Kenwood KR-6400 Receiver Protect Relay Issue

[Bret Fritch]

Hello, I picked up this nice Kenwood KR-6400 receiver and have this issue.
It worked for a few days then the speaker protect relay started to drop out and then come back on.
I removed the relay and cleaned the contacts. I have recapped the power supply board and the main amp board. I have 43 and -43 volts coming in on pins 9 and 16 of the amp board. I am wondering if Q26 (2sc1212A) on the main amp board might be causing this problem? Also wanted to see what others thought I might try for trouble shooting tricks. Thanks in advance for the help.

 

[Watthour]

I went through one of these back in January, and kept a few notes. The main amp has a pair of 2SC1451s in the Qe5 and Qe6 positions. I replaced both due to one dropping out randomly.

It would be good to check and monitor the bias currents as the unit starts cold and as it warms up for 30 minutes or so. You can also monitor the base voltage at Qe26 to see if/when it falls off below 0.6V.