.jpg
Re: Has my PSU been recapped already?
Posted: 28 Mar 2023 14:00
by rubber_jonnie
Slartibartfast wrote: 28 Mar 2023 13:10
Picture uploaded
Atari ST PSU.jpg
Ok, so one question, is there any hot snot around the bottom of the caps at all? There sometimes is and it is a giveaway that caps are most likely original. My feeling is that these are originals as I have caps with dots on them like this in my donor boards.
Regardless, if you are going to recap then I'd also recommend replacing the bridge rectifier with something a bit more substantial :)
Re: Has my PSU been recapped already?
Posted: 28 Mar 2023 14:44
by Slartibartfast
No, it's all clear around the base of the electrolytics and in fact they are all a couple of mm above the board.
I do see what you mean about the bridge rectifier, it does look a little... underwhelming... althouh I guess it doesn't have to handle much current.
I'm also please to see a decent X2 filter capcitor on the input side, not the rubbish ones you get in BBC Model B PSUs which tend to crack due to age and go pop the first time the machine is turned on after a long slumber.
Maybe I'll just play it safe and swap out the caps and the bridge rectifier anyway.
Re: Has my PSU been recapped already?
Posted: 28 Mar 2023 15:45
by rubber_jonnie
Slartibartfast wrote: 28 Mar 2023 14:44
No, it's all clear around the base of the electrolytics and in fact they are all a couple of mm above the board.
I do see what you mean about the bridge rectifier, it does look a little... underwhelming... althouh I guess it doesn't have to handle much current.
I'm also please to see a decent X2 filter capcitor on the input side, not the rubbish ones you get in BBC Model B PSUs which tend to crack due to age and go pop the first time the machine is turned on after a long slumber.
Maybe I'll just play it safe and swap out the caps and the bridge rectifier anyway.
TBH I've always found the SR98s to be reasonable PSUs, but don't touch the heatsinks when they're running, it's pretty unpleasant...