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Soundcraft CPS 450b, repair or replace?
Old 10th February 2011
  #1
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recordinghopkins's Avatar
Soundcraft CPS 450b, repair or replace?

Tonight the 17v +/- lights went out on my power supply. I have yet to remove it from the rack, but I was curious to see if anyone here has dealt with this before and might point me toward the right solution...
I CAN use a soldering iron with precision on pcb's, but I'm not skilled in troubleshooting components. I can, however, visually identify a burned component and drop a new one in, if it turns out to be that simple.

Any guesses?

More info: I use it with a 550/b supply on a sapphyre desk
Old 10th February 2011
  #2
Gear Maniac
 

look for burnt fuses. theres prob one on the outside and one/rail on the inside.

if its a fuse, try with a new one unconnected to the desk first. if the leds light up the psu might be fine. then hook it up with the desk and try it out. if the fuse will fail this time you have something wrong within the desk.
Old 10th February 2011
  #3
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Thanks, I'll look for internal fuses. The master fuse on the front panel seems to be ok, as the unit is still powering on and indicators show 7v, 24v, and 48v are working with no problem. I'm just gonna have to open it up and have a look.
Old 10th February 2011
  #4
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Ike Zimbel's Avatar
 

Quote:
Originally Posted by recordinghopkins View Post
Tonight the 17v +/- lights went out on my power supply. I have yet to remove it from the rack, but I was curious to see if anyone here has dealt with this before and might point me toward the right solution...
I CAN use a soldering iron with precision on pcb's, but I'm not skilled in troubleshooting components. I can, however, visually identify a burned component and drop a new one in, if it turns out to be that simple.

Any guesses?

More info: I use it with a 550/b supply on a sapphyre desk
I can't find my docs for that supply at the moment, but the most common failure mode is a bridge rectifier failing. Good idea to replace both while you are in there, AND any wiring to the bridges that may have overheated.
Best,
Ike
Old 10th February 2011
  #5
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Thanks Ike!
Old 10th February 2011
  #6
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Ike Zimbel's Avatar
 

Quote:
Originally Posted by recordinghopkins View Post
Thanks Ike!
Yer' welcome. I just found the docs. It could be just a fuse, F-1 or F-2, T5.5 (the "T" stands for "Time Delay" aka "Slow Blow"). UN-PLUG the unit from the MAINS AC before testing the fuses. Also take note of the condition of the fuse holders, are they tight? Burnt / crystalline looking? Dark marks on the circuit board?
If a fuse or fuses is gone, you may still have a problem downstream of there, in particular the diodes that make up the "bridge", D-3,4,5,6 and D-23,24,25,26 could have failed short. You may need to take this to a tech shop. I think I can recommend someone in your area.
best,
Ike
Old 10th February 2011
  #7
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Cool! I love GS. I only lurk on this board, and I was afraid I'd get one of those "you don't know what you're doing, take it to a shop" comments right off the bat. Instead, you've both given helpful suggestions. I know a little more about the internals of electronics than I let on. Just enough to be dangerous!
I'll pull it out and have a look in the next couple of days. Naturally, I will follow appropriate safety procedure.
Old 10th February 2011
  #8
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Remeniz's Avatar
 

I repaired a CPS 450 and CPS 550 last week....

It's strange that the 17V symmetrical supply has gone like that and although it could be F1 and F2 fuses you would need to find out why they blew in the first place.

The way the 17V symmetrical supply is configure is this...

It is made up of two separate 17V supplies with the positive of one joined to the 0V of the other.

The internal connection plugs/sockets can get bad over the years so check those and check D7 as well as the D1-D6/D32-26.
Old 11th February 2011
  #9
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Quote:
Originally Posted by Remeniz View Post
I repaired a CPS 450 and CPS 550 last week....

It's strange that the 17V symmetrical supply has gone like that and although it could be F1 and F2 fuses you would need to find out why they blew in the first place.

The way the 17V symmetrical supply is configure is this...

It is made up of two separate 17V supplies with the positive of one joined to the 0V of the other.

The internal connection plugs/sockets can get bad over the years so check those and check D7 as well as the D1-D6/D32-26.
Thanks Remeniz,
It happened during a mix session with 16 of 36 channels lit up and kickin'. All of a sudden, distorted audio and half of the mute switches and solo buttons stopped working.
Old 11th February 2011
  #10
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F2 was blown. I replaced it with a slow blow 5A, because that is what was in both F1 and F2. I powered on and 17v is back but 24V was now gone. Pulled each of the fuses and tightened the clips with some needlenose pliers, removed and cleaned each of the multipin connections, and now all is well.

I hope this thread helps someone else. Fuses are an easy fix and I would have found them on my own if I had just opened it up and looked before asking. Neverless, I was able to go straight to the problem, thanks to some slutz

One more question:
My power here fluctuates between 115 and 121 volts, usually around 118. The voltage selector was on 110. Could that be the reason it blew a fuse? Should it be on 120V instead, or will it be starving for power at 115? Often I hear the UPS that is connected to other devices on the same drop kick in for a moment when I switch on the desk.
Old 11th February 2011
  #11
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Remeniz's Avatar
 

Quote:
Originally Posted by recordinghopkins View Post
F2 was blown. I replaced it with a slow blow 5A, because that is what was in both F1 and F2. I powered on and 17v is back but 24V was now gone. Pulled each of the fuses and tightened the clips with some needlenose pliers, removed and cleaned each of the multipin connections, and now all is well.

I hope this thread helps someone else. Fuses are an easy fix and I would have found them on my own if I had just opened it up and looked before asking. Neverless, I was able to go straight to the problem, thanks to some slutz
Ah, good work

Their great PSU's with very little to go wrong in them and as long as the transformer is fine all the other parts are available cheaply, diodes, LM317, LM338 and the high voltage regulator for the 48+ volt phantom power.

Quote:
Originally Posted by recordinghopkins View Post
One more question:
My power here fluctuates between 115 and 121 volts, usually around 118. The voltage selector was on 110. Could that be the reason it blew a fuse? Should it be on 120V instead, or will it be starving for power at 115? Often I hear the UPS that is connected to other devices on the same drop kick in for a moment when I switch on the desk.
Very good point and having said that I would set the AC input to 120VAC.

Time to pop those rubber caps on the lid!

Old 11th February 2011
  #12
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Thanks!
Then that's what I shall do. Maybe it will save me a fuse or two. I changed them all while I was in there.
Old 11th February 2011
  #13
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Do you think that with these supplies being 20+ years old I ought to replace the capacitors in there sometime soon? Other than recent problems, I have no complaints about their performance, although I have no comparable new unit to test. My desk performs well, but if further improvements can be made, say, that might increase efficiency, decrease power consumption, or increase headroom, I'm all for it.
Old 12th February 2011
  #14
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Ike Zimbel's Avatar
 

Quote:
Originally Posted by recordinghopkins View Post
Do you think that with these supplies being 20+ years old I ought to replace the capacitors in there sometime soon? Other than recent problems, I have no complaints about their performance, although I have no comparable new unit to test. My desk performs well, but if further improvements can be made, say, that might increase efficiency, decrease power consumption, or increase headroom, I'm all for it.
I'd say that was optional. I have replaced all of the small and medium sized caps (iow; everything but the main filter caps) in a couple of CPS-2000 supplies that had been worked very hard in a broadcast truck and not one of the caps that I took out was in particularly bad shape for either ESR or value. Fuses and bridge rectifiers and associated wiring were in rough shape, but the caps had held up remarkably well. Of note: the supply that was in the worst shape had the voltage selector in the 110v position instead of the 120v. These trucks have regulated power at or near 120v, so this thing had been turning all that extra voltage into heat for a long, long time.
Old 12th February 2011
  #15
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Remeniz's Avatar
 

Quote:
Originally Posted by recordinghopkins View Post
Do you think that with these supplies being 20+ years old I ought to replace the capacitors in there sometime soon? Other than recent problems, I have no complaints about their performance, although I have no comparable new unit to test. My desk performs well, but if further improvements can be made, say, that might increase efficiency, decrease power consumption, or increase headroom, I'm all for it.
Personally I would replace them. Even though they may not show any physical deterioration they might still suffer from high ESR, which happens over the years as the cap's dry up, and this decreases their effectiveness. And if these are the originals they are 20 years old!

A pair of high quality 10,000uF/35V for the 17 volt symmetrical supply, one 10,000uF/40V for the 24 volt rail, a pair of 4700uF/16V for the 7.5 volt symmetrical supply and one 1000uF/100V for the 48 volt supply. Go for 105'C caps. These are the large filter caps across the bridge rectifier outputs. And the CPS 450 PSU uses separate diodes for full bridge rectification unlike the CPS 550 PSU which uses 'bridge rectifiers' mounted on the heat sinks.

There's 12 other small value electrolytic caps in the regulator feedback and across the regulator outputs that you can replace too.

There's no need to change the T03/T220 regulator IC's. Just ensure their seated on the heat sink properly.

All this might seem a bit over-the-top but doing this will mean another 20 years, at least, out of the unit and it is after all providing the 'juice' for your desk.
Old 12th February 2011
  #16
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Oh, I hadn't thought about there being less heat at 120v. Would it stand to reason that even less heat would be produced at 220/240v? I have been looking into installing a separate breaker box for my rig and isolating it from the rest of the house. It wouldn't be difficult at all to run it at high voltage.
Old 12th February 2011
  #17
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Remeniz's Avatar
 

Quote:
Originally Posted by recordinghopkins View Post
Oh, I hadn't thought about there being less heat at 120v. Would it stand to reason that even less heat would be produced at 220/240v? I have been looking into installing a separate breaker box for my rig and isolating it from the rest of the house. It wouldn't be difficult at all to run it at high voltage.
The same amount of heat is produced whether you choose to run the PSU at 120VAC or 240VAC. I.E. 4A @ 120VAC or 2A @ 240VAC. The same power is consumed and wasted.

I recommend 105'C caps purely because the PSU's are usually mounted in a rack and on long sessions it can get hot in the case so the 105'C caps will be more tolerant to the heat.
Old 12th February 2011
  #18
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Quote:
Originally Posted by Remeniz View Post
Running it at 120VAC or 240VAC makes no difference to the output voltage on the secondary windings on the transformer which also means the same amount of heat is produced.

I recommend 105'C caps purely because the PSU's are usually mounted in a rack and on long sessions it can get hot in the case so the 105'C caps will be more tolerant to the heat.
ah, I gotcha.
The last owner had them simply stacked on top of each other below the desk. I have them mounted in a rack with 1u between them, but they do get quite hot. In the winter time I put my socked feet up in between them when I kick back in my chair
Old 12th February 2011
  #19
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Quote:
Originally Posted by recordinghopkins View Post
ah, I gotcha.
The last owner had them simply stacked on top of each other below the desk. I have them mounted in a rack with 1u between them, but they do get quite hot. In the winter time I put my socked feet up in between them when I kick back in my chair
Sorry, I re-wrote my previous post.

So the 105'C cap's would be adequate and they'll keep your feet warm for many years to come...

Old 12th February 2011
  #20
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Ike Zimbel's Avatar
 

Quote:
Originally Posted by recordinghopkins View Post
Oh, I hadn't thought about there being less heat at 120v. Would it stand to reason that even less heat would be produced at 220/240v? I have been looking into installing a separate breaker box for my rig and isolating it from the rest of the house. It wouldn't be difficult at all to run it at high voltage.
No it's not the voltage itself, it's the mismatch between the supply voltage and the transformer setting. IOW, the 10 extra volts that the unit sees when it's set on 110v and being fed 120v that get turned into heat.
Before anyone jumps on this rather simplistic explanation, it's been a long week!
Old 12th February 2011
  #21
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I actually understand that. I think I was the one that was overly simplistic.

However, the desk stayed powered on for a few hours inactive, and then ten minutes after passing two channels of audio from itunes, out goes the 17v again.
Old 12th February 2011
  #22
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Remeniz's Avatar
 

Quote:
Originally Posted by recordinghopkins View Post
I actually understand that. I think I was the one that was overly simplistic.

However, the desk stayed powered on for a few hours inactive, and then ten minutes after passing two channels of audio from itunes, out goes the 17v again.
Mmmmm... Shame I can't look at it for you. Has it blown the fuse again?
Old 12th February 2011
  #23
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Quote:
Originally Posted by Remeniz View Post
Mmmmm... Shame I can't look at it for you. Has it blown the fuse again?
sure has. I'm gonna change the fuse again and unhook it from the desk and leave it on all day to see what happens.
Old 13th February 2011
  #24
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Ok, I've got it open again, but I have discovered that my two extra fuses fell to the floor and were stepped on, so I'm off to the radioshack to grab a couple more. Poking around, it seems that D25 has a broken solder connection on the underside of the PC board. It wiggles around and feels like there's maybe something going on there...

I could just put this in the shop and be done with it, there's a great one just one block away, but I would rather learn something along the way. If any slutz want to talk me through trouble shooting this myself, as in, look for x voltage across y and z, then check a, b, and c ect., this would be a great opportunity to gain some troubleshooting skills...

Edit: I still plan to replace the fuse and leave it on a while longer to see if it was just coincidence that it blew ten minutes after connecting the desk.
Old 14th February 2011
  #25
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Ike Zimbel's Avatar
 

Quote:
Originally Posted by recordinghopkins View Post
Ok, I've got it open again, but I have discovered that my two extra fuses fell to the floor and were stepped on, so I'm off to the radioshack to grab a couple more. Poking around, it seems that D25 has a broken solder connection on the underside of the PC board. It wiggles around and feels like there's maybe something going on there...

I could just put this in the shop and be done with it, there's a great one just one block away, but I would rather learn something along the way. If any slutz want to talk me through trouble shooting this myself, as in, look for x voltage across y and z, then check a, b, and c ect., this would be a great opportunity to gain some troubleshooting skills...

Edit: I still plan to replace the fuse and leave it on a while longer to see if it was just coincidence that it blew ten minutes after connecting the desk.
D-25 is part of the bridge rectifier circuit for one of the 17 volt rails. If it has failed, it could definitely cause the fuses to blow. That may also be the case if it is just a bad solder joint. You can test it, and the other diodes I mentioned above with the diode setting on your DMM. You should see a reading of around 500mv with the black lead on the band end and the red lead on the other end. You should see nothing, or a much higher reading with the leads reversed (you will often get inconclusive readings with these things in circuit). If one or more of the diodes reads the same low reading in both directions, it is probably shorted and should be replaced (if you find even one bad one, replace all eight of them). Hope this helps.
Old 14th February 2011
  #26
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Thanks Ike,
I used a continuity tester both ways to verify that the diodes were still doing their job and only allowing current one way. I will do as you suggest and use the diode setting on my multimeter. The one loose diode did indeed have a bad solder joint, as well as one of the pins on the orange/white/black multi. Lots of discoloration in that portion of the circuit when I looked at the back of the PC board, indicating that it has been a problem for a while. I am guessing that faulty connections caused increased load on the supply when the desk was connected, but it wasn't enough of a problem with the supply sitting on the bench, disconnected.
Anyway, I de-soldered and re soldered each of the diodes and pins on the power connection, and the desk has been working for about an hour now, with no problem. I think I am gonna close it up and keep my fingers crossed.
Old 14th February 2011
  #27
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Update: 8 hour mix session last night, no problems whatsoever.
I will be ordering replacement caps and diodes all around for both supplies in the near future.
Thanks again.
Old 14th February 2011
  #28
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Ike Zimbel's Avatar
 

Quote:
Originally Posted by recordinghopkins View Post
Update: 8 hour mix session last night, no problems whatsoever.
I will be ordering replacement caps and diodes all around for both supplies in the near future.
Thanks again.
Good stuff! Looks like you nailed it.
Best,
Ike
Old 14th February 2011
  #29
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Thanks Ike!
Old 15th February 2011
  #30
Quote:
Originally Posted by recordinghopkins View Post
Update: 8 hour mix session last night, no problems whatsoever.
I will be ordering replacement caps and diodes all around for both supplies in the near future.
Thanks again.
I use Nichicon VZ series for those. You can fit 10,000 uf's in place of the 4700 uf mains caps.
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