Yes you can buy a part to repair it but the difficulty will be working out which specific part you need to buy.
The fault you have is very probably a heat fault - i.e. a component failing to work correctly when it gets warm. It's unlikely to be the getting warm - electronic equipment usually generates heat and the components shopuld be able to cope.
One technique you might try, if you have the confidence, is to buy a can of freezer spray from an electronics store or on-line. Run the set with the covers off and wait for the fault to materialise. Then selectively spray freezer on components to cool them down. You will be trying to make the problem go away. First you work on the circuits area by area and when you find the area of the fault you work on component by component.
Then you change the component.
Sadly this technique does not always work as you would wish.
It can sometimes (but very rarely) happen that the component you think to be to blame is feeding a signal to another part and it's that second part that needs changing. I have seen this just once over a period of 40 years or so.
http://www.maplin.co.uk/images/Full/re77j_new07.jpg
Good luck...
Peccavi, August 2009
