This is topic CP200 Power supply problem in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by John Westlund (Member # 913) on 02-20-2005, 11:32 PM:
Well, thanks to everyone that has replied to my threads about the CP200 lately, I finally got everything wired up and working today. When we got the processor and 2 power supplies, one of the power supplies had a problem. When I would power it up, there is a sound of a clicking relay and the 24v light blinks on the front. The other power supply was working fine so I was using just that one. Today after I finished the wiring, everything was powered up for a while and I turned it off for a minute. When I turned it back on, there was a pop and the fuse immediately blew. I found that there was a problem with the surge protector(which I think started this problem), so I switched it out, replaced the fuse and it immediately blew again. So I unhooked the processor from the power supply and tried another fuse. Blew right away again. I hooked the processor up to the other power supply and the processor powers up fine but the 24v light continues to blink and the relay click continues. I checked all the fuses and they seem to be fine. I need to get at least one of these power supplies fixed soon.
Posted by Mark Gulbrandsen (Member # 72) on 02-21-2005, 07:27 AM:
The thing to do is see if the supply blows its fuse with all the cards removed from the 200 but still connected to it. Just pop them all back from their edge connectors and then power up. If the fuse holds the supply is probably ok then push the cards in one at a time till the fuse blows to locate the bad card. If the fuse still blows with all the cards removed then its in the supply...... or backplane, but backplane problems are rare. Seems to me that the 24 volt light will blink if the backup supply fails or is turned off. Power supplies were never Dolby's forte and I would reccomend rebuilding... replacing the bridges and electrolytic caps and re-capping both supplies for best reliability. Electrolytic caps normally have a rated 7 year useful life and they are way beyond thet now.... There are date codes on each cap so you can tell how old they are.
Mark @ CLACO
Posted by Gordon McLeod (Member # 33) on 02-21-2005, 08:59 AM:
Since it blows the fuse when seperated from the processor it is in the supply
probably a shorted cap or the bridge
all are common parts
Posted by Kenneth Wuepper (Member # 1174) on 02-21-2005, 10:16 AM:
John,
I have made a device for testing circuits WITHOUT BLOWING the FUSE.
I call it "Fuse Saver Test Rig".
It consists of an extension cord, a light socket with switch and a light bulb.
The hot lead (narrow plug pin lead) of the extension cord is opened and the lamp socket inserted there. The lamp is now in series with the load placed on the outlet of the cord.
The lamp will light of there is a short circuit. The lamp will glow if the circuit is the same or lower draw than the lamp. So, if you are working with a power supply without load, you can use a 25 Watt bulb. When the shorted component is lifted from the circuit, the lamp will go out or become very dim. This saves fuses and also gives you a way to turn the unit under test off and on without re-plugging it.
This device has saved me lots of fuses when servicing sound and electronic organ circuits.
Hope this helps.
KEN
Posted by Chris Trainor (Member # 9) on 02-21-2005, 02:52 PM:
I had a similar problem in the ps1b that I have. Turns out there was a shorted diode which blew a rectifier. The rectifier was physically damaged and that was obvious. So, if your ripping it apart make sure to check the rectifier and the diodes. Earlier Dolby powersupplies are an extremely simple design and are usually quite easy to fix. The other upside is all of the parts are easilly available.
--Chris
Posted by System Notices (Member # 2357) on 10-27-2006, 09:48 AM:
It has been 612 days since the last post.
Posted by Serge Bosschaerts (Member # 298) on 10-27-2006, 09:48 AM:
I also have a power supply problem, when the aux rack is connected to the processor unit this happens : the -15V line fuse blows immediatly when I turn on the power supply, system emergency blinks and when the 24V led lights up this 24V fuse blows also immediatly.
When I only connect the processor & control unit,and disconect the aux unit,no problem everything works.
Could this be the aux rack or is it the power unit ?
My second power unit is in repair and will be back next week.
Serge
[ 10-27-2006, 11:02 AM: Message edited by: Serge Bosschaerts ]
Posted by Sam D. Chavez (Member # 1841) on 10-27-2006, 11:08 AM:
It is something having to do with the aux unit for sure.
Take all the cards out of the aux unit and try it again.
If it still blows the fuse, remove the connecting cables starting with the ribbon cable to the aux and try it again until it stops.
Posted by Serge Bosschaerts (Member # 298) on 10-28-2006, 09:20 AM:
Following Sam's advice I just tried the following :
Took all the cards out of the aux unit : + & - 15 V ok, 24 V blows
(Cat 108C,158 Showscan card,2 cat22's,3 cat 64b's S P Q)
Disconnect the ribbon to processor : + & - 15V ok, 24 V blows
Disconnect above &ribbon to control : + & - 15 V ok, 24 V blows
Disconnect power from processor and connect the ribbon from control : all fuses fine
Connect the ribbon from processor also : all fuses fine.
I now suspect the backplane of the aux rack, I tried the power cable from the aux unit between processor and control unit and that was ok.
I've seen that there has been some modification on the back :
From SK 44(4) to SK41(7)
From SK 40(14) to SK41(13)
From SK 42 (6) to solderhole just above jumper PJ32
From SK 43 (6) to solderhole just above jumper PJ33
Spare slot SK44 contained no card.
If I'm reading the signal & block diagram 2.25 of the manual correctly SK 40(14) is on the 24v rail, could this be causing my problem ?
Serge
Posted by Sam D. Chavez (Member # 1841) on 10-28-2006, 10:35 PM:
Well, I would say you have located the 15 Volt problem to the aux.
The 24 Volt problem seems to be in the control unit. You have 2 differing problems.
I would go through the same drill again in the control unit until you localize the short.
Don't overthink the problem at this stage, just try to localize it to a circuit board, ie, process of elimination.
I would bet the mods you noted are for the SRA5 unit.
Does this have an MPU?
I am on the road and don't have CP200 books at my disposal.
Is this 200 comprised of parts from different processors?
Also, there are devices called transorbs on most of the logic cards which can permanently short out in a slight over voltage condition and this may be one of the problems.
Posted by Serge Bosschaerts (Member # 298) on 10-29-2006, 04:23 AM:
Hello Sam,
I removed all the cards from the control unit and the aux, connected the ribbons and power, 24 V fuse blows as soon as the led comes on.
I put all the cards in the Aux & control unit back in, connected with the ribbons, no power cord, and all fuses now stay fine.
The control & processor unit came out the same rack, I bought from this firm also the aux witch came from their used stock.
I got an MPU but this is not connected at this time.
The only mods that I could see on the processor and control unit are those for the SRA5 and those for the DA20, the unit has the 517 & 560 upgrades.
Serge
Posted by Steve Guttag (Member # 268) on 10-30-2006, 01:29 PM:
It appears that Showscan or whomever is using the Cat 158 slot for their own needs. They are stealing the 24 supply to feed the Cat 158 slot.
This is where I would start...remove the "thing" that is in the Cat 158 slot as well as any other non-Dolby cards and start from there.
Odds are, the Showscan card is taking advantage of the fact that tracks 2, 4 and 6 all go to that card. Thus, one could instead of having format 43 could create a 5.1 format and have track 6 be the subwoofer track with tracks 2 and 4 be discrete surround channels. This would work fine if one has a film so encoded (there was a version of 2001:A Space Odyssey struck like this in rather recent times). However, it is completely incompatible with existing systems and will likely blow the surrounds out if one is not careful (the subwoofer track is on the normal surround track).
Anyway...first plan of attack is to make it a stock CP200...get it working and then take it from there. My suspicion is the Showscan card is shorting the +24 rail. Since you know which pin it is coming in on...you can then trace what it is going to an perhaps find the faulty component.
As Sam noted eariler, Dolby normally puts clamping diodes on their cards on the power rails. That is, they are reversed biased ...if they short, they will short out the power rail. Fortunately, this rarely happens.
Steve
Posted by Serge Bosschaerts (Member # 298) on 10-30-2006, 02:05 PM:
Ok, Thanks Sam & Steve,
I'm going to remove that cat158 and the mods on the backplane from the aux unit and see if this solves my problem.
Will keep you updated here.
Serge
Posted by Serge Bosschaerts (Member # 298) on 12-06-2006, 01:03 PM:
Here's an update :
Removed all the mods, same result.
Today I replaced the Aux Unit with another Aux Unit, - 15 V & 24 V fuses keep on blowing.
I now suspect the problem lies elsewhere, maybe the control unit ?
Serge
Posted by Ben Wales (Member # 92) on 12-06-2006, 03:54 PM:
I assume that the PSU will work without blowing fuses if not connected to the Control unit?.
Sounds that there is some Grounding/Shorting Issues with either the PSU/Cables (have you tried another PSU?)or may be the Back Plane on the Control Unit if none of the Cards are sound at fault.