Profile Hard Drive PSU giving low voltages, any usually suspect caps?

[mikerofone]

Hi all,

(TL;DR: My Profile got more and more unreliable in the last two years: It worked fine two years ago, then sat for the better part of a year after which it required multiple power-off/power-on cycles to initialize properly. After an additional 20h of runtime Lisa started crashing more and more while loading / putting away programs, and now the drive no longer initializes or performs its selftest at all. Now the drive spins up and may move the heads for a second, the busy LED might be on or off, and maybe after 20-60 seconds it will move the heads a bit and the LED resets as if the init routine restarted and failed again.

I measured the voltages recently and the 5V rail was at about 4.39V - way too low and that might explain why the drive controller is malfunctioning. I assume the voltages kept sinking over time which is why the drive gradually became more unreliable. I took some pictures of the PSU internals and there is some suspicious black gunk or charring on the PCB close to / under whatever that big heatsinked flat silver component is. My first thought was bad or leaky caps, but before I go recapping the entire thing I wanted to check whether there's any usual suspect caps in Profile PSUs that typically fail. (Besides the RIFAs obviously, which I discovered to my great horror were not replaced by the seller even though he mentioned "necessary caps replaced" when seeling the kit.)
I see that most if not all are Nippon Chemicon SXA series caps, which I've seen a lot in similar vintage gear, and I don't remember seeing these spill their guts. Can't say the same about those Nichicon PL(M) series caps I've met in various places...

There also seems to be some discoloration of the PCB under and around that gunk. As someone who knows way too little about PSUs, could that indicate a problem somewhere else in the circuit which maybe damaged the caps, instead of the caps failing on their own?

Thanks for any insights you might have!

Cheers
mikerofone

 

[GiGaBiTe]

The board in the charred area looks like typical "wet" from leaking electrolyte. All of the caps need to be replaced, including the RIFAs.

Bad capacitors can be the source of the charring. The electrolyte is often conductive, so it can bridge different parts of the circuit that shouldn't be bridged and start cooking. Bad capacitors can also become electrically leaky and effectively turn into resistors, which can overload components both upstream and downstream of them and cause hideous amounts of damage.

The large TO-3 package IC screwed to the large heatsink is either a transistor or a mosfet, not sure. Someone more familiar with the SMPS from a Profile drive may know what it is. A common part used was a 2N3055.

 

[NeXT]

I second that. One or more of the 47uf 250v primary DC filter capacitors are leaking and the electrolyte is conducting in contact with nearby components.

(Besides the RIFAs obviously, which I discovered to my great horror were not replaced by the seller even though he mentioned "necessary caps replaced" when selling the kit.)

Which caps??? The RIFAs are not done and if I'm reading the Nippon Chemicons correctly the date codes are nearly 40 years old. This power supply looks completely untouched.

 

[mikerofone]

Thanks for taking a look and confirming my suspicion! So I'll replace them all and won't take any chances.

Which caps??? The RIFAs are not done and if I'm reading the Nippon Chemicons correctly the date codes are nearly 40 years old. This power supply looks completely untouched.

To clarify, the seller said he replaced caps "where necessary". Apparently, Rifas don't automatically make the cut for him. I checked my message history with him and he thinks that if they last 2h when testing, they'll last forever so he doesn't replace them. /o\ I did check the Lisa PSU afterwards and those Rifas were replaced by different models already, but I didn't think to check the Profile. Now I'm happy that it failed in this unspectacular and very fixable fashion, instead of letting out the stink in my home or during an exhibition.

Cheers
mikerofone

 

[GiGaBiTe]

That PSU will let out the stink when you start removing those capacitors. Touch any of that leaked electrolyte with a soldering iron and your whole house will smell like rotting fish for hours.

 

[NeXT]

To clarify, the seller said he replaced caps "where necessary". Apparently, Rifas don't automatically make the cut for him.

No, like unless he carefully peeled the warning label off the old capacitors in the primary side and stuck them to the new caps, all the capacitors have the same date codes. Every capacitor looks to be original with a 1984 date code. He flat-out lied to you and didn't change them.

 

[oldpcguy]

No, like unless he carefully peeled the warning label off the old capacitors in the primary side and stuck them to the new caps, all the capacitors have the same date codes. Every capacitor looks to be original with a 1984 date code. He flat-out lied to you and didn't change them.

Well, he did qualify it with "necessary" caps replaced. He could argue none were necessary.

 

[mikerofone]

That PSU will let out the stink when you start removing those capacitors. Touch any of that leaked electrolyte with a soldering iron and your whole house will smell like rotting fish for hours.

Yep, I'm familiar with that lovely odor and "looking forward" to that! -_- need to order the replacements first though.

No, like unless he carefully peeled the warning label off the old capacitors in the primary side and stuck them to the new caps, all the capacitors have the same date codes. Every capacitor looks to be original with a 1984 date code. He flat-out lied to you and didn't change them.

"Whoops, forgot to remove that bit in the listing, that was left in from the previous Lisa I sold." Possibly still a lie, but at least the Rifas in the Lisa PSU were replaced.
oldpcguy is kinda right, the seller replaced whatever was necessary to get about 60h of runtime out of the set before it broke down. Not quite "A++ would recommend!" and the price in my eyes was less justified after seeing this, but not a complete ripoff either. Oh well, live and learn!

 

[NeXT]

Well, he did qualify it with "necessary" caps replaced. He could argue none were necessary.

Ugh. That's greasy.