Repair and refurbishment of a 1971 AMI/Rowe MM5 Presidential jukebox
An AMI/Rowe 1971 MM5 Presidential jukebox has been knocking around my wife's family for years. It's been sat in our house for years and the last time anyone can remember it working was in 1989. As far as I knew it was wrecked, but in May 2021, I decided to see if I could get it working again.
The jukebox can hold 100 singles, has a vacuum tube 50-watt stereo amplifier with a Shure N-44 c cartridge and a Tiffany style front panel. There were 6 different front panels available and I think the Tiffany is the nicest looking. According to Toms Zone, a little over 9,000 of thse machines were made.
The six front panels the jukebox could be supplied with
In May 2021, I got both the user and service manuals for it, opened it up and had a poke around inside it. I got lucky, or thought I did at first. All I had to do is replace some of the fuses, reseat the valves, replace some of the fluorescent lights and do some small mechanical adjustments. The manuals are essential, without them I would be totally lost inside the machine.
This video is from the first time it was capable of playing anything in 32 years. It is filthy inside, and I'm slowly cleaning it up.
Unfortunately there's now a few problems with it. In December 2021, it started playing very quietly with a low frequency hum coming from the speakers. The numeric buttons, 1, 2, 3 and 4 will not stay pushed in, while numbers 5 and 0 sometimes do, sometimes do not. The jukebox does not always select the correct record, missing the correct one by just one or two records in the carousel magazine.
Even with a few problems I'm gradually working through, I don't think I'll ever tire of watching it do its stuff.
General Cleaning and Lubrication
What I use for general cleaning for the jukebox is LA's Totally Awesome. It's cheap, very effective, and hasn't harmed any of the surfaces I've used it on. I use it on a damp rag or for stubborn spots, an old toothbrush. I dab it off with a rag soaked in a little disinfectant in water, then dry it off with a clean rag.
I use DeoxIT D5 for cleaning electrical contacts. Rather than use abrasives I just wet a 3" strip of paper with it and run that across the contacts.
For lubrication I use 3-in-1 Motor Oil SAE 20 with the blue label. This is not the same as the 3-in-1 general purpose oil which has a black label.
Even the fuses were confusing at first. The manual mentions AGC, GLH, GMQ, and MDL type fuses.
AGC stands for Automotive Glass Cartridge and refer to fast-blow fuses. I couldn't find what GLH fuses mean but they were also fast-blow fuses. You can still obtain GLH fuses but Cooper-Bussmanm discontinued them in 2005 in favor of the AGC type. GMQ is another type I could not find what the initials mean but they are time-delay (slow-blow) fuses with built-in end-cap for the fuse holder. MDL stands for Method Detection Limit and these fuses have the wire wrapped around a core and are also time-delay (slow-blow) fuses.
Slow-blow fuses are normally used in situations where the electric current could spike. For this reason you can use fast-blow fuses where a slow-blow is specified but will more than likely blow the fuse more often. NEVER use a slow-blow fuse where a fast-blow one is specified - something will probably be irreparably damaged before the fuse blows. Another thing I have learned is never assume that the fuse you are replacing is of the rating or type that was originally specified. Someone working on it before may have used whatever was handy at the time. If fast-blow or slow-blow is not specified then use a fast-blow fuse.
People on the Pinside discussion forum make the observation that it OK to use a fuse rated for a higher voltage but NEVER one for a lower volatage. For example you could use a fuse rated at 110v in a 220v circuit but NEVER a fuse rated at 220v in a 110v circuit. The reason for this is that the current in the higher voltage could arc across the blown fuse.
It may seem obvious but when the manual says a 6-1/4 Amp fuse they mean a 6.25 Amp fuse; 2 8/10 Amp means 2.8 Amp; and 6/10 Amp means 0.6 Amp.
There are 6 fuses in this MM5. In the 100watt MM5s there are 8. All are located in the back left corner; 1 each on the amplifier and credit unit and 4 on the junction box.
2amp 120volt MDL slow-blow
50watt amplifier (601-04359)
3.2amp 120volt GMQ (with end-cap) slow-blow
100watt amplifier (601-03760)
2amp AGC fast-blow x2
100watt amplifier (601-03760)
0.6amp MDL slow-blow
Credit unit (603-03300)
6.25amp 30volt MDL slow-blow
Junction Box (401-05767)
8amp 120volt GLH fast-blow
Junction Box (401-05767)
2.8amp 30volt DC MDL slow-blow
Junction Box (401-05767)
2.8amp 6volt MDL slow-blow
Junction Box (401-05767)
My wife has been collecting 45rpm singles since long before we were married and has a collection of over 8,000 0f them. The jukebox is a great way of getting use of them rather than simply keeping them packed away in their boxes. That brings up the subject of the jukebox title strips, how to print them and how to change them. Perhaps the original manufactueres had their own own designs and colors but I couldn't find any information about them and our MM5 contains a mixture.
The label sizes appear to be a standard 3 1/16" x 1" (78×26 mm) and looking around the various forums the color most used was red with orange labels used for ballads and easy listening; blue for rhythm and blues; purple for oldies; green for Christmas and other holiday music and often used for country and western; yellow labels were used for comedy, novelty and childrens records. None of these color schemes are in any way standard.
When printing you usually need to ensure that any "fit to page" or scale option is turned off.
How to change the title strips is fairly obvious and the only advice I would give is do not drop the plastic holders as 50 year old plastic is brittle.
It's much easier to work on the jukebox with the front door removed. The thing to remember when doing this is to turn the power off and unplug any connections to the door itself. In the MM5 there's only plug to pull out and that's for the power cord to the fluorescent lights in the door. There is a catch and retaining wire on each side near the top of the door holding the it on. Just release both of those and the door can be lifted free. Once off, it can be seen that for the size of the jukebox, the electrics and mechanism is actually very compact. All the main electical and amplifier components are on the left, the electro-mechanical components are in the middle. Taking the front door off also makes working on it very much easier.
It is embarrassing to say how long it took to get the front door back on properly. On each side, near the bottom of the door is a metal sort of hook that goes into slots on the jukebox body. It took me quite a while to line these up to get the door back on.
There are times when the reord carousel or magazine needs to be rotated, for example when replacing the records or for some tests. One way to do this is to pull the lever on the Service Control Center, which is located on the left of the jukebox, to the Scan position. The magazine will then rotate anti-clockwise.
Another method is to "Release the detent pawl from the detent wheel on the sprag assembly"
A pawl is a lever that that prevents movement in a mechanism
A detent is a catch that prevents movement in a mechanism
A sprag is a type of clutch that only allows movement in one direction
It doesn't help that the manual says this assembly is "directly under the record transfer arm." It is actually about a foot below the transfer arm, behind the popularity counter and search unit which are at the front of the mechanism. With the detent pawl moved to the left, the magazine is free to rotate anticlockwise by hand.
Taking the popularity counter off is easy, just turn the center knob clockwise and pull. It can only go back in one position, then turn the knob counterclockwise to lock it into position.
The selector assembly is where the push buttons and their associated circuitry, relays and solenoids are located. Some of the buttons do not appear to be latching properly and sometimes the jukebox plays the wrong record. There seems to be two places to check for, one is the search and stop unit and the other is the circuitry in the selector assembly.
Simply pulling on the selector assembly pulls it forward about 8 inches. It locks into place again so cannot be pulled all the way out. This makes it easier to change the upper set of fluorescent lights but not very useful for pulling the buttons out to clean them or getting to the circuitry.
To remove the buttons and their circuitry 3 electrical connectors, two on the selector assembly and one down on the search unit, have to be disconnected and 5 screws removed. Four of the screws are on the selector assemble frame, the other is on the credit light assembly next to it. I found a nut driver is probably best to remove the screws.
The buttons sit on serrated bars. They should just pull off, but some are harder to remove than others. The buttons were dipped in LA's Totally Awesome, scrubbed with an old toothbrush, swilled in clean water and put aside to dry. Once completely dry they were put back on the unit. All of them are a little discolored where they have been so dirty for so long and a couple of them seem have to permanently discolored spots. I can live with that, the worst of it will be hidden when the unit is back in the jukebox.
When moving the selector unit I noticed that the latch solenoid or coil was loose. Looking at it I saw that it originally had grommets between it and the mounting plate, but that these had disintegrated over the years. I found it's almost as cheap to buy a selection of 180 than the five I need! In normal operation, when credit is available, the solenoid is energized allowing the buttons to be latched. When deenergized any depressed buttons will pop back out.
I asked on Jukebox Addicts why this solenoid needed to be isolated with grommets. From that and other sources it seems that solenoids can be noisy, sometimes described as a buzzing "like bees", and the grommets are used to dampen the noise and vibration. There is also another grommet through the side of the mounting plate that the arm attached to the solenoid rests against. All 5 old grommets were removed and replaced with new 5/16" ones. After I screwed it back down, I tested the coil for continuity to make sure I hadn't damaged it.
The selector assembly also contains several relays. Given the state of the rest of jukebox these probably had not been cleaned for at least several years. I cut paper tapers around 1/4" wide and 3" long, wetted them with DeoxIT DN5, then pulled them through the contacts while applying a little pressure to them.
After a good cleaning and putting the selector unit back into the jukebox, all the buttons now latch properly. Unfortunately the jukebox still sometimes play the wrong record, usually just one or two away in the magazine it is supposed to be playing. The next job appears to be taking a look at the the search and stop unit. The knowledgeable people in the Facebook Jukebox Repair Help! group also suggested I look at the sprag gear and stop pawl.
Tone Arm to Preamp Cable
Even when I first looked at this cable I thought there was something not quite right about it. The clues were the loose shielding around the RCA phono plugs and electrical tape around the tone arm connector. Sure enough, a couple of months later, in December 2021, the right hand speakers stopped working apart from a hum. By swapping the left and right plugs over at the preamp confirmed that it was nothing past these connectors that was the problem which might have been complicated to repair.
When I looked the cable, I thought the tone arm connection was a 7-pin DIN (Deutsches Institut für Normung, or German Institute for Standardization) connector, but it is not, it is actually a 7-pin B7G mini tube connector. This connector is also discussed on the Jukebox Addicts and Antique Radios discussion boards.
The female socket for this connector is riveted to the bracket and lever assembly (part no. 201-10785) of the tone arm assembly (part no. 306-05124) and people have drilled the rivets out and replaced the B7G connector with DIN connectors. Hopefully I won't ever have to.
I replaced the RCA phono plugs with ones that are properly color coded - red for the rand-hand speakers and white or black for the left-hand speakers. The wiring colors are right-hand speakers, center pin wire is brown, outer sleeve wire is green; left-hand speakers, center pin wire is red, outer sleeve wire is black.
A continuity meter should show no electrical connection between the center pin and sleeve. If there is and it is plugged into the preamp then that channel will be muted.
The adjustment section of the manual says the tone arm force pressure should be between 4 and 5 grams. When I measured it, it was 4.6 grams so didn't have to adjust the counterweight.
Sources and Resources
I had no idea there were so many websites about jukeboxes! Here is a list of the ones I found most interesting or useful.