Quark FALCON 1000 KW FM Transmitter - Alarm LED illuminated

[R_J]

Re: Quark FALCON 1000 KW FM Transmitter - Alarm LED illuminated

The output transistors are likely under the two heatsinks next to the heated resistors. A dummy load would be required to check it, you should be able to turn the power output down in the menu so you don't need a 1000watt dummy load, the station should have one. It could be that the alarm signal is due to a antenna/transmission line problem and not the transmitter.
I don't have access to any manuals so I don't know what the alarm would be for.

[dicky96]

Hi Guys

Here is an unusual one (for me anyway)

It s Quark 1KW FM radio exciter/transmitter

I think it is the Falcon 1000 but there is actually no model number on it, I just went by the pictures on http://www.quarkelectronics.it and the fact the radio station who own it, tell me it is 1KW

The Alarm LED is illuminating, apparently. I haven't powered it up on the bench and I don't know if I can as I don't have a load to connect to the RF output.

Originally they brought me just the green PCB with the four buck regulators (see pics) They asked me to change the LM2576HVS-ADJ voltage regulators which I did, they supplied new parts. However after doing that I tested the PCB stand-alone on my bench PSU and found there is an open circuit track between the 48V input terminal and the inductor L1.

You can see I bridged this open circuit track on the pics, and then the regulator board seemed to work OK, I have two outputs of 14V, one of 28V and the other read 30V, but my bench PSU only goes up to 31.5V and the input should be 48V so the last regulator is probably somewhere above 30V if I had the correct input voltage.

I checked the resistance from LM2576 pin 4 to Vcc and Ground for each regulator, and the resistances I see are suggestive that I should have 2 channels equal (I have 2 x 14V), one channel higher (I have 28V) and one higher again - which is the one reading 30V

So I am pretty convinced that regulator board is working now.

Anyway a couple days later they brought me the whole transmitter and say it still doesn't work and the ALARM LED is lit.

There are two resistors near the front of the Power Output PCB that look like they run so hot I can't even read the markings. They both read 0R6

There is this device marked RL500 100 that I assumed was the output transistor but the datasheet says it is a Flanged Microwave Resistor
https://broadcastconcepts.com/500W-100ohm-resistor.html

Anyway it reads very low resistance

Any ideas how I can proceed with this repair? It's outside of my knowledge zone. I only know I should need a dummy load as I used to repair CB radios back in the 80s

best regards
Rich