Problem with Quadra 650

[pizzigri]

H! I have found a Quadra 650 cheap on a local online classified. Too bad it was crazy dirty and the seller said it started for a second and turned off. The battery was depleted but did not release acid, and the dirt was mostly... dirt (dust, Nicotine, hairs yuck and stuff).
So I cleaned completely the board, with IPA, where the dirt would not want to go away i used a Q-tip with distilled water, and I sprayed Wurth dielectric contac cleaner an the various connectors, claning as much as possible.
So, I hook it up with only the loudspeaker. monitor and keyboard, power supply mounted and no RAM (there's 8 mb onboard) and only the HD as a form of load to start the PSU. Yeah, and a fresh 3.6 battery.
I hear a faint short hissing noise coming from the PSU upon pressing the power button, for half a second, no bong, no light on the LED, basically nothing. At the secod try, same thing, except a second later, BOOM. Lots of smoke, I pull the cord off the socket and try to understand what happened!
Well, C40, a 22uF 20V Tantalum Kemet cap exploded and burned with a nasty smell. I cannot see any other damage. I used a hot air station to remove the burnt cap and clean up, and it looks like there's indeed no damage. What could have happened?
There are still traces of the contact cleaner, but it is supposed to be inert (non conductive)?
I do not have a replacement Tantalum cap on hand, and I really would love to recover this board. What should I look for? I do have a fairly equipped lab but am an Audio hobbyst have no clue when Computers give problems.

ETA image

 

[3lectr1cPPC]

Old tantalum caps do that sometimes, it happens. Likely it was shorted which was what caused the computer to start then shut off. Eventually, it just couldn't take the pressure and blew up. I can't tell what value it is based off the numbers on the one to the left unfortunately, someone else probably could. @1200XL M.U.L.E. what do the markings for that cap say on on your board?

 

[1200XL M.U.L.E.]

I will double check my board when I come home tonight. The photo on my phone of the entire board is a little blurry because I'm zoomed out to capture it all. However, I can see that C39 and C40 have the same markings. Maybe this is consistent with the Quadra 650 as well?

 

[3lectr1cPPC]

Centris and Quadra boards should be the same besides the CPU.

 

[lobust]

Since I happen to have a wombat board right here next to me, I can confirm that C39 and C40 are identical.

Looking closely at your photo, I can see that there is a lot of sludge remaining in the bottom of the scsi connector - if it's there it's likely elsewhere too... It may be that your board requires a deeper clean. Do you have an ultrasonic cleaner?

Also, idk how 650 PSU's are as I don't own one, but I can tell you from experience that Q800 (same logic board, different case) PSU's are pretty much guaranteed to be dead or dying now and recapping those is mandatory if you want a working one.

 

[Phipli]

Since I happen to have a wombat board right here next to me, I can confirm that C39 and C40 are identical.

Looking closely at your photo, I can see that there is a lot of sludge remaining in the bottom of the scsi connector - if it's there it's likely elsewhere too... It may be that your board requires a deeper clean. Do you have an ultrasonic cleaner?

Also, idk how 650 PSU's are as I don't own one, but I can tell you from experience that Q800 (same logic board, different case) PSU's are pretty much guaranteed to be dead or dying now and recapping those is mandatory if you want a working one.

My 650 has a delta psu, which seem to be survivors.

 

[pizzigri]

Hello and thank you for the replies. I used the same PSU of the 700, and it’s a Delta. Strange enough, the original psu of the Quadra 650 has the same power rating of the 700, that is,112w.
i was under the impression that the 650 would have a higher power rating, being with a CD drive and all. I can look for a standard electrolithic radial cap to bodge on the board, I sure don’t have a 22uf Tantalum.
I unfortunately don’t have a ultrasound cleaner, any alternatives? Is IPA sprayed liberally over the board good enough?

 

[Phipli]

I can look for a standard electrolithic radial cap to bodge on the boar, I sure don’t have a 22uf Tantalum.

Just remember that -ve is marked on an electrolytic and +ve is marked on a tantalum! Don't put the different type in backwards. Seems a shame to put an electrolytic in a tantalum board.

 

[pizzigri]

You are absolutely right, it is only to check if it works. I already placed in my next “to buy” project at Mouser 10 Kemet caps of the right form factor and values. Sill take some time to build up the minimum to waive shipping tho...