Hi there guys have any one of you fix this problem. I have a UHF msf5k amp that the output slowly increases as you apply PTT to the amp. I replaced with another good amp and it works fine, so is not the power supply, nor the controller. Any ideas.
Luis
MSF5000 Power amp slow response
Moderator: Queue Moderator
MSF5000 Power amp slow response
Love to bring back old radios
Does it start out lower, then end up at the same power as the one you swapped, or does it start out at the proper power, then creep upwards like it's out of control?
Even though you've isolated it to the PA, check the power going from the IPA to the PA input with a wattmeter. Make sure it's not changing, since that's what controls the output power of the PA - more input means more output.
First thing I'd check are the little Omega clips - those U-shaped connecting wires that are used between the boards. They allow the boards to expand and contract with changes in temperature. Maybe one of those has gotten unsoldered.
Then check the input power splitter and the output power combiner for burnt components and/or solder joints that have become overheated.
If there's a circulator in the PA (you have to open it up to determine that), it, or its dummy load, could be going bad, due to previous operation with a high amount of reflected power or spurious emissions being fed back into the antenna port.
Bernie will probably add more to this when he reads it.
Bob M.
Even though you've isolated it to the PA, check the power going from the IPA to the PA input with a wattmeter. Make sure it's not changing, since that's what controls the output power of the PA - more input means more output.
First thing I'd check are the little Omega clips - those U-shaped connecting wires that are used between the boards. They allow the boards to expand and contract with changes in temperature. Maybe one of those has gotten unsoldered.
Then check the input power splitter and the output power combiner for burnt components and/or solder joints that have become overheated.
If there's a circulator in the PA (you have to open it up to determine that), it, or its dummy load, could be going bad, due to previous operation with a high amount of reflected power or spurious emissions being fed back into the antenna port.
Bernie will probably add more to this when he reads it.
Bob M.
My two bits worth:
Not much I can add to Bob's analysis.
There is a failure, and it will likely get worse.
Gueses are always risky in theis business, my guess is a burnt solder joint in the output circulator.
Stations that shipped with the internal duplexer option are supposed to have the "tripple circulator"
The circulator has to be removed from the PA chassis, a messy job due to the heat sink compound.
The output terminals of the circulators often burn.
If operated in this condition the preceding circulator load will likely be distroyed. I have successfully repaired these if the damage is not too excessive. Note: The load resistor is the same as in the 800 70W MICOR.
Alternatively, the circulator could be replaced with an external single circulator.
I have several spares.
The built in metering jacks in the PA can be a great help in locating which PA module is defective if that is the case.
The transistors are made into modules, which are very reliable.
If a PA module fails, the "balancing resistor" which is located under the output board is often distroyed.
The output board must be removed to inspect the resistor, which is a special item.
Not much I can add to Bob's analysis.
There is a failure, and it will likely get worse.
Gueses are always risky in theis business, my guess is a burnt solder joint in the output circulator.
Stations that shipped with the internal duplexer option are supposed to have the "tripple circulator"
The circulator has to be removed from the PA chassis, a messy job due to the heat sink compound.
The output terminals of the circulators often burn.
If operated in this condition the preceding circulator load will likely be distroyed. I have successfully repaired these if the damage is not too excessive. Note: The load resistor is the same as in the 800 70W MICOR.
Alternatively, the circulator could be replaced with an external single circulator.
I have several spares.
The built in metering jacks in the PA can be a great help in locating which PA module is defective if that is the case.
The transistors are made into modules, which are very reliable.
If a PA module fails, the "balancing resistor" which is located under the output board is often distroyed.
The output board must be removed to inspect the resistor, which is a special item.
Aloha, Bernie