My First Recap - LC

[JustG]

I finally worked up the courage to start desoldering the bad caps on the LC logic board I found at a local electronics recycler.

About an hour later, not a single pad lifted.  The board is now drying after being washed in some very diluted soapy water.

This LC didn't power on so I'm going to attack the power supply next, is there a pinout so I can test that the supply is outputting the correct voltages after I replace the capacitors?

Also, I noticed the IC at UC9 which I believe is the audio amplifier has shorted or burned up.  Would it be safe to attempt to power up the computer without replacing this component?  I did a decent job pulling the bad capacitors (my first time doing surface mount work) but I'm a little nervous about trying anything with more than two solder points. 

 

[AlpineRaven]

Google is your friend  

http://old.pinouts.ru/Power/mac_lc_power_pinout.shtml

Good on you doing re-cap... Ive done so many of those!
Cheers

AP

 

[JustG]

Thank you for the link, I should have done some searching before asking the question!

I did a partial recap of the power supply following the suggestions from maccaps on which to replace.  I now get a clicking  from the power supply.  I’m going to try to do a little more cleaning of that board and if that doesn’t work, replace the rest of the capacitors.

 

[Elfen]

Recapping a board (and power supply) is an all or nothing endeavor. You can not just "replace some of the caps" and think it will work. It also sounds like you are skipping a lot of steps too.

- When you removed the caps, even though you did not lift a trace, did you check the connections?

- When you removed the caps, did you check the traces that were under and around the cap area?

- When you removed the cap, did you clean the area where the cap was with a q-tip and acetone?

Now, you can replace some of the caps and test it, but then you need to replace more caps and test it again and again until you replaced all of the caps. But you do have to replace ALL of the Caps!

And NEVER EVER Put the Power Supply in water. You need to clean the area under the cap with a q-tip and acetone to clean up the goo and when wipe it down with alcohol soaked q-tip to wipe the area clean.

Be careful with the power supply. you can get caps that are the right ratings but the wrong size. This will make things hard to put back together. I fixed 2 LC-Series PSU with the wrong size caps, and though it was a tight squeeze, they do work. Other LC PSUs I got the right sized caps and they fit perfectly. If you can, measure the caps and order the rating and size cap you need for the PSU. This will add more time but to get a perfect fit, it is needed.

When you check for traces, 1) you check the route they go through and see where it goes. If that traces changes color (like from light green to dark green), check the ends with a meter and see if it connects. If not, you are going to have to bridge that line with a tin wire. A trace that changes color usually means that the connection broke where the color change happens. 2) The LC (as I remember) needs both RAM and VRAM in order for it to turn on.

The broken chip should not be a problem. If it is a sound amplifier, then you will have a mute (silenced) LC. It may be fixable but who knows. My Classic II (Based on the LC/LC II board) has a broken sound chip, and is mute. But for what I do with it, sound is not a priority.

 

[olePigeon]

I agree, replace ALL the caps.  I've encountered caps that didn't look like they were leaking, but when I removed them, all the electrolytic stuff was completely dried and the cap was almost useless.

 

[JustG]

I'll be ordering the rest of the caps for the power supply.  Not a drop of water will touch the supply, I'll be doing a cleaning of it with DeoxIT and IPA.

Definitely will be testing traces before I put the effort into soldering new capacitors onto the logic board.  I think I may attempt to replace that amplifier chip, I ordered a replacement with the initial batch of caps.

I appreciate all the suggestions, hopefully I can get this guy back up and running!  I'll keep everyone posted.

 

[LaPorta]

As for the size of caps, especially if in a power supply, be sure that they also are not too SMALL. You may have the correct voltage and capacitance, but if you get a cap that is 1/4 the size of the original, you are going to possibly have a serious heat dissipation issue. Now, if you are like me, and some of these get used once in a blue moon for a special purpose for maybe a half hour, a cap a bit smaller will not matter. But if you plan to use this a lot, and the caps are far smaller (a little smaller is fine), you may run into issues.

 

[Zippy Zapp]

One thing about cap replacement is you may not find the exact size at the value you are looking for.  The caps on these systems, are 25 years old and since then technology has improved so some caps, even though they are the correct value, are going to be smaller.  Maybe not too much smaller but there may be instances where you can only get close.  Don't fret about that and more importantly make sure you get caps with good Lifetime @105 degrees specs and from a quality brand.  Nichichon and Panasonic is what I usually buy.   

 

[Elfen]

I tend to over voltage my caps, if it says 25V, I'll put in a 30V or 35V cap but nothing more than 15% over.

When I did the PSU on my LCs, even if I were stuck with same voltage caps, they were too big in size. But looking over the list on the website after my orders and receiving the caps, some (a lot but not all) caps has their physical measurements on them. I should have measured the caps to order the correct size but I did not. So if you can give the extra time, measure the physical size of the Cap on top of the uf and V of the Cap. then see what is there and order what you need.

 

[Elfen]

A lot of times with these old systems (Macs, PC, even VCRs and TV; and one time I seen it on a washing machine!), Bad caps on the logic/mother board can keep a system from turning on. this would make you think that the PSU is bad when it is not the case. But with these little LC PSUs, it's a must to recap it. But if you recapped the board, chances are the PSU will be able to turn on the system even with bad caps in it. Even though it does, does not mean that the caps in the PSU shouldn't be changed, they should.

Ha! In thinking about the washing machine, I have to wonder. It was built in 1990-something, and it refused to turn on. My friend (who fixes ACs, Washing machines and other appliances) was stumped by this one. He swapped out the controller board, the motor, switch sensors, electric valves, everything but it would not turn on. Then I saw this large filter cap in the side of the machine's innards and told him, "See this? Change it." He did after searching most of the day for another one, and the freaking machine turned on! Then I told him to put back the original parts and he did, to his surprised nothing was wrong with the original parts! After that night I was helping him through Newark and Mouser website, where he found the filter caps on one of them (Mouser I think) and he bought 10 of them for around $50. And since then, the first thing he tests/replace is the filter cap. Ha!

 

[JustG]

Again, I appreciate all the advice!  I'm taking my time with this LC as it's the first recap I've ever done and if successful, not the last.  I haven't ordered the rest of the capacitors for the power supply yet so I will definitely pay attention to the physical measurements along with the values.

All the components I have ordered so far have been the higher rated and from the better brands.

One more question, I should order a replacement for the BIG capacitor in the power supply as well I'm assuming?

 

[eraser]

 I haven't ordered the rest of the capacitors for the power supply yet so I will definitely pay attention to the physical measurements along with the values.

One more thing to consider:  Identify the SERIES of capacitor in the original design because that matters too.  I'll give you a real-life example.  The power supply in the Quadra 630 uses quite a few United Chemi-Con SXE capacitors.  If you look up the SXE series you will find that these caps are low impedance.  When choosing your replacement cap you will want to also find one that meets all of the specs above (capacitance, voltage, temperature, size) but also is a low impedance design.  You will also find caps in Macs that are low ESR (effective series resistance) and a few other features.  Keep in mind that specialty caps like low impedance and/or low ESR are more expensive and if the engineers and bean counters decided that they were worth the cost then there is probably a good reason why they're there.  If you can't identify the series of capacitor or if it seems generic then chances are it's just a "general purpose" cap.  I'd also mention that you shouldn't use those specialty caps in place of general purpose ones because they can cause problems.  The design of a particular circuit may depend on the resistance and/or impedance of the capacitor to function correctly.  Suddenly eliminating that characteristic will change the behavior of the circuit in possibly undesirable ways.  

One more question, I should order a replacement for the BIG capacitor in the power supply as well I'm assuming?

Yes.  All the electrolytics must go.  All other components can stay as long as they are not obviously burned or physically damaged.  If you see a scorched component or PCB in a power supply that is a sure sign that something went very wrong at that spot.