I best start off by saying that I've zero recapping experience, although I do have some casual experience with soldering and desoldering components. So I'd really appreciate any assistance.
I have a very old Compaq SLT/286 laptop which I keep alive as a hobby of mine. It dates from late 1989 or early 1990. Useless by modern standards but it's an oddity I like to keep running; it's certainly a head turner when anyone sees it!
Up to now, the only bit of physical maintenance I had to do was to replace the Dallas DS1287 RTC with a DS12887 to replace the CMOS battery. But recently it began showing some signs of what I suspect are capacitor issues. On some occasions when you power it down, it won't come back up until you unplug it from the PSU and let it sit for a while. I don't know how long exactly, but it would be within 15 minutes. Also, it recently did something it never did before. When you power it up, it goes through the POST sequence and performs a memory test. After the memory test, it spins up the hard disk. This time, I had it on for a few hours when it spontaneously rebooted itself and the hard disk spun down. At the stage of the POST where it would normally spin up the hard disk, I could hear the drive starting to spin up, but then it rebooted again and spun down the disk. I powered it off to prevent it from possibly getting damaged further.
It sounds to me like there's not enough power being provided to spin up the hard disk. Due to the age of the system, I suspected that the electrolytic capacitors are drying out. There's no electrolytics on the motherboard itself, they're all confined to two PSU boards - the AC adapter and a secondary one in the laptop itself. Here's a photo of the two boards, with the caps numbered for reference. Also a CSV of the caps and what values they are.
https://dl.dropboxusercontent.com/u/.../slt286psu.jpg
https://dl.dropboxusercontent.com/u/...bc/SLTcaps.csv
One thing which has me scratching my head is the caps that I marked as 10 and 11. They're Sprague 678D caps but with three legs. I've never seen a three legged cap before but I do have a Vishay datasheet for the 678D series, so I've at least got something to work off.
I've tested all 13 electrolytics with an inline ESR meter, and there are some notable results. The Nichicon VTs (which I numbered 1, 7 and 8) are reporting a higher ESR than I'd expect (2.05, 1.53 and 1.89 respectively). The reported ESR on the two three legged caps isn't something I know for sure. If I test using the two legs on the left, I get a near zero reading. But if I use one on each side, I get a very high ESR reading, 3.6 ohms on the 1800uF cap and 2.54 ohms on the 3300uF cap. So either I'm testing them incorrectly or the ESR is very high and they need to be replaced.
So I suppose my question is, where should I go from here? I'd like to replace the caps with good ones such as Rubycons or Panasonics, but the two three legged ones are confusing me.
I have a very old Compaq SLT/286 laptop which I keep alive as a hobby of mine. It dates from late 1989 or early 1990. Useless by modern standards but it's an oddity I like to keep running; it's certainly a head turner when anyone sees it!
Up to now, the only bit of physical maintenance I had to do was to replace the Dallas DS1287 RTC with a DS12887 to replace the CMOS battery. But recently it began showing some signs of what I suspect are capacitor issues. On some occasions when you power it down, it won't come back up until you unplug it from the PSU and let it sit for a while. I don't know how long exactly, but it would be within 15 minutes. Also, it recently did something it never did before. When you power it up, it goes through the POST sequence and performs a memory test. After the memory test, it spins up the hard disk. This time, I had it on for a few hours when it spontaneously rebooted itself and the hard disk spun down. At the stage of the POST where it would normally spin up the hard disk, I could hear the drive starting to spin up, but then it rebooted again and spun down the disk. I powered it off to prevent it from possibly getting damaged further.
It sounds to me like there's not enough power being provided to spin up the hard disk. Due to the age of the system, I suspected that the electrolytic capacitors are drying out. There's no electrolytics on the motherboard itself, they're all confined to two PSU boards - the AC adapter and a secondary one in the laptop itself. Here's a photo of the two boards, with the caps numbered for reference. Also a CSV of the caps and what values they are.
https://dl.dropboxusercontent.com/u/.../slt286psu.jpg
https://dl.dropboxusercontent.com/u/...bc/SLTcaps.csv
One thing which has me scratching my head is the caps that I marked as 10 and 11. They're Sprague 678D caps but with three legs. I've never seen a three legged cap before but I do have a Vishay datasheet for the 678D series, so I've at least got something to work off.
I've tested all 13 electrolytics with an inline ESR meter, and there are some notable results. The Nichicon VTs (which I numbered 1, 7 and 8) are reporting a higher ESR than I'd expect (2.05, 1.53 and 1.89 respectively). The reported ESR on the two three legged caps isn't something I know for sure. If I test using the two legs on the left, I get a near zero reading. But if I use one on each side, I get a very high ESR reading, 3.6 ohms on the 1800uF cap and 2.54 ohms on the 3300uF cap. So either I'm testing them incorrectly or the ESR is very high and they need to be replaced.
So I suppose my question is, where should I go from here? I'd like to replace the caps with good ones such as Rubycons or Panasonics, but the two three legged ones are confusing me.
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