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Old 14th Jun 2018, 5:08 pm   #21
Steve Erskine
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Default Re: Murphy A855G- no sound.

Hi,
I have managed to remove the workings and I would appreciate knowing what and how to test.
I have carried out a capacitor test, to the best of my ability.
The readings for both were .113 and if I reversed my test needles, the reading was 217 for both. I presume that this is not correct and points to something wrong (probably me).
Thanks, Stephen
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Old 14th Jun 2018, 5:20 pm   #22
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Default Re: Murphy A855G- no sound.

Posts 11 and 12 give you some information to start with. I would check the two diodes as per post 12 first, you may require to disconnect one end of each diode to test them. Take plenty photos and make diagrams so you know where each item fits before disconnecting. The power requires disconnecting to test those diodes.

If you work on the player with the voltage applied take all safety precautions.
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Old 14th Jun 2018, 6:00 pm   #23
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Default Re: Murphy A855G- no sound.

Hi Frank,
I wil set to work.
I will most definitely be working unplugged.
Do the burnt / blackened windings look ok?
Thanks
Stephen.
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Old 14th Jun 2018, 6:10 pm   #24
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Default Re: Murphy A855G- no sound.

I must admit they don’t look very good to me.

An easy test for the transformer is to disconnect the secondary windings and check if it still gets hot and burns, if it does that with no connections then it is faulty.

Of course it could be other parts in the player that have damaged it including those diodes.
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Old 16th Jun 2018, 8:45 am   #25
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Default Re: Murphy A855G- no sound.

Hi,
I have released one side of each diode and the readings were .597 and .583.
Should I release all the wires on the bottom of the transformer?
The wax from the transformer has melted off and is lying on the cabinet base?
Regards
Stephen
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Old 16th Jun 2018, 9:15 am   #26
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Default Re: Murphy A855G- no sound.

How did you test the diode and is that .597 ohms or 0.597k ohms?

Wax dripping onto the cabinet could be normal.

Removing those wires on the secondary and seeing if the transformer still overheats is a reasonable test.
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Old 16th Jun 2018, 9:24 am   #27
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Default Re: Murphy A855G- no sound.

Quote:
Originally Posted by Steve Erskine View Post
Hi,
I have released one side of each diode and the readings were .597 and .583.
Stephen
That's the forward volt drop, which is OK. You need to reverse the meter leads and check the backward resistance which should be infinite.

The first post in this thread will give you the idea:-

https://www.vintage-radio.net/forum/...ad.php?t=42194

There are three diodes (there should be four), but you've only quoted two readings.
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Old 16th Jun 2018, 6:34 pm   #28
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Default Re: Murphy A855G- no sound.

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Quote:
Originally Posted by Steve Erskine View Post
Hi,
I have released one side of each diode and the readings were .597 and .583.
Stephen
That's the forward volt drop, which is OK. You need to reverse the meter leads and check the backward resistance which should be infinite.
I must get a meter with a diode test position, I have just used an ohmeter for so many years I never think about the diode test.
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Old 17th Jun 2018, 9:12 am   #29
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Default Re: Murphy A855G- no sound.

I have used the diode position on the multimeter.
I done a reverse test on the diodes and, even with the help of a third hand to ensure proper contact with the diode ends, the meter did not register any movement.
I can only see two diodes.
I removed all the wires from the bottom of the transformer and left it on for four hours and it remained cold. I tested the turntable and it was still receiving power.
Thanks
Stephen
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Old 17th Jun 2018, 9:26 am   #30
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Default Re: Murphy A855G- no sound.

If feel confident enough can test the voltages on the secondaries of the transformer, these will be AC so you need to select AC volts of an appropriate range, they have no load so will be a little higher than expected.

You can connect the meter leads if they have clips on, then switch on power, be safer than having your hands inside while power is on. Unless of course you feel safe enough.

If the voltages are OK and the transformer cool it is probably ok.

Then comes the question of why does it get hot.

Edit, be careful of the power input tags on the transformer shorting on anything, in the photo it looks as though they are resting on the metal trim.
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Old 17th Jun 2018, 10:30 am   #31
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Default Re: Murphy A855G- no sound.

Hi,
Before I switched it on, I removed all of the wires shown in the picture.
I have read up on how to do a voltage test, but I don't know what to test as far as which terminals to test and with which probe.
Cheers
Stephen
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Old 17th Jun 2018, 10:45 am   #32
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Default Re: Murphy A855G- no sound.

The two brown wires that feed the pilot lamp will have 6 to 8 volts AC.
The centre tap on the main winding will have been connected to the electrolytic capacitor., from that tag to either of the two tags that connected to the diodes will have 30 to 40 volts AC, I cannot give exact voltages.

If you look at the circuit of the transformer you should be able to follow how the wires are connected.

Edit. Correction for the connection to the centre tap of the transformer.
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Old 17th Jun 2018, 10:57 am   #33
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Default Re: Murphy A855G- no sound.

Quote:
Originally Posted by Steve Erskine View Post
I can only see two diodes.
Stephen
Sorry I confused this with another thread. There are only two diodes.
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Old 17th Jun 2018, 11:03 am   #34
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Default Re: Murphy A855G- no sound.

Quote:
Originally Posted by Steve Erskine View Post
Hi,
Before I switched it on, I removed all of the wires shown in the picture.
I have read up on how to do a voltage test, but I don't know what to test as far as which terminals to test and with which probe.
Cheers
Stephen
Set your meter to read 200 volts AC, then referring to the photo in Post 29:

Row of 3 tags, black meter probe to middle tag, red meter probe to the left hand tag, measure and record the AC voltage reading, then red probe on the right hand tag, measure and record the AC voltage reading, the black probe is on the middle tag for both measurements.

Then go to the two tags below the three tags, black probe to one of those two tags, anyone will do, then red probe to the other tag, measure and record the AC voltage reading.

Lawrence.
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Old 18th Jun 2018, 11:27 am   #35
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Default Re: Murphy A855G- no sound.

Hi Many thanks for the detailed instructions, it’s just what I need and it helps me learn. However, I found a wire hanging by a thread feeding the very burnt coil. I have no idea as to cause or effect. Thanks Stephen.
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Old 18th Jun 2018, 11:34 am   #36
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Default Re: Murphy A855G- no sound.

Do the long wires in your picture actually go into the windings? If so make sure they're not touching each other. Otherwise snip them off.
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Old 18th Jun 2018, 2:45 pm   #37
Steve Erskine
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Default Re: Murphy A855G- no sound.

Hi,
These two pictures show the wires better in situ.
Thanks,
Stephen.
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Old 18th Jun 2018, 2:54 pm   #38
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Default Re: Murphy A855G- no sound.

Are you uploading from a phone? The file name is probably the same for both photos. Had that problem myself.

I am not sure about the thin wires, as Graham asked, do they go into the windings?
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Old 18th Jun 2018, 7:09 pm   #39
Steve Erskine
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Default Re: Murphy A855G- no sound.

Hi,
Yes, they are fed into the coil from the main feed coming in.
The wire from the blue mains is still firmly attached, but the one which has almost become detached is fed from the brown one.
Regards
Stephen
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Old 18th Jun 2018, 7:26 pm   #40
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Default Re: Murphy A855G- no sound.

The picture in post #37 shows the incoming mains to the transformer primary windings with wires going off to the terminals. This looks OK to me.

A clear picture showing all the tags on the secondary side would help.
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Last edited by Station X; 18th Jun 2018 at 7:37 pm. Reason: Posted rubbish!
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