KK4ICE

FCC Licensed Amateur Radio Operator, Extra Class

KE4COL Mastr II 2 Meter Repeater Repair

KE4COL’s 145.230 MHz Gold Hill, AL 2-Meter Mastr II repeater developed some issues a while back, and I finally got around to putting it in the rack and troubleshooting it today. He’s been running his Fusion repeater as a backup during that time, but we’ve all been looking forward to getting the Mastr II back online for multiple reasons, including starting his AllStar linking node back up and the fact that the Fusion just doesn’t stack up to the Mastr II in terms of overall performance. After fixing a couple of issues on the Mastr II today, it appears ready to go back into service.

Just a tiny bit of pressure on or around this RCA type plug and connector would cause notable changes in the receive performance on this Mastr II.

I found in intermittent receive quality problem when probing around in a particular area of the receiver/front end of the Mastr II. Someone in the past had obviously replaced a component on the receiver board and had left a LOT of solder flux in the area. It had migrated over to the area of an RCA jumper connector, which I noticed that even the slightest touch of the connector’s plastic housing (or the slightest pressure on the circuit board near it) would cause noticeable changes in the receive quality. Sometimes letting the pressure off the connector or board would cause it to return to normal, and sometimes it wouldn’t.

You can see the tremendous amount of solder flux which had been left on the board. That stuff has corrosive and oxidizing properties which can often wreak havoc on circuits if it’s not removed after the soldering work is done.

Disconnecting and cleaning the RCA plug and jack with an alcohol/acetone mixture seems to have eliminated that intermittent problem. Pushing, pulling, twisting, torquing, flexing, banging on the board, raising and lowering the receiver tray (and literally “slamming” it to jar and vibrate it as much as possible), etc. seems to make no difference or trigger any issues in the receiver now. Hopefully that issue is eliminated.

The other problem I noted was that the transmit frequency was off by around 500 Hz. That might not sound like a lot, but when you’re using CTCSS on the OUTPUT of the repeater, shifts in the carrier frequency

Exciter crystal netted to within 5 Hz of the desired 145.230 MHz transmit frequency. Much better than the 500 Hz or so shift I noted when I started working on the machine this morning.

beyond more than a few Hz can sometimes cause issues. The CTCSS/PL tone in use on the transmitter output of this repeater is used to control an AllStar linking node. The repeater was occasionally failing to activate the node, and I suspect that it was because the carrier shift was resulting in just enough distortion/displacement of the output tone for the linking radio to demodulate it as slightly off the desired tone frequency, therefore failing to open the squelch on the link radio’s receiver. We’ll just have to see if fine tuning the exciter in the Mastr II to within a few Hz actually has that problem fixed.

We hope to have the Mastr II back in the rack at the repeater site within the next few days, schedules permitting. If all goes well, the KE4COL AllStar linking node will back back online within the next few days as well.

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