Hello everyone,
I have an MSF Limited VHF repeater model C63RLB7106BT that has two beep error (PA problem). Whenever I key the repeater, the PA Full LED just flicker (doesnt light up steady) and only makes 50watts out to a Bird 43 and dummy load. I then connected the Bird43 between the IPA and PA, and I get 1 watt of drive power going to the PA. Is this 1 watt normal? What is the maximum drive input for the PA? I have also checked the PO adjust at the front panel, I can lower the outpout smoothly, but still get the two beep error. Any inputs or additional info what to check are highly appreciated.
Thanks.
jay
MSF Limited error beep
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Re: MSF Limited error beep
Normal IPA output power is 2-4 watts, although it's capable of 6-12, and it would make that much in a station without a PA.
The PA itself probably won't be happy with much more than 5-6 watts. The power control circuitry uses feedback from the PA output to control the IPA drive. The circuit responds very fast and has high gain, so a little change to IPA power could make a big difference to PA output power.
If there's not enough feedback from the PA, or if the IPA has to put out too much power (according to the PO adjustment), you could get the two beeps. But the flickering LED is the giveaway. Once that stops flickering and stays on solidly, the alarm should go away.
I had an 896 MHz station that did something similar. There was some kind of conductive crud build-up on one of the pins in an interconnect filter that the RF Tray's Uniboard plugs into. It was causing leakage in the power control circuit and it upset the delicate balance. I think the pin measured something like 50k ohms to ground after removing the filter assembly from the chassis; it should have been infinite resistance. I cleaned the crud off the filter, put it back in, and that took care of it. It was not easy to find.
Bob M.
The PA itself probably won't be happy with much more than 5-6 watts. The power control circuitry uses feedback from the PA output to control the IPA drive. The circuit responds very fast and has high gain, so a little change to IPA power could make a big difference to PA output power.
If there's not enough feedback from the PA, or if the IPA has to put out too much power (according to the PO adjustment), you could get the two beeps. But the flickering LED is the giveaway. Once that stops flickering and stays on solidly, the alarm should go away.
I had an 896 MHz station that did something similar. There was some kind of conductive crud build-up on one of the pins in an interconnect filter that the RF Tray's Uniboard plugs into. It was causing leakage in the power control circuit and it upset the delicate balance. I think the pin measured something like 50k ohms to ground after removing the filter assembly from the chassis; it should have been infinite resistance. I cleaned the crud off the filter, put it back in, and that took care of it. It was not easy to find.
Bob M.
Re: MSF Limited error beep
Hi Bob,
I'll be looking into the interconnect filter that you've mentioned and will be cleaning all dirt that I could see. By the way, just to check if the IPA is producing the rated output, I noticed one thing in the IPA, I disconnected the 6pin molex going to the PA to let it run without the PA based on the article at Repeater builder. I accidentally, keyed the TX in the front panel switch and it generated more or less 10watts into a wattmeter-dummyload, funny thing is I haven't connected the resistor to the green wire from the 6pin molex to the 9.6v. And I still get the 2beep error. I'll keep you posted Bob for anything.
thanks.
jay
I'll be looking into the interconnect filter that you've mentioned and will be cleaning all dirt that I could see. By the way, just to check if the IPA is producing the rated output, I noticed one thing in the IPA, I disconnected the 6pin molex going to the PA to let it run without the PA based on the article at Repeater builder. I accidentally, keyed the TX in the front panel switch and it generated more or less 10watts into a wattmeter-dummyload, funny thing is I haven't connected the resistor to the green wire from the 6pin molex to the 9.6v. And I still get the 2beep error. I'll keep you posted Bob for anything.
thanks.
jay
Re: MSF Limited error beep
With the Molex plug disconnected, the power controller loses its PA output feedback signal, so it would think the PA has failed and you'd get the beep. Also the IPA would briefly put out as much power as possible, up to about 12 watts which you saw. Then it shuts down to protect things. So it needs that Molex connection.
Bob M.
Bob M.
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MSS-Dave
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Re: MSF Limited error beep
Bob..
Does the Limited VHF station have the JU1 or whatever test jumper bypass that allows the thing to run WFO when the molex control line is removed? I know my CXB UHF and the CLB 900 stations had that. I could test into a dummy on the PA output side and the IPA output side without the power control loop being active. I usually found a bad circulator or LP filter on the 900 stations and a couple of bad PA's (spurious) on the UHF stations over the years...
Dave
Does the Limited VHF station have the JU1 or whatever test jumper bypass that allows the thing to run WFO when the molex control line is removed? I know my CXB UHF and the CLB 900 stations had that. I could test into a dummy on the PA output side and the IPA output side without the power control loop being active. I usually found a bad circulator or LP filter on the 900 stations and a couple of bad PA's (spurious) on the UHF stations over the years...
Dave
Re: MSF Limited error beep
I have cleaned the pins at the interconnect but still get the 2 beep errors. I connected back the 6 pins molex and measured the voltages in every pin. I have correct voltages in the other pins except in the green wire (forward voltage pin). Based on the info I got from the RB site, that pin should have 0.09V on RX and 2.92V on TX. What I get is 0.2V on RX and 0.5V on TX. Thinking that it could be some cold solder, I resoldered the connections in the small circuit board in the PA which has reflected and forward voltage, but still couldnt get the correct voltage in the green wire. Any other thoughts or suggestions?
Does programming the frequencies, especially the TX away from the specified band range would cause this 2-beep error? This MSF is a range 2 (146-174mhz). Out of curiosity to check, I programmed the TX at 143mhz, The VCO locked and transmitted at full power without any errors. I then shut it down, turned it back on after a few days then I get the 2-beep error.
I have been also looking for the JU1 to bypass the error. I found a JU1 jumper near the TTRC board but seems it is not the one for it.
Thank you.
jay
Does programming the frequencies, especially the TX away from the specified band range would cause this 2-beep error? This MSF is a range 2 (146-174mhz). Out of curiosity to check, I programmed the TX at 143mhz, The VCO locked and transmitted at full power without any errors. I then shut it down, turned it back on after a few days then I get the 2-beep error.
I have been also looking for the JU1 to bypass the error. I found a JU1 jumper near the TTRC board but seems it is not the one for it.
Thank you.
jay
Re: MSF Limited error beep
Only the EPROM-programmed (CLB) stations have JU1 to put the station into test mode. The RSS-programmed (CXB, RLB, and GFB) stations use a switch sequence to temporarily disable the power control error checking.
The forward power indication on TX has to be a couple of volts; the exact value is not important. It's related to the output power coming out of the PA. More power = more voltage. There's no definite numeric relationship (in other words, no specific voltage is equivalent to, say, 75 watts).
Check the crimped connections at the Molex connector pins. Solder them if possible.
Could be a component failure inside the PA where the forward power is sampled and fed back down to the Molex connector, especially if you're getting normal output power.
Bob M.
The forward power indication on TX has to be a couple of volts; the exact value is not important. It's related to the output power coming out of the PA. More power = more voltage. There's no definite numeric relationship (in other words, no specific voltage is equivalent to, say, 75 watts).
Check the crimped connections at the Molex connector pins. Solder them if possible.
Could be a component failure inside the PA where the forward power is sampled and fed back down to the Molex connector, especially if you're getting normal output power.
Bob M.
Re: MSF Limited error beep
hi bob,
While doing some searching here on the board for topics about msf5000, i came across on one of your posts a few years back about running the msf5000 without the PA. You've mentioned that, connecting the green wire from the molex to a 9.6v supply with a 2.2k resistor, the beep errors will go away as the IPA will assume that a PA is connected. The MSF that I am working on still has the beep errors even if I have already done the modification. Any inputs on where to look or which part of the rf tray is causing this problem?
Thank you.
jay
While doing some searching here on the board for topics about msf5000, i came across on one of your posts a few years back about running the msf5000 without the PA. You've mentioned that, connecting the green wire from the molex to a 9.6v supply with a 2.2k resistor, the beep errors will go away as the IPA will assume that a PA is connected. The MSF that I am working on still has the beep errors even if I have already done the modification. Any inputs on where to look or which part of the rf tray is causing this problem?
Thank you.
jay