Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: ALS-600 Supply Smokes  (Read 3306 times)
W4OEQ
Member

Posts: 176




Ignore
« on: September 06, 2010, 03:17:55 PM »

ALS-600 and matching MFJ 50v power supply.  If driven with more than about 25 watts, the amp power supply starts literally smoking and must be shut down.  Can drive the amp to 375 or 400 watts but only for a few seconds before it faults.  ALC has been successfully set.  Does this on CW or SSB.  Dummy load or antenna.  Sometimes, it will operate for a minute or two before it faults and shuts down or starts smoking, even using it at 300 watts PEP.  Exciter is a TS-480SAT that is in perfect working condition.  Power supply previously was sent to MFJ for repair and they said "Nothing's wrong."  In other words, the tech did not duplicate the condition.  Any ideas?  Thanks.  Tom, W4OEQ
Logged
KA5N
Member

Posts: 4380




Ignore
« Reply #1 on: September 06, 2010, 03:46:22 PM »

Repairing a switching power supply is difficult unless you know the circuit inside and out and have all the correct replacement parts. 
Obiviously something is wrong.  You should be able to see burnt parts if something is smoking. 
You have a few options:
1.  Run the amp until the power supply burns up (not a real great option).
2.  Buy a new power supply.
3.  Send the thing back to MFJ and hope for the best.

Consider that the problem might be inside the amplifier and it is pulling way too much current from
the power supply.  Therefore there would have been no fault in the PS (until you let some of the smoke
out).
Best bet is to send the whole kabootle  back to MFJ and carefully and wordly explain the problem.
And then await the bad news.

Good Luck

Allen
Logged
W8JI
Member

Posts: 9748


WWW

Ignore
« Reply #2 on: September 06, 2010, 04:07:52 PM »

ALS-600 and matching MFJ 50v power supply.  If driven with more than about 25 watts, the amp power supply starts literally smoking and must be shut down.  Can drive the amp to 375 or 400 watts but only for a few seconds before it faults.  ALC has been successfully set.  Does this on CW or SSB.  Dummy load or antenna.  Sometimes, it will operate for a minute or two before it faults and shuts down or starts smoking, even using it at 300 watts PEP.  Exciter is a TS-480SAT that is in perfect working condition.  Power supply previously was sent to MFJ for repair and they said "Nothing's wrong."  In other words, the tech did not duplicate the condition.  Any ideas?  Thanks.  Tom, W4OEQ

I'd say the step start relay is not pulling in, and the inrush current limiting resistor stays in line.

I haven't seen exactly how they do the step-start in the 600 because that was added after I did the supply years ago.

As far as I know though, the step start relay would run off the 12 volt positive or negative line. that's the only way possible to do it.

Pop the cover off and look for a 10 watt low resistance resistor with a relay near it on the RFI filter near where the power cable comes out. Check the solder connections on the relay and be sure the line that pulls the relay in is coming up to 12 volts DC.

If you are comfortable working around 120 volts you can work on that supply with the cover off. If you are not, get someone else to look at it for you.

Did you send the amp in with the supply, or just the supply? If you only sent the supply in it is possible your amp has a partially shorted 12 volt line and not allowing the step start to close.

It could be something else, but this is the first thing I would check.

That 10 or 20 ohm step start resistor should show signs of heating.

73 Tom
Logged
W4OEQ
Member

Posts: 176




Ignore
« Reply #3 on: September 06, 2010, 06:50:38 PM »

Thanks, Tom.  The power supply and the amp were returned at the same time.  We will take the cover off and see what we can find. 
Logged
W8JI
Member

Posts: 9748


WWW

Ignore
« Reply #4 on: September 07, 2010, 03:29:16 PM »

Thanks, Tom.  The power supply and the amp were returned at the same time.  We will take the cover off and see what we can find. 

Let me know.

Sometimes the relay can be intermittent. Check the solder joints around the step start relay with the amp UNPLUGGED.
Logged
KD7HB
Member

Posts: 0




Ignore
« Reply #5 on: September 18, 2010, 03:49:59 PM »

Perhaps I can help. I am the second owner of my ALS-600 and switching power supply. Not many hours on it when I bought it. I ran it for several months with no problem, when suddenly I smelled smoke when I turned the unit on. 120 VAC. Thought it was the amp, but was the power supply. With cover off, I could see the big varistor was smoking. That is not your problem, so I will not go into the fix.

With the varistor disconnected, the power supply and amp worked fine, except for low power out. I traced that problem to the big, heavy ground wires in the back of the power supply. There are several that are soldered to a small circuit board on the back panel. The wires were rather loose, and when I pulled, they came loose from the board. They were held there by the solder flux. Who ever assembled the unit did not get the solder hot enough to melt the solder right at the circuit board surface.

The joint was a significant resistance to ground when transmitting. By using the largest soldering iron I had, I properly soldered the wires to the board and that solved my problem of low power output.

I suspect you have the same problem in your power supply. See if you can move the ground wires and if so, get the largest wattage iron you have and resolder the wires. Even if you can't move the soldered connection, you might check the resistance of the joint.

If you need more help, I can pull the cover and take some pictures of the problem area on my unit.

Paul, KD7HB
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!