[Jukebox-list] AMI carriage junction box revisited

[Joey McDonald]

Hey all,

I have been working out some selection problems with my AMI F120 over the past 2 weeks.
I included some past posts here as a reminder of the topic.
I am still tring to resolve this issue with the contacts arcing. I have installed 2 1amp mdl fuses in the
8/10 fuse holders of the power supply. The fuses do not blow.
This power supply has a new rectifier in it as Aaron stated.

I have a spare power supply with the original selenium rectifier. It looked real clean so I swapped it out
for the rebuilt one. I thought this might be dangerous so first, I powered it up with jumpers and a load resistor
as described in the manual under testing the power supply. It worked without smoke. So, I didn't let the smoke out
so it must be still kinda OK?? 

I swapped out the power supplies and made sure the correct fuses were installed.
Turned on the juke and it works. Made some selections and the RR relay is noticeably
not snapping as loud and the blue color arc is much dimmer. This must prove that there is
a voltage problem.

So, the point I am at is that I am not sure where to take the voltage measurement.
I measured in many places and all voltages are different. Should the voltage at the fuse holders
be accurate? Not sure here.

Also, I have been checking out fuses. Some fuses are rated different as far as voltage and dc or ac voltage.
I checked the schematic and parts lists. There is no note of what voltage the 8/10 fuses are or if they are a/c
or d/c fuses. I did not know there was a difference between a/c and d/c fuses and voltages or is there??
These fuse questions may be very novice to some. Sorry, but I think this is relevant to this problem.

Just a note here, all the fuses were oversized in my spare power supply. Also, 8/10 MDL fuses
are not readily available. Antique Electronic Supply sells a 1amp slo blow and also the 8 amp
is only available as a 9 amp. 

Joey McDonald




Argh!!!! Steve and Ron...you guys may have hit it right on the head!!! I always swap out those old GE rectifiers with brand new ones and the voltage always tops off at 32 volts even under load. I don't have any clue where my manual is, but I thought the voltage in the circuit was at least 30 volts. Not thinking that 32 volts was too high, I never thought about bringing the voltage down with a power resistor. Darn it! I want to try that right now, but my son isn't feeling well so no jukeboxes tonight.

You mention a 5w resistor - obviously a power resistor... but what value would you recommend? This is great stuff because this will solve this annoying problem for all of us that own these jukes. At first I thought about putting a diode across the relay to short the arc to ground (like I do in the credit units), but for some reason I never did it. Using the diode in the credit unit almost eliminates the annoying popping sound that comes from the credit unit when a selection is made while the juke is playing...or when you press a button and no credit is available. My G was notorious for that. The diode fixed it.

I'll have to really look into the dynamic braking thing. I know that the RR is shut off by the action of the tone arm cam against the cam switches....which are the only switches I can think of in the circuit that could cause the "should not be open or closed, but they are" deal. 

Joey....I'm going to look into my G sometime over the weekend and I'll see if I find anything that could be causing the arc based on what's been discussed here. If I find anything, I'll post it to the list for everyone.

Aaron Heverin

Aaron,
>   As for the fuse--AMi did increase the value of that fuse in later
>   production from the 8/10 to a 1 amp SB. 

1. Since it doesn't stick out very much the way Ron said it, I thought
   I'd stress the *SB*, which means slow-blow.  Aaron, if you've been
   using regular fuses there, the slow blow type will probably cure
   the problem of blowing fuses.  (Slow blow lets you draw much more
   current for a very short time period, but blows for a sustained
   high current draw.)  It won't do anything to cure the arcing, but
   it'll at least keep you going while you fix the problem, if you're
   not satisfied to just leave it that way.

2. Esp. to Ron, if this is in the dynamic braking circuit, is there a
   chance that contacts are mis-adjusted?  That is, as I understand it
   dynamic braking puts a dead short across the motor so it stops
   quickly rather than slowing to a stop (and overshooting the desired
   stopping place).  If the shorting contacts "make" before the
   contacts supplying current "break", that would be a quick dead
   short across the power supply, causing a lot more current to flow
   and thus a larger arc when the contacts separate.

   I haven't looked at the schematics nor the actual relay(s) to see
   if that question makes any sense at all.

3. I've heard of capacitors being put across contacts to prevent
   arcing.  Would this be a possible place to apply this idea?  How
   would one choose the propper size capacitor?

Just trying to be helpful, although I'm paying close attention in case
I ever see this on my F, which for the time being is still running
with the original rectifier, to the best of my knowledge.

--> Steve Wahl


Aaron,
  Going from my great, but not too long memory, because I have mis-placed my "900 Mechanism book" (or did they call it a "record changer"), and notes--
  I think this is a problem with the "dynamic brake" circuit. I  seem to re-call that if you have replaced the selenium rectifier with a silicone type, there in lies this problem. The solution is to 1.) check and be SURE that all contacts in the circuit are making WELL. 2.) add a resistor in series with the output of the rectifier, to bring the voltage down to under 28vdc. (Sorry-don't recall the value--but think I used a 5w ww)
  My memory says that there should be no power to the magazine motor when that relay opens--it should have been shorted out (dynamic brake) when the pulled pin was sensed, by the "stopping switch" (either # 1 or # 2). I would think that somewhere, when you get the arc, there is a contact which should be open, that is closed---
  As for the fuse--AMi did increase the value of that fuse in later production from the 8/10 to a 1 amp SB. If the box with the rectifier and transformer does not have a 2 amp fuse in the primary circuit, I would suggest that one be added, as per later production units.
  Ron Rich



Hi all.
I'd like to put this out there on behalf of Joey because of a problem he's having with his AMI F...and for the exact same problem I'm having with MY G-120. While I'm not sure it's an actual issue that would cause a meltdown of the jukebox, it's an annoyance just the same. What happens is that the RR relay on the carriage junction box arcs every time the mech comes to rest and the relay opens and cuts the power to the mech. I had this problem on my G, and every time the arc would happen, the 8/10 fuse would blow. So after testing the relay...and making sure that all of the switch contacts on the relay were polished, I tried it again. Relay opens, pops the fuse. I was having the exact same problems with Joey's F...and when I went back to look at my notes, I found that quite a few of the Fs and Gs I restored had the same problem - plus or minus intensity of the arc per machine. On Joey's F, the arc was quite bright and powerful. It didn't seem to hurt the mech at all or hinder operation...it just opened and popped the fuse.

On my G, I had put in a 1 amp fuse and that seemed to solve the problem for a while, but every once in a while - in a way that was not in any kind of pattern to try and troubleshoot - the arc would be bad enough to pop the fuse. So I put in a 2 amp fuse. Now before any of you tune me out and start yelling :) -  let me point out that I went through every ounce of the mech and carriage junction box to make sure that when the arc occured that something wasn't getting shorted out - and thus by putting in a larger fuse, I wasn't going to be causing any damamge to the mech or the main junction box. I assumed that since the arc was causing the fuse to blow - and not a dead short - that the 2 amp fuse would take up the relay's bang, but still pop if a REAL short occurred. Perhaps my thinking was wrong...and that's why I'm posting this question.

Any idea why that relay would be arcing so roughly? I've always seen some type of arcing in ALL of the relays in those jukeboxes....even in the credit unit. What I'm wondering is if the arc is occuring because there's too much current being pulled from some place. The only thing I can think of is the carriage motor since that's connected to the RR relay. But on both Joey's F and my G, the motor doesn't show any signs of being under a heavy load nor does it seem to be struggling to move the gripper arm. 

Like I said...this is more of an annoyance rather than anything else...but I'm curious because I'd like to not have an arc at all.

Thanks all!

Aaron Heverin