Soundcraft CPS-150 power supply repair

[thared33]

Here's the famous plan for upgrading this thing: http://juggernautmusic.com/wp-content/uploads/2013/10/cps-150-mod.pdf

I replaced the bridge rectifiers, huge caps and resistor with these exact parts:

https://www.mouser.com/ProductDetail/nichicon/uvr1v153mrd/?qs=a9YHeVlNhjEieJD0LNteWA%3d%3d&countrycode=US&currencycode=USD
https://www.mouser.com/ProductDetail/Vishay-General-Semiconductor/BU1006-M3-45?qs=u%252Bh7cTrMUz8NUr6J7cWJWA%3D%3D&countrycode=US&currencycode=USD
https://www.mouser.com/ProductDetail/YAGEO/CFR100JT-52-2K7?qs=gt1LBUVyoHlH9i0E7Pd%2F9w%3D%3D&countrycode=US&currencycode=USD

Upon power up the 48v LED was off. Before I knew it I saw smoke coming from the PSU. I shut it off, looked inside and noticed caps C33 and C34 bulging and smoking. I don't believe they were bulging beforehand. I don't know why/how this happened as others have done exactly what I've done and their PSU was fine.

I got advice on another forum and I was told to remove caps C33 and C34 (the smoking/bulging ones) and test it again. I did that, then jiggled the 48V LED to see if it had come loose but seemed fine. I powered it up and the 48V LED works without C33 and C34.

I was recommended to either:
1) upgrade C33 and C34 to 100v and put in a new LED, or
2) "upgrade C33 and 34 to 100v, by omitting the LED from the control loop so that the 2k7 resistor will be connected directly to ground, and the LED is connected using an additional resistor of, let say, 22k to 48V output (similar to how it was done for indication + 17V power supply). The 48V output voltage needs to be readjusted." Here is a picture:



Being new to this stuff, I have no idea what the second method entails. Over my head. I just tried to mod my PSU before it blew up (as they all do), then ran into all this trouble. I've got a good desoldering gun, iron, good flux etc so if I need to replace something I can, I just don't know electronics well at all. Do you think I should just do mod #1 to get it working? If someone could give me instructions I could do #2 but I want to check here first.

[David_AVD]

Perhaps you installed the capacitors with the wrong polarity?

[thared33]

Perhaps you installed the capacitors with the wrong polarity?

I quadruple checked and the big caps I put in seem to be the correct orientation according to the markings on the board. I'm going to quintuple check tomorrow.

[David_AVD]

Maybe post a pic of that area of the board?

[David_AVD]

Also, did you measure the 48V output when you had the caps disconnected?

If something else went wrong, there may be more than 63V across them.

Lastly, what are the specs (capacitance / value) of the new C3 and C4 that you used?

[tunk]

From the schematics C33+34 are 63V. Those in the link are 35V, so if you used them ......

[mikerj]

Which capacitors did you originally replace?  I'd assumed you mean the main filter caps (C1, C21) but if so then the 35v rating you have used is not sufficient.  This would not have caused the demise of C33/C34, but it's possible you cause short circuit around REG3 whilst replacing the filter caps which lead to the unregulated supply voltage being applied to the output.  That would certainly have smoked the caps.

[Audiorepair]

Maybe you installed the bridge rectifier the wrong way round.

Look at the capacitors and diodes to see what would happen if you did that.

[thared33]

Maybe you installed the bridge rectifier the wrong way round.

Look at the capacitors and diodes to see what would happen if you did that.

Here's a picture of one of them, including one of the big caps, and the backside:
https://ibb.co/YTg9Wtb
https://ibb.co/p0JDjcF
https://ibb.co/ThN56NZ

The marking on the right side (negative) of the big cap is opposite of the + symbol on the board itself as you can see. The other big cap is oriented the same way. The rectifier pictured is definitely the correct orientation, and the other one matches the + symbols too.

Which capacitors did you originally replace?  I'd assumed you mean the main filter caps (C1, C21) but if so then the 35v rating you have used is not sufficient.  This would not have caused the demise of C33/C34, but it's possible you cause short circuit around REG3 whilst replacing the filter caps which lead to the unregulated supply voltage being applied to the output.  That would certainly have smoked the caps.

Weird, the reason I went with the exact caps I posted earlier is that a guy named Jim Williams and two others used those exact same caps. I even asked why those would work being only 35v but I never got an answer. Beats me, but I trusted them and ordered the ones they posted.

Also, did you measure the 48V output when you had the caps disconnected?

If something else went wrong, there may be more than 63V across them.

Lastly, what are the specs (capacitance / value) of the new C3 and C4 that you used?

15000uf 35v. Ok, here's the thing. I'm not a tech and don't know electronics well. I was going to simply replace the parts I posted earlier and hope for the best, since other people have done the same thing with good results. I mention all of that because being kind of new to this, I honestly can't figure out where to put my probes to test, and how to readjust the 48v output (and neither could another guy I talked to but his was 100% fine after modding it just like I did).

I was hoping to save $250 on shipping and tech service fees and do it myself, and most importantly learn a bit in the process. We all have to start somewhere, and I guess my journey into electronics starts with smoking capacitors 

[David_AVD]

Unless the original caps were faulty in some way, just reuse those.

The circuit calls for 47uF 63V and they are cheap and easy to get. An example from Mouser: https://au.mouser.com/ProductDetail/Nichicon/UVZ1J470MED?qs=j5iQOXvqZx9y2rYc7AJ25Q%3D%3D

[thared33]

Unless the original caps were faulty in some way, just reuse those.

The circuit calls for 47uF 63V and they are cheap and easy to get. An example from Mouser: https://au.mouser.com/ProductDetail/Nichicon/UVZ1J470MED?qs=j5iQOXvqZx9y2rYc7AJ25Q%3D%3D

Do you mean reuse the caps that smoked, or the original big caps? The original big caps I still have but as mentioned I've heard a lot about how replacing them with the ones I got is a good idea since the original ones are underpowered (capacitance I guess). The other two caps that smoked are kaput. I've got them out and will need new ones for sure. Someone recommended 100v ones as mentioned, but it probably won't hurt to replace them 1:1.

[David_AVD]

Why were you even wanting to replace the 47uF 63V caps in the first place? Changing them to much higher capacitance ratings can cause problems.

What are the "big caps" you're referring to?

[thared33]

Why were you even wanting to replace the 47uF 63V caps in the first place? Changing them to much higher capacitance ratings can cause problems.

What are the "big caps" you're referring to?

I never replaced or even wanted to replace C33 and C34 which are both 47uf/63v caps. But they're the ones that started smoking. The ones everyone replaces are C1 and C31. They are originally 4700uf/50v but I was recommended to replace them with the ones I posted above, 15000uf/35v.

[David_AVD]

If C33 / C34 smoked after you started playing around, then there is likely an issue around REG3, causing the voltage across C33 / C34 to be way higher than it should be.

Swapping out C1 / C21 for hugely larger values is also a bad idea. It will cause a lot more stress on the diode bridges, fuses and transformer.

It seems like the original advice you got was bad and you've caused additional problems while working on the board.

Time for someone who knows what they're doing to fix it now, before more damage occurs and you smoke the console too.

[thared33]

It's beyond me how so many other people have used those same capacitors, including a guy who's rebuilt them for years, and they all turned out fine. Not sure what to think at this point, but I guess I'm just gonna have to bite the bullet and send it to someone.

I'm just about positive that I didn't actually damage anything though, and I mean as far as a bad soldering job, breaking a trace etc. I used a good desoldering gun etc, and just switched the parts cleanly and that was it.

[mikerj]

35V rating is ok for C21, but for C1 you are using a 35V cap on a rail with a nominal 31V.  This isn't sufficient margin, the voltage will rise under low load and also if the line voltage increases.  Also using such a high capacitance puts a lot of stress on the rectifiers as the conduction angle gets very narrow and peak current very high.

[andy3055]

I am only looking at the first partial image from the PS diagram you posted. You may be having a failed regulator. From that first image you have posted, C31 is 470uf/100v, C33 and C34 are both 47uf/63v. In one of your replies you are talking about a 15000uf and a 4700uf caps. Is that a typo? If not where did you install them? You should stick to the original values of the caps (uf) even though it is OK to increase the voltage ratings as that will be  better for safety.

[thared33]

Hi again. I gave up on it after I posted but I still want to get it back up and running. I think it's best to send it to someone since more than anything I'm just plain curious as to what in the world went on with it. It still doesn't make sense seeing that I used exactly the same parts that a lot of others do (including experienced techs).

I am only looking at the first partial image from the PS diagram you posted. You may be having a failed regulator. From that first image you have posted, C31 is 470uf/100v, C33 and C34 are both 47uf/63v. In one of your replies you are talking about a 15000uf and a 4700uf caps. Is that a typo? If not where did you install them? You should stick to the original values of the caps (uf) even though it is OK to increase the voltage ratings as that will be  better for safety.

C1 and C21 are the ones that have gotten the 35v/15000uf treatment. They were originally 50v/4700. I used these since I saw a few others using the same ones. David_AVD seems to think that was bad advice. Not sure why some techs would rebuild them that way if they're not good to use, but I'll let techs with more knowledge sort that out.

Anyone know someone here on the forum that could take a look at this for me? I'll pay all shipping/fees of course. I'm in the USA.

[andy3055]

It is not so difficult to find the problem if you go about it in an orderly manner. Like some of us said, check the regulator and put the original caps that are good and not bulging etc. in place. Replace only the bad caps. By now, you may have busted some resistors even. Make sure the caps are properly oriented. Check the diodes and bridge rectifier. There are just a few things to check. Go about it slowly and you will be able to get it going. Where are you located anyway?

[Audiorepair]

A faulty D32 could produce those symptoms.

Or maybe it is fitted the wrong way round.

[Audiorepair]

Also, and this is a long shot, should there be an insulator between the regulator and its heatsink that is missing?

This would normally short its output to ground, but perhaps the heatsink isn't a direct ground.

[thared33]

It is not so difficult to find the problem if you go about it in an orderly manner. Like some of us said, check the regulator and put the original caps that are good and not bulging etc. in place. Replace only the bad caps. By now, you may have busted some resistors even. Make sure the caps are properly oriented. Check the diodes and bridge rectifier. There are just a few things to check. Go about it slowly and you will be able to get it going. Where are you located anyway?

I'm going to order those caps and put them in. I should probably test everything beforehand so I'll look into that and update this thread soon. I'm in the south, Louisiana USA.

Also, and this is a long shot, should there be an insulator between the regulator and its heatsink that is missing?

This would normally short its output to ground, but perhaps the heatsink isn't a direct ground.

The only thing about the regulator that I noticed is that I left some Kester around it since I soldered in the new resistor. It's non-conductive though so I don't think that had something to do with it. But now that you mention it, I actually put in some heatsinks on the bridge rectifiers. On the back side of the rectifiers there is a sheet of metal and I simply put some thermal paste on it before screwing the heatsinks down. If this had something to do with why it went haywire then that's actually good news since I'm closer to figuring this whole thing out.

[thared33]

It is not so difficult to find the problem if you go about it in an orderly manner. Like some of us said, check the regulator and put the original caps that are good and not bulging etc. in place. Replace only the bad caps. By now, you may have busted some resistors even. Make sure the caps are properly oriented. Check the diodes and bridge rectifier. There are just a few things to check. Go about it slowly and you will be able to get it going. Where are you located anyway?

Also, the only parts I'm missing are the two C33 and C34 caps (they burnt) and the original resistor (not worried about that though). I still have the original big filter caps and bridge rectifiers. Maybe I should desolder the two big caps and the rectifiers I put in and put in the old ones (along with some replacement C33 and C34) and then start testing. Would that be the best course of action?

EDIT: I just realized something I forgot to mention: I don't know if this is typical but there were two different rectifiers in there. Here they are:

https://www.mouser.com/ProductDetail/Taiwan-Semiconductor/KBU603?qs=xguzDneKu5CI0Ee%252BTPlYbg%3D%3D
https://www.mouser.com/ProductDetail/Rectron/RS403L?qs=G5AQjGfRJcJNDTJssLdP8g%3D%3D

I replaced both with this:

https://www.mouser.com/ProductDetail/Vishay-General-Semiconductor/BU1006-M3-45?qs=u%252Bh7cTrMUz8NUr6J7cWJWA%3D%3D&countrycode=US&currencycode=USD

Not sure that has anything to do with it. But other than everything I've posted, I'm dumbfounded. I'll get to work on it soon, just want to hear back first. Thanks for all the help 

[andy3055]

That rectifier you put in has much higher ratings than the other two which is good unless you mixed up the pins by putting it the wrong way or the heat sink you used is touching something.. in case the heat sink is internally connected to one of the legs which is kind of strange. Putting in such big caps may have stressed other things. Your regulator must be already kaput along with a few components around it.
Check the resistors and diodes out of circuit. Those are common diodes and are cheap. Just replace them along with the regulators. Basically you are rebuilding the power supply!
If you were in the SF bay area, I could have helped.

[thared33]

I have to say a very, very big thanks to Andy. He went way out of his way to help me. I'm not sure why he did it, but he schooled me in electronics and I've now got a working power supply. I'm not even sure what the problem was in the end because a lot of different stuff was replaced. It works now, at least.

Also, and this is a long shot, should there be an insulator between the regulator and its heatsink that is missing?

This would normally short its output to ground, but perhaps the heatsink isn't a direct ground.

I somehow missed this post. Do you mean REG3? There is an insulator between REG3 and its heatsink and it's a pretty tiny heatsink. REG1 and REG2 are on the actual heatsink which is a giant thing on the back of the supply, and those both have insulators.

What I wonder is if me putting heatsinks on the bridge rectifiers had something to do with it. The rectifiers have a flat metal side and I attached these little heatsinks to them using only thermal paste. Now I'm wondering if not having an insulator on them caused any of this.