Power supply issue

[TonyV225]

I turned on one of my power supplies today and it made a loud hum and thump like a jump noise and fuse blew I tried another fuse tonight same thing. I pulled cover off and looked everything over moved things around (incase of a short) And again hum and a thump there went the fuse. Any ideas or anyone else out here heard of this or had it happen? Thanks in advance people....Tony

 

[W5LZ]

Tony, Sounds like you've got a short on the secondary side of the transformer. You might do some continuity checking, capacitors especially. Anything that provides a path to ground actually. - 'Doc

 

[bob85]

i would say more then likely the rectifier went short with the inrush current, bridge blocks are somewhat prone to this if they are not well over rated for the job, second choice would be the a reservoir capacitor short,
unhook the transformer secondary from the rectifier and see if it still blows, if its ok unhook the rectifier and measure that and the caps for shorts,
good luck.

 

[AudioShockwav]

i would say more then likely the rectifier went short with the inrush current

I will bet $5.00 on that " I would say."
You have no Idea how many power supplys I have seen with underated Bridge Rectifiers........

73
Jeff

 

[TonyV225]

Now I just need to find it in this thing I imagine its burried in the back

 

[AudioShockwav]

What kind of supply is it Tony?
How big is your supply?
Most bigger amps use bridge rectifiers that look like a square black block of plastic, has 4 terminals on them, 2 of them come from the transformer.
Most of them have spade connectors on them, unplug them, and fire up the supply, if the fuse don`t blow, the problem is downstream of the transformer.
To learn how to test the block with your meter, go here:
http://www.highlandelectrix.fsnet.co.uk/repair/bridge.html
Or here is some copy and paste from the web....

A bridge rectifier is 4 diodes. Test them as such. A diode conducts in one direction and not in the other.

Any simple continuity tester or mutli meter can be used.

Usually when diodes fail they start to conduct in both directions and you know its bad because it blows fuses, trips the breaker etc supplying it.

Take a multi-Meter and switch it to Ohm x 1
Test between one of the "~" and "+" legs.
You should get either an almost-zero reading in one direction, and when you reverse the test probes, you should get an almost infinite ("sleeping 8") reading.
Now try the same between this "~" leg and "-".
Same as above.
Now repeat the same tests with the other "~" leg, and "+", and then "-".
Same as above.
If you either get almost zero or almost infinite in BOTH directions, then the rectifier is fried.

If it is a small supply, you can get them cheap from RadioShack.

73
Jeff

 

[TonyV225]

Thanks Jeff I am familiar with the testing its is the same for a coom repair of reverse polarity 9protection diodes) I was wondering where in the unit it is the back I was guessing . I also need someone to tell me if radio shack has BF245 transistors or if they can be cross referenced they are for repairing a recieve amp project thanks Jeff your a huge help I appreciate it and others do aswell Im sure theres nothing like laymens terms.

 

[TonyV225]

Ok Jeff it most certainly is the rectifier I did some testing and then to confirm my findings I disconected the rectifier out and plugged the power supply in and it didnt blow the fuse and the meters which have lights in them Lit up so now the hunt is on for a KBPC3501or A replacement .

 

[AudioShockwav]

Tony, replace it with a [FONT=Verdana, Arial, Helvetica, sans-serif]KBPC50-10 If you can, they are 50 amp insted of 35 amp. I know that RF Parts has them cheap, but the problem there is that they have a $25.00 Min Order and they are only about $3.50. [/FONT]
The Biggest B/R Radio Shack carries is 25 amp, you could stack two of them, but that would be a pain.
There might be some one here on the Forum that has a source for just one.
If you can not Find one local, let me know.

73
Jeff

 

[TonyV225]

Yah I remember that when I orderd from RFparts they had that $25.00 Min. I usually use Westgate Laboratories and they also have $25.00 Min any idea on these BF245 aswell

 

[bob85]

glad you found the fault tony,
i just had 6 of the kbpc50's shipped via a friend over there, i had used the frst 4, i replace the 25 and 35 amp ones found in power supplys and the kl550 base amps which blow on switch on, a slow start would help but so far none of the 50ampers have given me any trouble,

good info there jeff

 

[TonyV225]

I have a ITALY KLV 550 base amp I wonder if I should change that right away to??

 

[bob85]

i have 2 550's they both blew the bridge on turn on, even though there is not enough reservoir capacitance for the job they do theres still enough inrush to take out the bridge, changing the rectifier is a pain in the ass.

 

[AudioShockwav]

They really need to build a soft start into thoses things......Oh wait I forgot what we are talking about.
They have to know that the inrush current will damage the amplifier after a while.
I guess I should not bag on them like that, even Ameritron won`t build it into there Amps...but they will charge you $80 for a outboard one :bored:


73
Jeff

 

[TonyV225]

i have 2 550's they both blew the bridge on turn on, even though there is not enough reservoir capacitance for the job they do theres still enough inrush to take out the bridge, changing the rectifier is a pain in the ass.

OMG!!! DONT TELL ME THAT:blink: I guess Ill leave mine alone it may have been changed already Justin had gave mine a complete overhaul transformer keying circuit the whole shabang and I am not seeing a power rush its smooth as glass. I orginally purchased it about a 1 1/2 ago or so from a mod on this forum I had this sent right to Communication Experts for a complete overhaul transformer keying curcuit ETC so I wouldnt have to worry about any BS Ive been pretty happy its been trouble free other than the preamp has never worked and I didnt care I never run them anyways I contacted RM ITALYs tech department and they are the ones that told me if I want to fix it what to replace. I am gonna sell it or trade it off for a nice mobile I was gonna post it on the forum here but last time I did all I got was people with AM amplifiers and I need one thats biased for Sideband because ofcourse I am a SSB user mostly. I actually was supposed to trade this for a 6 pill I believe it was but the guy just dissapeared off the forum so until I sell it or get the right trade Ill keep using it as far as the inrush mine has no signs of it as I said its smoothe as glass when turning it on I just want something different and like I said Ive got an 88 Amp power supply to run a nice mobile which will also give me a little more room.