[R-390] R-390 POWER SUPPLY

[Flowertime01 at wmconnect.com]

CLARENCE LOZANO

HELLO,I HAVE A R-390 POWER SUPPLY MAKES A HUMMING SOUND-NOT AC SOUND ,IS THE 
POWER SUPPLY REPAIRABLE WITH THIS TYPE OF PROBLEM?

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Clarence,
This is an R390. Do not panic. It is repairable.
We need some more information from you.
Please read the other mail to you.

Is this an R390 or R390/A.
The R390 power supply is a bit more complex than the R390/A power supply.
At worse you may need to simply replace the power supply deck.
Likely you can fix the problem.

Check your fuses and make sure you are not running with any one
over fused at this time.
Make sure the oven heaters are turned off.
Pull the RF and Audio decks for a visual inspection.
Tell us what you find.
Do you have solid state diodes in or are you running tubes?
If tubes what type? (there are some mods away from the 26Z5's)
Do you have a transformer hum?
Do you have a hot transformer? (should at least be able to touch it as warm)
Do you have any arcing noises?
Do you blow fuses?
Do you have the 150 volt voltage regulator tube lighting up?
If it is an R390, how are the series regulator tubes doing.
Is the noise in the audio output?

The power supply also has a selenium rectifier that operates the antenna 
relay.
These things go bad. They will load the transformer and cause a hum.
ground the standby pin on the back terminal board and switch the function 
switch
to standby. The antenna relay should operate. Listen for a change in hum.
check the fuses after this test. If you have a bad rectifier stack, it is 
best to 
replace it with a modern silicon bridge.

Unplug the IF deck, RF deck and VFO deck harness.
Did the Hum quit?
If you have an R390/A unplug the Audio deck.
You cannot do this to an R390 because of the series regulators in the Audio 
deck.
Every thing quits in the R390 when you unplug the audio.
It does not hurt any thing, its just not a useful test.
Take the time and test all the tubes.
A shorted or bad tube will pull current and cause the RF deck to hum at
strange frequencies.

If you find, unplugging a deck stops the hum, do not consider you need to 
move over
to that deck. You may have a filament winding gone bad. When you unplug the 
deck,
you unload the winding and the hum may stop. Grab your schematic and start to 
unpug tubes to find the filament winding causing problems. If you isolate the 
problem to a filament winding, test all the tubes on the winding for shorts.

Bad tubes will cause a power supply hum. Replacing the tubes will fix the 
problem.

You need to isolate the exact problem in your receiver before 
you consider the repair options.

The transformer is sealed into a can. Soldered but openable.
Inside the can is a typical transformer with laminations.
Some transformers were bolted. Some were welded some were
strapped and clamped. 

The winding lead were soldered to the other end of the feed through lugs on 
the can.
Some times when soldering to the lugs, on the transformer, the solder inside
over heats and moves into places it should not have. While you can replace a
transformer on the deck, aggravation almost exceeds return. After meeting the
cost of a transformer, the cost of a deck and the trouble saved makes it worth
cleaning up a new subassembly. You start trading subassembly wiring and
harness connector problems for transformer wire problems. A good straight
chassis deck, green screws and some desired factory ink, may cause you to
want to keep the deck you have. (Read all matching modules in the receiver.)

However, transformers have been opened and rewound. You can go the full route 
if you have the interest. You can open the can and do repairs. You can pull 
and replace the transformer. Once you find the real problem and consider the 
"historic value" to you of the bad part, you can select your repair solution.

OK so what goes wrong. After time the laminations come loose in the 
transformer
and eddy currents let the lamination plates oscillated in the magnetic 
fields. This
makes mechanical noise. So why is it not a 60 cycle hum? It may be. But the 
mounting hardware, mechanical mass, sealing varnish, and other (do not tell 
OSHA) included goop changes the resonant frequency. Power transformers have been 
heard with all sorts of sounds. 

If its not getting hot, blowing fuses, and really annoying loud, you could 
live with it.

Likely its annoying loud and you would like to fix it. Also there are other 
things like
shorted winding that lead to problems. Soon (100 hours of operation) the 
vibration will wear through some varnish on some windings and things will go from 
bad to very bad. So you should not just let the problem go. But it will let 
you operate the receiver long enough to isolate the problem to a bad part.

While you may have a power transformer hum, the cause may not be in the 
transformer.

Do some checking, let us know what you find. Watch what some of the other
fellows say and ask you to check. Take your time, enjoy your puzzle.

Once you get to the problem, report it here. If you need parts ask here first.
If you need some more help, warm up the keyboard and ask away.

Roger KC6TRU