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Rock ola 474 amp



 
 
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  #1  
Old August 10th 20, 08:37 PM
Dave N. Dave N. is offline
Junior Member
 
First recorded activity by CollectingBanter: Apr 2017
Posts: 11
Default Rock ola 474 amp

I just pick up two Rockola 474's and the one I'm working on has static in the right speaker all the time sometimes you can hear it over the music. I have replaced most all of the electrolytic capacitors on the driver board, the pre amp and the power board with no change in the noise. has any one ever had this before.

Thank you for your help

Dave Niccum
Georgetown, Il USA
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  #2  
Old August 11th 20, 05:50 AM posted to alt.collecting.juke-boxes
John Robertson
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Posts: 901
Default Rock ola 474 amp

On 2020/08/10 12:37 p.m., Dave N. wrote:
I just pick up two Rockola 474's and the one I'm working on has static
in the right speaker all the time sometimes you can hear it over the
music. I have replaced most all of the electrolytic capacitors on the
driver board, the pre amp and the power board with no change in the
noise. has any one ever had this before.

Thank you for your help

Dave Niccum
Georgetown, Il USA





Unlikely to be a capacitor, more likely a resistor or transistor or even
a noisy electrical connection.

First, try unplugging the input to the amp. If that solves the noise
then check the cartridge and wiring.

When you adjust the volume does the noise go up/down with it?

If yes, then the problem is either the volume control or in the pre-amp.

If it doesn't change then the problem is most likely in the power amp
section.

An audio signal tracer is what you want to track that down!

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."
  #3  
Old August 12th 20, 08:26 PM
Dave N. Dave N. is offline
Junior Member
 
First recorded activity by CollectingBanter: Apr 2017
Posts: 11
Default

Quote:
Originally Posted by John Robertson View Post
On 2020/08/10 12:37 p.m., Dave N. wrote:
I just pick up two Rockola 474's and the one I'm working on has static
in the right speaker all the time sometimes you can hear it over the
music. I have replaced most all of the electrolytic capacitors on the
driver board, the pre amp and the power board with no change in the
noise. has any one ever had this before.

Thank you for your help

Dave Niccum
Georgetown, Il USA





Unlikely to be a capacitor, more likely a resistor or transistor or even
a noisy electrical connection.

First, try unplugging the input to the amp. If that solves the noise
then check the cartridge and wiring.

When you adjust the volume does the noise go up/down with it?

If yes, then the problem is either the volume control or in the pre-amp.

If it doesn't change then the problem is most likely in the power amp
section.

An audio signal tracer is what you want to track that down!

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

Thank You I will check it out
  #4  
Old August 13th 20, 07:17 AM posted to alt.collecting.juke-boxes
John Robertson
external usenet poster
 
Posts: 901
Default Rock ola 474 amp

On 2020/08/12 12:26 p.m., Dave N. wrote:
John Robertson;700563 Wrote:
On 2020/08/10 12:37 p.m., Dave N. wrote:-
I just pick up two Rockola 474's and the one I'm working on has static
in the right speaker all the time sometimes you can hear it over the
music. I have replaced most all of the electrolytic capacitors on the
driver board, the pre amp and the power board with no change in the
noise. has any one ever had this before.

Thank you for your help

Dave Niccum
Georgetown, Il USA



-

Unlikely to be a capacitor, more likely a resistor or transistor or even

a noisy electrical connection.

First, try unplugging the input to the amp. If that solves the noise
then check the cartridge and wiring.

When you adjust the volume does the noise go up/down with it?

If yes, then the problem is either the volume control or in the
pre-amp.

If it doesn't change then the problem is most likely in the power amp
section.

An audio signal tracer is what you want to track that down!

John :-#)#


Thank You I will check it out



Hi Dave,

These tests are done when the machine is playing a record and you are
hearing the noise...

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."
  #5  
Old August 14th 20, 09:06 PM posted to alt.collecting.juke-boxes
Jay Hennigan[_2_]
external usenet poster
 
Posts: 4
Default Rock ola 474 amp

On 8/10/20 12:37, Dave N. wrote:
I just pick up two Rockola 474's and the one I'm working on has static
in the right speaker all the time sometimes you can hear it over the
music. I have replaced most all of the electrolytic capacitors on the
driver board, the pre amp and the power board with no change in the
noise. has any one ever had this before.


If you have an oscilloscope you can probe the same points on both
channels looking for the noise.

Otherwise you can narrow it down, does the volume of the static vary
with the volume control or is it always at the same volume? Does it go
away during scan when the box is muted?

It's most likely a transistor. Without test equipment you can often
narrow it down by temperature. Most noisy components are noisier when
warm. Get a can of freeze spray (or computer duster, just turn it
upside-down) and give a light spray to each transistor during operation.
The one that causes the noise to go away or drop substantially is the
culprit.

 




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