My 8663A was a real sick puppy in need of TLC 15 years ago, or thereabouts.
The re-build took 9 months, I thought I had replaced all that had failed even the o-rings in the attenuators.
I was never happy with the PSU as the linear reg input voltages were to high, terefore the linear section was dissipating to much heat, it really showed on warmer days.?
It turned out that the +5V sense resistor R12 was way out of spec, (0.005 ohm ) was actually 0.008 ohm. This change was enough for the feedback loop to drive the primary to a higher duty cycle, further stressing the PSU.
Replaced R12 with a 0.5% 0.005 ohm resistor and the change made all the difference.
Regards
Gerald
VK3GM
