Philips FCD565 midi system ~1987 - Transformer buzz

[budm]

Is there a plug at the end of the grey/red cables (two greys and one red) on the power supply board to the main board, they are the secondary side of the winding of the transformer, if you can disconnect the cables then you can install the transformer back in and power up and it will not have any load on the secondary side if we disconnect the grey/red cables.

[quattro alex]

Is there a plug at the end of the grey/red cables (two greys and one red) on the power supply board to the main board, they are the secondary side of the winding of the transformer, if you can disconnect the cables then you can install the transformer back in and power up and it will not have any load on the secondary side if we disconnect the grey/red cables.

The one red wire goes to the top pcb (8204 090 45003) on connection D112. and the two grey's go to the main board. I have highlighted these in red.

I have removed these connections leaving just the yellow and black wires connected (highlighted in purple)

Transformer has been soldered back in and is still buzzing unfortunately

[quattro alex]

This lacquer is available down the road, is it suitable ?

http://www.toolstation.com/shop/p44132

[999999999]

^ Looks like it might work but being a spray does it come with a straw or else you have one that will fit? It needs some way to get into the tight areas for highest likelihood of success. Might work without a straw if you take off the copper belly band and the steel wrap around the core to apply it, then spray again after the steel wrap is put back on (or leave it off).

[ben7]

Did you test the big filter caps and replace any bad ones?

[budm]

You mat as well take a reading of the voltage of the secondary side so you will know what the AC output voltage is if you need to get the new transformer.

[quattro alex]

Did you test the big filter caps and replace any bad ones?

I have replaced 20 caps on the main board, 7 on the top board and 5 on the equaliser. The main filter cap has been tested with an ESR of 0.03

I have just picked up some PCB lacquer from maplins so I will have a go at the transformer this evening. I will also take some voltage measurements from the secondary side aswell.

[quattro alex]

Ok so I've removed the steel outer band to reveal the copper belly band, and you can see from the photo that the joint is already cracking. I have also removed the plastic cover around the copper coils.

I am assuming I can get spraying at the copper coil section and then once dry reinstall the plastic cover and copper belly and finally the outer metal band and then spray those components as well?

[999999999]

^ Yes. Also spray the core laminations, around the perimeter, in the holes, in the slight gaps on the sides of the coils. I'd probably put some masking tape or similar over the pins on the bottom so you don't have lacquer to clean off, though some types allow soldering still, it just burns or melts off when soldering.

Be sure to put a lot on, enough that it's dripping off and really saturating the coils. Once dry, decide if it needs another coat. It may take a long time to dry, if the air dry type then a fan may speed that up or you might want to leave it outside as it may stink from fumes. It may be difficult to get the copper belly band soldered back together again, I suspect a pencil torch would work as well as a soldering iron unless it's a quite powerful iron... but might as well try an iron first.

[quattro alex]

999999999 - Thank you for your advice - it gave me the confidence to go ahead. I used the nozzle from an air spray can with a straw and directed it into all the nooks and crannies and used copious amounts. I repeated this process 3 times allowing time to cure in between coats.

The copper belly band was quite difficult as it was soaking up all the heat from the iron, but I got there in the end. Unfortunately I couldn't get the external banding to fit tightly so I used some electrical tape around instead.

Anyway the end result is a silent transformer! My colleague has tested it and he is delighted - he thought it wasn't working initially as he was so used to noises when switching the unit on.

Thank you to everyone who's helped me in this post.