A very common problem with the BBC computers is the failure of one or more smoothing capacitors in the power supply.
If you have turned on an old BBC computer which gives a "popping" and "crackling" sound, followed by your room being filled with foull smelling smoke, then this is your problem.
If you remove the power supply and send it to me, then I will replace the capacitors, test and return the power supply to you. If it cannot be repaired, then there is no charge other than the return postage.
Click on the Shopping Cart button to checkout and pay and post your PSU to me to the address on the "Contact Me" page.