Extron ADA 6 300 HV PSU Repair

[don.r]

Just thought I would note a repair I did of an Extron ADA 6 300 HV Video Distribution Amplifier power supply. The PSU itself is made by Skynet and has an SK-8085 PWM controller. The common-mode choke shorted on the live side and let the magic smoke out. The corresponding leg of the following bridge rectifier was shorted. After replacing these and testing the major caps and the output diodes I was beginning to suspect the SK-8085 since it wasn't pulsing the switching MOSFET. As it turned out, the timing capacitor for this controller, a tiny 1uF electrolytic, was measuring 900pf and >100 ohms of ESR. Swapped that out and she is up and running.

I know lots of people use the Extron ADA series as 10MHz distribution amps in their labs so I thought I would point out a rather obscure failure point.