Magnum 2000 resistor repair.

[doffo]

Hello,

The two amps came in today about half hour ago, and to be sure one of the amps wasnt too rusted inside, I had a peek inside, and by the looks of it, maybe it was fed with a bit too much power? Some of the resistors near the power level selector have been crisped up pretty well. I was hoping one of the settings it would at least show up some. To my knowledge, the amp is at least outputting some power. Though the Palomar Skipper was doing well over 200+ PEP on max, it seemed that the Magnum 2000 would almost reach that on the max setting. Maybe it has something to do with those burned up resistors?
I also did notice one of the screws to the transistor is broke off, so if anyone knows the exact screws used, id greatly appreciate it.

 

[BC Coyote]

Ouch. It looks like the whole thing has seen some serious heat.

 

[doffo]

Ouch. It looks like the whole thing has seen some serious heat.

Hard to say just for how long they were burning stuff up... But as of now it is outputting power on each setting, just not as much as the Palomar Skipper 350 is. For now just going to run the Palomar until I can gather enough parts and information to get the Magnum 2000 back in working order.

 

[BC Coyote]

as of now it is outputting power on each setting, just not as much as the Palomar Skipper 350 is.

You definately need to replace that missing screw on the one transistor there because that transistor will run hotter than the other with one screw missing like that as it is no longer making a flush contact with the heatsink.
I would replace the scorched resistors behind the power level switch. Not sure how they got burned up like that? I wonder if somebody overvolted the amp rather than overdriving it?
If there are other heat-stressed parts I would replace them too.

Pretty sure it will make full power once you do those things.

 

[doffo]

You definately need to replace that missing screw on the one transistor there because that transistor will run hotter than the other with one screw missing like that as it is no longer making a flush contact with the heatsink.
I would replace the scorched resistors behind the power level switch. Not sure how they got burned up like that? I wonder if somebody overvolted the amp rather than overdriving it?
If there are other heat-stressed parts I would replace them too.

Pretty sure it will make full power once you do those things.

If I understood correctly, if you drive the amp with a bigger radio like a 10 meter radio. (One doing 30+ watts.), that would cook those resistors nice n toasty. Good eye on the missing screw. I did not even dare to key up long at all.. I was just after if any kind of power output was happening. Glad it was.

I will need to hunt down the size of screws those are.

 

[Nick Gans]

If I understood correctly, if you drive the amp with a bigger radio like a 10 meter radio. (One doing 30+ watts.), that would cook those resistors nice n toasty. Good eye on the missing screw. I did not even dare to key up long at all.. I was just after if any kind of power output was happening. Glad it was.

I will need to hunt down the size of screws those are.

Very simple task.. Remove one of the other screws and size/measure it.. A well stocked hardware store will have what you need... A tiny easy out will aid in removing the broken screw....

Not the exact extractor, for example only:

DPK-01-EX-2 Spiral Flute Screw Extractor 5/32"-7/32"

DPK-01-EX-2 Spiral Flute Screw Extractor 5/32"-7/32" 4mm-6mm Recommended drill size is 7/64"

www.freedomracing.com

 

[SuperLid]

Very simple task.. Remove one of the other screws and size/measure it.. A well stocked hardware store will have what you need... A tiny easy out will aid in removing the broken screw....

Not the exact extractor, for example only:

DPK-01-EX-2 Spiral Flute Screw Extractor 5/32"-7/32"

DPK-01-EX-2 Spiral Flute Screw Extractor 5/32"-7/32" 4mm-6mm Recommended drill size is 7/64"

www.freedomracing.com

Pull the device and grab the screw with pliers or needle nose vise grip

 

[Xracerx13]

I would remove both transistors and recoat the bottoms with fresh good thermal grease after you clean the areas. Replace all the screws with new ones. Use metal oxide 3-5 watt resistors to replace them all while your at it.

 

[doffo]

Thank you everyone for your input. I like all the suggestions.

 

[doffo]

Pull the device and grab the screw with pliers or needle nose vise grip

Took my time and it worked out...

(Please ignore the nasty bits of dust/crumbs/flux splatter from the amp. I cleaned it all up, but just took the pictures right quick to post.

 

[doffo]

I would remove both transistors and recoat the bottoms with fresh good thermal grease after you clean the areas. Replace all the screws with new ones. Use metal oxide 3-5 watt resistors to replace them all while your at it.

Going to order some. The two that are nuked are 100 ohms, and the two top ones closer are 33 ohms. (For some reason on the right-top on the selector in the picture, that one should be exactly like the other one left of it with the 2 bands of orange. The other picture of a Magnum 2000 on here has it exactly like that. Maybe mine they replaced it at some point with what they had on hand?)

 

[nomadradio]

Screw should be an american thread #4-40 thread pitch.

Looks like it was driven with a radio almost as big as the amplifier.

73

 

[doffo]

Screw should be an american thread #4-40 thread pitch.

Looks like it was driven with a radio almost as big as the amplifier.

73

Thanks to your advice in the past, that was my guess that it was driven wayyyy too hot. Maybe feeding it with 30+ watts? I will go to the hardware store tomorrow to see if I can source some for this amp. Appreciate it.

 

[c316buckeye]

a souped up cobra 29 can burn up an amp and a dual final radio swinging 3w ssb can talk on a magnum 4000 all day. i wonder if it made a sound when that one resistor blew up. guessing that operator got some smoke

 

[doffo]

a souped up cobra 29 can burn up an amp and a dual final radio swinging 3w ssb can talk on a magnum 4000 all day. i wonder if it made a sound when that one resistor blew up. guessing that operator got some smoke

Looking at the fuse, it went through some heat stress.... Can those Toshiba finals take a beating like that?!?! I figured they would of burned up from the heat if a small power supply was being used.