[vcf-midatlantic] Atari 800 power issue

[W2HX]

I wouldn’t increase the heat, what you need is a bigger iron with more thermal mass. Try a "gun" style soldering iron instead of a pencil type. 
Regarding the cap, try this. Turn on the Atari and then turn it off. Then short the cap you think is suspect. Then see if the Atari will turn on immediately or not. If it does turn on then you might consider using a bleeder resistor across the cap. Just size it properly for heat dissipation. 

I doubt you could have damaged the cap to produce the results you are observing.  But look at the voltage on the cap with a scope and see what the ripple is. If the cap were faulty, it would likely have higher ripple.


73 Eugene W2HX
My Youtube Channel: https://www.youtube.com/@w2hx/videos
 

-----Original Message-----
From: vcf-midatlantic <vcf-midatlantic-bounces at lists.vcfed.org> On Behalf Of James via vcf-midatlantic
Sent: Thursday, June 20, 2024 7:12 PM
To: vcf-midatlantic <vcf-midatlantic at lists.vcfed.org>
Cc: James <tenprintclearhome at gmail.com>
Subject: [vcf-midatlantic] Atari 800 power issue

Hi all, yesterday I recapped my Atari 800 using a recap kit from Console 5.
All of the caps went in easily except for the two large ones. I blame my recapping skills and not the kit to be clear.

I struggled to get the heat right on the two 4700uF caps, particularly the negative side due to the large ground areas on the board sucking up heat.
To compensate, I bumped up the heat to 750F and applied heat a bit longer than I would have liked (though under 10 secs). How hot/long can I go before damaging a 4700uF 25v cap? I was nervous to go hotter than 750F.
It's possible I have a cold joint.

When I got the machine back together it booted up fine and was usable.
However, I noticed that if I turned the machine off, I could not turn the machine back on again unless I waited a minute. I tried multiple known working power bricks to the same effect.

This is leading me to believe I have a capacitor issue (because that's what I changed and I can rule out the power bricks which worked fine prior to the recapping and again after the machine sat for a minute).

Do you think I...

(A) fried one one the capacitors and it's now faulty? Is there a way to test this without removing it from the board? I clipped the wires so I'd hate to try and solder it back in if it's good.

(B) I have a cold solder joint (very possible given I struggled to keep the solder fluid. However, I would have expected the machine to not function at all if this were the case. Unless my issue is the capacitors are not discharging properly which is why I need to wait a minute before turning back on??

(C) Something else?

Any thoughts on diagnosing this is appreciated.

Best,
James