[Premium-Rx] Collins HF-2050 power supply

[Karl-Arne Markström]

Gentlemen,

This is to advise of a quite nasty problem with the HF-2050 power 
supply.

As well known, it operates too hot to be well in the long run. 

This causes the electrolytics to dry out, and the voltage regulators 
become prone for
instability and self-oscillation.

My own HF-2050, manufactured in 1987 and purchased from Mike Marchand 
in 1997,
recently became "flaky" with sudden restarts and random lighting of 
the "Fault" indicator.

Cycling the AC power sometimes cured the situation, but too often 
various "grunts"
emanated from the power transformer without any restart of the 
receiver. 

An oscilloscope investigation of the + 5,2 V supply line
revealed that the regulator had turned into a power oscillator, with a 
fundamental in the 200 Hz range and 6 - 7 V peak-to-peak 
amplitude and also a superimposed RF oscillation in the 2 MHz range.

This output waveform sometimes caused the output SCR crowbar to fire 
and short-circuit the supply output causing 
audible "grunts" from the transformer.

The SCR crowbar saved the irreplaceable "innards" of the receiver main 
digital board from overvoltage destruction.

Replacing all electrolytic capacitors in the power supply restored 
operation.

Moral: Check the purity and stability of the output voltages of the HF-
2050 power supply if any strange things happen during operation.
Also check that the overvoltage crowbar is positively operational and 
has a correct threshold setting.

I am currently researching for a "quiet" switching power supply to 
replace the old unit, enabling 230 V operation and reducing heat.

73/
Karl-Arne
SM0AOM