| Author |
Message |
    
Jp1116
| | Posted on Sunday, September 29, 2002 - 8:33 pm: | 
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I have a Messenger 500 that is giving me a lot of trouble. Sometimes (but rarely) it will key full output. Most of the time it will key nothing or greatly reduced power. Most of the time, low will key nothing but will modulate forward over 150 watts. Most of the time high will key 100 watts and modulate forward a couple hundred watts. The modulated power is erratic with the amp meter on the power supply bouncing all over, same with the watt meter. When I measure the bias voltage it is erratic as well, when not producing full output.
I have substituted the driver pill, both relays and both bias diodes. I have also pulled the four 2879’s and they test good. I have bypassed the power level selector also. I’ve tapped all the components looking for loose connections. Now I am totally stumped. Does anybody have any suggestions. Could a final that tests good be bad under a load and cause this? |
Tech671
| | Posted on Monday, September 30, 2002 - 6:00 am: |
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Ideal situation:
60a off current supply, 6ga or larger wire feed, 1kw dummy load. With amp on high the radio driving should be around 2w carrier and 20w peak and amp should key around 150 and peak around 500.
I have seen bad so239's cause goofy problems, and check your jumpers/coax ends. |
Jp1116
| | Posted on Monday, September 30, 2002 - 7:55 am: |
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The power output is about what I get the brief moment it will key full power. The rest of the time it will key 100 and swing a little over 300 on high but be bouncing all over. I have two 6 volt pallet jack batteries in series for the power. I have tried another Messenger 500 on the same setup and it other works perfect. I put it on the power supply on low just to see if it was drawing any current when the dead key is zero or if I was losing the signal elsewhere in the amp. I've had bad trimmers kill the output signal before. It is not drawing any current on low or putting out any signal until modulated. |
Tech671
| | Posted on Monday, September 30, 2002 - 9:49 pm: |
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It's hard to diagnose behind a monitor. Maybe an intermittent fault in the input trimmer, maybe a faulty power selector switch, so239, relay..... |
2600
| | Posted on Tuesday, October 01, 2002 - 2:03 am: |
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My vote is for the relay. Moving parts are a safe bet most days. I would recommend tapping on the relay body, but unless you do it on low side, it could draw an arc across the contact points and blow itself to the devil. Tracing the RF signal to see how far downstream it gets takes more than a voltmeter. Just don't use your fingers to tap on stuff, use a plastic tool handle. It's running on 12 volts, but the RF can still bite.
73 |
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