Am hum in receive

[MadisonMod]

Hello. I bought a president dwight base station. The unit turns on and meters light up. There is a hum on receive. I unplugged the speaker and tried a set of headphones. The hum is still there . What can I check or replace so the receive is clear ?

 

[Shadetree Mechanic]

Hello. I bought a president dwight base station. The unit turns on and meters light up. There is a hum on receive. I unplugged the speaker and tried a set of headphones. The hum is still there . What can I check or replace so the receive is clear ?

Welcome! Usually with a radio of that vintage, it can be expected that all the capacitors should be replaced. You could replace the caps for the problem you have now, only to have a different cap related problem a few months down the road. One of our members refers to this as capacitor whack a mole.

Our member @Klondike Mike has some excellent recap kits for sale, it would definitely be worth looking into for the radio you have.

 

[sp5it]

Before starting ripping radio apart I would try to diagnose first.
Connect radio to external power supply for a test.

 

[MadisonMod]

Before starting ripping radio apart I would try to diagnose first.
Connect radio to external power supply for a test.

Okay . I unplugged the power cord and used 30 amp power supply with mobile cord plug in back of radio. The hum is still there. I notice if I turn the volume all the way down so no receive is heard, the hum is still there. If you turn the power/ volume nob off and then back on it takes a second or two but the hum comes back. Based on the couple of posts I would say possibly try the recap kit ? If so how do I get ahold of the kit ?

 

[groundwire]

Okay . I unplugged the power cord and used 30 amp power supply with mobile cord plug in back of radio. The hum is still there. I notice if I turn the volume all the way down so no receive is heard, the hum is still there. If you turn the power/ volume nob off and then back on it takes a second or two but the hum comes back. Based on the couple of posts I would say possibly try the recap kit ? If so how do I get ahold of the kit ?

Order it online there are two, depends on version of radio.

President Dwight D (v1, µPD858 PLL, PC-198AA) electrolytic capacitor kit

Electrolytic radial capacitor kit for President Dwight D (v1 with upd858 PLL and PC-198AA main board. This kit includes 36 components in total.

klondikemikescapkits.com

Cobra 1000 / 89 / Teaberry Stalker XII (PC-407AC) electrolytic capacitor kit

Electrolytic capacitor kit for Cobra 1000 / 89 / Teaberry Stalker XII (PC-407AC) The board number that this kit has been built upon is PC407AC. The Cobra 1000 GTL, Cobra 87/89 GTL, SBE Land Command LCB-8, Uniden Zachary T (late model), Dwight D (late model) and the Teaberry Stalker XII all share...

klondikemikescapkits.com

 

[Shadetree Mechanic]

I found a neat video a while back about recapping a radio.

Thread 'Capacitor Replacement' https://www.worldwidedx.com/threads/capacitor-replacement.264684/

 

[sp5it]

Is radio connected to antenna or just a power supply? Is that switching or linear PS?
Could you post audio recording of that hum?
Mike

 

[Brother DXer]

I have a Uniden Washington that has the hum. I unplugged it and put it on my 12v supply. It stopped, which tells me I need to find a new transformer. Been looking, but I just can't seem to find one. So until I do, it will run on the 12v supply.

 

[grimace]

I have a Uniden Washington that has the hum. I unplugged it and put it on my 12v supply. It stopped, which tells me I need to find a new transformer. Been looking, but I just can't seem to find one. So until I do, it will run on the 12v supply.

So you did try testing the capacitor in the power supply board didn't you?

 

[nomadradio]

tells me I need to find a new transformer.

NOPE!

The transformer is not the cause of this fault. The electrolytic capacitors on the power-supply regulator board ALL have to go. I'm pretty sure they are all mounted to that small pc board in this model. Some radios have one large filter capacitor clamped to the chassis, separate from the regulator circuit board. I think all of them are on that board in your radio.

The transformer is pretty much a go/no-go component. Either it works, or pumps smoke into the room, or goes totally dead as post. Very long shot to blame a hum fault on that part.

Very long.

73

 

[Brother DXer]

Well, it looks like this will be going to the technician tomorrow.
Thanks for the heads up.

 

[Gary L Boyett]

If you are using a battery charger stop using it. The battery charger is not switched and is creating the hum noise or you have a bad capacitor in the power supply not filtering out the AC hum of the incoming current from the wall. Either use a charger connected to a 12 volt battery or use a switching power supply that is rated enough amps to run the device plugged into it like the radio. I use a 30 amp power supply on my Quad 6 radio so it gets enough power for the voltage and current the radio is going to pull at 60 watts output on SSB. 030 Gary here in AR. in the N.W. corner. Rogers, AR. to be more exact.

Hello. I bought a president dwight base station. The unit turns on and meters light up. There is a hum on receive. I unplugged the speaker and tried a set of headphones. The hum is still there . What can I check or replace so the receive is clear ?

 

[Gary L Boyett]

Okay . I unplugged the power cord and used 30 amp power supply with mobile cord plug in back of radio. The hum is still there. I notice if I turn the volume all the way down so no receive is heard, the hum is still there. If you turn the power/ volume nob off and then back on it takes a second or two but the hum comes back. Based on the couple of posts I would say possibly try the recap kit ? If so how do I get ahold of the kit ?

I have had some power supplies that are very noisy and I must complete the circuits myself to get the noise out of noisy power supplies. I use a couple very large capacitors in parallel to filter out the noise or an added inductor to stop the hum from getting through a noisy power supply. But the radio itself might need recapping too. Or something around the house is causing the hum to go in through the antenna side of things. Or on the house supply wire itself. Bad transformer on a power pole can cause it but check to make sure you do not have any fluorescent or LED lights going in the house when the hum is present they will cause havoc on radio equipment too. 030 Gary Mud-duck Sparky. 27.385 & KI5UHA on the Ham bands. I always check the little things before I attack the big expensive ones. Good luck.

 

[groundwire]

NOPE!

The transformer is not the cause of this fault. The electrolytic capacitors on the power-supply regulator board ALL have to go. I'm pretty sure they are all mounted to that small pc board in this model. Some radios have one large filter capacitor clamped to the chassis, separate from the regulator circuit board. I think all of them are on that board in your radio.

The transformer is pretty much a go/no-go component. Either it works, or pumps smoke into the room, or goes totally dead as post. Very long shot to blame a hum fault on that part.

Very long.

73

Exactly. Filter caps in the power supply circuit probably bad. Ac ripple on the dc line causing noise.

 

[unit_399]

Before you start tearing into everything, Put the unit into PA mode, hook up an external speaker and see if the hum is still present. If not, that eliminates the power supply as the culprit. If it's still there, you have narrowed it down to the supply or the audio section.

- 399