Repair stereo transformer ~ possible?

[gbd1010]

Hello,

I have a stereo that is labelled as Planetron 2000.
~ I believe that my stereo is also the same as the Brother BR-5.

Issue:
Unfortunately, my 120V stereo was plugged into a 220V socket directly and my testing indicates that the transformer which supplies the amplifier and radio is blown (at the very least)
(the offender had the wherewithal to use a plug adaptor but not a voltage transformer...sigh!)

I'm aware that there could be other issues, but I'd like to replace or repair the transformer first and then see how things are.

I have trawled the Internet and posted on a number of different forums but unfortunately I have being unable to track down a service manual or schematic for the stereo so I am unsure what voltages the step down transformer supplies. I have also been unable to track down the transformer based on its labelling. (see photo attached). Therefore, at this point I am unable to replace it.


So, I'm hoping that somebody can advise on the possibility of repairing the transformer.
Perhaps the input wire on the transformer is melted/shorted (see testing results below) and I could replace the wire...is this possible? Is it simply a case of unwrapping the wire and counting the number of turns and replacing it with a similar wire with the same amount of turns? Note that I opened up one side of the transformer (the side with the 2 white wires) as I read that some transformers can have fuses, but I saw no sign of one.


The transformer
- See photo attached
- It's labelled as AC-159C (but I cannot find any reference to this on the Internet).
- There are 2 wires (both white) on one side which I am assuming are the input wires (assume 120V).
- There are 5 wires (2 x red, 1 x black, 1 x green and 1 x yellow) on the other side which I am assuming are the output wires. I have no idea what voltage they provide.


Transformer Testing
I removed the transformer from the stereo and tested the resistance between all the wires.

- White -> White = No measurement (Open circuit I assume)
- White wires to all other wires = No measurement (Open circuit I assume and expect)
- Red (#1) -> Red (#2) = 3ohms
- Red (#1) -> Yellow = 2.2ohms
- Red (#1) -> Green = 3.2ohms
- Red (#1) -> Black = 3ohms
- Red (#2) -> Yellow = 2.1ohms
- Red (#2) -> Green = 3.2ohms
- Red (#2) -> Black = 3.2ohms
- Yellow -> Green = 1.6ohms
- Yellow -> Black = 0.9ohms
- Green -> Black = 1.9ohms

 

[PETERDECO]

Welcome to the forum. If you can, remove the shell on the white wire side. You may be lucky and find a fuse inside.

 

[Harald Kapp]

I agree. Although it is unusual to have the primary side and the secondary side on the same connector.

 

[gbd1010]

Hi, thanks very much for responding.
I already opened up the shell on the white wire side and there was no sign of a fuse.
See photo attached.
Is there anything else I can check or do?
Is my suggestion of unwrapping the wire and counting the number of turns and replacing it with a similar wire with the same amount of turns madness?!!

 

[Martaine2005]

Are there any references to voltages on the PCB?. Near the connector?
There seems to be 3 or more outputs, any capacitor max voltages on each rail? Voltage regulators? Just a thought..
I see you didn't have any luck on the audio/hifi forums.

Martin

 

[gbd1010]

I can't see anything obvious in relation to what voltages the transformer is supplying. The output from the transformer plugs into a socket which then feeds into the proverbial rats nest of wires and components ~ I am very much an amateur/novice and I have seen the inside of a few systems but this one is proving too hard for me to follow. So much of it is unlabelled.

"I see you didn't have any luck on the audio/hifi forums." ~ Ha ha ~ No I didn't! But I'm nothing if not determined!

Does anyone have an opinion on my suggestion of unwrapping the wire and counting the number of turns and replacing it with a similar wire with the same amount of turns?

 

[Bluejets]

Does anyone have an opinion on my suggestion of unwrapping the wire and counting the number of turns and replacing it with a similar wire with the same amount of turns?

Forget it.
There are possibly a thousand turns on there and wound close together to minimise the finished size.
These are wound on a former initially and then fitted to the laminations, not the other way around.
I have done it a few times so have some idea.
Before you do any damage, you could take it to a motor winding shop and have them do it.
They would obviously rewind the whole thing, not just the primary for obvious reasons.
You would need deep pockets though.
Other alternative is to keep an eye out for a second hand unit.
They are out there, however being collectable these days, would be difficult.
Perhaps old radio stereo sites would be a good place to start.

 

[gbd1010]

Forget it.
There are possibly a thousand turns on there and wound close together to minimise the finished size.
These are wound on a former initially and then fitted to the laminations, not the other way around.
I have done it a few times so have some idea.

Thanks Bluejets ~ that's one avenue of repair ruled out!

I have been looking out for spare parts on the web. Unfortunately, these stereos are not very common and tend to be sold as complete units rather than broken up for individual parts. This is looking very much like a long term project! Thanks again.

 

[Bluejets]

Transformers these days as a whole are becoming rare.
Yes I realise one would need to buy the complete s/hand unit, not parts.
Pioneer blu ray I had here turned out the same.
Much cheaper and less hasle to buy a s/hand unit.
Depends how badly you need to hold on to the past.

Waited for a cartridge for the one below for 6 months and it is a common part to many different brands.

 

[Harald Kapp]

Have you repeated the measurement white<>white directly at the transformer?

Just to rule out a defect within the white wires

 

[gbd1010]

Waited for a cartridge for the one below for 6 months and it is a common part to many different brands.

Well done. You got there in the end. A fantastic looking stereo.

I have wondered since my issue arose if these Planetron/Brother stereos are related in some way to the Weltron stereos as there are a lot of similarities in their external appearance at least. But I haven't come across anything to prove this. If I could prove it, then perhaps I could purchase a Weltron transformer and swap it in. Or, perhaps they were all just adhering to some shared 'spaceage' look and just ripping off each others ideas!

Internally, there is a similarity too in that they both take in one input feed and then have to provide the appropriate voltages to the record player (120V) and the lights, radio, tape (or 8 track player) and the amplifier.

 

[gbd1010]

Have you repeated the measurement white<>white directly at the transformer?
View attachment 52070
Just to rule out a defect within the white wires

Great suggestion and it gave me a glimmer of hope!
But unfortunately testing has confirmed that there is continuity along both white wires and no continuity between the exposed wires coming out of the transformer.
Thanks though for your suggestion.

 

[Audioguru]

I think the transformer burnt because the over-voltage caused a few hundred amplifier parts to short which overloaded the transformer.
Repairing or replacing the transformer will not fix the problem.

 

[Bluejets]

As mentioned previously, transformer primary do occasionally blow.
As for overload, it is well known transformers can handle loads above their rating without blowing up.