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Help with Rigonda Bolshoi radiogram

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soldier101983
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have a Rigonda Bolshoi radiogram with a problem with the power supply unit when the power supply is turned on the transformer makes a loud buzzing noise and starts to get very hot to the point it starts to smoke. this is not a problem with loose core. anyone herd of this kind of fault before?

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Topic starter Posted : 27/11/2019 1:22 am
Nuvistor
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There is either too much load on the transformer or the transformer has shorted turns or both.

Disconnect any load on the output of the transformer, if the transformer still gets hot and smokes it requires replacing. The fault could be just the transformer or a fault in the load, rectifier, reservoir capacitor etc could have damaged the transformer.

Test the transformer and also check for shorts in the load.

Obviously don’t leave the gram unattended while it is  powered on and take any safety measures required while testing.

Check the correct fuses are in place.

Mod assistance: Snippet of PSU cct from full Bolshoi Circuit in data library. Hope it will assist in aiding diagnosis
bolpsu

 

 

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Posted : 27/11/2019 9:32 am
soldier101983
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@nuvistor

hello thanx for some advice, I have removed the power supply unit from the the rest on regonda. even not connected to the regonda the transformer makes this loud buzzing and gets very hot. all the caps on the power supply was replaced. so even when there is no load on it this is happening. does it seem to be a short on a winding? also the chassis the transformer is bolted to is reading 110v you get a shock when touch the core of transformer

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Topic starter Posted : 27/11/2019 2:53 pm
soldier101983
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@nuvistor

also do you have the full schematic in English as ive only been able to find it in russion? much thanx

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Topic starter Posted : 27/11/2019 2:57 pm
Nuvistor
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Even though you have removed the power supply chassis the rectifier and smoothing components are still connected.

Its very likely that the transformer is faulty, however did it just fail or did some other part of the PSU damage it. Those bridge rectifiers are a possibility, those short circuiting would put a large load on the transformer and could damage it. The capacitors have been replaced, is this fault since the replacement? If they have been fitted incorrectly they will fail and overload the transformer.

Has per my first post remove the connections to the secondary winding, there should be no conduction from any of the windings to the transformer core. A test meter is low voltage, worth checking with that first, if it seems ok, then test with power. The transformer then getting hot would confirm it is faulty.

The 110 volts on the chassis and getting a shock points to a transformer winding failing to the core. How did you measure the voltage?

If you are getting a shock I must emphasise safety, that’s in your hands.

EDIT. I only have that snippet of the circuit posted by the mods but there is enough information in that to service the PSU.

 

 

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Posted : 27/11/2019 3:20 pm
soldier101983
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@nuvistor

ok thanx I will try what you said. my dad bought the item not long ago to restore, the transformer was doing the fault intermittent also when you did give it a little hit it would tend to stop, he changed the caps thinking that could be the problem but it still doing the same. none of the windings on the transformer are bridged to the core so im not sure where its picking up this 110v. I will try as you have suggested much thanx

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Topic starter Posted : 27/11/2019 3:30 pm
soldier101983
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@nuvistor

i have disconnected the bridge rectifier and the transformer has stopped the buzzing would this mean I have a faulty bridge rectifier and its not the transformer hopefully

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Topic starter Posted : 27/11/2019 5:20 pm
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Nuvistor
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Does the transformer still get hot and smoke, is that 110 volts still on the chassis, how did you measure that voltage.

Disconnecting one of the bridges has removed a load off the transformer, check that circuit carefully for short circuits and leaks.

The transformer smoking and that 110 volt concerns me.

 

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Posted : 27/11/2019 6:49 pm
soldier101983
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@nuvistor

the transformer does not get hot with the rectifier not connected also the 110v on the chassis is not there without the rectifier. I put 1 meter lead to negative on the power in and touched the other meter lead to the chassis and it did read 110v. but now without the rectifier the 110v has gone

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Topic starter Posted : 27/11/2019 8:17 pm
Till Eulenspiegel
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Is this an all valve Rigonda  Bolshoi radiogram or is it solid state?

Till Eulenspiegel.

 

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Posted : 27/11/2019 8:42 pm
soldier101983
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@till

hi its the all valve

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Topic starter Posted : 27/11/2019 8:51 pm
Till Eulenspiegel
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@soldier101983

I remember the Bolshoi radiogram.  The wholesaler Brown Brothers in Newcastle were the distributors for the North-East of England.   Fantastic value for the money.

Is the HT rectifier a valve, selenium rectifier or silicon diodes?

https://www.radiomuseum.org/r/radiotehni_rigonda_symphony.html

 

Till Eulenspiegel.

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Posted : 27/11/2019 9:54 pm
Nuvistor
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The PSU in the RM link is much less complicated than the one posted earlier. One has two bridge rectifier the other one.

Which type is there in the faulty machine?

 

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Posted : 27/11/2019 10:22 pm
PYE625
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Is the 110v that can be measured an AC or a DC voltage?

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Posted : 27/11/2019 10:24 pm
soldier101983
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I will post pics of the power unit and the rectifier I hope this clears it up

IMG 20191127 201109
IMG 20191127 201103

 

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Topic starter Posted : 27/11/2019 10:40 pm
soldier101983
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simf003 04
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Topic starter Posted : 27/11/2019 10:52 pm
Nuvistor
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I can see 3 silicon diodes, presume the 4th is hidden and a variable WW resistor so I would say it’s the more complicated PSU.

I would go with Andrews excellent suggestion of a leak to chassis in the bridge rectifier. Testing will prove if it is.

 

 

 

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Posted : 27/11/2019 11:08 pm
PYE625
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I would hazard a guess that the main HT rectifier is shorted (or intermittant short) on an AC input to ground.

(I mentioned this earlier as Frank said, but I edited it out it until we knew whether the voltage measured of 110v was AC or DC.)

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Posted : 27/11/2019 11:18 pm
Nuvistor
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I wondered where it had gone, thought I was seeing things, think I will just have another whisky. ? 

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Posted : 27/11/2019 11:43 pm
soldier101983
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i have ordered some bridge rectifiers I will post update when they arrive and fitted to weather the problem is fixed or not. hopefully yes as I really don't want to rewind that transformer haha 

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Topic starter Posted : 28/11/2019 9:14 pm
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