|
Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
|
Thread Tools |
4th Apr 2020, 2:55 pm | #1 |
Tetrode
Join Date: Sep 2018
Location: Inverness, Scottish Highlands, UK.
Posts: 74
|
1970s Rock-ola 473 jukebox rumbling noise
Hi all,
When switched on, the speakers make a rumbling noise, as if someone’s rubbing a piece of paper along the record needle. It also sounds like the echoes of thunder. If you switch off, the noise gets slightly louder and pops a little, before fading away. If I disable the mute relay, it gets slightly louder and has more treble. If I disconnect the pickup jack, no change. It continues over the music from a record. The noise is unaffected by the volume control. It’s much louder from the large speakers, but is just present in the smaller ones. It’s equally present in left and right sides. From this, I’ve concluded the noise is not from the pickup, and must be after the volume control. The service manual details input level, balance and bias adjustments. I’m happy to go through these, but this problem sounds more like a fault than a bad adjustment. My hope is that the noise is a distinctive sign of a particular fault that someone can identify. Many thanks Andy |
4th Apr 2020, 3:18 pm | #2 |
Dekatron
Join Date: Jun 2013
Location: East Sussex, UK.
Posts: 3,315
|
Re: 1970s Rock-ola 473 jukebox rumbling noise
Clean the tone control switches and the volume control plug/socket with Servisol 10 switch cleaner. Check those yellow capacitors on the output and power supply boards. If you unplug the audio leads to the output boards it will just leave the o/p boards connected and if the noise stops then it's before them. If it really is both channels then it points to a power supply fault and is most probably capacitors.
|
4th Apr 2020, 4:04 pm | #3 |
Tetrode
Join Date: Sep 2018
Location: Inverness, Scottish Highlands, UK.
Posts: 74
|
Re: 1970s Rock-ola 473 jukebox rumbling noise
Thanks for the quick reply.
Tone control and switches and volume plug cleaned. They don’t seem to affect the noise. Yellow cap ESRs: Driver board L (assume this is what you’re calling output): 22u 75V 0.33ohm (ref 1.5ohm) 10u 75V 0.50ohm (ref 5ohm) Driver board R: 22u 75V 0.32ohm 10u 75V 0.57ohm Supply board: 47u 10V 0.74ohm (ref 2.5ohm) So the yellows look OK. Unplugging the audio leads to the output (labelled driver) boards makes the sound much louder, especially on the right. So after the driver boards? I’ve included a photo to show I’m listening! Andy |
4th Apr 2020, 6:28 pm | #4 |
Tetrode
Join Date: Sep 2018
Location: Inverness, Scottish Highlands, UK.
Posts: 74
|
Re: 1970s Rock-ola 473 jukebox rumbling noise
I’ve done some more troubleshooting. The right side is considerably worse than the left. It’s hard to hear directionally with such low noises.
The signal path appears to be: tone -> L+R driver -> L+R heat sink -> capacitor board If I disconnect signal between tone and driver, the noise gets worse. If I disconnect between heat sink and cap board noise disappears. So the problem is either driver or heat sink. Heat sink is where the output transistors are. If I swap driver boards left-right, then noise follows the driver, ie swaps right to left. So it looks like the driver board is faulty on the right hand side. |
4th Apr 2020, 6:49 pm | #5 |
Dekatron
Join Date: Jun 2013
Location: East Sussex, UK.
Posts: 3,315
|
Re: 1970s Rock-ola 473 jukebox rumbling noise
These are a little easier to diagnose as you can swap left to right and narrow it down. Well done.
|
4th Apr 2020, 7:05 pm | #6 |
Tetrode
Join Date: Sep 2018
Location: Inverness, Scottish Highlands, UK.
Posts: 74
|
Re: 1970s Rock-ola 473 jukebox rumbling noise
Thanks. The problem is, I can’t find anything significantly different between L and R driver boards. A few resistors over tolerance but nothing significantly worse on the right than left.
I’ll try a few substitutions. |
4th Apr 2020, 8:03 pm | #7 |
Dekatron
Join Date: Jun 2013
Location: East Sussex, UK.
Posts: 3,315
|
Re: 1970s Rock-ola 473 jukebox rumbling noise
It’s worth a close look at the pins of the connector, I’ve had it where they were not pushed completely through the board and after all these years became dry joints.
|
5th Apr 2020, 4:47 pm | #8 |
Dekatron
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
|
Re: 1970s Rock-ola 473 jukebox rumbling noise
From your description, it sounds very much like the kind of noise associated with a poor connection. So the prime suspects would be a dry solder joint, possibly on a connector; or a failing component, more likely to be a resistor or capacitor than anything else because semiconductors usually bow out with a bit more show.
Crimped connections don't usually play up, but you can generally pop the individual contacts out of the housing with a small screwdriver to test for soundness. If one is bad, the wire will just come straight out with a gentle pull. Those carbon resistors are notorious for going noisy with old age; the connection between the lead-out wire and the resistive element deteriorates. They often test fine, because the change in resistance value is over quicker than the meter can respond to it. If you're resigned to resoldering every joint, you might as well just replace them all with modern metal film ones of similar physical size (they will be more than good enough for the power dissipation; modern resistors can stand higher temperatures, which means more Watts per cubic millimetre than Ye Olde Days). S*d's Law says when you get to about the third or fourth one, it will come loose of the board after unsoldering one end, and you will have found the original cause. But persevere with the resistor replacement anyway, because the rest of them are just as old and not getting any better for it. I can also see some kind of ceramic hybrid circuit on there. This could be the culprit, which would be bad news if it is, but there are plenty of more likely suspects to eliminate first.
__________________
If I have seen further than others, it is because I was standing on a pile of failed experiments. |
5th Apr 2020, 8:24 pm | #9 |
Tetrode
Join Date: Sep 2018
Location: Inverness, Scottish Highlands, UK.
Posts: 74
|
Re: 1970s Rock-ola 473 jukebox rumbling noise
Thanks to you both.
I’ve just spent an awful lot of time swapping components around to no avail. In the end, I powered the board up on the indoor bench (the jukebox is in an outside workshop) and watched the noise on the scope. It appears to be ‘loudest’ near pin 6 of that hybrid, although swapping hybrids between boards didn’t have the effect I expected. I could build a copy of the hybrid, but it’s not my jukebox (rather ugly, in my opinion) but has sentimental value for the owner. I cant be sure my hybrid will work any better. I found a pair of driver boards online for £34 and ordered those. I can’t explain why swapping components seemed to have little effect on the noise. Only the complete left-hand board was quiet(ish). (I did reflow all the joints.) Perhaps an interaction between two or more components? Anyway, an intellectually frustrating but easily solved problem. |
6th Apr 2020, 9:47 am | #10 |
Dekatron
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
|
Re: 1970s Rock-ola 473 jukebox rumbling noise
It's not inconceivable for the board itself to be the source of the noise. Perhaps there is a microscopic crack in one of the copper tracks, or some slightly-conductive dirt on it? Still, I don't suppose it matters much if the replacement driver boards work.
Anyway, it's good that you could clone the hybrid if necessary.
__________________
If I have seen further than others, it is because I was standing on a pile of failed experiments. |
6th Apr 2020, 9:53 am | #11 |
Moderator
Join Date: Feb 2006
Location: Wembley, Middlesex
Posts: 7,219
|
Re: 1970s Rock-ola 473 jukebox rumbling noise
I repaired one of these a while ago. The hybrids are passive and in my case not the source of the noise. I replaced all the electrolytic capacitors, the presets and the transistors, using TIP41/42.
|
8th Apr 2020, 11:22 am | #12 | |
Tetrode
Join Date: Sep 2018
Location: Inverness, Scottish Highlands, UK.
Posts: 74
|
Re: 1970s Rock-ola 473 jukebox rumbling noise
Quote:
Since substituting components singly didn’t solve it, I assume it was two components interacting; perhaps some kind of oscillation? In some desperation I did try poking and flexing the board but nothing seemed to make any difference. I’ll be setting the bias, etc with the new boards in place soon. Is a Fluke meter, with 10M input impedance suitable? I’ve heard that older, analogue meters are better because they more closely match the meters available at the time. |
|
8th Apr 2020, 11:23 am | #13 |
Tetrode
Join Date: Sep 2018
Location: Inverness, Scottish Highlands, UK.
Posts: 74
|
Re: 1970s Rock-ola 473 jukebox rumbling noise
Just adding another reply to turn on notifications...
|
8th Apr 2020, 12:38 pm | #14 | |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,526
|
Re: 1970s Rock-ola 473 jukebox rumbling noise
Quote:
If you're looking at a varying reading, an analogue meter may simply be easier to use.
__________________
....__________ ....|____||__|__\_____ .=.| _---\__|__|_---_|. .........O..Chris....O |
|
8th Apr 2020, 9:18 pm | #15 |
Nonode
Join Date: Oct 2017
Location: Bristol, UK.
Posts: 2,358
|
Re: 1970s Rock-ola 473 jukebox rumbling noise
Had similar probs with a Beomaster 3000 and the fault turned out to be bad preset pots. Dirty tracks, corroded wipers and some would not respond to switch cleaner as crimped contacts had gone south. Cheers, Jerry
|
10th Apr 2020, 3:54 pm | #16 | ||
Hexode
Join Date: Oct 2019
Location: Weymouth, Dorset, UK.
Posts: 473
|
Re: 1970s Rock-ola 473 jukebox rumbling noise
Quote:
|
||
11th Apr 2020, 11:51 am | #17 |
Tetrode
Join Date: Sep 2018
Location: Inverness, Scottish Highlands, UK.
Posts: 74
|
Re: 1970s Rock-ola 473 jukebox rumbling noise
Just out of interest, while waiting for the new boards, I desoldered the pots and replaced them with suitable resistors. Still noisy on the scope!
|