New member, working on a MSR2000

[W5KVV]

Hi everyone. My name is Matt, W5KVV. QTH is McAlester, Oklahoma. I'm President of the local ARC.

We recently picked up a continuous duty MSR 2000 in the VHF flavor. I have it here in my shack and have been working with it the last few days. This is my first MSR, but I am familiar with the Micor line as the club has several on the air. I see quite a few similarities between the two. This MSR is the repeater version C73KSB. It's duplexed, has the repeater back plane and still has the baby cans in the bottom of the cabinet.

Initially when I brought it home I did all the basics. Cleaned it up, gave it a good visual inspection etc. It's been in dry storage for almost a decade, so it was a bit dusty. Everything cleaned up and quite honestly it looks like new on the inside, so very little work was done there.

At this point I'm just doing some initial testing with it on the as received frequencies into a dummy load.
TX: 158.940 RX: 155.775. It has both the 2A (114. vibrasponder and sender installed. (which just happens to be our assigned PL).

The only problem I can find as of now is the output power is a little flaky. Sometimes I'll bring it up and it'll be full 100 watts. Other times, it goes straight to 50 watts like someone has turned it way down. It holds steady at 50 or 100 watts, no fluctuation. I've looked over all of the wiring and associated connections going up to the PA. I'm currently reading thru the PA manual.

Any of you guys ever had a MSR or Micor do something like this? I'm wondering (and hoping) it's common.

-Matt

[PETNRDX]

I have seen that a few times. The pot on the power control module in the PA. Or the connections to that little module.
Try tapping on that board lightly with a screwdriver handle and see if that is it.

[kcbooboo]

I had a similar dirty pot on the power control module in a 120w VHF Micor mobile. It went open and was probably putting out over 250w. Eventually blew the big fuse in the A+ line after a LOT of talking.

Probably a good idea to twirl every pot you can find just to clean the wiper and the carbon.

Bob M.

[W5KVV]

Thank you guys for the help. You are both exactly right. I pulled the PA and put it on the bench. Took the back cover off and cleaned both the power limit pot and the power set vc and CAREFULLY cleaned up the board with deoxit. It is now producing 100 watts every time as it should.

Now, my next question... What would you guys run the power at? I've got a good AC muffin fan to put on the backside of the PA, so the trustee and I are contemplating leaving it at 100 watts. I know these big moto PA's don't like to be turned down too much.

[JeffFireRadio]

We ran our public safety unit (also continuous duty) for a decade+ at 85w and never had a problem. Not applicable to this discussion, but my hometown PD cheaped out and bought the standard duty one (with continuous duty cycle-type utilization) and had PA problems for the entire life of the unit. Enjoy your repeater. The MSR2000 is a great worker!

[Bigred]

MSR's do get wonky over time with all the mechanical connections. Probably time to do the whole enchilada. Card edges, channel elements, pots, etc. Scrub everything down with contact cleaner and then secure it with deoxit or stabilant 22. May save a mountain top trip or two.

[W5KVV]

Sage advice guys. I appreciate it. I'm gonna leave no pot un-turned. I did scrub the cards and the back plane down, so that's taken care off.

I have always been told to steer clear of the MSR intermittent duty PA's. Seems the heat generated from long qso's causes them to expand and contract something fierce, breaking solder joints all over the place. That wont work with the gas bags that will be using this machine.

[W5KVV]

Ok guys. After several delays, I'm working on the MSR 2000 again. Other projects with priority over the MSR came up, bla, bla,bla. Anyways.

Here's where I'm at: My new crystals came in from ICM. I have them in the channel elements. Everything is back together. I'm on step 4 of RX alignment in the service manual. It says " Quiet the radio by injecting a strong on channel signal into the antenna connector, adjust quadrature detector coil to obtain the same meter reading in step 3". Here's the problem: The repeater will not RX. No matter how many uV I dump into it. It's like the xtals are not even in line. It has power to the PA, power to the backplane, power to the receiver and exciter. But it will not hear anything nor will it even attempt to key up the TX via the station control card.

Please tell me I'm stupid and missed a simple step somewhere..... Steps 1-3 went like butta, but now I'm at a dead stop. I tried everything I can think of including swapping in a set of known good channel elements.

Any help is greatly appreciated.
Matt
W5KVV

[kb4mdz]

Couple tips to try:

(I can't remember the IF of an MSR2000; maybe something like 10.7 MHz? )

Can you get the receiver to quiet by (figuratively) slamming a signal at the IF frequency at the Receiver?

Or, can you measure the injection frequency after it's been multiplied up from the channel element? Should be 10.7 MHz below the Receiver frequency; you should be able to see it as a spike on a spectrum analyzer with a length of co-ax from the Spec-Analyzer input & hovering inside the Receiver section of the Mitrek.

Are you using the Mitrek tuning meter thingy, that plugs into the round plug on the board? If so, do your meter readings jibe with the suggested readings in the tune-up procedure?

[W5KVV]

I'm using the MSR station meter, TRN5080. It has the small uA meter & a speaker built in. All of the measurements are correlating with the service manual.

The IF of this particular repeater is 10.7MHz. The MSR's came in both 10.7 & 10.8 IF's, depending on your RX setup. I've tried injecting 100uV of signal on everything from DC to 500 MHz, still nothing.


I believe the problem is with the channel elements themselves. Everything was working fine prior to the crystal swap. I was meticulous with the removal of the old xtals. Used my Hakko 808 to remove them, cleaned up the board and used good Kester flux and solder to put the new ICM xtals in. Poor soldering is a pet peeve of mine, so I strive for perfection in that area.

Matt
W5KVV

[kb4mdz]

OK, then your meter TRN5080 should indicate by some reading that the crystal is oscillating at its fundamental frequency, and maybe be being multiplied up to the L.O. injection frequency.

Was the RX working on its original frequiency before you started? How far a freq. change is this? Have you tuned the preselector?

[motorola_otaku]

I ran into a similar issue with a Mastr IIE a while back... turned out the channel elements from ICM were a full kilohertz off and couldn't be brought on-frequency. I'm told their TCXO guru either left or was let go a year or two prior to them closing up shop so it doesn't surprise me that their quality control went downhill.

edit: Did you send the entire channel element to ICM, or did you just buy new crystals and try to convert the channel elements yourself?

[W5KVV]

^^^ That's exactly what I thought. I tried to send them the complete elements so they could be temp compensated, but they advised they were no longer offering that service. So I just had them send me the xtals while they were still taking orders.

However... After a couple of evenings worth of work, I have it up and running. The RX and TX were way, WAY out of alignment after the frequency change. I'm very surprised how sensitive the adjustments are on these old repeaters. If you get in a hurry with the preselector, you can blow right past the "money spot." It takes quite a bit of time to get it perfect. At least it did in my case. This is my first MSR/Mitrek, so it was a learning experience.

The xtals are right on the money so far thank God. The TX side needed cleand up a little with the IDC adjustment, but not much. RX just needed dialed in. Squelch opens at .22uV, PL decode comes online at .28uV.

Thank you guys for the help. I do appreciate it.

Matt
W5KVV