Batboard

I have a UHF Micor repeater that the 75 watt PA went out on. That part I am not concerned with at this point. I can not get any ouput from the low level amp. I checked the low level amp on the bench by its self and it checked OK. What I find in the repeater is that the 9.6 volt source to the LL amp goes away when I key the repeater. Any suggestions??? The Main PA is completely disconnected so I would not have any problems with the control lines to the PA wanting to shut down.

In behind the power control board is a small diamond transistor. That was usually the source of the problem you describe. Also, you could have a bad antenna network module, mounted on the back where the antenna hooks up. It has to detect power to supply the 9.6 you're missing.

Hope that helps.
Danny

To test the RF portion of the transmitter. Hook the white control line on the back plane to 12v, you should get rated power, that will tell you if it is in the RF or Power Control sections of the repeater. Then test the hidden transistor, if thats good you may have a circulator problem,causing eroneous reading to the power control circuit.

Thanks for the suggestion I will give that a try. The problem is that everytime I key the transmitter the power to the low level amp seems to go away. Its there until I key up. The manual says that if the power out is not at a certain level it will shut down, but how can it do that if the power will not come up.

If you are up on Micor repeaters I may need to pick your brain until will can get our repeater back on the air.

Thanks!!

First questions:
What band?
And what (if any) MOT cards are in the shelf?
Unified chassis or non-unified?
If the "Station Control Module" is in, pull out all the others and key with the Station control PTT slide switch, and report what happens.
I am always working on MICORS, I will review the PTT circuit and see if I can come up with a couple of tests to find the problem.
Usually its one of the other cards, so we need to know if you are using any.

Thanks for the replies. Heres what I have at this time.

Micor UHF C64RCB-1105AT 75 watt repeater.
only two cards. squelch gate and station control.
It is a "UNIFIED CHASSIS"

I am pretty sure the PA has died but not for sure yet. I get nothing out of the tripler/low level amp. I did put the low level amp on the bench apllied A+ and a 500mw signal in and got 1 to 1.5 watts out. So that seems to be good. put it in the station and nothing. the three power connections on the low level module are as follows. the tripler has 9.6V continous the other two sources for the low level transistors are 13.2V and when I key the station it drops to around .5V and nothing happens.

I just tried the trick that RADIOMAN2002 suggested and hooked 12V to the control line that connects to TB2 on the back and I get about .5 watts or 500 mw out of the BNC before it goes up to the main PA, but the low level is still loosing power.

Sound like the problem is in the low PA or the tripler. You should get 2 watt out of the BNC. Check the power out of the exciter, it should be about 500 mw, at around 70 mhz, depending on your freq. After that it may be easier to just replace the tripler if you can find one, they are a pain to work on without the right tools. Also I don't know if you can get the transisters anymore. Some of the transistors are the same that were used in the mobile.
Good Luck!
They are good machines, I have about 10 of them.

I can run the tripler/ low level amp on the bench and get 1.5 watts out which the manual says is ok. But when I put it in the repeater I can't get anything out because the voltage goes away when I key up.

Alright maybe you have a 12v or ptt problem, have you checked for the correct votages comming out of the station card. Also is the channel element ground actually going to ground. The first thing I would do is see if I get 500mw at the exciter output. Divide the freq by 3 the 2 that sould be about 70mhz. Make sure you have a good signal.
I'll be back have a call to attend to.
Jim

Exciter functions normally. The tripler is also working, but after that everthing stops. The voltage to the low level amp is what has me miffed. Why does it go away on PTT.

My two bits worth:
I am on vacation at the moment, so I don't have a manual handy.

I think that the problem is in the transmitter interconnect board.
Specifically a bad solder joint on the 9.6V pin of the trippler connector.

The 9.6V line to the trippler has developed a high resistance, and when the trippler attempts to draw power the voltage drops due to the resistance.

I have had this problem before. You have to remove the back plane,
and the exciter to gain access to the interconnect board. This is also the part most likely to be damaged if water, or "critters" gets into the station.
Aloha, Bernie

I may have found the problem!! On the back plane TB-2 has three terminals, 1=A+ 2=A- 3=PA control. The voltage I have at 1 and 2 goes away with PTT. Is there suppose to be lines from the power supply hooked to these pins?? I think some one has diconnected them.

My two bits worth:
The A+ and A- terminals are connected to the "Main" 13V output of the power supply. There is a fuse in the red A+ line. This line is usuially tucked into the left rear of the case.

This is "raw" A+ used for non critical circuits such as the audio PA.
I think that this is also the A+ for the trippler.

There is a regulated 13.8V supply for critical circuits, which is supplied by the same connector as the 9.6.

The PA control goes to the yellow wire on the PA. This terminal will have about 7V in a PROPERLY FUNCTIONING station. If for some reason that the PA does not come up to a certain output the voltage will go to 0 in 100 MS. This a protect circuit in operation.

I presume that you have output from the exciter, with reasonable meter readings. If so then you must have 9.6 V on the TX interconnect board.

Follow Nand's trouble shooting procedure.

You will need a service manual, both RF and control, as well as a test set
to work on this station.

THAT WAS IT!!!! I ran + and - from the power supply to the terminals at TB-2 and everything came to life. Thanks guys for sticking with me on this one and getting this resolved.

Big BOB