I have noticed that over the past few weeks that the Voltage is wavering when turned all or most of the way up to full power (15v) ... The meter sporadically dips to 10 volts and sometimes less and then goes back up to full voltage ... seems to do it on its own with no load and a normal load ... I am wondering where I can start to troubleshoot this behavior ...
Thanx in advance

 

Service manual here..

https://elektrotanya.com/pyramid_gold_series_ps-26kx_power_supply.pdf/download.html#dl