Film-Tech Forum ARCHIVE: Not enough power from solar cell to CP500

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Posted by Demetris Thoupis (Member # 833) on 10-15-2003, 12:48 AM:

Hello all,
I have been recently to a local theater trying to figure out some custom made devices which where sold to the theater regarding first of all a custom rectifier with a custom lamphouse and even a custom solar cell assemply!! After hours of research and struggling I was able to ignite the lamp in this strange custom made Cinemeccanica lamphouse with a custom made rectifier. My problem now was this. I did all the necessary things required to do alingment for the cell. I got a PERFECT result regarding crossover talk, good illumination and identical osciloscope lines when the dolby tone was played. I had a huge problem though. There was not enough input from the cell to the CP500 for me to be able to configure HF and gains. Imagine that I had the gains of each channel at FULL and only the lower red lamps of the Tone alingment unit lit. All my connections seemed fine and the strange thing is that I got PERFECT results on the alingment but not enough power from the cell to the Processor. I forgot to mention that we are talking about a Cinemeccanica Victoria 4 Projector and reminding that is a custom made solar cell assembly with little cabapility of alingment made in Greece.
Any information will be appreciated.
Demetris Thoupis

Posted by Paul G. Thompson (Member # 655) on 10-15-2003, 01:37 AM:

If you got Dolby Tone to calibrate but not the HF, one thing comes to mind. Your slit lens is shot. Could be oil fouled, dirty, or just plain shot. Also make sure the exciter lamp is properly aligned and make sure the exciter lamp is operating with sufficient voltage/current.

Make sure the dolby tone strip is in properly. (emulsion towards the slit lens.) If it is in wrong, a several db error will occur. It could be enough to screw you up. Also make sure the solar cell is properly loaded. I don't think this would be a problem since it is loaded within the CP-500. Change out the slit lens and I think your problem will go away if you do not or cannot retrofit with a reverse scan kit.

Posted by Peter Hall (Member # 695) on 10-15-2003, 05:06 AM:

Sounds more like low exciter lamp voltage. You need to sort the level problem before tackling the hf..

The exciter lamp should be @ around 5.5VDC and should look BRIGHT. Poor illumination will have a more marked effect at higher frequencies - you say all sets up well - how flat is the response on the CP500 ? Focus being way out or vertical misalignment of the cell would also cause low levels. Does Left / Right set up OK (this would not do so if the focus or azimuth were so far out as to lose the levels). In my experience even the most shagged slit lens will give Dolby level - typically a V4 / 5 / 8 / 9 would only require the manual level controls on a CP500 to be at 30%..

Posted by Demetris Thoupis (Member # 833) on 10-15-2003, 07:30 AM:

Well,
I forgot to mention this before but the lamp was at full and it was as bright as it could. It was alingned fine and the light output on the slit was very bright. I cannot figure out what can be happening. My intuition tells me that they will probably need to buy a normal cell bracket with a new solar cell even though I cleaned both the cell and the slit lens still the outcome was the same.
Any ideas??
Demetris

Posted by Gordon McLeod (Member # 33) on 10-15-2003, 09:04 AM:

I would replace it with a proper cell but where did they get a split bilateral cell in the first place as the chip is not that common by itself ecept the standard oem replacement one so the bracket shouldnt make a difference
Check the slit for clouding

Posted by Christos Mitsakis (Member # 143) on 10-15-2003, 09:41 AM:

Dimitris,
Welcome to the custom made world that we are used to here. Custom made machinery work fine until you have to replace a part. Some Lamphouses and rectifiers though are excellent designs that rival pricey renown brands.
As far as the sound pickups, I am used to fixing really awfull retrofits or awkward modifications (cell without bracket sitting on a wooden drum etc).
I've got exactly the same problem you have a month ago with a philips DP65 with standard philips soundhead (ie no custom made modifications etc.) and a CP65.
Since you said everything is ok from the point of alignment and exiter power and light output I have to ask three questions:
1)Did you check the slit lens for any physical damage either on the lens or the lens barrel? (perform also an illumination uniformity test with cat. 566)
2)Did you try to change the inputs on the CP500 (from proj1 to proj2 so that you make shure the problem is not in the CP500 preamp).
3) How old is the cell? It seems some cells with much use (and bad treatment) give lower and lower output with time. That is my case I mentioned before. The problem appeared last year were you have to crank up the pots to get almost dolby level. A year later pots cranked up all the way, No Dolby level and of course modulating noise (pumping) is very audible. If this is your case the only suggestion is to change the cell (either with "original" bracket or just the cell in your custom made base). The point is CAN YOU FIND a cell in Cuprus with ease? Here it is almost impossible to find one even from Dolby dealers.
Do tell me about your findings.

Regards
Christos.

Posted by Jean-Michel Grin (Member # 1360) on 10-15-2003, 04:37 PM:

Dimitris,

I remember one time, one of my colleague had constated a verry important loose of signal at the dolby processor input.The exciter lamp was ok the cell too and the light path was excellent. After a long time to locate the fault. it appears that the shielded cable between the cell and the dolby processor was defective: It was not short circuited, but he had a bad capacitance inside. (Sorry for my weak English, I hope tha You understand me )
If You are sure of the cell and the processor, Inspect the cell cable, or try with a new one.
I hope this can help You.

Best regards,

Posted by Randy Stankey (Member # 64) on 10-15-2003, 05:26 PM:

In working with Simplex projectors that have the Jax-Light retrofit I have found a similar problem with low output. For some reason, over time the cell seems to burn out. (For lack of a better term.)

In a normal alignment the "picture" of the light coming from the exicter/slit lens should land upon the upper 1/3 of the solar cell. After a while it just stops working the way it should. The way I fixed it was to move the cell so the light landed on a different part of the cell. Maybe 1/2 or 3/4 of the way from the top instead of the usual 1/3. It is a simple matter of loosening the bracket and moving the assembly so that the light lands on a differnt part of it.

Maybe your problem is of a similar nature? I don't know but it's worth a shot. It couldn't hurt.

If that doesn't work I agree with the others. Check your optics. Ensure that the exciter is aligned with the slit for maximum light throughput. Check the slit and lens assembly for cleanliness and possible damage/wear. Fail that, start replacing things.

One last thought... I don't know if this applies to you or not, though. In some systems like the Jax-Light, there is a small preamplifier between the cell and the processor. On the Jax-Light it's mounted inside the exciter lamp compartment. On occasion it would go bad and cause all sorts of problems. Among them would be low signal or even no signal at all. In my case, replacement of the preamp was necessary. If you have some kind of preamp I suggest you give it some consideration as well.

Posted by Demetris Thoupis (Member # 833) on 10-16-2003, 12:41 AM:

Hello all,
Thank you for your replies. Well the most possible error that is the problem probably is what Christos and Jean Michael have said. Christo YES I am working with the only Dolby supplier in Cyprus as a technician and I can aquire easily a stereo solar cell, but this particular cinema does not want to spend any more money on Cinema equipment. It is either the cell, which looks quite old, although I cleaned both the cell and the lens well before any of my tests, or the cable. Jean Michael and all others, the cable that has been used from the guy who just took the projector there and did a preliminary set up is a normal stereo wire (like the ones that we use for Non Sync) from the solar cell to the processor and in the plug, there is an interconection between the shield and the L- R- connections. I have to check it out.
Thanks again