Electronics > Repair

Need help with a Metcal MX500

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Corporate666:
I have an MX-500 with exactly the same problem and manifests exactly the same behavior as yours.

Stumped me too but I didn't have a lot of time to mess around with it.  Hope you will keep us updated if/when you figure it out. 

kff:
For me, it was a short in T2 -- after desoldering it, the resistance between all 4 terminals is 0.3 ohms. Here is how I figured this out:

1) Made a poor man's signal generator by ordering an AD9850 module on Amazon (http://www.amazon.com/Huhushop-Active-Generator-0-40MHz-Equipment/dp/B00IR5I886/ , $9.99 shipped) and hooking it up to a TI Tiva launchpad board ($12 shipped).  Took only 30 minutes to figure out the protocol and have the board generate a 13.5Mhz square wave with +-2V amplitude.

2) Hooked up the generator across C26. The output at the coax connector was only +-0.3V, so there was leakage somewhere. Desoldered C25 to figure out whether the leakage was to the right or left of it -- it was on the transformer side (i.e. without C25, there was no leakage).

3) Checked capacitors C21 and C22 and they were fine. At this point it could only be T2.

Now, the question is how to replace T2. The schematics specify it as "transformer toroidal 9uH, 10.75 turns each side". Would any other 9uH transformer work here, as long as the number of turns is equal?

wraper:

--- Quote from: kff on January 21, 2015, 09:49:12 am ---Now, the question is how to replace T2. The schematics specify it as "transformer toroidal 9uH, 10.75 turns each side". Would any other 9uH transformer work here, as long as the number of turns is equal?

--- End quote ---
I don't think so. Better to rewind it.

bingo600:
Wasnt there some torroid Winding info in the 13.5 MHz metcal psu thread

/Bingo

N8AUM:
Just a totally wild ass guess: Q4 goes into parasitic oscillation just long enough to wipe itself out ?

Good luck !!!!

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