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Old 22nd Jul 2021, 10:14 am   #1
Murphy1969
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Default Murphy A855g Record Player - Intermittent power issue.

Hi - I recently acquired a Murphy AU855G record player which worked fine for a couple of weeks, then when I turned it on one day recently , although I got a hum from the speakers, the red power light didn't come on and the deck didn't function - turntable wouldn't turn etc.

A week later, I tried again and all was fine again. I have used the record a fair amount recently and used the record player last night and the same issue has occurred today - I get the normal speaker hum, but no light and no action from the deck :-(, and the red power light doesn't come on.

I know little about these things, but could it be a simple wiring issue /
loose connection somewhere? I note the power cable comes in at the back of the unit and goes underneath the deck to the front of the unit to the speaker etc. I am thinking there is a power feed underneath the deck itself (powering the deck) which may need attention?

I note there are 4 screws which seem to be holding the deck onto the main unit. Will it be simple enough to remove these screws and lift the deck to take a look? Is there anything I need to be careful of, apart from disconnecting from the mains of course .

I believe it is the same construction as the Bush SRP51 and has a BSR UA65 autochanger.

Any help/advice appreciated.

Thanks,

Ian
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Old 22nd Jul 2021, 10:27 am   #2
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Default Re: Murphy A855g Record Player - Intermitent power issue.

Extract from circuit to aid any member offering assistance.

Symptoms seem inconsistent to me.
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Old 22nd Jul 2021, 11:01 am   #3
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Default Re: Murphy A855g Record Player - Intermitent power issue.

Question for the OP.

With the fault present does stroking the stylus result in noise from the speaker?
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Old 22nd Jul 2021, 12:27 pm   #4
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Default Re: Murphy A855g Record Player - Intermittent power issue.

The symptoms certainly are inconsistent.

The transformer supplies the amplifier from one of its secondary windings and the lamp from a second separate winding.

Seeing that circuit clip reminded me that this is the model that's notorious for its mains transformer burning out. There have been several of these in recent years of both Bush and Murphy models featured on the forum with burnt out transformers and none have ever reached a satisfactory repair conclusion. The problem is as to what actually goes faulty to cause this burn out in the first place and the unavailability of a suitable replacement transformer seems to cause the owners to just give up with them.

So what I would say is that with the above in mind, don't leave the player powered up for any length of time when under the fault condition, but quickly do as Graham suggested and stroke the stylus with the volume control turned fully up to see if you get noise from the speaker. If the transformer was being heavily loaded by an amplifier short circuit fault then this could possibly cause the winding that supplies the lamp to drop its voltage, but that still doesn't answer the question as to why the record deck stops working, as this is powered from the mains input primary side of the transformer.
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Old 22nd Jul 2021, 12:45 pm   #5
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Default Re: Murphy A855g Record Player - Intermittent power issue.

Just to clarify something that I forgot in the above post.

The inconsistency is that the OP says that a 'hum' can be heard from the speaker under the fault condition, yet no indicator lamp illumination and no deck operation. I'm wondering if the 'hum' isn't actually from the speaker but is actually the transformer itself buzzing due to being under extreme load due to the fault condition - but then why is the deck not functioning...guessing that by not functioning we're talking about 'mechanically' here and not it's audio output?
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Old 22nd Jul 2021, 12:48 pm   #6
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Default Re: Murphy A855g Record Player - Intermittent power issue.

Thanks for all your replies so far. Amazing!

Yes - there is noise from the speaker when I stroke the stylus.
I currently still don't have a power light on , nor is the turntable turning when I try to operate the deck / arm.
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Old 22nd Jul 2021, 12:54 pm   #7
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Default Re: Murphy A855g Record Player - Intermittent power issue.

As stated the symptoms are totally inconsistent. For the amplifier to work the mains transformer must be working and if the mains transformer is working the indicator lamp should be lit. As for the motor not working that's totally independent from the transformer.

Assuming the symptoms have been correctly reported you have multiple faults which for some reason manifest themselves simultaneously,

You're going to have to get yourself a DMM (Digital Multi Meter) in order to carry out diagnostic tests.
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Old 22nd Jul 2021, 12:54 pm   #8
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Default Re: Murphy A855g Record Player - Intermittent power issue.

The unit is currently off and I always turn it off when not in use. If its of any help, the latest occurrence of the problem occurred last night immediately after I played one 7 inch single after playing 2 sides of an LP.
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Old 22nd Jul 2021, 1:01 pm   #9
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Default Re: Murphy A855g Record Player - Intermittent power issue.

Apologies - I have just checked again and the turntable is working - I hadnt moved the selector to manual - I just moved the arm over. DOOOOH . So playing records again. The power light isn't on, but I'm not too bothered about that. The humming sound got louder when I turned the volume up.
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Old 22nd Jul 2021, 1:51 pm   #10
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Default Re: Murphy A855g Record Player - Intermittent power issue.

These are notorious for bad connections in the bulb holder causing the lamp to be sometimes on and other times not - just the same as in the earlier valve version of this player.

I would be worried if the hum level was loud enough to be heard over the music when playing - it could be an indication of failing smoothing, the rectifier 'half-waving', or the amplifier output stage drawing too much current from the power supply. All of these faults have the potential to damage the transformer, so if the hum is 'excessively' loud, or the fault condition happens again, then switch off and don't use the player again until you've asked for advice on here - otherwise carry on using the player, but keep a careful eye on things and don't leave it unattended when powered on.
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Old 22nd Jul 2021, 2:05 pm   #11
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Default Re: Murphy A855g Record Player - Intermittent power issue.

I've just thought of something else regarding these players and that is that there was some talk of the bulb holders (lamp holders) going short circuit. If this happened it would certainly load the mains transformer and cause voltage drop and hum, eventually burning out the transformer. So it might be an idea to just investigate that lamp and its holder - should be easy enough to get at...unscrew the lamp and screw it back in again and make sure it's illuminating to its correct expected brightness, which it won't be if the holder is shorting out.
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Old 22nd Jul 2021, 2:51 pm   #12
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Default Re: Murphy A855g Record Player - Intermittent power issue.

Quote:
Originally Posted by Murphy1969 View Post
Apologies - I have just checked again and the turntable is working - I hadnt moved the selector to manual - I just moved the arm over. DOOOOH . So playing records again.
The forum member who recently advised me to assume nothing when reading a post was obviously correct.
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Old 22nd Jul 2021, 3:15 pm   #13
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Default Re: Murphy A855g Record Player - Intermittent power issue.

Quote:
Originally Posted by Station X View Post
Quote:
Originally Posted by Murphy1969 View Post
Apologies - I have just checked again and the turntable is working - I hadnt moved the selector to manual - I just moved the arm over. DOOOOH . So playing records again.
The forum member who recently advised me to assume nothing when reading a post was obviously correct.
Indeed. And my question about "assumptions" was 'what does the OP mean by "so playing records again" '. Does he mean just that the turntable is now rotating, or that he's getting the expected audio from a record through the loudspeaker (albeit with some hum)?

Mike

Last edited by Boulevardier; 22nd Jul 2021 at 3:35 pm.
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Old 22nd Jul 2021, 4:41 pm   #14
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Default Re: Murphy A855g Record Player - Intermittent power issue.

Thanks for all the help everyone. I know Iím a dope . Never assume is true. Thanks for the tip regarding the bulb holder. I will take a look when I get chance. The hum is only slight, so probably normal. But I wonít be leaving it turned on when not using.
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Old 22nd Jul 2021, 4:54 pm   #15
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Default Re: Murphy A855g Record Player - Intermittent power issue.

Members have differing views as to how much hum is normal or acceptable from a record player. Personally I reckon that hum between tracks is OK, so long as it's drowned out by the music.
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Old 22nd Jul 2021, 8:24 pm   #16
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Default Re: Murphy A855g Record Player - Intermittent power issue.

There are two presets, RV4 and RV5, they should be replaced and set up according to the manual.

May I suggest that failure of these, especially RV5 is the cause of the mains transformer burning out.

One other thing. If the transformer fails, you could replace it with at a 20 or 24V transformer with two secondary windings and chane the lamp from a 6.5V to a 24 V across one of the secondaries.
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Old 22nd Jul 2021, 9:06 pm   #17
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Default Re: Murphy A855g Record Player - Intermittent power issue.

I have accessed the bulb holder . I didn’t remove it. Just unplugged from mains, gave it a wiggle and it’s working again. So back to normal now. Many thanks everyone ��
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Old 23rd Jul 2021, 10:34 am   #18
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Default Re: Murphy A855g Record Player - Intermittent power issue.

Quote:
Originally Posted by Michael Maurice View Post
One other thing. If the transformer fails, you could replace it with at a 20 or 24V transformer with two secondary windings and chane the lamp from a 6.5V to a 24 V across one of the secondaries.
A 24 volt transformer might be pushing it a bit, I would go with a 20 volt one.

27.5 VDC + 0.7 * 0.707

Lawrence.
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