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 Post subject: Rowe AMI JBM Jukebox fix-up.
PostPosted: Jan Mon 08, 2018 12:11 am 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 753
Location: Dallas, TX
No sooner than I finished up work on a Wurlitzer, I was told about a Rowe AMI box that wasn't working. It was working before it was moved to a new owner. Now it simply resets as soon as a selection is made. It hasn't been re-caped or much of anything maintenance-wise done. I didn't find anything loose when I looked it over. I decided to remove everything except the sound system, which I will recap later and the lighting, and bring those items to my place to work on them. I forgot to take any pictures of the out side of the box but this short video shows an identical unit.
https://www.youtube.com/watch?v=JoG4y9W5uok
And here is a video of the mechanism working on a similar unit.
https://www.youtube.com/watch?v=8GCw4hAlU-w
Here are some pictures I took of the mechanism removal.
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DoorOffE1.jpg
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MechanOutE1.jpg
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PartsAtHomeE1.jpg
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Here are views of the mechanism. This one was light enough and small enough to move.
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MechanFronE1.jpg
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MechanLeftE1.jpg
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MechanBackE1.jpg
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MechanRighE1.jpg
MechanRighE1.jpg [ 148.47 KiB | Viewed 893 times ]

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 Post subject: Re: Rowe AMI JBM Jukebox fix-up.
PostPosted: Jan Fri 12, 2018 4:11 am 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 753
Location: Dallas, TX
I noticed something not right about the phono cartridge. It had been replaced, but if you watched the video of the similar mechanism in action the tonearm is unusual. Instead of the tonearm following the record groove, the tonearm leads the record groove. The cartridge therefore needs to be installed backward from usual. When the cartridge was replaced it was installed the usual way, which is wrong in this case.
Attachment:
UnderToneE1.jpg
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The side view also shows that the stylus would miss the brush in this position.
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SideToneE1.jpg
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The end view shows that the cartridge isn't level because a spacer is missing. Luckily I found it in the bottom of the cabinet.
Attachment:
EndToneE1.jpg
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I removed the search unit and then removed all 200 of the pins and cleaned them. This is after re-assembly. I moved a few of the pins to the selected position.
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SearchUnitE1.jpg
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Another view.
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SearchUnitE2.jpg
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This is a view of the stop switches and reset solenoids where the the search unit attaches.
Attachment:
StopSwitchsE1.jpg
StopSwitchsE1.jpg [ 143.05 KiB | Viewed 843 times ]

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 Post subject: Re: Rowe AMI JBM Jukebox fix-up.
PostPosted: Jan Sat 20, 2018 9:11 pm 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 753
Location: Dallas, TX
I make a cart some time ago to hold large projects I would work on. I hadn't used it much, but it was handy for the jukebox mechanism. I used some small scrap boards that I clamped to the cart to hold some of the associated parts like the credit unit and control switch board. This allowed me to power things up and test.
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TestCartE1.jpg
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I remounted the cartridge the correct direction for this tonearm.
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ProperCartDirectionE1.jpg
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I discovered what was probably the major problem. A screw had fallen out of one of the relay and allowed the contacts to jam. Luckily I had collected some loose things on the floor of the jukebox and the screw was one of them.
Attachment:
RelayConLooseE1.jpg
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I used some thread locker since there were no lock washers on the screws.
Attachment:
RelayConFixedE1.jpg
RelayConFixedE1.jpg [ 125.26 KiB | Viewed 774 times ]

I think another problem was that the black wires from the turntable motor were jamming the transfer arm actuating cam. I re-routed them just in case. Maybe the last person to work on it got it wrong.
Attachment:
TTMotorWiresE1.jpg
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I found a discrepancy in the manual regarding the wiper timing on the search unit. It was off by two segments causing the wrong record to be selected. This is where it should be with "B1" selected. It is a different circuit board than the one in the manual. Now everything seems to be working fine.
Attachment:
NumWipeTimeE1.jpg
NumWipeTimeE1.jpg [ 143.23 KiB | Viewed 774 times ]

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 Post subject: Re: Rowe AMI JBM Jukebox fix-up.
PostPosted: Feb Thu 01, 2018 7:11 pm 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 753
Location: Dallas, TX
I got the mechanism back in the cabinet.
Now I will start on the amplifiers. The amps are in two sections, power amp and control amp. The power supply is included in the power amp section. The volume control is in a separate small box which I also removed. I've already replaced or re-stuffed the crossover caps.
Attachment:
CrosovrRestufE1.jpg
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RoweAmpE1.jpg
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RoweAmpE2.jpg
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Attachment:
ControlAmpE1.jpg
ControlAmpE1.jpg [ 121.17 KiB | Viewed 672 times ]

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 Post subject: Re: Rowe AMI JBM Jukebox fix-up.
PostPosted: Feb Wed 14, 2018 10:51 pm 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 753
Location: Dallas, TX
Nearly done on the amps.
Re-stuffed an E-cap can on the control amp. I was able to put all the new E-caps of the power amp under the chassis.
Attachment:
ECapStuffE1.jpg
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Underside of control amp.
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ControlAmpE3.jpg
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Underside of power amp.
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PowerAmpE3.jpg
PowerAmpE3.jpg [ 159.72 KiB | Viewed 586 times ]


Just need to get delivery of a couple of tubes I ordered.

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Tim
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 Post subject: Re: Rowe AMI JBM Jukebox fix-up.
PostPosted: Feb Fri 16, 2018 6:00 am 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 753
Location: Dallas, TX
I got my tube order and learned something. One of the tubes I needed was a 7868. ( I know most people like to replace them in pairs in P-P outputs.)
I got a new production 7868 made by Electro-Harmonix (Russia). It didn't fit the tube socket. It seems that new production and NOS from Europe have a Magnoval base which has thicker pins that the USA NOS Novar base. The Magnoval pins are about 25 % larger diameter than the Novar pins. I'm surprised that the two versions have the same tube number, I would have thought that at least one or the other would have a suffix.
So I am ordering a NOS 7868 tube ($$) and sending the E-H back.
Another option would have been to change out the socket to Magnoval and keep the E-H one.
While researching this problem I came across some suggestions to insert 10 ohm 1/4 W resistors to protect the output transformers in case the output tubes draw excessive current due to grid emission or bias failure. They would act like fuses. The design already has a 10 ohm 1/2 W resistor in line with the plate on ONE P-P tube. I'll install 1/4 W resistors in line with the plates on both output tubes of each channel.

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Tim
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 Post subject: Re: Rowe AMI JBM Jukebox fix-up.
PostPosted: Mar Tue 06, 2018 2:26 am 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 753
Location: Dallas, TX
I got the NOS 7868 and it works fine. I noticed more hum than I thought there should be. I eventually traced it down to film B+ dropping resistors that that I hadn't replaced. They measured correctly at 1K, but on closer inspection they looked overheated. I think excessive current draw caused by bad filter E-caps and other problems damaged them. I replaced the 1K half watt resistors with one watt ones and it greatly reduced the hum. I don't know why the resistors caused this problem unless the resistance changed under load.
When I was trying out the jukebox another problem showed up. It would sometimes continually repeat the selection. It also wouldn't play new selections. Seems like the problem is a micro-switch on the selection gear assembly.

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 Post subject: Re: Rowe AMI JBM Jukebox fix-up.
PostPosted: Mar Thu 08, 2018 10:34 pm 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 753
Location: Dallas, TX
I replaced the micro-switches on the selection gear. I took the switch apart that I suspected of causing the problem. I wasn't dirty or corroded like I thought it would be, the contacts were eroded. This can happen if the current or voltage is too high. I added a 0.1 uf 400V cap across the contacts, this helps absorb kickback spikes when switching inductive loads like a solenoid. I later noticed on the schematic that this switch also would charge a 100 uf cap, one that I had routinely replaced. Maybe the 100 uf cap had so much leakage that the current was more than the switch to handle in the long term.
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StopGearBeforeE1.jpg
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Attachment:
StopGearAfterE1.jpg
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With everything back in place the jukebox works fine. I'm calling it done!
Attachment:
JBMFinishedEF01.jpg
JBMFinishedEF01.jpg [ 127.13 KiB | Viewed 403 times ]

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Tim
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 Post subject: Re: Rowe AMI JBM Jukebox fix-up.
PostPosted: Mar Fri 09, 2018 11:23 pm 
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Joined: Nov Wed 14, 2007 11:37 pm
Posts: 1450
That's a beautiful machine! Nice work!


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 Post subject: Re: Rowe AMI JBM Jukebox fix-up.
PostPosted: Mar Sun 11, 2018 12:26 am 
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Posts: 9957
Location: Redlands CA
Great job! Gotta say that mechanism makes the Seeburg system look dead simple.


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 Post subject: Re: Rowe AMI JBM Jukebox fix-up.
PostPosted: Mar Sun 11, 2018 1:43 am 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 753
Location: Dallas, TX
Eric H wrote:
Great job! Gotta say that mechanism makes the Seeburg system look dead simple.


Well, its compact. Seems like all the early (mechanical) jukeboxes had Rube Goldberg involved!
Its kind of more interesting to watch the mechanism than listening to them, especially when you know what's all happening behind the curtain.

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