View Single Post
  #2 (permalink)  
Old 08-17-2017, 3:35 PM
majoco's Avatar
majoco majoco is offline
Join Date: Dec 2008
Location: New Zealand
Posts: 2,752

IMHO I suspect that the 500uF 12v capacitor across the supply has finally given up! It was pretty marginal right from the the start with only a 12v rating. Unfortunately it's not an easy thing to get to, you have to take the chassis out of the cabinet - it's on the front of the chassis directly under the speaker hole, big black thing. Replace it with a modern 16v 470uF unit and while you're in there, you might as well change the two others, especially the awkward one by the tone control.

If you have a voltmeter, check the standing current in the output pair of transistors - the schematics show a variety of values for the bias resistor some show 27ohms, some 33 and others 36. Just check to see that the pair of transistors between the transformers are still good, they have absolutely no protection if they go into thermal runaway! Also be very careful with the AC supply, they can put out more voltage than is on the label as the radio draws so little current.
Cheers - Martin ZL2MC - Palmerston North
Reply With Quote