Film-Tech Forum ARCHIVE: 60 cycle hummmm on CP200

This is topic 60 cycle hummmm on CP200 in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Raymond Watson (Member # 3644) on 10-25-2006, 07:56 PM:

Like the title says , I have a 60 (sounds like it anyway) cycle hum on my cp200.
It happens when....
I run the sound system.....
1. in any proj. position
2. with everything else in building turned off
3. in any format... ie. format 3,4,5,10, etc.
4. on either the main or the aux power supply

It does not happen when any of the following cards are out of circuit....

In the processor...
1. Right 207
2. 150E
3. Either of the 141's
In the control unit
4. right 517
5. right 64c
6. or the 137? modified link card (in between the 517,s I think thats the right model #)

This happened all at once,and I leave unit powerless when not in use. (feeder power off)

I feel I have a electrolitic cap gone bad,(given the age) but I need help to identify the correct component, and card.

Any help is greatly appreciated....!!!!

Guttag , Gulbrandsen....... you guys got your guns ready?

Thanks to all in advance.... Ray

Posted by Mark Gulbrandsen (Member # 72) on 10-25-2006, 09:11 PM:

This is something that GUttag and Sam Chavez are much better versed on but I would check the following....

Since it happens running on either supply look for an open ground from the power supplies to the procecssor, or an open earth ground. If you can put a scope on the DC lines be sure they are running very clean... basically no ripple at all. Also check the fader line! I would find it hard to believe that both supplies suffer the same problem but you never know at this age. Ripple in the low millivolt region would probably be acceptable on the rails.

If you do need a power supply rebuild there are much better capacitors available today than there were when the supply was designed and built. Go for 105 deg. C. rated caps instead of the cheesy 85 deg. c. caps when and if they rebuild it. Caps made today are also much smaller so they will have to be fit in place securely.

Mark

Posted by Steve Guttag (Member # 268) on 10-30-2006, 01:50 PM:

CP200 hums come from two places...the power supply and something contaminating the signal ground...like a Dolby DMA8.

The power supply is a good place to start, even if it is a sudden change like you describe. It is easy enough to pull it out, take off the cover and then make sure all of the capacitor screws (the ones that hold the wires on, not the clamping screws) are tight. This is the most notorious thing that will beget a hum or even a oddly functioning CP200.

I am now replacing the filter caps as a matter of course if I open a PS1(B). They went out of production 13 years ago so all of the caps that one may run across are now suspect anyway.

The diameter of the caps are 35mm and that is still a standard size today. However, one may be surprised that an equvalent capacitor (working voltage and capacitance) will be about 1/4 as tall! I get PCB mounted caps and then solder on wires. I then solder these wires to the PCB with any other wires that may have been screwed down before. After all, once soldered, the age old problem of the screws loosening up will now be gone too. The orignal clamps will hold the new caps in place if you got 35mm diameter ones.

While you are in there...check out the bridge rectifiers. If you have a later unit they will both be of the large square package variety (the package number escapes me at the moment)with a mounting screw through the middle. If you only have one of those with the other looking like an upside down Stonehenge monument. You should give serious consideration to replacing that before it blows out too. It is relatively easy to install the square package rectifier. I use the 25A/600PIV variety since it has come in handy for many things and it is cheaper to stock a lot of one type than a few of many types. The only trick to that is to countersink the mounting screw for it so the unit will slide back into place. Other than that, the wires are long enough to retrofit the new rectifier in place.

That is about all there is to a CP200 power supply.

Now all of that said, given your description, you seem to have a card failure since removing a card silences the problem. A power supply will cause all cards to have various issues that use the affected power rail. I'm leaning towards the Cat 150....its always the Cat 150, right Sam? [Wink]

If you dial up format 42, that would bypass the Cat 150...is the hum there? How about a Non-Sync format like format 60...is the hum there? If the answer is no, then you are down to the Cat 150 and prior.

Let me know and we'll work through the problem.

Steve

Posted by Louis Bornwasser (Member # 3063) on 10-30-2006, 02:06 PM:

The 150, because of its complexity, is always a good starting point. Louis

Posted by Gordon McLeod (Member # 33) on 10-30-2006, 04:49 PM:

The meter cards can also be a source of hum