LC Fan and Speaker Clicking

[AwkwardPotato]

I don't see any more corroded traces, but I do see some crusty vias. Is there continuity between Pin 2 of UG5 and Pin 15 of the EGRET? What about between Pin 20 of UF8 and Pin 4 of the PSU connector?

 

[agg24]

Yes, there is continuity between the aforementioned pins. I wouldn't be surprised if power isn't getting somewhere on the board, given the traces I had to bypass (the caps near the power connector were the worst), but I have tested continuity on those bridges, and have verified proper voltages in the HD power connector.

You are certainly dedicated. I appreciate all of your help

 

[kani97]

I recently recapped a LC and TDK PSU that was entirely unresponsive. As seems to be somewhat typical for the LC, several caps had fallen off of the board and the traces were very corroded. Before I started the recap, I did the heating test on the PSU, which greeted me with some signs of life from the system. When the power supply was turned on, the LC speaker would begin clicking, and the fan would whirl for a short period, with a frequency of about 1 second, assumedly around the same frequency that LC PSUs typically click at when they're bad.

After a recap, I am still presented with these same results. I have checked the voltages of the PSU, both with and without load. Without load, the numbers seem fine, but under load (the LC itself), the voltages fluctuate up a bit, then dive towards 0 with the click. I assume this indicates that something is still bad in the PSU, but I thought I would ask those who are more knowledgeable than me. I am somewhat worried about the machine having been "powered" (even with this bad PSU) when caps were missing from the board, possibly messing up something else.

Hi Did any of you guys try removing the power connector first and turning on the power supply? then connecting the power connector to the logic board? This worked fine with me. It seems like the PSU cannoth handle the startup current.

 

[bibilit]

In my opinion, problem is on the Logic board side, not PSU. 

If voltages are ok without load, chances are something is wrong in a rail, pulling down voltages. 

Any shorted capacitor ?

 

[agg24]

I did not try adding power after the PSU turns on. It's an interesting idea, though I agree with @bibilit that I think it's a logic board issue.

Are you suggesting that one of the caps on the logic board could be shorted?

 

[bibilit]

Can be, use a multimeter, you will soon have the answer (you should have no continuity on both sides of the capacitor)

Capacitor's fluid is conductive, so can be the issue here.

 

[AwkwardPotato]

Just noticed something -- in the pictures you posted, it looks like many of the 10uF capacitors (C7, C6, C111, C5, C1, C3, C105, C108) have been replaced with 100uF parts. This may be at least part of the problem.

 

[bibilit]

No. 

There is no problem going higher. 

 

[mdeverhart]

There is no problem going higher.

Sorry, but that’s not correct. You can go higher on the voltage rating if you want (e.g. use a 16V rated cap instead of a 10V rated one), but the capacitance value should match the original value.

For power decoupling caps, the capacitance value is important for filtering out different frequencies, so you’ll often see a few large caps, a few medium caps, and a bunch of smaller value caps - the large caps filter the lower frequencies, the smaller the high frequencies.

For in-circuit caps, the values are even more important, as they directly impact the operation of that part of a circuit. For example, a cap might be paired with a resistor to form an RC circuit, where the cap is designed to charge and discharge in a specific amount of time. Changing the cap value will change that time constant, which will cause that part of the circuit to operate poorly or not at all.

If some of the 10uF caps have been incorrectly replaced with 100uF, I would highly recommend they be replaced with the proper values.

 

[agg24]

Looking back at my recapping efforts, I had the same question of whether or not those caps were 10uF or 100uF. I ordered https://www.mouser.com/ProductDetail/Wurth-Electronics/875105359001?qs=sGAEpiMZZMvR1wrj203KOEwKeIe4y6sVy4VYRQR%2b0T7xq1e22dz4ww%3D%3D, but the 100 on the top indicates they are 100uF, not 10uF. I suppose I was too lazy/cheap to order a new set to see if there was a difference.

 

[mdeverhart]

It looks like there may be a significant amount of corrosion / cap goo under and around UB9, UB10, and UC9. If that’s the case (hard to tell from the pictures), you may need to remove those components and clean under them. I don’t have the schematics, so I’m not sure what those components do.

I agree with your reading of the capacitor data sheet - those are all 100 uF, looks like 8 of them should be 10uF and only one 100uF:

http://www.maccaps.com/MacCaps/Capacitor_Reference/Entries/1990/10/15_LC_I%2C_II%2C_III_Power_Supplies_2.html

 

[agg24]

Replacing the incorrect 100uF caps unfortunately appears to have made no effect. I am planning to go back over and verify continuity, but I doubt I'll find anything. It's likely that one of the corroded chips is crucial, or otherwise there are corroded traces preventing proper operation, and I lack the skills to properly deal with either.

Back to the shelf this poor LC goes