Micor Repeater Exciter working but no PA output

[kf4kjt]

I have a UHF Micor Unified Compa-Station Repeater. I have got the reciever receiving great, and the exicter is working. I can key the repeater up and it works. I hear the courtesy tone every time I key it up. the trouble is that I have hooked the PA back up but no output power is being read from the output of the repeater. I am a little confused on the TB2 connection to control. It is connected to the PA Control. When I disconnect the PA control (Yellow Wire) from TB2, it measures 7v, but when I hook this wire back up it drops to 1v or less. It doesn't change whether transmiting or recieving. Also changing the power output control does nothing. I do not have a good watt meter, but the output from the exciter is not moving my meter at all. (I can move it with a ht with 50mw). So I am puzzled. This is my first repeater and I feel I have succeeded so far with so little test equipment but I am stumped right now. Thanks alot....

Scott
KF4KJT

[KI4M]

Scott;
Carefully check the power control board especially the potentiometers. I had a MSR-2000 continuous duty repeater (uses a P.A. that is nearly identical to a Micor) a few weeks back I was working on and could not get any output power. The symptoms were very similar to yours. I found out that I had a bad potentiometer on the power control board. I have since replaced it and the P.A. works wonderfully. Go through the troubleshooting section in the manual on that and follow it step by step.

[RADIOMAN2002]

For a quick test you can bypass the controlled stage of the PA by putting 9.6v to the white wire going to the PA. That will tell you if it's in the unified chassis or the PA strip.

[PETNRDX]

Congratulations... Just getting a Micor to work is sometimes a challenge.
I LOVE Micors, but they can be confusing. Here are a few more things to check.
Your exciter should put out at least 400 mw at ONE THIRD the freq of your TX. Meaning if you have a 440 repeater, the exciter should make near one half a watt in the mid 146 mhz range. ( Either divide your 440 carrier, or do the math to multiply the crystal)
Directly behind your exciter ( hidden ) is a three stage tunable filter.
You might want to tune that on your freq to get the max thru it to drive the tripler/low level amp.
Out of the front of the unified chassis there is a BNC connector and cable going to the PA ( its the one on the left ) and a BNC connector and cable coming FROM the PA to go thru the power control circuit and circulator.
You can connect your watt meter to that left BNC connector and verify that you are getting 800 mw out of the tripler/ low level amp.
If you are NOT getting 400 mw of VHF to drive the tripler, or you are NOT getting 800 mw of UHF to drive the PA, they may not work. They need those drive values ( or pretty close to that ) in order to work.

[wa6ylb]

I have a UHF Micor Unified Compa-Station Repeater. I have got the reciever receiving great, and the exicter is working. I can key the repeater up and it works. I hear the courtesy tone every time I key it up. the trouble is that I have hooked the PA back up but no output power is being read from the output of the repeater. I am a little confused on the TB2 connection to control. It is connected to the PA Control. When I disconnect the PA control (Yellow Wire) from TB2, it measures 7v, but when I hook this wire back up it drops to 1v or less. It doesn't change whether transmiting or recieving. Also changing the power output control does nothing. I do not have a good watt meter, but the output from the exciter is not moving my meter at all. (I can move it with a ht with 50mw). So I am puzzled. This is my first repeater and I feel I have succeeded so far with so little test equipment but I am stumped right now. Thanks alot....

Scott
KF4KJT

There is a PNP pass transistor (M9701) that is mounted on (top) the exciter chassis if memory serves me correctly. (seems to me its on the triplier assembly, in the middle, mounted on a vertical wall of the tripler). This PNP passes keyed voltage on the yellow wire to the PA. This same part is how the Micor sets the power out. To tell if the transistor is dead, place a DC volt meter on the yellow lead. The yellow wire will show some positive voltage while the station isn't transmitting, but when you do transmit, the voltage mushes down to 0 or even slightly negative. (it should stay at 7-10 volts in transmit if it is working) If not, its time to change this transistor. We have seen this a lot with our fleet of UHF Micor repeaters over the years, so much so that we kept a bottle of these transistors at each site.
The M9701 is held in with two 1/4 hex head screws. Remember to use the heat sink compound on the insulator.

The exciter output that goes to the PA is fully at UHF frequencies - we have bypassed the PA and let the exciter go to the duplexer in a pinch before.
We've even used a UHF portable, at low power (just under a watt - like 1/2 watt), to be the exciter for the PA, for testing. We have to supply a varible voltage to the yelllow wire lead to the PA. Never run the yellow wire at 13.8 VDC - that's way too high. It usually is around the 7-10 volt range or so.

B.

[kf4kjt]

I want to thank everyone for your help so far. I have a update. I now have about 800mw out of the low level amp. I removed the exciter and the bandpas filters behind the exciter and tuned them for max power and now I have almost 1 watt out of the low level amp. The repeater sounds great with 1watt. Now back to the PA not working. When I connect the control cable up to control on the backplane and transmit, it shows power on the watt meter then drops instantly, like there is a short. I also have a question about several 10watt resistors connected in series between 12v and Control on the backplane. The total resistance seems to be about 20ohms roughly. So I am still stumped about the PA not working. I do not know if it has worked recently, I never fired the PA before I removed it from the commercial band. Another piece of info is that there are no cards in the machine. Just PL decoder in the reciever chassis. And a NHRC3plus controller that I have hooked up.

Again about the transistor on the chassis of the power control board, what is the best way to test this transistor. I am measuring 12v on it all the time, if I checked it right. Thanks for all of your help. I would have never known about the filters behind the exiciter if you guys wouldn't have told me. This is my first repeater, I have learned a lot so far.

[kf4kjt]

An update....

I have hooked up a ht to the pa and on 465.000 it puts out 5 watts with 1 watt of drive. But when I try it at 442.000 it puts out less than I put in. Any help would be appreciated. Thanks

[kf4kjt]

Any answers so far?????

[federall]

Sounds like a PA issue, have you fiddled with the power control board? Hook the HT up as you just did and make sure its 1 watt going in, take the PA control wire and move it to A+ on TB2, not very long just enough to test it. Before you transmit take off the shield on the Power Control Board if its not removed already. Adjust Drive Limit on the PCBoard to halfway up, then adjust 'power set' on the PCBoard fully clockwise. Now key the handheld and measure the watts coming out of the PA, if its the same, as you mentioned above it could be the exciter try replacing that. I just replaced pretty much my whole TX section of my micor and had no luck. Luckily i had spare parts to do this come to find out after replacing the following:Antenna Network, PCBoard transistor,PCBoard,the entire PA replaced and the tripler, it was the exciter the whole time. The control wire on my PA was measuring before with the defective exciter .880 volts on idle, and the same on TX, now it reads 9.6 volts on idle and 12.8 on transmit. Hope u figure it out these micors are bricks. 73's
KD0IUH