Rockola 470 questions

I recently purchased a Rockola 470. Typically I work on arcade games, so this is my first jukebox. I have it working pretty good and followed maintenance and adjustment directions in the manual. I do have several questions though.

1. At this time all 100 selections (A side) are playing and most 200 selections (B side). However, there seems to be a problem with only selection 293 and 204 (switches right next to each other). The write-in side flips the proper switch. The read-side arm spins around. When it gets to the flipped switch 293 or 204, you hear the solenoid firing but the arm keeps on going and you can see the switch was not flipped. The records do not get selected and the arm keeps spinning, firing each time it passes the 293 or 204 switch. I checked both switches and they are not stuck. I can manually move them. All other 200 (B side) selections work and I did the Read-Out and Write-In adjustments according to the manual. I'm at a loss as to why those switches are flipping even though the solenoid appears to be firing in the right spot. I've used Deoxit on all contacts also to try and resolve the issue.

2. There is a slight, low hum coming from the speakers. Without doing a complete amp rebuild, could this be fixed by replacing the large silver 2000mfd capacitor sticking out of the amp box? The hum occurs even when nothing is playing and the motor is not spinning.

3. I'd like to run other line sounds to this. It appears that this could be done through the microphone input jack and more specifically pins 1, 2 and 3 (ground, left, right) going to a line or headphone jack. I wired up a temporary connector and connected an MP3 player for testing. It worked great, and has awesome sound piping through the jukebox amp. However, when I turn off the MP3 player and even unplug it, simply having the cable plugged into the jukebox gives off a loud hum when playing 45's. Unplugging the cable takes away the hum. Playing the MP3 player also takes away the hum. It's almost as if the plug wire is acting like an antenna. I did use a shielded cable. Is there something that can be done about that or is there a better way to run a setup like that?

4. The turntable top has an ever so slight wobble. It doesn't seem to affect the sound, but you can see the tone arm bobble ever so slightly when playing. I took off the turntable, cleaned and inspected the shaft and it looks good. I checked the motor and idler wheel with a flashlight and they appear completely still/stable in place when spinning. Is this wobble normal, or what can I do to fix it?

5. Is the turntable top supposed to be hard? It seems like there is a thin hardened rubber surface that the 45 sits on. Should that be replaced and where would I get that, what is it called?

6. I thought about hooking up additional external speakers. In the back is a speaker terminal strip which is numbered for the ohms to hook to the transformer assembly. As long as I move existing and extra speakers to the appropriate same number on the terminal block for ohms, is that safe to do without blowing the existing speakers or amp? Has anyone else done that with their home setup?

Thank you for any and all help that you can provide. Getting this working at 100% will make this the pride and joy of my home arcade.

Hi,
I'll attempt to answer these questions--hoping someone else with more RO experience chimes in--
1. This indicates a poor contact in this area--it can be anything from the "pin", or as you call it, the "switch" not making good ground contact thru to the slip-ring on the read out arm. I think I would try Deoxit sprayed into the pin bank and working the pins that won't fire by hand a few times--do not "flood" it with Deoxit--Also, re-clean the area on the read out slip ring.
2. Maybe ? But a full re-cap is indicated here.
3. Try useing a "drain shield" back to the amp. (two wires inside the shield--one "hot", other "ground" braid connected only to the ground at the amp.).
4. I have seen this before on RO's--only answer I have--obtain a new TT ?
5. Yes-no--Depends on how hard is "hard" ? Usually called a Turntable ring. Available from some of the suppliers listed above--in --"announcement--where to find".
See your Service Manual package for all proper speaker hook-ups.
Ron Rich

Definitely the slip ring(s) need to be cleaned, have come across this many times before where one or two selections would not play. Regarding the dreaded hum, its probably a good idea to check the tone arm cartridge and the tone arm cable connection, also clean the tone arm connection to the amp, the volume control connection at the amp, possible interference from florescent lights or bad grounding somewhere on the machine, i was recently working on a cd jukebox where the amp was hanging loose on the chassis and causing hum, as soon as it was tightened to the chassis the hum went. Sometimes changing the large cap has worked for me but it is advisable to change all electrolytic caps(i know it's a pain). I haven't seen a case where the turntable rubber would cause the record to wobble unless it wasn't level, could be the turtable grommets that hold the turntable motor in place, they may be perished, be careful removing and replacing as there are spacers under the grommets and are easily lost
regards
clones

I was able to dig into this a little more today. The drain shield back to microphone input got rid of the hum. However, depending on the device it was hooked up to the sound of the 45's playing would be slightly lower when the external device was turned off. I could unplug the device and leave the cable hanging without the hum, but that defeats the purpose of having the system wired up. I'm guess this has to do with how the original electronics would mute the sound when it sensed a mic signal. At this point I will have to abandon the idea of leaving an external device plugged in.

As far as the separate low hum when playing 45's, I pulled the tone arm wiring connector (during play) from the pre-amp/control box and the hum is still there. so it seems that the problem persists in that large cap or another ground issue and not the tone arm. I suppose the next step is to replace the large cap and further troubleshoot from there.

I was able to work on selections 293 and 204 not picking up when selected. Spraying Deoxit at the pin/switch and on the slip rings was able to resurrect selection 293 and it is now playing. However, selection 204 which is right next to 293 still won't play. I have repeated the Deoxit and cleaning process over 5 times now without any success on the last selection of 204. I also unplugged a large connector coming from that area and cleaned it as suggested somewhere else on the internet. After having thoroughly read the manual, I am still unclear on exactly how the read arm knows which location to fire the solenoid when it is turning. I understand the write side as there are a series of circular contacts which pinpoint location. Again, when the read arm appears to move over the selected pin 204 I hear a solenoid firing but the pin is still down and the arm keeps moving. Can some sort of alignment be off to where the solenoid is firing slightly before or after the selected pin? What else can I check? Thank you on the suggestions.

Suggestion on the external connection--
You might add a relay to that circuit--
As for the what stops the mech--it is the contact of the sensor on the read-out carriage, "seeing ground".
If the pin is not supplying enough current to that sensor ( which is what I suspect, since all others are OK), it will not have enough "power" to stop the mech at that selected spot.
Did you try 'Deoxing", the pin itself, as I suggested earlier ?
Ron Rich

Ron Rich wrote:Suggestion on the external connection--
You might add a relay to that circuit--
As for the what stops the mech--it is the contact of the sensor on the read-out carriage, "seeing ground".
If the pin is not supplying enough current to that sensor ( which is what I suspect, since all others are OK), it will not have enough "power" to stop the mech at that selected spot.
Did you try 'Deoxing", the pin itself, as I suggested earlier ?
Ron Rich

Thank you for your response Rich. Each time I had cleaned the area, I had sprayed Deoxit on the slip ring and at the pin in question. If you may indulge me as I'm trying to understand the read out operation. Again, after reading the manual it wasn't immediately clear as to the physical part of that operation. Is the pin itself the ground connection? If the pin itself is the ground connection then does that touch a metal contact on the readout arm or is there a switch inside the drum that the pin is connected to? I hit that pin (and the slot) again with Deoxit and a cloth rag after I got home and the read arm still isn't stopping on it. Just curious, wouldn't hearing the solenoid fire when it passed over the pin mean it got contact somehow? Something is firing when it passes that pin and it seems it fires from the read arm, because there is a slight jerk on the arm when it happens similar to finding other readout selections.

I have another question. Where would I find the large silver filter cap to order? I am familiar with electronics and ordering parts, but I'm searching high and low for a Mallory 2000mfd 75vdc capacitor and can't find a source or proper size. I've tried Victory glass but their search function keeps giving off errors and other sights cap kits don't seem to include the large filter cap.

Going from my great, but not too long memory--that circuit operates as follows:
Once a pin (rocker) is "hammered" to the selected state, it should provide a "ground pulse" to the sensor, when the sensor reaches it. This ground is provided thru the overcenter spring, axle, or physical contact with the drum, or all of the above. I suspect the pulse is weak.
What I would do is remove the read-out carriage, check the tension on the "fingers", and sensor--
Also check the area that the carriage rides on there, for "k-rap" that might just lift the carriage as it hits that pin ? Check the area of the pin itself, for any oxidation, or other defects--
What I might try, since you hear a "pulse", is to select that pin, and un-plug the basket motor just prior to the carriage reaching that pin--then hand turn it to the pin--this MIGHT "burn" a path strong enough to work ? Otherwise, it's into the drum assembly, you will need to go-- I would think--
Ron Rich

I just wanted to post an update. After many, many times of using Deoxit on pins, connectors and the rings, apparently overnight after one of those times did the trick. At this time every selection is picking up and has for the last many days. Deoxit really is the miracle cure for bad contacts.

On another note, I decided to replace the motor grommets to see if it helped with the slight hum. Unfortunately I didn't any change in the hum or turntable wobble. However, the grommets were definitely hardened to the point of breaking apart upon removal. In the end, I'm glad I still replaced them as general maintenance.

I did email Vern Tisdale at vtisdale at vtisdale@cox.net more than a week ago asking if the large silver filter cap was included in the cap kits. Unfortunately he has not responded. Does anyone know if the cap 2000mdf 75vdc for Rockola cap kits is included in his kits? I'm still having a problem sourcing these.

Jason is having a somewhat hard time with his "communications" at the moment--he's working on this problem--try re-contacting him--I would think that cap is included --
As for the new grommets, did you use the correct white ones--blacks will cause hummmmm on RO's !
Ron Rich

Three different places I looked only had black grommets and specified that it worked with Rockola jukeboxes. Where do you get white ones specifically for Rockola? The jukebox had the same minor hum with the yellowed and hard grommets, as it does with the soft new black ones. You would think if that was a source of hum that there were be something that sounded different, even if it wasn't silent.

Lift your tone arm off the record--if hum disappears, the source is the turntable grommetts.
Check above in "--announcement" "used, new parts--where to find---" for a supplier--
Is the motor attached with "e" clips ( sirclips) or screws, or nuts ?
Ron Rich

Ron Rich wrote:Lift your tone arm off the record--if hum disappears, the source is the turntable grommetts.
Check above in "--announcement" "used, new parts--where to find---" for a supplier--
Is the motor attached with "e" clips ( sirclips) or screws, or nuts ?
Ron Rich

Its the clips with a washer. Good call on lifting the tone arm. Low hum is still there when lifting arm. Like I said, its barely noticeable when playing music but I like to strive for perfection. I guess that means filter cap or full cap kit will be the next step.

OK--the clip type unlike the other types have "built in spacers". Often spacers are lost, resulting in hum--but no worries here--Another source of hum on these, is the ground connections--find the common ground with all the green-green/yellow wires in it, remove and clean all of them, make sure the nut securing them is brass. Ron Rich

Ron Rich wrote:OK--the clip type unlike the other types have "built in spacers". Often spacers are lost, resulting in hum--but no worries here--Another source of hum on these, is the ground connections--find the common ground with all the green-green/yellow wires in it, remove and clean all of them, make sure the nut securing them is brass. Ron Rich

I was able to get some time to disconnect every green wire ground connection, clean the connectors and reconnect. I even found one wire that was dangling and tucked away and reconnected it back to a chassis ground connection spot. Unfortunately the hum still persists. Something that I didn't notice before is that there is a tiny hum through the speakers upon turning the jukebox on. That hum is amplified slightly when playing a record. Changing the volume knob doesn't change the hum level, it is just slightly louder when playing a record. I also disconnected both fluorescent tubes just to see if it went away and it did not. It seems I am down to the cap kit and that filter cap as next steps. I tried emailing Vern at vtisdale@cox.net again and didn't receive a response. Is there another address that I should contact him at? Thank you for all your knowledge and help up to this point.

I am posting this as a follow up in hopes that it can help others. I never did get a reply from Vern on his cap kits, but I was finally able to find an alternate source for the big silver filter cap. The new cap didn't have solder tabs but instead had screw terminals so it took a little working to get it mounted securely in there. However, after replacing the filter cap the very low hum is now completely gone. Most people wouldn't have noticed the hum as it was very transparent especially when music is playing, but it bothered the heck out of me. Now months later this jukebox is hum free for the first time. Thirty six year old original filter cap in the jukebox? It definitely needed a replacement and it was well worth it.