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Service Notes on ROWE CD-51 jukebox sound system (CD 51 ownersplease read)
On Friday, November 13, 2009 at 7:20:30 AM UTC-8, kreed wrote:
Some of you may be aware of this, especially if you had a number of CD51's in operation, but thought I would pass on these observations on to avoid anyone else being caught. Note that while these machines are probably not used on location as much these days as in the past, many have been possibly been converted to digital, and use the same amplifier and sound system regardless, so this is still valid for these people. Bought one of these on location from another operator who was sick of it and the problems, hadn't done any maintenance on it for years, and didnt have a broad technical knowledge, usually calling me from location when stuck. As the machines aged, the problems grew more and more varied, driving him to want out of the business. The machine had loads of intermittent faults, but earned well, and the location owner was a pretty good guy and had been amazingly tolerant of the faults over some time. Usually in cases like this, I would simply replace the entire machine with one of ours (known good, all mods done) and bring the other home to go over it and overhaul thoroughly. In this case, literally nothing other than a CD 51 will fit in the confined alcove space its in, Its been there since it was bought new, and it cannot be moved elsewhere due to lack of space, and CD51 seem impossible to find in this country, so can't get a replacement. I wish he has bought a CD 100 instead ! AS such, I replaced the boards, power supply, checked the harness connectors and naturally have been ironing out the few remaining problems quite successfully so far as they have popped up. After copping a complaint of "low maximum volume" I checked the volume control, amplifier, and apart from finding it to be an amp from out of a CD-100 (7 band graphic equalizer) rather than the 3 band EQ used in the CD 51, I also found the left channel of the amplifier, power driver board had many of the transistors burnt up, and charring on the board under them. Hadn't seen anything like that before, usually the output devices just die for no particular reason, blow their associated fuse(s), and the driver PCB is unharmed. Usual procedure = Replace transistors (and fuses) check and balance the idle current if needed and all is well for another few years. In this case, I fortunately had a spare, known good CD51 amp that I had obtained from somewhere in the past, tested it, took it to the locatio, and put it in. Substantial increase in volume, great sound quality, everyone happy. Location owner really happy, "sounded better than it had in 4 years" etc. etc. At that time that I checked the crossover board for dry joints, shorts etc as I was very suss about the unusual driver board damage.) Found that 4 of the 2W resistors had overheated and gone a bit black, the ones that divide the signal for the tweeter, but still measured what looked like sensible values (couldn't read the coloured bands) ok. They were getting quite a bit warmer than I would like when playing loud, but I didn't have replacements on me. Noted down to bring 5w units next time and replace them. Thought it strange that this would happen. Listened carefully to tweeters, no distortion, drops in volume or other signs of distress that may have meant shorting internally, which would cooking their resistor, sounded ok even at high volume. Back at the workshop, checking the Amplifier, I found the preamp had failed also. One channel had no sound and the other had a faint "crackle". After a lot of mucking around, it was discovered that one set of contacts on the Reed relay (mute) had welded shut, killing the sound on that channel. This was totally unexpected and as a result wasn't easy to diagnose. This led me to believe that when the transistors failed and burnt up on the power amp driver board, a high voltage (+ or - 40v rail) managed to travel back up the line level input to the preamp, welding the relay contacts. before the fuse blew. There was still distortion, even with the relay fixed. Not trusting IC's that I suspect have been subjected to substantial over voltage, I replaced all the op-amp IC's on the board just to make sure. They are cheap and easy to do so what the hell - Worked fine after this. --------------------------------- 2 week later, get a call from the location, "it sounds terrible, sound is broken up". Thought one of the amp channels had blown an output transistor and the thing was distorting. Took spare amp, and photocopied the pages related to the crossover to help with replacing the resistors, which I also took. Took a spare crossover from out of a CD-100 model, noted it had all 5w resistors, not 2w carbon ones. Got there, machine had no bass whatsoever, but no distortion in the mid and upper, amp was ok. sounded absolutely horrid - if you don't believe me, disconnect the woofers from your juke and listen to how incredibly bad it sounds and how much "volume" you lose I was getting very concerned, checked the crossover for, bad terminals etc, but all was ok. Pulled out one of the woofers, was open circuit. Pulled out the other, same. Was dumbfounded as to how this could happen, have never seen this before, not in both woofers. The last time I saw a problem like this, the wire that ran from the speaker cone to the terminals had failed (from metal fatigue?) and would intermittently work/not work, arcing like crazy when it did work temporarily welding itself back ?- it was only one speaker not both. Pulled out the crossover. 2W carbon Resistors had burnt badly and one had charred the PCB. Open circuit, both channels. Replaced them with 5W units of same value.. Ended up having to get a pair of woofers and bring them and fit them. Sounded great. After studying the circuit and finally noted on paperwork that I copied of wiring diagram between crossover and amp "connect to E6 E6 maximum" Noticed previous op had put terminals on E7 E7, this is probably what blew up the old amp and overheated the resistors before it did. Then when a new amp was put in, the speakers **** themselves and the resistors finally cooked. Amazing it didnt blow a fuse. This speaker wiring hadn't been noticed, as the title rack totally covers the amp transformer, terminal strip area. Dropped them to E5 - E5. (32W) This still gave adequate volume and good sound quality. Put on several tracks of a "Hilltop Hoods" album (Rap, ghetto kinda stuff, very heavy bass - to test the new woofers) and turned the volume up loud. 20 mins later, no problems, resistors not hot. Only sore ears, and frustration listening to their last song about and aged war veteran, who got mugged on the train for $2 and his pension card. . Geez - If we had tried anything even 10% as bad as that that when I was a kid, we would have had the living daylights flogged out of us with a belt, and then got the cane wrapped around our arse when we went to school the next day. God knows what the cops would have done. Where has our society gone ? Location owner, "you didn't have to rush here, they (patrons) were still playing it and didn't complain". How anyone could have put up with that sound, let alone paid to do so is beyond me ! ------------------------------------------------------------- Moral of the story: 1 don't run these machine's internal speakers on E7 taps, especially in a place where they wind volume up full all the time. I have seen it done on Cd 100's, but don't try it on a 51. The woofers in the machine won't survive it. If you have a CD-51 then please check this. If you need more volume, you probably have to consider suitable external speakers, or if you know what you are doing, upgrade the woofers and the crossover resistors to suit. (Don't use 4 ohm car units, unless you match the impedance correctly. this would likely mean isolating the bass section on the crossover and bringing a second set of wires out to the appropriate Ex terminals as per the speaker chart.) (not recommended) 2 crossover board is different and one of the plugs has different pin configuration to a CD 100 on one of the plugs. Swap them, and you will get no bass. 3 Maybe consider upgrading the resistors on the crossover board to 5W units, if any heat damage or discolouration is noted. 2W may be cutting it a little bit fine, even on E6 - E6 power levels ? 4These same points probably apply to other "compact" Rowe machines with 8" woofers, such as the MMCD series, possibly even the RI 3,4, & 5 series ? The RI-1 and 2 might not have enough amp power to do this damage (25 & 50w respectively) and use a 10" woofer similar to in the full size machines. Hello. I have a question I hope you can help me with. I am a musician/audio engineer whose knowledge does not extend to building or repairing gear. ("Take it to the shop!") I sometimes install sound systems in bars and restaurants but prior to my last job I had never had to integrate a jukebox into the system. I want to disable the power amps and speakers in the jukebox and run an unbalanced line out that I can put through a DI and go from there, through a Mackie board and into powered QSC K8's. The last job had a newer jukebox with RCA line out jacks inside, no problem. The new job has a mmcd-1 which doesn't appear to be as accommodating. Can it be done? Thanks for your help! |
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