Care and feeding of your power supply

[Matt_H]

I'd been having trouble with they keyboard on my 4000T - dropping dead randomly, sending garbage input, and other symptoms that make it unusable. I replaced 2 of the capacitors within the keyboard, and that seemed to help, but it had no actual effect. My tests post-replacement were both false positives for success.

Today I started stripping down the machine, desperately trying to figure out what other component might be broken and interfering. I was getting nowhere, until I pulled the motherboard power leads on a whim. Yikes! The 5V rails are all fried. I'll bet money that this is the problem.

I installed this PSU in 2006. I thought that I would have gotten a little more life out of it (the original one lasted from manufacture in 1996 until my replacement). Is this damage to the leads indicative of something to do with my machine, or was this just a crappy PSU? It's 300W, driving a CSPPC, 2 hard drives, 2 CD drives, and 5 Zorro cards.

[Tenacious]

Those burn marks don't necessarily mean that the PS has failed.  It means those 4 pins are heating up.  If you have a digital meter, check the +5VDC rail at an unused drive plug, and then check it somewhere on the motherboard (be careful NOT to let the probe slip and short adjacent traces).  They should be close to 5.00 and NOT jumping around and should be near identical.  If MB reads less or is fluctuating, those 4 pins might have some resistance and be a bad connection.  Look at the actual metal mating surfaces, are they shiny or burned and discolored?  You could try to clean them up.

All of the drives are probably feed directly from the power supply.  They should be.  The CSPPC and 5 zorro cards (and MB), on the other hand, are drawing their current thru those 4 pins.  You might have too much load going thru them.  Can any of the cards be supplied seperate from the MB?

Finally, check the 5 volt rail in the keyboard.  It should read the same as above.  I have seen the processing chip in keyboards go flakey and then fail.

Good Luck!

[mechy]

That is a typical case of old connectors, i even see this on the A4000 desktops quite often now. replace the connectors on the psu and the one on the motherboard and you will probably get another 15+ years life.
As tenacious pointed out the connections develop resistance(usually they tarnish a bit which is the cause) and then start heating until stuff starts discoloring and melting.
Buy quality replacement connectors and your in business.I doubt the psu has gone bad.

-mech-

I'd been having trouble with they keyboard on my 4000T - dropping dead randomly, sending garbage input, and other symptoms that make it unusable. I replaced 2 of the capacitors within the keyboard, and that seemed to help, but it had no actual effect. My tests post-replacement were both false positives for success.

Today I started stripping down the machine, desperately trying to figure out what other component might be broken and interfering. I was getting nowhere, until I pulled the motherboard power leads on a whim. Yikes! The 5V rails are all fried. I'll bet money that this is the problem.

I installed this PSU in 2006. I thought that I would have gotten a little more life out of it (the original one lasted from manufacture in 1996 until my replacement). Is this damage to the leads indicative of something to do with my machine, or was this just a crappy PSU? It's 300W, driving a CSPPC, 2 hard drives, 2 CD drives, and 5 Zorro cards.

[Matt_H]

I don't trust myself to be able to replace the connectors correctly, either on the motherboard or the PSU itself. I've got a replacement PSU coming in the mail - any suggestions on what I can use to polish up the motherboard connectors? Good ol' isopropyl alcohol, maybe?

EDIT: Just to clarify, the keyboard is actually fine (I think) - it's working on another machine.

[Tenacious]

I don't trust myself to be able to replace the connectors correctly, either on the motherboard or the PSU itself. I've got a replacement PSU coming in the mail - any suggestions on what I can use to polish up the motherboard connectors? Good ol' isopropyl alcohol, maybe?

EDIT: Just to clarify, the keyboard is actually fine (I think) - it's working on another machine.

Isopropyl is a start, so is a an can of Contact and Tuner cleaner (use this sparingly) from Radio Shack.  I have used pink pencil erasers to rub away oxidation followed by a cloth to remove any eraser residue.

Look at the pins (and PS female sockets) with a magnifying glass and decide your attack.  You want as much clean surface area as you can get.  Those connections are the current bottleneck in the power flow, that's why they're burned.

If the pins are discolored, burned, and pitted, you could try abrading them with sandpaper (use a very fine grit!) as a last resort.  Vacuum out the metallic dust.

[spirantho]

I had a similar problem with my A4000 (towered). I was getting a green screen without sync and the keyboard would hang, whenever much was happening with the chipset or the CPU.

Since I replaced the PSU with a new one (a Corsair CX430) so far it's been just fine - and the PSU is practically silent - recommended so far.

[Matt_H]

Thanks, all. There's no obvious damage to the motherboard connectors, but I will take a closer look tonight and report back.

[Matt_H]

Well, there was some discoloration of the 5V pins on the motherboard. I rubbed them down with a cloth and an eraser as best I could (I know I didn't get everything) and then replaced the PSU. Everything seems to be stable now, but I'll be keeping a close eye on these things in the future.

Lesson learned: if your keyboard is doing insane things and your Caps Lock light is going crazy, check your power supply!

[Thorham]

Everything seems to be stable now

Good to hear that

[freqmax]

Stable now, fireworks tomorrow.. :p

[Daedalus]

Well, there was some discoloration of the 5V pins on the motherboard. I rubbed them down with a cloth and an eraser as best I could (I know I didn't get everything) and then replaced the PSU. Everything seems to be stable now, but I'll be keeping a close eye on these things in the future.

Lesson learned: if your keyboard is doing insane things and your Caps Lock light is going crazy, check your power supply!

Great to hear that it seems to be sorted! From using various "exotic" power supply setups on my Amigas, I can attest to that. I often got crazy keyboard behaviour (caps lock light flashing, stuck keys, random gibberish) on an A1200 until I checked the PSU with a scope and found it had some high frequency noise on the +5V line. Didn't affect anything else so far as I could tell, but eliminated the noise and the keyboard started working again. That one took a while to sort out!

[Matt_H]

Stable now, fireworks tomorrow.. :p

Let's hope not!

Great to hear that it seems to be sorted! From using various "exotic" power supply setups on my Amigas, I can attest to that. I often got crazy keyboard behaviour (caps lock light flashing, stuck keys, random gibberish) on an A1200 until I checked the PSU with a scope and found it had some high frequency noise on the +5V line. Didn't affect anything else so far as I could tell, but eliminated the noise and the keyboard started working again. That one took a while to sort out!

Yup, those were the exact symptoms I had. And now that I think about, I believe the same thing happened on my old 1200T system many years ago. I ended up not fixing it, though, since that machine was replaced with this 4000T around the same time.

So now we've got the solution. Hopefully people with similar problems in the future will be able to find this thread!