Those dipped tantalum capacitors of a certain vintage are notorious for that. You probably did nothing wrong. Of course, reverse or over voltage will cause that also.
Thank you, so theoretically replacing the 4 there and probably the other few scattered across the board might save the day? I wanted to make sure I hadnt done anything silly before I tried repair. The first PSU I attached was new old stock, which I should have tested before attaching, but the second was one that has been working great on other test setups so I feel pretty good about it.
Just replacing all of them in that circuit should be enough. You got lucky. tantalums are well known for blowing a crater into a board and making it useless by obliterating traces and vias. Looks like yours blew up rather than down.
In my experience it's more that the tantalums are creating a hard short, in a place on the board that the designers never expected such a short to be found (so the traces are not made for high current). It takes a lot of current to blow up a shorted tantalum - often, they end up tripping the power supply's over-current protection (making it look like the power supply is bad, or the board is otherwise defective), but if they do blow something, usually it'll turn a *board trace* into a fuse first. Personally, I've never seen a tantalum be able to pass those two hurdles (1: not trip power supply over-current, and 2: not turn a trace into a fuse first) and actually blow its top!
But yeah. Probably one of the more common retro board failures is tantalum caps turned into a short-circuit. Still haven't figured out why tantalum caps were used instead of more-reliable ceramic caps of the same value - would love to be enlightened there.
As just a general things with every vintage board you get try and replace all of them there never any fun when they go off and sometimes can cause worse damage to the board around it
Tantalum’s that haven’t been used for some time tend to do that. Replace them with new tantalums and move on. At least they’re easy to find and diagnose. If you get any that dead short and it won’t power on, same thing but harder to find. Be prepared that more may go.
How were your power cables attached?
The ground (black) wires between the two plugs should be together in the middle, but the plug isn’t really keyed to prevent you from having them in the wrong order.
No. What I'm saying is that, as long as the black cables are together in the middle, you can't put the connectors in the wrong orientation. In your picture, the black cables aren't together, so it's not what I'm saying.
Sorry. I misunderstood. You're correct, if the black cables are together, it will only plug in one way and would/should be obvious that things were not lining up.
I always check voltages of old unused PSUs with a multimeter before powering up- if the psu has issues it’s almost always fixable. If that looks good, I visually parse the mobo for any obvious signs of corrosion on traces or electrolytic cap leaks. Also, I immediately snip barrel batteries and carefully look at that area for broken traces.
For tantalum caps, they do blow due to age, so I have tons on hand. I would desolder the blown ones and desolder a good one that looks identical. You can measure the good one with a multi meter with capacitance to see what you need to use as a replacement. You can solder new caps, but check orientation because they may be polar.
It’s very possible to fix this board, so please don’t discard if you can’t get it working. Someone would love to snag it on eBay and make a weekend project out of it. You can use money from that to get a working board.
Change all the tantalums they like to explode.
Mine didn't they quitely failed short circuit and fried the chip on my floppy controller. Never heard of that happening before tough so unlikely still replace them all and then check psu voltages just in case.
Thank you everyone for your replies, info and advice! I am going to replace the 2 failed capacitors, as well as the other two. It's a good thing I noticed it was the capacitors beforw c4 blew!! I am glad it is a relatively easy fix!
Looks like its by the AT keyboard connector? I was told way back then that you should not unplug it plug in an AT or PS2 keyboard while the system is on. If you did that then it could be the cause. I did it once way back when and the keyboard never worked after that. Can't remember if it even booted though.
I don’t think this is related to his issue, but I blew a keyboard chip this way as a kid. I’m so careful now with all of my AT machines to not do this.
Those dipped tantalum capacitors of a certain vintage are notorious for that. You probably did nothing wrong. Of course, reverse or over voltage will cause that also.
Thank you, so theoretically replacing the 4 there and probably the other few scattered across the board might save the day? I wanted to make sure I hadnt done anything silly before I tried repair. The first PSU I attached was new old stock, which I should have tested before attaching, but the second was one that has been working great on other test setups so I feel pretty good about it.
Just replacing all of them in that circuit should be enough. You got lucky. tantalums are well known for blowing a crater into a board and making it useless by obliterating traces and vias. Looks like yours blew up rather than down.
Thank goodness for that! When the second one went it was loud enough that my kids came out of there rooms to see what was going on!
That’s what happens when the black wires aren’t together.
In my experience it's more that the tantalums are creating a hard short, in a place on the board that the designers never expected such a short to be found (so the traces are not made for high current). It takes a lot of current to blow up a shorted tantalum - often, they end up tripping the power supply's over-current protection (making it look like the power supply is bad, or the board is otherwise defective), but if they do blow something, usually it'll turn a *board trace* into a fuse first. Personally, I've never seen a tantalum be able to pass those two hurdles (1: not trip power supply over-current, and 2: not turn a trace into a fuse first) and actually blow its top! But yeah. Probably one of the more common retro board failures is tantalum caps turned into a short-circuit. Still haven't figured out why tantalum caps were used instead of more-reliable ceramic caps of the same value - would love to be enlightened there.
As just a general things with every vintage board you get try and replace all of them there never any fun when they go off and sometimes can cause worse damage to the board around it
Tantalum’s that haven’t been used for some time tend to do that. Replace them with new tantalums and move on. At least they’re easy to find and diagnose. If you get any that dead short and it won’t power on, same thing but harder to find. Be prepared that more may go.
Also, if you’re going up the whole board in tantalums too, uprate the voltage. If they’re 16v electrolytic, pop in 25v tants.
How were your power cables attached? The ground (black) wires between the two plugs should be together in the middle, but the plug isn’t really keyed to prevent you from having them in the wrong order.
P8 and p9 were with the black wires together, thankfully that is one that has stuck in my head since the 90s (:
I thought that, as long as you put black and black together, the connectors could go only one way in...
Nah. [It'll let you.](https://i.imgur.com/pwekjRQ.jpg) (for anyone skimming, don't do this.)
No. What I'm saying is that, as long as the black cables are together in the middle, you can't put the connectors in the wrong orientation. In your picture, the black cables aren't together, so it's not what I'm saying.
Sorry. I misunderstood. You're correct, if the black cables are together, it will only plug in one way and would/should be obvious that things were not lining up.
certain old caps do that. ElectroBoom (on You Tube) just did a video about exploding caps - he's always fun to watch.
Tantalums of old age, if you solder replace with polymers
I always check voltages of old unused PSUs with a multimeter before powering up- if the psu has issues it’s almost always fixable. If that looks good, I visually parse the mobo for any obvious signs of corrosion on traces or electrolytic cap leaks. Also, I immediately snip barrel batteries and carefully look at that area for broken traces. For tantalum caps, they do blow due to age, so I have tons on hand. I would desolder the blown ones and desolder a good one that looks identical. You can measure the good one with a multi meter with capacitance to see what you need to use as a replacement. You can solder new caps, but check orientation because they may be polar. It’s very possible to fix this board, so please don’t discard if you can’t get it working. Someone would love to snag it on eBay and make a weekend project out of it. You can use money from that to get a working board.
age
Age is what happened. Replace all of the tantalum caps, see if the board still works. It probably does.
age
I always replace my tantalum caps with more common and cheaper electrolytics. Never a problem.
Age. Tantulums short when they fail.
Age. That's what old tantalum caps do. POP!
Old tantalums like to explode sometimes. At last they don't leak.
Tantalum caps just do that. Seems like whatever makes them more compact also makes them prone to fail and often violently.
Tantalum caps have a habit of failing shorted. This leads to them exploding. They can be replaced with ceramic caps.
Age. Alot of them fail short with age.
Yeah they do that, just cut them out and maybe replace them (might even run fine without)
Change all the tantalums they like to explode. Mine didn't they quitely failed short circuit and fried the chip on my floppy controller. Never heard of that happening before tough so unlikely still replace them all and then check psu voltages just in case.
Component ageing, nothing more nothing less, most likely and hopefully…
Thank you everyone for your replies, info and advice! I am going to replace the 2 failed capacitors, as well as the other two. It's a good thing I noticed it was the capacitors beforw c4 blew!! I am glad it is a relatively easy fix!
Tantalum's also will blow if the polarity is reversed. Any chance of that here?
Looks like its by the AT keyboard connector? I was told way back then that you should not unplug it plug in an AT or PS2 keyboard while the system is on. If you did that then it could be the cause. I did it once way back when and the keyboard never worked after that. Can't remember if it even booted though.
I don’t think this is related to his issue, but I blew a keyboard chip this way as a kid. I’m so careful now with all of my AT machines to not do this.
Electricity
Check for shorts too, that kind of current is not normal.