genel
Windows User
C= 64 NTSC, PAL, SX, 128 (Flat) Sony monitor capable of all standards, also 80 columns.
Posts: 4 
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Post by genel on Mar 2, 2016 14:01:02 GMT
I have three flat 128's, and use one for powering my 128's and my PAL 64.
I noticed recently that I was getting very random video flashing on both computers.
I got suspicious so I took it apart. One blown lytic cap.
Long story short, I recapped all three power supplies, and renewed the old heatsink compound.
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Post by hydrophilic on Mar 4, 2016 11:26:57 GMT
Interesting... in my experience, capacitors don't normally "blow up", the usually just "fade away". Usually when a cap "blows up" it is because of something else... either a power surge, or a shorted diode/transistor. If replacing the cap makes it work, then you got lucky (no shorted diode/transistor).
Anyway, glad to hear you were successful in "restoring" all 3 of your PSUs!
[Edit]
The only bad C128 PSU that I've had so far (knock-on-wood), simply had a cracked circuit board. Soldering a few jumper wires over the cracks fixed it. The only PSU that I ever had to rebuild was for a PlayStation (I think it got fried by a power surge).
Just my experience... I hear people in 220V countries have more trouble with PSUs...
[/Edit]
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Post by motrucker on Mar 10, 2016 1:53:56 GMT
I just recently realized there are more than one type of PSU for the C-128! I have a few of the 4.3A power supplies, but I have discovered two different part numbers for 2.5A units.
Since I have run across this, I aim all of the 2.5A units for use on C-64s. The ratings are always printed on the case, so check yours to make sure what you are using.
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genel
Windows User
C= 64 NTSC, PAL, SX, 128 (Flat) Sony monitor capable of all standards, also 80 columns.
Posts: 4
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Post by genel on Mar 14, 2016 13:14:59 GMT
Interesting... in my experience, capacitors don't normally "blow up", the usually just "fade away". Usually when a cap "blows up" it is because of something else... either a power surge, or a shorted diode/transistor. If replacing the cap makes it work, then you got lucky (no shorted diode/transistor). Anyway, glad to hear you were successful in "restoring" all 3 of your PSUs! [Edit]
The only bad C128 PSU that I've had so far (knock-on-wood), simply had a cracked circuit board. Soldering a few jumper wires over the cracks fixed it. The only PSU that I ever had to rebuild was for a PlayStation (I think it got fried by a power surge). Just my experience... I hear people in 220V countries have more trouble with PSUs... [/Edit]Ok, I didn't literally mean "blown up". The cap had overheated, and the shrink tubing with nomenclature had shrunk. (However, I have seen caps blow, with the guts blown out of the bottom.) Anyhow, now I will do a recap of the 128 itself. |
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Post by zap on Mar 16, 2016 3:27:38 GMT
I have found when Caps in power supplies burst it's from ac getting to the dc rail caused by faulty rectifier diodes or a higher voltage compared to the rated voltage of the Cap caused by faulty regulator circuits. For a C-128 power pack to have a deformed or leaky Cap one would think the rectifier diodes would be suspect first and then the regulator chip next. Less the poor girl has been heated from lack of air to keep it cool or over worked.
Of cause aged kills caps as well especially when they have been not used for many years.
zap.
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Post by hydrophilic on Mar 29, 2016 1:57:15 GMT
Thanks for clarification, genel. The only bad caps I've ever discovered are "literally blown-up" (quoting your elegant phrase) or else just "withered away" (way outside a 10% tolerance). In particular, I've never seen a "melted/shrunken" capacitor before. Something new to look for... thanks! I agree with zap, caps that literally blow-up usually get the wrong polarity (bad diode / transistor). I'm not sure if any "blown-up" caps (in my experience) were due to over-voltage, but that sure sounds reasonable... yet another good thing to know for repair purposes!! I also agree that general overheating (no air flow / over-worked) might also cause this, although it seems less likely than options 1 and 2. |
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genel
Windows User
C= 64 NTSC, PAL, SX, 128 (Flat) Sony monitor capable of all standards, also 80 columns.
Posts: 4
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Post by genel on Mar 31, 2016 0:48:49 GMT
I used to work as a computer power supply tech way back when. We didn't see many problems with smaller caps, but the large electrolytics were another thing. The usual problem from the production line is they would connect a cap backwards, a 100,000 mfd cap at 25 vdc blowing is a sight to behold. They create a huge white "mushroom cloud" of electrolyte out the bottom of the safety vent when they blow. As a joke, I once connected a 100,000 mfd cap to a line cord, and plugged it in another tech's power strip. When he came in, and turned it on, it made a whooshing sound, and completely enveloped him and his test bench in the cloud. He came out of it hacking and coughing! No-one ever told him who did it, and he didn't guess me.  |
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Post by hydrophilic on Mar 31, 2016 1:08:49 GMT
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