[Premium-Rx] Collins HF-2050 power supply

[Berbari, Edward J.]

Karle-Arne,

A few years ago I replaced the power supply in my HF-2050 with a switching supply.  I posted this on the list then.  I believe I used an Acopian supply- can't remember the model, but it was about 1/3 the size of the original  and did not run hot.  I did not find any birdies, but I was not very thorough.   

Ed, W9EJB



Sent from my iPad

On Nov 22, 2012, at 7:57 AM, "Karl-Arne Markström" <sm0aom at telia.com> wrote:

> 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
> 
> 
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