Looks like a tantalum (tantrum) capacitor that went up in smoke. Welcome to the forums. Also, looks like the other red ones might be the same Microfarad and voltage. I would replace all of those caps if I were you since their days might be numbered as well.

I did find an old technical reference manual for my Tandy 4000 online here:

ftp://ftp.mindcandydvd.com/pub/tvdog/other_ta … x86/4000trm.pdf

On page 150 of the pdf there looks to be a schematic for the AT bus which looks like what I may be dealing with. In the lower right hand corner there appears to be a label for C162 which looks like the part that failed. I'm assuming based on what I see there that i may be looking for a 12V 33uf capacitor. Does that sound/look right based on the schematic?

If so if there a specific type or material I should be looking for in that capacitor?

Based on everything above i'm thinking that these could potentially replace the blown cap. The main question I have is the correct voltage. I'm not seeing any 12V ones, but am also not sure that 12V is required. Any ideas?

https://www.digikey.com/products/en/capacitor … e=2&pageSize=25

Usually the recommended replacement for tantalums these days is solid polymer caps. It would be helpful if you can find any markings wrt series so replacement can be found with appropriate ESR and ripple handling. Also, caps with higher max voltage handling will be just fine.

Just curious, how long had it been since this system was last powered on and how often was it used? Generally, people say that tantalums are actually incredibly reliable if they are used regularly, with most failures of this kind occurring after 20+ years of being unpowered. I'm always interested to hear about exceptions to "rules" like this though.

I had it powered on last about a month ago and have used it at least monthly for the last 6-12 months. Before that however, it was unpowered for 10 years or more.

Tantanulms often go up in smoke, my previous 386 had them explode every once in a while. After replacing the bad part, things continued to run.

I don't see any marking on the capacitor in question other than a single white line that I assume marks the + leg of the capacitor. Is there a way that I can tell the ESR and Ripple without markings or do I just have to guess when buying the replacement?

Is something like this an appropriate replacement?
https://www.mouser.com/ProductDetail/Ni ... Brrw%3d%3d

I'd go with 33uF poly caps. Something like these:
https://www.digikey.ca/products/en/capacitors … e=1&pageSize=25

It's purely for decoupling, so lower ESR shouldn't be a problem.

.
I strongly recommend checking the voltage output from and capacitors in your PSU.

I took a quick survey of 16v 33uF Tantalums and the typical ESR is 1.6 ohms.
( Most datasheets use milliohms. 1.6 Ω = 1600 mΩ )
Any wet-lytic or polymer should do. (Tantalums are still available if you care about the vintage look.)
I would choose polymer so long as the physical size and correct lead-space is available.
As said lower ESR is not likely to be an issue.

The ones gdjacobs linked to will work fine so long as there is room for 6.3mm diameter caps.
That's about as small as polys get in 33uF.
If you need even smaller wet-lytics have 5mm options.

Dagdamor67 wrote:

Based on everything above i'm thinking that these could potentially replace the blown cap. The main question I have is the correct voltage. I'm not seeing any 12V ones, but am also not sure that 12V is required. Any ideas?

Capacitor voltage ratings don't work that way.
The voltage rating of a cap is max a limit, not a target.
The cap voltage rating should be higher than the in-circuit voltage.
Normally 12v circuits use caps rated for 16v but sometimes it's higher, particularly if voltage spikes are expected.
(As like circuits where a cable might get yanked out under power or that may take a hit from static discharge.)
.

I purchased the suggested caps from DigiKey. Now I wait 😀

I will update once they arrive and I have attempted the repair.

Thank you to everyone who replied and helped me determine replacement parts!!

Received the replacement caps and just finished installing them. VIOLA!!. The old girl lives again!! I really appreciate everyone who helped me out with this issue. You guys/gals are the best!!.

Groovy!

I hope you're going to replace the rest of them. Old tantalum caps really are ticking time bombs, and I really think Tandy machines are something special.