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Well, the 200 supply was a little strange and sized barely big enough to run a full 200. I think Guttag rebuilt his supplies with slightly larger switch mode supplies. Yes, the 100 supplies were built in and a PIA, but they typically ran for 20 to 25 years. I can remember at least 8 CP-100's I worked with. or on and the things just ran and ran and ran. I even soup'd some of them up by adding newer 517 cards and making them do things they weren't designed to.
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Hello,
Kieran, thank you for that lead I will contact them today, I ordered the capacitors and will change them out as it would be very satisfying to have made a successful repair but if not hopefully I will be able to get a new replacement supply.Comment
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Before randomly changing capacitors I would check the voltages using a multimeter. Test points are on the CP650 itself. See if you see any instability, particularly after a while. An oscilloscope would be better but not everybody has it. Then re-seat all the boards and looms. Two voltages can be adjusted via trimmers on the PSU. You may want to see if those voltages are ok and then "clean" the trimpots by moving them all their way up and down (with the unit powered down!) and then setting them back where they were. Just in case the voltages are oscillating because of them.
That PSU is a bit of a pain as everything is very tight. I guess that replacing capacitors won't hurt.Comment
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For the record, our PS1(B) (CP200 power supply) upgrades came in two forms...one was a change in the electrolytics that were solder in and slightly larger in capacitance. One of the issues with the PS1 was that the fasteners for the capacitors could loosen up and reduce their effectiveness (get lots of ripple). And yes, the PS1(B) really couldn't handle the CP200's power needs well. Measure the ripple on the +/- 14V rails...its pretty rough. They often sagged down to about 12.5VDC and quite measurable ripple. Some would move the little voltage selection board to choose 100V rather than 120V to tap the transformer different. I never did that. The CAT517 upgrade used the +24 and -14V rail to get a better swing and less ripple (the +24VDC did better as it was only supporting the metal face cards like the CAT22s and the MPU.
Our second and final PS1(B) upgrade was to swap out the linear stuff for switch mode supplies. The current/power capabilities was the same as the original (same fuses on the PS1B) and we set the +/- 14V rails to +/- 13V. If you do some math, you can see where Dolby clearly used the sagging rails in their calculations. The DIP relays on the back are 12VDC relays, for instance. They can withstand 13V but not 15VDC (for protracted periods of time). At +/- 15V you'd be dancing right with every card's protection diode and the CAT517 would be right at the limit with the +24 and -15V...39V...again, you'd be right there. I think I calculated that +/- 13.5V was the maximum one could safely go and not flirt with damage. However, it is a near zero ripple power that doesn't sag based on what options you may have. The noise improvement is is substantial and audible. The only operational difference, once modified is that the pilot lamp, which we changed to an LED, is now powered off of the 24VDC supply rather than the (none existent anymore) 24VAC supply so it comes on when the 24VDC supply does. I did that rather than tap off of the 120V and current limit down for the LED.Comment
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The easiest way of testing capacitors is by individually testing them using an ESR meter, which tests the actual capacitance of the capacitor. In many cases you can even test them pretty reliably without de-soldering them first. I found this easier and more consistent than testing them with a scope, as the numbers on the ESR meter can be easily matched with the specs.Originally posted by Marco Giustini View Post
In practice though, I've often seen that capacitor failures don't come alone. Many capacitors don't fail completely, but just loose a sufficient amount of their capacitance over time to cause headaches. Sometimes, a circuit will fail, because it was designed way to critically and if a few capacitors loose like 15% of their initial specs, then that may not be enough for any individual capacitor to turn out as bad, but still impact the correct workings of the circuit.Comment
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Yes, but it's not worth spending the time to test a half dozen caps that cost about ten bucks to buy. I always just recap an item if it's ten or more years old.... Neil could also check the voltage outputs of the supply to see if IT is actually what is at fault.Originally posted by Marcel Birgelen View PostComment
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True it is not worth the time to test if there are only a few caps to be done, but....Originally posted by Mark Gulbrandsen View Post
Partially true. Bad caps MAY give a voltage reading that is good or in the tolerance range, but they WILL have ripple that will not show up with a standard voltmeter. That would need a 'scope or to take a second reading using the AC range on the voltmeter, (which can still fail to show ripple if it is not large, but of enough magnitude to affect sensitive circuitry.)Neil could also check the voltage outputs of the supply to see if IT is actually what is at fault.
Example: I have an audio mixer that had bad caps in the power supply. The voltages were all spot-on, and I could not get measurable ripple with my voltmeter on the AC range. So I replaced the caps anyways and solved the problem. (Noise and oscillation in the audio output.) I took the old caps to a friend who has an ESR meter and every one of them tested bad. I bought an ESR meter the next day.
Last edited by Tony Bandiera Jr; 06-08-2021, 12:19 PM.Comment
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Thats why I rebuilt power supplies at 10.years Tony. Since I did many.in the field I am not likely to have my cap tester with since it was really a bench type instrument. In my experience 85 deg C. capactors have an average life span of 7 to 10 years before they start to deteriorate. I always used 105 deg C. caps when I replaced any. I also did gobs of gen 1 XD-10 motherboards, all in the booths to save on shipping and possible freight damage to the shop back and forth. I also did several hundred QSC power amp rebuilds. All electrolytics get replaced there too. This habit came from my Broadcast days where equipment down time was often critical.Originally posted by Tony Bandiera Jr View Post
True it is not worth the time to test if there are only a few caps to be done, but....
Partially true. Bad caps MAY give a voltage reading that is good or in the tolerance range, but they WILL have ripple that will not show up with a standard voltmeter. That would need a 'scope or to take a second reading using the AC range on the voltmeter, (which can still fail to show ripple if it is not large, but of enough magnitude to affect sensitive circuitry.)
Example: I have an audio mixer that had bad caps in the power supply. The voltages were all spot-on, and I could not get measurable ripple with my voltmeter on the AC range. So I replaced the caps anyways and solved the problem. (Noise and oscillation in the audio output.) I took the old caps to a friend who has an ESR meter and every one of them tested bad. I bought an ESR meter the next day.Last edited by Mark Gulbrandsen; 06-08-2021, 02:37 PM.Comment
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A QSC 1700 that was 15+ years old at rebuild time.You do not have permission to view this gallery.
This gallery has 1 photos.Comment
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Broadcasting is all about reliability.Originally posted by Mark Gulbrandsen View Post
It was interesting to hear from a former colleague, that even though FM broadcast is eventually to end within predictable time, as actually EU directive was 2014., they installed new FM transmitters and antennas on some sites. All a matter of contracted downtime maximum per year.
Ok, cinema has never been critical, as the possible losses are relatively low, or none in a multicomplex with more than 8 screens. But I never understood, why gear was used until it actually failed.
Good example are these QSC universal amps, designed in the 1970s, sold in the 80s and 90s. There are operations I know, that they do have a lot of those, that are "still working fine". And most have the genuine electrolytics. At first glance you don't notice the degrading of sound. There still is sound, as a result of the circuitry. As long, as one cap has a little capacity, it amplifies.
Still seeing CP 55s or 65s with DA converters...and 1990 speakers. Someone proud of his "only 38 year old movie seating", an industry I find increasingly difficult to understand.
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I disagree on cinemas being non critical. Independent theaters playing first run movies that lose a day or two revenue can be painful for the theater owner. Its less critical in plexs where movies can.be stacked... if distribution alliows that. Anyway, in my mind cinemas should get nearly the same attention that broadcast gear gets. This eliminates what could be costly down time. BTW, the main capacitors in those old QSC amps are actually quite critical as they are not in the circuit the usual way.Last edited by Mark Gulbrandsen; 06-08-2021, 11:06 PM.Comment
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Hello all,
Just to say a thank you for the information you have all added to this thread so far, it is both interesting and very useful. I hope to work on the 650 this weekend and will pass on the results.
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QSC used to sell "renew" kits for their amps, particularly series 1 through the MX/EX series. The kits had all of the parts that tend to age. So, anyone wanting to "renew" the amp, and was up to the soldering could certain keep them up.
I've found that cinemas tend to not want to spend money on such maintenance and, as others have pointed, will take great pride in stuff going 20+ years. There is also the "if it works, don't fix it" crowd and once you take a piece that was working, open it up and change things...if anything goes wrong with one of them...they won't remember the 20 things you kept from failing, they'll remember the one that was working and, if it fails within say 2-years of the work, you broke (even if your work had nothing to do with the failure.
It was easier for mechanicals as everyone has a sense that as a mechanical thing operates, it wears and eventually wears out. For electronics...the perception is that it is perfect until it is broken. There is very little in between.
If you are looking for someone that really knows his stuff on electronics, I highly recommend Mr. Carlson of Mr. Carlson's Lab (on YouTube):
https://youtu.be/lLQThhf3Brc
He designed his own leakage tester (low-voltage) and will make his designs available.
https://youtu.be/LhovRIM5xAoComment
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Steve, I watched enough of his videos to see what he's up to. His home made tester won't do much good for a lot of amplifier main caps. He complains of ESR testers being so expensive, but he obviously doesn't realize that you are paying for all the safety stuff built into them so you don't end up stopping your heart..Comment
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