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!