cps 150 failure

[5.333V]

i bought an old psu for my soundcraft dlx delta some months ago.

it has been working fine until the other day when i couldnt get the + - 17V out of it.

opened it up and one T3.15A had burned.

i got new ones today.

plugged one in and fired it away.

but the new one just flashed and was burned at once...

doeds anybody has a good clue and/or some schematics for this psu?



ps

before when the psu was working it made som physical huming noise and took some seconds to get the most intensivety from the leds on the front... just if this could tell something about my problem..

[m.master]

I would be also more than happy to to have it... tracks are black from heat

[Matt Syson]

Hi
Probably failed rectifier. Fit a 400 Volt 35 Amp job and forget.
Matt S

[5.333V]

im susspecting the rectifier br2 on the -17V side.

gonna try test it before desoldering it.

btw, heard some about moding theese psu´s and the desks they supply as well. where can i find info on this topic??

[memphisindie]

Replace the main filter caps with 10,000 uf low impedance caps if you can get them, change the voltage regulator resistor to 2.7k, change the rectifiers to what Matt suggested, 400 volt 35 amp.
I would also check your fuses and make sure you have the proper values in there and that they are good. Check resistors downstream from the rectifiers an make sure they are good all the way inside the board.

I have one for sale that all that work has been done.

It doesn't hum anymore.

PM me if you want it.

[5.333V]

thanks!!!

i desoldered the rect´s and found a short in the one i susspected was bad. gonna buy two new simillar to the once matt sugested!

im not sure which caps and res are thoose you told of!?

i have a scheme but i can only guess. could you explain in a way i can get which parts youre talking about?!

the fuses are the right ones as explained on the pcb.

where was your huming coming from? physical or elecrtronical?

[5.333V]

do you think rect with 25A 600V will work aswell or should i try find better?

[Matt Syson]

Hi
That will be fine.
Having rectifiers rated far in excess is useful 'insurance' as at a customer level the extra couple of Dollars for a 25 / 35 Amp 400/600 Volt unit is worthwhile, especially if you have to pay postage . travel costs to get any replacement.
Make sure that the new ones have at least some heatsinking, either bolt it to the chassis or a piece of metal bolted on. This may not be so pretty but overheating is one of the main reasons for PSU failure.
Matt S

[5.333V]

hm..

they dont come with a heatsink. maybe possible to bend some piece of metal like a clamp and stick it on..?

ill guess they live longer than the old ones anyway!?

[Matt Syson]

Hi
A scrap of metal a couple of inches square (or whatever shape will fit in the space) would be fine although bolting it to the box would be better still.
Matt S

[5.333V]

aaahh..! like sticking it to the box!?

if you have pics, feel free to show how it could look like!


im puting together a shoppinglist over parts for the mods also.
i dont know what low impedance is refered to for the main filter caps?
and i just guessing here that you (memphisindie) were talking about the three big caps!?

and the voltage reg resistor i guess is the pot on the base side of the regulator?
did you mean for both - and + side? what about 48V?

[memphisindie]

Originally Posted by 5.333V

aaahh..! like sticking it to the box!?

if you have pics, feel free to show how it could look like!


im puting together a shoppinglist over parts for the mods also.
i dont know what low impedance is refered to for the main filter caps?
and i just guessing here that you (memphisindie) were talking about the three big caps!?

and the voltage reg resistor i guess is the pot on the base side of the regulator?
did you mean for both - and + side? what about 48V?

Nope, it's regular resistor at the base of the small transistor voltage regulator. Can't miss it. It's on the right rear area if you're looking at the front.
Correct on the filter caps, they're the big ones. Get low impedance caps to replace them. When you do a search specify low impedance. If they ain't there, anything will do.

[5.333V]

hey this is great!

you must mean r32! i read that it should be 1/2W instead of 1/4W... must i specify this when i ask for 2.7Kohm resistor?

and should i replace filter cap for 48V aswell!?

again... thank you guys alot. lots of info and help!!!

[memphisindie]

Originally Posted by 5.333V

hey this is great!

you must mean r32! i read that it should be 1/2W instead of 1/4W... must i specify this when i ask for 2.7Kohm resistor?

and should i replace filter cap for 48V aswell!?

again... thank you guys alot. lots of info and help!!!

Yes, yes, and yes (why not? while you're in there). You're welcome.

[5.333V]

i ended out buying 8A rectifiers instead together with zinks almost to big to fit next to the main caps. hope it will hold for another 10 years atleast...

and everythings running and working.

got about +17.4 -17.4 and +48.4. tell me if you think this should be corrected.

just one more thing... but it might not be able to fix.

the bloody transformator is making some buzzing sounds. feels like more than before or maybe im just hallucinating...

[memphisindie]

Originally Posted by 5.333V

i ended out buying 8A rectifiers instead together with zinks almost to big to fit next to the main caps. hope it will hold for another 10 years atleast...

and everythings running and working.

got about +17.4 -17.4 and +48.4. tell me if you think this should be corrected.

just one more thing... but it might not be able to fix.

the bloody transformator is making some buzzing sounds. feels like more than before or maybe im just hallucinating...

That's because your rectifiers are smallish value-wise, and you're still using the stock filter caps, which could be the cause of your strain buzzing on the rectifiers.
(the 35 amp versions I used won't fit and had to be mounted on flexible extensions with "home made" thick silicone heat pad insulators, they don't buzz).
I believe the stock rectifiers are 6 amp, 8 amp isn't much improvement.

Did you measure the voltage after the console is connected? It should be 16 volts. You might cook that sucker dialing up too high running close to tolerance limits.

[5.333V]

i also bougt 10 000uF caps (not low imp though) at the same time. the old once has been replaced!


the rectifiers i pulled out were RS403L and should be 4A 200V.

the scheme i have over the cps 150 shows 2.5A rectifiers.


i measured when hooked up with the board and powerd on. i took my tests in the psu right after the regulators on the resistors and caps.


my new rectifiers seems to be quiet althogh rather hot...

other parts that are rather hot (after 4h running) is the transformer and the regulators.

how hot should this box get?!?!


the only thing that buzzes (physical) is the transformer. i can play with the sound by pushing and pulling it.

[memphisindie]

Good work getting the rest done, did you also change the resistor on the voltage regulator?

The rectifiers are your main problem, weak link, as stated previously.
They are what failed in the first place, I bet the place where you soldered them has burn marks before you started, eh?
They're hot because they are severely underrated. They would be the hottest thing in there, regulators can get hot too, transformers get warm to hot.
My 35 amp rectifiers don't get hot. When they don't get hot, other things don't get as hot. My PS doesn't hum at all anymore.

Go get some 35 amp rectifiers. You'll have to be creative about how you get them in.
I would solder the wires from the chord going to your mixer from the supply onto the pins inside the supply, if they come loose and knock the rails off on one side there could be problems too. It will be less noisy too.

[5.333V]

resistor is also changed!

there where traces of heat but not coal black.
i think the rectifiers speak for their one safety! im not the expert here but the rectifiers shouldnt disturb other elektonix!?!?!
gonna get a batch of better rectifiers anyway!

but what you said about 16V conserns me alot i must say!

should i have + -16 inside the psu when hooked to the desk and power on?

[memphisindie]

Originally Posted by 5.333V

resistor is also changed!

there where traces of heat but not coal black.
i think the rectifiers speak for their one safety! im not the expert here but the rectifiers shouldnt disturb other elektonix!?!?!
gonna get a batch of better rectifiers anyway!

but what you said about 16V conserns me alot i must say!

should i have + -16 inside the psu when hooked to the desk and power on?

Don't ya hate having to keep reopening this thing?

If they get that hot, the rectifiers can affect anything affected by heat, like your capacitors, if they are underrated, they can affect your transformer.
I Think, the thing is, you're trying to get it to store enough reserve so that it isn't constantly trying to draw full maximum limit and heating up AND be fast enough and complete enough at delivering what is asked of it without bottlenecks to keep it stable.
Any shortage or bottleneck will cause heat.
The CPS 150 was known to be seriously NOT robust enough for most of it's uses. You have to beef them up. There should be a very noticeable sonic improvement when you do. Like more controlled low end and less foggy lower mids in your board.

[5.333V]

thats the beuty of good old audio technology! i never get tired of it!


and i havent closed it yet


got 25A rects today.


ill try install theese in some way tomorrow and see what i got...


thnks again memphy and hope youll stay with me for a another run

[memphisindie]

25's oughtta do it.

[The dman]

Originally Posted by memphisindie

The CPS 150 was known to be seriously NOT robust enough for most of it's uses. You have to beef them up. There should be a very noticeable sonic improvement when you do. Like more controlled low end and less foggy lower mids in your board.

Nice , I'm going to be installing a power-one next week and am looking forward to hearing the difference.

[memphisindie]

Originally Posted by The dman

Nice , I'm going to be installing a power-one next week and am looking forward to hearing the difference.

Make sure it's got enough wattage for what you're doing or it won't be any different.
Make sure R32 is 2.7k 1/2 amp too. Readjust the 48 volt supply after.

[Jim Williams]

That 150 supply should not be used for anything larger than an 8 channel console or maybe an outboard piece. It is designed to fail. The power transformers have loose wraps and most of them buzz. A Power One HDD-15-AG is a great sub.

I have 3 busted 150's here if anyone wants one for parts...

Jim Williams
Audio Upgrades

[The dman]

Originally Posted by memphisindie

Make sure it's got enough wattage for what you're doing or it won't be any different.
Make sure R32 is 2.7k 1/2 amp too. Readjust the 48 volt supply after.

Thanks for that info. My tech friend is putting it together for me, I'm just a button pusher. Is there anything else that we may need to know about the new psu?

Thanks

And Jim I'm very much looking forward to sending you my Delta master section in a couple of weeks.

[memphisindie]

Originally Posted by The dman

Thanks for that info. My tech friend is putting it together for me, I'm just a button pusher. Is there anything else that we may need to know about the new psu?

Thanks

And Jim I'm very much looking forward to sending you my Delta master section in a couple of weeks.

"If this attaches" here is the mod schematic. I haven't had any luck attaching schematics in pdf form that fit the criteria.

[Matt Syson]

Hi
An interesting load of crXp from people who don't understand power supplies. Putting bigger caps in stress the rectifiers MORE for a start.
Tomorrow I have a couple of blown up Power One modules to fix, tedium personified!
Matt S

[memphisindie]

We were just waiting on you to set us all straight.
Yes, but, to keep it in context, the existing rectifiers are severely underrated even for the stock 4700uf caps. Those caps and the power supply were spec'd for duty when the board was built ... when target market wouldn't have any, or, many cheap chinese, condensor mics to power up.
I did mine, it doesn't hum at all, barely gets warm, it works, better than stock.

[Matt Syson]

Hi
There are 2 important aspects to rectifiers, surge current (peak) and the RMS which is better related to maximum power dissipation. the capacitor is charged at voltage (current) PEAKS and as soon as the AC input falls below the capacitor voltage the diode switches off.
The peak current is determined by the circuit resistance which is made up of the capacitor ESR + load, the diode 'resistance' and the transformer winding resistance mainly.
Just looking at some rectifier specs. There are some 4 Amp 'RMS' devices which have 500 Amp surge capability. There are some 8 Amp devices that are 200 Amp peak ratedand some 25 Amp RMS devices that are 300 Amp peak rated. Indeed the 35 Amp units are 400 or 475 Amp rated.
Obviously rectifiers are not all created equal.
The second aspect is the AVERAGE current which is better related to the heating aspect of the rectifier. The larger RMS capabilities are in packages which have efficient junction to heatsink transfer, the lower ratings being thick plastic housing which is poor in this respect and the higher current units are metal or at least metal based so allowing a heatsink to remove the heat.
Heat and thermal cycling are the main killers.
If for example the transformer winding has a resistance of 0.2 Ohms. The capacitor uncharged could be considered to be a short circuit. The transformer has a 28 Volt (peak) secondary. The diode 'impedance' is say 0.2 Ohms then the maximum peak current would be 28 divided by 0.4 which is 70 Amps which is the peak level for the duration of the first half cycle of the mains before the capacitor starts to charge up. Following this the peak current will fall.
Note for this discussion I have considered the capacitor to be a 'short circuit' so it's actual magnitude is irrelevant. The peak current is around 70 Amps for which all but 2 Amp or less 'rated' current diodes ARE suitable.
The average or RMS current then comes into play and it is this aspect that defines the heating of the rectifier. A typical rectifier will drop up to about 2 volts maximum and with a RMS current of say 2 Amps for a CPS150 will therefore dissipate 4 Watts of heat. There are tables and heatsink specifications that would then tell you how hot this would get.
Most packages then without a heatsink will get pretty hot and will be more prone to failure.
Note that generally with silicon devices the power rating is subject to a 'derating' curve which shows that above about 50 Centigrade the unit MUST have the maximum power limited to the extent that it must not dissipate any power by the time the temperature is at typically 150 Centigrade.
This is of course a limited and simplified discussion but it does point out that it in most cases it is the heat dissipation capability which is more important that the 'headline' current rating.
My suggestion of a 35 Amp unit is based on the fact they are cheap and being in a relatively large, easy to mount block which can dissipate a reasonable amount of heat on it's own.
Increasing the value and a lowered ESR of the 'reservoir' capacitor increases the peak current since there is less time to charge the capacitance up during each cycle.
Matt S