[1000mp] Switching supply slow to start

[WD8ARZ]

Thanks for the info Rick, I love my MP too.

Sometimes when I have RF in the shack, I have had to ground the desk mike 
goose neck to the chassis of the radio to keep RF out of the mike element. 
(used alligator clips hi).

Good job on troubleshooting and repair that supply!

73 from Bill - WD8ARZ

----- Original Message ----- 
From: "Rick Stealey" <rstealey at hotmail.com>
To: <1000mp at mailman.qth.net>
Sent: Sunday, August 09, 2009 6:25 PM
Subject: Re: [1000mp] Switching supply slow to start
>
> Here's a followup to this problem I reported back in November.  Thanks 
> Mike, W2AJI for the tips.  I found a shorted FET in the switching part of 
> the supply, (replacement is STP16NM50N $3.52 at Mouser) which didn't fix 
> the problem.  Then I found an open 10 ohm resistor in the input area and 
> that got it running again.
> Apparently it was acting as a fusible resistor. For what it's worth here's 
> what I learned:
> the supply is made by Futaba.  I could find no info about it on the net.
> I traced out some of the circuitry and found a rather straightforward 
> input, isolation transformer (110v in, 110v out), a bridge rectifier 
> giving around 260 vdc with 2 big electrolytic caps.  Then that 260 volts 
> runs the switching part of the supply where there are 2 big FETs.
> As an aside I was motivated to get back to work on this supply because I 
> was running an external 12 v supply and hearing very loud pops when I 
> keyed the rig.  I also got a report of chirp.  I found 1000 mv of RF on 
> the 12 v lead when I was on an antenna, but nothing when I was on the 
> dummy load.  I installed 0.01 cap on the PS but I guess the long leads 
> were delivering RF into the rig.
> You can read below to get some background on this problem.
> What a fantastic rig.  I still love it after 12 years.
>
> Rick  K2XT