MSF5000 UHF E49 but RX Lock light is on

[ny1a]

I am troubleshooting a UHF MSF5000 At the boot the RX Lock light is not on, but after flagging an E49 error in the display, the light comes on. When the ID runs, it is preceded by two beeps. In spite of all this, the receiver works normally and has normal sensitivity. I have tried resetting/restarting the repeater, reprogramming it, unplugging and reseating cables, and replacing the RX VCO with a known-good VCO from another identical repeater. I am guessing there is something wrong with the SSCB. If that is the case, what can I do about it other than replace it?

Suggestions?

Thanks.

David, NY1A

[kcbooboo]

If the VCO isn't tuned properly, it could be taking too long to lock, hence the RX LOCK LED not on when it first starts up and the E49 error. If the LED comes on and the error goes away, I wouldn't worry about it too much. Check the tuning anyway; it should be 38uA +/- 2uA for both the TX and RX VCOs.

It could be some leaky capacitors around the synthesizer, but this is all on the Uniboard in the RF Tray.

Bob M.

[ny1a]

Thanks for responding. The VCO's are both tuned to 38µA using the factory test set, so that's not it. I'll take a look at the caps.

David

[Bigred]

If you can get 38 microamps on the VCO I'd say that's solid.

If your suspicions lead you you to the SSCB, I'd replace the big filter caps just after the 5V regulator as a matter of principle (kinda like Spectras). I've just seen too many weird probs when the 5V rail gets noisy.

[ny1a]

Sounds like good advice. I am hearing a strange buzzing sound over the speaker in the test set. I suspected that was related, once I noticed it tonight.

Thanks very much.

David

[Will]

You could try adjusting the VCO's slug to where it locks right away on power up.

Tin whiskers comes to mind too.....

Replacing the caps IS recommended, as these stations are old but NOT obsolete..

Use low ESR capacitors on the 5 volt line.

[kcbooboo]

I've had stations with buzzing sounds in the metering panel audio; doesn't seem to hurt anything and the audio going through the station is clean. That might be a separate issue.

The slowness in locking up is most likely caused by a problem around the synthesizer or leakage on the VCO steering line. The SSCB only sends digital programming data to the Uniboard (multiple times before throwing the error) and that either succeeds or fails, although a bad connection could give you some issues. There's the flat cable connector at the SSCB, and all the interconnect pins on the filter assemblies that pass signals between the interconnect board under the RF Tray and the Uniboard. I've seen crud on these filter pins that acts as a large leaky capacitor and upsets things. Each pin should have infinite resistance to ground. You can remove each filter assembly from the top and verify the resistance of each pin. Reseating everything just might make the problem go away for a while.

The TX LOCK LED is lit directly from the TX synthesizer on the Uniboard. The RX LOCK LED is lit by the microprocessor on the SSCB and it gets its input from the RX synthesizer. They do this because you could have two RF Trays for multiple receivers, and they want to be able to indicate the lock status separately with only one LED.

Bob M.