Film-Tech Forum ARCHIVE: Substitute power supply for a CAT700.

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Posted by Eric Robinson (Member # 2966) on 06-19-2007, 06:14 PM:

My CAT700 power supply board has burned components as well as the PCB. I have been quoted $288.00 for a repair exchange. It seems to me that I could probably come up with my own power supply for less$$ Has anyone else done this?

Posted by Louis Bornwasser (Member # 3063) on 06-19-2007, 06:27 PM:

Anything that will fit and that will light up the bulb with DC. Try Mouser electronics. Louis

Posted by Sam D. Chavez (Member # 1841) on 06-19-2007, 07:26 PM:

Actually, it doesn't even need to be DC, but it's much easier to vary the output of a DC power supply. The idea is to get 4 Volts of video.

Posted by Mark Gulbrandsen (Member # 72) on 06-19-2007, 07:54 PM:

The way to keep the Dolby power supplies from failing... almost all of em... DA-20 included is to eliminate the nylon molex connectors completely. Had Dolby not used these crappy connectors they'd have had almost no power supply failures in the CAT 700's and 701's, and DA-20. Sure its not an instant change out of the supply after you make the change but reliability goes way-way up.... it might take you a half hour to replace it... big deal. They went from single sided female inserts in the Molex's to a type that touches the pin on three sides... those may also eventually fail. There are telltale signs of this... and the best way to get ahead of the problem is to check them as you go around and look for toasty(browned) looking molex connectors... Even just slightly toasty molex's signals eventual disaster. On the solder side you might also notice that the molex pins soldered to the pcb have cold looking solder joints. Thats another sign of impending disaster. I feel this is more a fault of the plating on the pins than anything else.

I've modded all the units on my service routes this way and I have not seen a power supply failure in many, many years.

Kelmar has also experienced similar fate with these connectors in their reverse scan power supplies.

Mark

Posted by Monte L Fullmer (Member # 2797) on 06-19-2007, 09:33 PM:

Mark -

Since I have 4 of these CAT-700 units and one PS did fail, in as well having 5 of these DA-20 units, basically what you're saying to actually hardwire the connections together and eliminating such weak points through the Molex male/female connections...

..that'd be an easy one to do mods on ... thx-Monte

Posted by Mark Gulbrandsen (Member # 72) on 06-19-2007, 09:58 PM:

Yea, but you may find that I've already done some of them. Not Ontario though. Funny thing is that even the 2-3 volt LED connectors cook in the 701. I would expect to find this more in corrosion borne places than out here.... Thats why I think the plating has something to do with it.

Mark

Posted by Steve Guttag (Member # 268) on 06-19-2007, 10:07 PM:

I've been coming across an odd quirk in a set of DA20s (similar serial numbers)....the power rails (All three) sag over time and then send the DA20 into reboot. If you turn the supply off and then back on again...the same thing occurs as it heats up.

Least you think it is the molex connectors you can measure the supply right at the supply (before the dreaded connector) and the you will read the same thing under load. I've had three units do this now. One did it within the first year...the last two have happened 4 years later but within 6-months of each other!

Steve

Posted by Mark Gulbrandsen (Member # 72) on 06-19-2007, 10:30 PM:

Hard to say whats going on there... possibly a bad run of supplies since some of them are pretty close together time wise and you're seeing similar symptoms. Have you noticed any cold looking solder joints on the PCB's? I've seen these connections get hot enough to melt the solder on the boards at the Molex's. Seen this in the Kelmar's too. If thats happenning it might cause a drop in the ability of the joint to pass enough current. I literally have not replaced a 700, 701, or DA-20 supply now in close to 5 years since soldering them in place. We did loose one CP-500 power supply though a couple of years ago... that one I hadn't permanently connected... never syspected the 500's supplies.

Mark

Posted by Louis Bornwasser (Member # 3063) on 06-20-2007, 08:19 AM:

At least on the Kelmar boards, resoldering has taken care of the problem 100%. The DC power to the preamp gets erratic. There is a small resistor which runs hot near the plug. It appears that the supplier-to-Kelmar has a solder problem which does not manifest itself unless the part runs hot.

The Dolby boards appear to be similar....off the shelf...probably with the same problems. (This is not to diminish the well-known Molex problems.) Louis

Posted by Richard Fowler (Member # 893) on 06-20-2007, 08:51 AM:

Ahh, not Rocket Science. The CAT 700 EPT is a 10.8 Volt bulb drawing 43 watts; a typical 12 VDC 50 watt switcher with +/- control of 10%
(10.8 to 13.3 volts) for around $40.00 or less can handle. some 12 volt 50 watt bulbs with the same filament configuration and multifacet reflector for fiber optic use work well as a substitute.
White molex connectors, which are great for manufacturers to spit out cheaply with proper tools, also suffer if exposed U.V. light ( xenon / sunlight ) which make them turn brittle.

Posted by Sam D. Chavez (Member # 1841) on 06-20-2007, 11:10 AM:

There are other bulbs besides the ones Dolby provide that would seem to work but the focal length is not always the same and you get some strange and uneven illumination.

Posted by Mark Gulbrandsen (Member # 72) on 06-20-2007, 02:30 PM:

quote:
At least on the Kelmar boards, resoldering has taken care of the problem 100%.

Yea, as long as you catch it before it becomes charcoal. Some older Strong Switchers also have inrush current limiters that turn the board to Charcoal if the air flow is cut down.... again an easy fix before it goes charcoal.

With Dolby I'm pointing pretty much exclusively at the Molex's because there are no parts in the vacinity of the molex that would cause the "Kelmar Syndrome" to occur. Also because Dolby changed from the single insert female contact to the three sided female contact and the problem still persists. Lets face it they will never get a Technical Oscar for the power supplies they use!

Posted by Eric Robinson (Member # 2966) on 07-02-2007, 01:42 PM:

I suspected I could use a cheap susbstitute power supply. I decided; however, to get the repair exchange so that the next poor sap that comes along won't be confused by the non-standard parts.

The PCB was indeed melted and burnt, but not where the leads attach from the projector bulb. The burning occurred at the base of a small transformer at the bottom center of the PCBV board. Probably due to bad solder joints. The wires from the bulb terminate on the PCB as spade connectors which are screwed to a terminal strip on the PCB.

I'll have to admit, this was one of the easiest repairs I've come accross for a while.

Posted by David Graham Rose (Member # 1450) on 07-05-2007, 01:12 PM:

Greetings Louis

Over here I always replace R5 and R7 with a 3W resistor and leave the tails long but covered in sleeving in order to assist heat dissiption. This coupled with high temperature lead free solder eliminates the erratic behaviour of the preamp supply. Also we put a limiting resisitor so that the LED voltage will not rise above approx 7v.

From a wet Cambridge

Goodnight

David