Author |
Message |
Pinger
| Posted on Saturday, January 25, 2003 - 1:32 am: |
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I have a messenger m-800, and i had some problems with it. There are a couple of resistors that are cooked, but i'm not sure if the pills are bad. It still does about 300-400 watts, and has a bad swr on the input side. On med and high, it hangs up on transmit really badly. Do you think that replacing the bad resistors could solve the problem? |
Tech671
| Posted on Saturday, January 25, 2003 - 4:28 pm: |
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Kind of doubt it |
Pinger
| Posted on Saturday, January 25, 2003 - 6:34 pm: |
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Do you know anyone that could fix it? I would love to get this unit going! |
Fewb
| Posted on Saturday, January 25, 2003 - 9:01 pm: |
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yes it will. |
2600
| Posted on Sunday, January 26, 2003 - 12:20 am: |
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The resistors aren't the problem, they are a SYMPTOM of the real problem, INSIDE the RF power transistors (pills). The problem with those pesky pills, they never LOOK bad once they suffer damage. The damage is all inside that tough, white ceramic, where you can't see it. The internal short-circuit that takes place inside the pill is what smokes the resistors you describe. You will find them in two generic places. 1)The small, half-watt part that goes from the base (input) leg to ground is usually ten or fifteen ohms resistance. When the pill is good, this part doesn't get much power thrown at it. Remember, it's on the INPUT side. Some folks use quarter-watt instead of half-watt resistors there. When the pill breaks down inside, the 13.8 Volt (or whatever) power supply now feeds directly into that little resistor. This now causes 15 or 20 Watts of power to be thrown to this little part. Doesn't take it for long. "Snap" and smoke. 2)The other resistors you will see go down in a box with 4 or more pills are stretched across the toroid "doughnut" combiner coils. These are the larger ones that join pairs of pills leading to the output side. When all the pills are running, delivering equal power those resistors will throw a half-watt or watt of power each. They routinely use a two or three watt part there. When one or more pills stops delivering power, that resistor now gets slapped with about half the power delivered by the remaining pills that still work. Not for long, though. Shorted (or open) defective pills cause one other nasty habit. They create unwanted POSITIVE feedback, from the output side back to the input circuit inside the linear. Kinda like holding a hand mike flat against a talkback speaker. That trick will get you an audio "howl" feedback. The internal feedback caused by one or more blown pills causes the RF equivalent. The RF "howl" inside the amplifier fools the keying circuit. It can't tell that you unkeyed the radio, if the amplifier is creating its own carrier, causing the relay to stay pulled in. There really is no cheap, easy fix for this breakdown, unless you get your RF transistors for free. 73 |
Pinger
| Posted on Sunday, January 26, 2003 - 4:56 pm: |
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There are two resistors that have heated up, and i can't tell their value. All of the other resistors like it are 100 ohm, so i'm guessing that's it. They are the resistors under 2 of the combiner coils. Those are the only 2 things that have visual damage. I'm not exactly sure how to test the RF transistors, especially since they are in-circuit. Since there are 8 transistors and a driver transistor, would i have to buy a matched set of 8 to repair it? |
Crafter
| Posted on Monday, February 10, 2003 - 4:00 am: |
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Pinger I sent you some e-mails hope it helps. I got a m4000, wonder if their close to the same. let me know if it works out for ya. John |
Pinger
| Posted on Sunday, February 16, 2003 - 3:31 pm: |
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Crafter, i haven't gotten anything from you yet. Drop me an email. |
Crafter
| Posted on Sunday, February 16, 2003 - 8:55 pm: |
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Hmm..I'll re-send them again. i wonder were it went I didnt get it back. |
Pinger
| Posted on Saturday, February 22, 2003 - 10:09 pm: |
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How many watts should i be getting out of this amp? I'm only getting about 300 watts |
Tech671
| Posted on Saturday, February 22, 2003 - 11:35 pm: |
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What are the transistors and quantity thereof, what wire are you feeding it with hot and ground, what drive is it getting, what alternator do you have, what is the voltage at the amp under load, what antenna, what swr, what meter. |
Pinger
| Posted on Sunday, February 23, 2003 - 9:00 pm: |
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SWR is 1.1-1.2. It has Eight MRF454s, 4ga wire (about 5 feet) to the battery (+ and -). I haven't tested the voltage at the amp under load, but i only have a stock toyota alternator. I'm using a Diamond SX-100 meter for output, but for setting the swr i used an MFJ swr analyzer. I'm driving it with a 2.5 watt deadkey and 12-15watt swing(AVG). |
Jpryorx2
| Posted on Monday, October 27, 2003 - 12:53 am: |
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if you can send me a pic of where the burned ones are i'll let you know what they are i'm running a m800 that the driver has been changed to a 2290 and with 1.5 watts drive i get around 600-650 watts out of it jason jpryorx2@yahoo.com |
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