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Magnum 4500 4 X MRF 454 Help needed please

grasshopper1031

grasshopper1031

Member
Oct 17, 2006
55
2
18
ALBERTA, CANADA
i have a palomar magnum 4500 with a 4x454 pills, im using it yesterday and smell something burnt so i shut it off rightaway. removed the bottom cover and found a resistor and an electrolytin cap thats burnt. can anybody please tell me whats the value of these components so i can replaced them thanks in advanced.........grasshopper1031:oops:
 
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Are there 2 resistors together where the one is burnt or just one?If it is just one i'd say it's 100ohm at least 1watt.The capacitor i'm thinking is around 1000uf at least 25vdc.If you have 2 resistors together it would be 200ohm 1watt.Might not be a bad idea to check the pills.Did your wattage fall off at all?
 
only one resistor is burnt, the top one (combiner) and its 100 ohm 1 watt resistor . now the cap got a marking of 220k(i think its a K) its hard to tell its kind of melted). tnx for the help....grasshopper1031
 
hopefully happy hamer will see this as im reading an old post of his and he got the same burnt resistor from the combiner. hopefully he can tell me the value of the cap thats burnt too.
 
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Sorry i couldn't be of more help to ya grasshoopper.I looked all over the place and couldnt find a schematic diagram on it anywhere.Hope you get it straightened out!
 
Umm...

You can read the color code on that resistor.

The cap, you can read the value on, and get it off an online calculator.

TYPICALLY, when you lose a combiner or splitter resistor, you've had a problem with at least one transistor..... And if you took out the capacitor in the bias network (odd, actually), you probably SHORTED a transistor, which is even a bit MORE odd.

Yet another reason for a 2 cent steering diode on the base supply, but I digress.....

The wilkinson splitter / combiner actually dumps the power into that resistor when an imbalance happens.... So, when everything is working correctly, that resistor sees NO power. As SOON as an imbalance happens, the resistor eats up the power needed to keep the power split evenly... IE, lose 1 transistor in a 4 pill, that transistor is dissipating either 25 percent of the rated power out or in.

If it's a pair, 200 ohms. If it's a single, then it's a 100 ohm resistor. You can use a half watt there, and you want non-inductive.

The cap is.... Well, I'll let you figure that part out, you actually HAVE a part nomenclature. Google is your friend.

--Toll_Free
 
grasshopper1031 said:
220k marking is 220 pico farads and the k is tolerance?? thats all the info i found dont even know if its correct.....grasshopper1031:(
Click to expand...

That is correct. 220K is a 220 picofarad capacitor and the letter K means it has a 10% tolerance. The resistor you are speaking of is a 100 ohm resistor and it looks like a one or two watt device. You can always replace resistors with a higher power rating without harm but never the other way around.

Good link to capacitor marking codes. http://my.execpc.com/~endlr/markings.html

grasshopper1031 said:
need help about the value of the cap and voltage pls. tnx...........grasshopper1031
Click to expand...


Most small value capacitors like that are rated for either 35 or most often 50 volts so you don't have to worry about that. The larger metal can type electrolytic capacitors are the ones to worry about and should be rated for at least 25 volts in a mobile device because the next lower rating of 16 volts is pushing the limit and is too close to it's max voltage.
 
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captain kilowatt, ive checked the value of the 220pf in durham radio site under parts/capacitorhttp://www.durhamradio.com/capacitors.html and they the 220pf cap looks different than the one i have. mine looks like the one in their list but only for 2.2mfd,220mfd,2200mfd,.22mfd.i google my blown cap and its an axial electrolytic cap style.now im more confused. sorry for all the questions sir and thanks for all your help.....grasshopper1031
 
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Am I the ONLY one not ignoring the fact that since he can read the parts values, they probably aren't blown????


You can use a 1/2 watt device across combiners and splitters. If you're dissipating that much in your combiners, you need better RF layout. Matter of fact, combiners and splitters work FINE WITHOUT that resistor. IT ONLY HEATS UP WHEN THEIR IS A FAULT!!!! No fault, no problem. Nine out of ten times, you smoke that resistor, you probably smoked the insulation on the combiner, as well. Splitters, not always, but combiners get HOT when imbalanced (a single 2 watt resistor DOES get warm when trying to dissipate 80 to 200 watts... Or more, depending on how many pills.....)

BUT, if those pix are of HIS amplifier in it's current (no pun intended) state, those parts aren't his problem.

The cap is in the bias circuit. It will probably blow and make a BIG mess when it does. If it gets leaky and shorts, it will spew it's goo. If it opens up, they usually don't make a big mess, but they do bulge and heat.... Causing the case to split and the 'wrapper' to at least split, if not seperate from the cap.

Just sezzin.

--Toll_Free
 
my first pic is not my actual amp, i thought it will be just easier to just circle the parts that needed. anyways heres the actual pics . tnx.................grasshopper1031

note: see first ficture posted for actual location of the resistor and capacitor.
 
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Oh-Tay!!! (in my best Eddie Murphy Butt-Weat voice)... This is making more sense now.

22 uF for the cap. It's in the bias circuit, I'm almost certain. If not, it's the ssb delay. Either way, it's not HYPERCRITICAL to the performance to your amplifier, nor would I think they are related.

100 ohms on the resistor.

Judging from the discoloration, though, the resistor isn't bad.... And like I said earlier, that resistor doesn't even have to be in the circuit to have the circuit functional.

BUT, as myself and others have said: When that resistor goes out, there IS another reason: Nine out of 10 times, it's that you've either lost 1 (usually) or more transistors. The ONLY time that resistor sees any current is when you have an imbalance.

You can increase the value of that cap, if it's in the bias network, it will help with regulation. If it's in the SSB delay, you'll know it because your receive will take longer to "come back" after you unkey vs before.

Sorry, thought the pix you posted before where of the actual amplfier... BUT, I'd still say that resistor is ok (I've cooked them to the point of not being anything more than dark brown or black, and they still read fine), and your cap doesn't look all that bad, either... Have a cap meter?


--Toll_Free
 

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