MSF5000 Receiver Help

[TARRA_Mick]

I have a VHF MSF5000 73CXB7106B. I have no idea why, but the receiver has lost sensitivity. My receive frequency is 146.13 MHz. I used to get around .125 microvolt to open the squelch. Now it is much worse. I went up on the mountain this morning and checked it again. It is taking .446 microvolt to open the squelch. I have gone through the preselector several times to tune it. I never seem to get any better. I am stuck for any ideas of what may be wrong or what to do next with it. I am looking for someone who is willing to help me to try to fix this issue. Or if there is someone out there who I may send it to for repair. I would expect there is someone out there who knows far more about the MSF5000 who may be able to help me or repair this for me. I sure would like to have it working better again.

Mick - W7CAT

[Doug]

If you have a test set available, plug into the receiver (front panel left side) set your test set to meter position 3 (meter switch set to negative) what kind of micro amps are you seeing. It's been a while since I've done a VHF station, I seem to remember it should be between somewhere in the 24 to 30 micro amps . Knowing that will help with your diagnosis.
Doug

[kcbooboo]

There's also a similar thread WITH A POSSIBLE CURE in the System Infrastructure forum.

Bob M.

[TARRA_Mick]

Bob, please give me an idea of what I am looking for.

[TARRA_Mick]

Doug, I will be going up on the mountain tomorrow to get some more readings and information.

[TARRA_Mick]

I went up and worked on the repeater for short time yesterday. The M3 reading was 36, which I think should be plenty good enough. Per Bob M's advice, he suggested backing the tuning lugs all the way out and starting over. I did that, almost. L5 is very hard to turn and it may be what is keeping me from getting where I need to. When I was done, I was opening the squelch at .251 microvolts. And .354 microvolts through the duplexer. So I don't think I am losing much through the duplexer. What has me baffled is that when I change the Acc Dis / Reset switch back to the middle, then it takes .5 microvolts to open the squelch, and that is without the transmitter on.

L5 is very hard to turn. I have tried to lube it and no real luck with that. I have tried enough to turn it that I am afraid of damaging the end of it. I would like to replace the lug but don't have a part number for it. If someone can give me a part number or happens to have one. Not sure if I can still buy one. It would also be good to run a tap through it, but I don't know what the size and thread is.

One other thing, I looked at the firmware versions when it booted up. They are 5.45 & 5.34. Not sure if that makes any difference. I don't have any others to load in to it.

Mick - W7CAT

[kcbooboo]

I will presume that the front-end tuning slugs are identical to the ones they use in other stations. If so, there's a thin jam nut that you can loosen; that should make L5 easier to tune. You can also completely loosen the nut and unscrew the tuning slug, clean it off with a brass bristle brush, and reinstall it. Make the jam nut just tight enough to keep the slug from turning by itself. All of the tuning slugs should be stiff enough that you can't turn them without the 5mm hex wrench inserted.

There are two EEPots that adjust the squelch. It sounds like yours are way too tight. Usually it's the "PL DIS" switch that changes the squelch sensitivity though. In any event, connect a computer and digital metering panel and observe the RCVR UNSQ and RPTR UNSQ LEDs and use the computer to set the appropriate EEPots so the LEDs just go out, then increase the setting by 3-5 so it stays closed.

Bob M.

[TARRA_Mick]

Thank you for the reply Bob, I hadn't even seen there was one. I know about the jam nut and have it loose (really loose). I am thinking about pulling the preselector off and bringing it back down where I can work on it and see what is going on. Work to get the slug loose enough to be able to get it functional. Of course once I put it back in I'll have to tune it, and at that time I'll work on the squelch too. I hope and think we'll get this going again. Thank you for your help Bob!