Galaxy saturn power supply hum

[smokinjoe]

I have a Galaxy Saturn main board #360014B that has a power supply hum it looks like someone has removed the original transformer and power supply board and installed the inner parts of a external power supply because the board is different and the transformer is not sealed all volts are correct going to the radio and the power supply board has 2 4700uf capacitors on it that check good is there any way to filter the power leads going to the main board to eliminate the hum? Thanks you for any information that may solve this problem.

[zodiac]

Screen the transformer with copper foil or thin copper plate and solder it to the case of the transformer.

[frogman296]

http://www.galaxyradios.com/regulator.html

are you sure it is the power supply, and not the freq counter??

[smokinjoe]

Thanks for the information Frogman296 i have hooked the radio up to a external power supply and the hum was not there. Zodiac thank you also I may have to try what you suggested to see if it works. I was also wonder if installing the power input PCB board on the AC line with the 2 chokes and the 4 capacitors on it will help solve the problem this was also removed. I have one laying around here some were. I have heard others call this a AC hum not sure if this will make a difference or not. Thanks for your help

[zodiac]

It does work. I've done it to many a home base radio when I've had to fit a new transformer other than the original type.

[frogman296]

It does work. I've done it to many a home base radio when I've had to fit a new transformer other than the original type.

thats super

[smokinjoe]

Zodiac thanks for the information i will get back to you on how things work out having trouble finding copper foil or thin sheets of copper in my area. Thanks

[smokinjoe]

Zodiac still can't find any copper foil or thin sheets of copper in my area would the copper braid from the shield of coax cable work to help eliminate this or do you have any other suggestions on what else would work? Thank you for your help

[zodiac]

Well you could use a tin can but count your fingers first.

[smokinjoe]

Thought i would update every one on this radio i shielded the transformer and still have power supply hum in the receive only. In transmit every body that i have talked to said there was no hum in the transmit. Any ideas as to what i can do to eliminate the hum in the receive? Thanks for your help.

[ramblingman]

Anytime you have ac ripple getting into the dc audio.
It is usually caused by a bad filter capacitor.
The filter cap.,should be on the power supply board.
Should be a large elec. cap.,usually 4700 uf or larger.
Also your hum maybe due,to poor grounding.
I have seen this more than a few times..Make sure
the power supply board and radio pcb share the same
ground..There are two different types of ground.chassis
ground,,and circuit board ground.If someone has done what
youve suggested and replace power supply board.It is
possible they didnt ground it properly..Thats what it sounds
like to me..Poor grounding,rather than bad filter caps
Due to the fact,it is only on receive audio.

[smokinjoe]

Thank you for your help on this ramblingman i have checked the caps and they both check good it has two 4700uf caps on the power supply board and they share the same ground as the main PCB board on the radio. I have also unhooked frequency counter to make sure this wasn't the noise i was hearing but it still has faint power supply hum in receive only i can move transformer away from the radio and the hum goes away. Do you think separating the grounds will help stop the hum? I have run out of ideas on this one. Thank you for your time.

[ramblingman]

How did they mount the transformer.Or is it the original
transformer,and just the power supply board that was changed???

[ramblingman]

Try this--Unsolder your Black (Negative) wire from the top side
of the power supply p.c.b.,Then re-route the Negative wire through
one of the chassis holes,to the bottom of the power supply board.
Foil side,and Locate the negative terminal of the 4700 uf filter cap.
And solder your Negative wire directly to the negative terminal.
The negative side of the cap. should be marked with a black stripe.

[Rick]

Is the radio fitted with the original Main PCB?
I ask this question as I have come across problems like this before, when someone has taken the Main PCB from a mobile radio and put it in the home base.

[smokinjoe]

Rick i thank you and ramblingman for your time. The radio has the original main pcb board in it and the only thing that has been changed is the transformer and the power pcb and i found out they came from a 10 amp Pyramid power supply. ramblingman the ground wire is run exactly as you described and the transformer is bolted directly to the chassis with 4 bolts. Thank both of you for your time and information.

[Rick]

From the two power cables, which come from the PSU PCB, you should have one disc ceramic of 0.01uf (10nf) in value, across the positive and negative, and one disc ceramic of 0.01uf (10nf) in value from negative to chassis earth and not chassis ground.

In addition, the original transformer was mounted on four rubber grommets with steel sleeves, so the transformer it self was not earthed and not connected to chassis ground.

You could try putting some caps 0.022uf to 0.047uf across the bridge rectifier.

[smokinjoe]

Rick thank you again for your time i will try mounting the transformer different to see if it helps if not then i will try the caps and let you know how things turn out. Thanks

[ramblingman]

Have you fixed your problem yet??????
If not,i have a thought.Maybe your problem is
noise transfer..In otherwords,if the transformer
is not mounted correctly,on the rubber gromets
as rick refered too in his earlier post.If the transformer
is just hard mounted directly to the radio frame.
It could be transferring the hum noise from the
transformer to the radio chassis.Noise getting into the
audio that way..So it diffently needs to be mounted on
the rubber gromets..Not only for isolation purpose,
but also to prevent noise transfer..Just a final thought.

[smokinjoe]

Thank You to everyone who has helped me. I remounted the transformer properly and now the hum is just very faint with volume turned all the way down. With volume turned up you can't hear the hum in the receive anymore. Thanks again for your help