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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 24th Jul 2012, 12:04 pm   #41
steve_gus
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Default Re: Bush SRP 31D not producing sound!

Hi

your statement a few posts back is interesting

1= loud buzz (same as when you touch the bare tone arm wires) and 0v


So, if you touch the wires to the pickup, you get a loud hum? This kinda indicates the amp is working.

Are you sure its not just a dodgy pickup cartridge, as you mentioned it worked and faded out a few times in the past. I would re-connect the pickup wires, touch them, and see if you get a buzz that can be controlled by the volume knob. If it can, perhaps its a dodgy pickup?

Be very careful when touching things in the main chassis, as 215v will be a bit more than a loud buzz
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Old 24th Jul 2012, 5:19 pm   #42
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Default Re: Bush SRP 31D not producing sound!

Oh no, I meant usually when it's working if you touch the bare pick up wires it buzzes but now it doesn't. I tried a different cartridge and got no response.

I am sure something has died in the circuit but I don't know what and I am new to all this so don't even know what to test. I'm still very worried about the horrible noise the speaker makes when you turn the machine off now. :S
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Old 24th Jul 2012, 10:07 pm   #43
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Default Re: Bush SRP 31D not producing sound!

Hi guys,

I don't know if this is any use but I did some reading on how to test an electrolytic capacitor as I hear they can blow when they get old. I tested the two red and white ones on the 20k setting on the multimeter and found that one was 0.12 whereas the other was 1.97, could this be the reason?

They are meant to be the same capacitor and also I was thinking about how it started to die off, the sound phased out like a battery running down.

Last edited by Spencervs; 24th Jul 2012 at 10:16 pm.
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Old 24th Jul 2012, 11:12 pm   #44
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Default Re: Bush SRP 31D not producing sound!

You cannot test the electrolytic capacitors in circuit, as they are shunted by other components.

You say, in post #23, that you get a loud buzz when you touch pin 1 of V1. What do you get when you touch the centre tag of the volume control? There's only a 220K resistor between the two points.
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Old 25th Jul 2012, 12:11 am   #45
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Default Re: Bush SRP 31D not producing sound!

Do you mean the tip of the pentometer? the thing that the volume dial is actually attached to?

just tried touching that bit and there was no joy there. I am still concerned about the horrible lingering noise the machine makes after it is turned off too. Is there no way to test those electrolytic capacitors?

Last edited by Spencervs; 25th Jul 2012 at 12:25 am.
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Old 25th Jul 2012, 1:31 am   #46
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Default Re: Bush SRP 31D not producing sound!

The volume needs to be turned up when you do the touch test on the control.
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Old 25th Jul 2012, 7:42 am   #47
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Default Re: Bush SRP 31D not producing sound!

Quote:
Originally Posted by Spencervs
Do you mean the tip of the pentometer? the thing that the volume dial is actually attached to?
On the volume potentiometer you will find three solder tags. The centre tag is connected to the wiper. The outer tags are connected to the ends of the track.

Turn up the volume and touch each tag in turn with a screwdriver blade.
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Old 25th Jul 2012, 8:28 am   #48
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Default Re: Bush SRP 31D not producing sound!

And don't put your fingers anywhere near the mains switch, which I think is on the back of the volume pot!
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Old 25th Jul 2012, 12:10 pm   #49
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Default Re: Bush SRP 31D not producing sound!

OK, touched the tags on the volume dial and all I got was a quiet click but no live buzz from the red wire going to the fuse bulb. Nothing from the white and black wire (see post 36 for pictures) However I did get a live buzz from the treble potentiometer but I don't think I got it from the Bass potentiometer though.
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Old 25th Jul 2012, 12:16 pm   #50
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Default Re: Bush SRP 31D not producing sound!

Is it not the 220K resistor that has gone open circuit?
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Old 25th Jul 2012, 12:39 pm   #51
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Default Re: Bush SRP 31D not producing sound!

Quote:
Nothing from the white and black wire (see post 36 for pictures)
Are you sure you're touching the wires on the volume control potentiometer? The wires you mention seem to be connected to the mains switch which is ganged with the volume control. ie it is operated by the same knob.

Look at the bass and treble controls. The tags connected to their potentiometers are clearly visible.
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Old 25th Jul 2012, 12:52 pm   #52
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Default Re: Bush SRP 31D not producing sound!

Well there are four tags on this potentiometer in a rhombus the left and bottom tags are exclusively live and neutral from the mains. The top and right tags have two sets of wires connected, that is live and neutral to the motor in the turntable and the second set of wires are from the top tag (black to the motor) is white to the top of the mains transformer and the right tag (red to the motor) is a red wire to the fuse bulb which then leads onwards to the top tag of the transformer, which I hope is clearer in the photo attached

I touched the two wires to the mains transformer. I got the small click from the red wire to the top tag of the transformer
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Old 25th Jul 2012, 12:55 pm   #53
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Default Re: Bush SRP 31D not producing sound!

Please read the last paragraph of post #51.
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Old 25th Jul 2012, 12:58 pm   #54
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Default Re: Bush SRP 31D not producing sound!

Quote:
I touched the two wires to the mains transformer... I got the small click from the red wire to the top tag of the transformer
Please STOP now before you kill yourself!
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Old 25th Jul 2012, 1:02 pm   #55
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Default Re: Bush SRP 31D not producing sound!

ahh ok forgive me, I must have missed that last bit. just checked the bass and treble and the middle pins (and left pins) make the live buzz, although the treble one is much louder than the bass one

and I meant with screwdriver as instructed, not with my hands, am I doing it wrong? :S
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Old 25th Jul 2012, 1:07 pm   #56
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Default Re: Bush SRP 31D not producing sound!

So going back several posts, what do you get if you touch the middle tag of THE VOLUME CONTROL POTENTIOMETER?
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Old 25th Jul 2012, 1:08 pm   #57
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Default Re: Bush SRP 31D not producing sound!

I agree with Station X here. You could easily suffer a massive electric shock here or even damage the unit!

If you want someone to look at it for you and take you through the repairs, then ask. I'm in Bolton but there's bound to be someone closer. It is better to learn than die.

Cheers,

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Old 25th Jul 2012, 1:13 pm   #58
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Default Re: Bush SRP 31D not producing sound!

Oh! sorry I didn't see the three tags on the volume because they were hidden by a fuse and I thought the four on top were the only ones. Found then however and yes I get a nice responsive live buzz!
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Old 25th Jul 2012, 1:17 pm   #59
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Default Re: Bush SRP 31D not producing sound!

OK.

Turn up the volume and touch each end of R2 in turn.

If you get a buzz here, the problem must be in the wiring between here and the co-axial socket from which (in post #39) you say you got no response.
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Old 25th Jul 2012, 1:30 pm   #60
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Default Re: Bush SRP 31D not producing sound!

aha! R2 produces a loud buzz when the ends are touched! and according to my understanding of circuit diagrams (lacking, I'll give you that) the only thing that can go wrong is C2, right? it does look darker than the rest of the ceramic caps (I'm guessing its ceramic as it is similar to the disk ones), infact it seems to be wet or like it was wet and dried but I'm sure not gonna touch it to find out!

Last edited by Spencervs; 25th Jul 2012 at 1:43 pm.
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