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Old 10-21-2020, 04:16 AM   #1
dicky96
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Default Quark FALCON 1000 KW FM Transmitter - Alarm LED illuminated

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
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Old 10-21-2020, 11:32 AM   #2
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Default 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.
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Old 10-21-2020, 01:08 PM   #3
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Default Re: Quark FALCON 1000 KW FM Transmitter - Alarm LED illuminated

disconnect the PA stage and check how much rf power you get at the pre driver, then the driver stage. broadcast transmitters go off the air if there is an alarm on the front panel and stay off until someone clears it. probably lightning killed the PA. The radio station owner / engineer should have software + manual to program the transmitter and you are going to need that.

Last edited by CapLeaker; 10-21-2020 at 01:26 PM..
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Old 10-22-2020, 03:20 AM   #4
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Default Re: Quark FALCON 1000 KW FM Transmitter - Alarm LED illuminated

Quote:
Originally Posted by CapLeaker View Post
disconnect the PA stage and check how much rf power you get at the pre driver, then the driver stage. broadcast transmitters go off the air if there is an alarm on the front panel and stay off until someone clears it. probably lightning killed the PA. The radio station owner / engineer should have software + manual to program the transmitter and you are going to need that.
Unfortunately I don't have anything to measure RF power with. Thanks guys but I don't think I have the equipment for this repair.

I doubt lighting killed it - it hardly ever rains in the South of the island, and even then it is a quick shower. A thunder storm happens maybe every 5-7 years - we last had one a couple years back and it was spectacular!!
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Old 10-22-2020, 07:55 AM   #5
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Default Re: Quark FALCON 1000 KW FM Transmitter - Alarm LED illuminated

measure the RF transistors in each rf section (pre driver, driver and PA) probably there is a short. IF you do some soldering in there, make sure to use silver solder (unleaded). It's a bitch to solder, but in commercial systems like this things can get hot and unsolder themselves if it isn't properly soldered or leaded solder used.

Last edited by CapLeaker; 10-22-2020 at 07:58 AM..
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Old 10-23-2020, 10:25 AM   #6
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Default Re: Quark FALCON 1000 KW FM Transmitter - Alarm LED illuminated

Leaded silver solder was known to be the lowest temperature eutectic solder...
Unleaded solder is high melting point solder?

I suspect if you just use normal unleaded solder it's also got a higher melting point than regular leaded solder anyway.
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Old 10-23-2020, 04:13 PM   #7
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Default Re: Quark FALCON 1000 KW FM Transmitter - Alarm LED illuminated

silver solder has a higher melting point than leaded 60/40 solder.
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Old 10-24-2020, 03:39 PM   #8
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Default Re: Quark FALCON 1000 KW FM Transmitter - Alarm LED illuminated

Well that's the problem,
63Sn/37Pb (Eutectic) melts at 183C
60Sn/40Pb (close to Eutectic) melts at 183-188C
and leaded silver solder is 62Sn/36Pb/2Ag which melts at 179C - lower than the others.

Maybe you mean some other silver alloy, but the common electronics silver solder is lower melting point.
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Old 10-24-2020, 05:50 PM   #9
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Default Re: Quark FALCON 1000 KW FM Transmitter - Alarm LED illuminated

what fault sets the alarm state ? what does not work ?
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Old 10-25-2020, 10:15 AM   #10
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Default Re: Quark FALCON 1000 KW FM Transmitter - Alarm LED illuminated

There is a video showing the eagle 1000 going into alarm (reflected power protection) when the antenna/load is removed, so it could be similar to the alarm protection on the falcon 1000.
https://www.facebook.com/Quarkbroadc...related_videos
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Old 10-26-2020, 05:38 AM   #11
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Default Re: Quark FALCON 1000 KW FM Transmitter - Alarm LED illuminated

Yeah - the driver stage output FET PD55025 looks OK, or at least it isn't reading short

One of the PA output devices looks rather like it has seen better days!
mrfe6vp5600hr6

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Old 10-26-2020, 05:49 AM   #12
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Default Re: Quark FALCON 1000 KW FM Transmitter - Alarm LED illuminated

Oh!! The other one doesnt look too clever either!
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Old 10-26-2020, 03:22 PM   #13
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Default Re: Quark FALCON 1000 KW FM Transmitter - Alarm LED illuminated

well, i guess you found the problem! these are about CAD$ 180 each! mouser has em. Did you try to take these rf transistors out, or did someone else monkey around with it before you got it? post 1, pic 5.

Last edited by CapLeaker; 10-26-2020 at 03:32 PM..
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Old 10-26-2020, 04:12 PM   #14
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Default Re: Quark FALCON 1000 KW FM Transmitter - Alarm LED illuminated

Quote:
Originally Posted by CapLeaker View Post
well, i guess you found the problem! these are about CAD$ 180 each! mouser has em. Did you try to take these rf transistors out, or did someone else monkey around with it before you got it? post 1, pic 5.
No I didn't try to desolder them and the self tapping screws through the top heatsinks into the bottom heatsink were quite tight and I don't think they have been removed before, but really, who knows the history of this thing???

Yeah I have seen the price of those output devices, though I suspect that is only 10% or less than the cost of a scrapped 1KW FM radio transmitter, even with my repair charge on top.

Having said that, two things worry me about taking this repair further:

1. those things don't look easy to rework/replace because of the amount of heat I would need to get into them with my hot/air and T12 - plus it looks like there are these two coax type cable coming off the arse end of them and I worry they may melt? But I suspect the advice/expertise is here on this forum to get around that problem

2. Even if I can rework them - why did they self destruct in the first place? Also I would like to know the correct value for those two overheated 2Watt-ish resistors next to the output devices.

Last edited by dicky96; 10-26-2020 at 04:23 PM..
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Old 10-26-2020, 04:57 PM   #15
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Default Re: Quark FALCON 1000 KW FM Transmitter - Alarm LED illuminated

I think you need more power than a t12. you could cut the main transistor out, just leaving the legs. Then unsolder one remaining leg after the other.

Here is a critical part / advice: When you do put the new RF transistors in, you have to mount them down with screws FIRST before you solder them. If you do solder them first, then mount them to the heatsink, you run a high chance of splitting the new RF transistors, popping the white cap off.

Why they distructed first place? Lightning, high swr, running too hot, bad coax, etc.
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Old 10-26-2020, 07:41 PM   #16
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Default Re: Quark FALCON 1000 KW FM Transmitter - Alarm LED illuminated

100w iron should shift them pretty quick enough .i would think you could test the drive circuits when the old ones are pulled .
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Old 10-26-2020, 07:46 PM   #17
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Default Re: Quark FALCON 1000 KW FM Transmitter - Alarm LED illuminated

There is a high vswr LED, I'd hope someone was monitoring SWR before letting it fail...?
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Old 10-27-2020, 07:59 AM   #18
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Default Re: Quark FALCON 1000 KW FM Transmitter - Alarm LED illuminated

A bit off topic but anyway....

Really I have never been able to understand this SWR thing. I mean, I know it exists and you have to match the load impedance but

In the case of an Audio PA - If it is rated with a minumum impedance (speaker) of 4ohm, and you connect a 2 ohm or 1 ohm load, then the current flowing through the load at full power is going to be twice or four times what the amplifier can safely supply, so it makes sense that without some sort of current monitoring/protection circuit that something in the output stage is going to go bang.

But If I connect an 8 ohm load or a 16 ohm load or even no load to the amplifier then it can't come to any harm as I am now running the amp at a half or a quarter of it's rated maximum current or in the case of no load the amplifier is driving no current at all. It could run for years like that, no problem.

So an RF amplifier to me is just like an audio amplifier the same (Class A, AB etc), it just runs at higher frequencies that's all. Where I can understand a lower than normal impedance load could easily cause things to go bang (without protection circuitry), I can't get my head around why a higher impedance or open circuit load would bother it at all.

Last edited by dicky96; 10-27-2020 at 08:02 AM..
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Old 10-27-2020, 10:53 AM   #19
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Default Re: Quark FALCON 1000 KW FM Transmitter - Alarm LED illuminated

https://www.arrl.org/files/file/Tech...f/q1106037.pdf
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Old 10-28-2020, 07:26 AM   #20
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Default Re: Quark FALCON 1000 KW FM Transmitter - Alarm LED illuminated

OK, so now the client tells me it is under warranty anyway!! He paid me for my diagnostic time and took the transmitter, He says he has two more jobs for me tomorrow.

Rich
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