Quark FALCON 1000 KW FM Transmitter - Alarm LED illuminated

[llonen]

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

With a sufficiently bad impedance miss-match it is quite possible to have very high voltages coming back down the feed line, this tends to be what causes damage in a high vswr reflected RF scenario.

[eccerr0r]

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

Weird they went for a third party first instead of going straight for warranty service.

Do they have a spare transmitter? I would hope they would...

It's a pity RF transistors are so fragile...

[dicky96]

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

[petehall347]

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

https://cdn.badcaps-static.com/pdfs/...ee264b0c44.pdf

[dicky96]

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.

[eccerr0r]

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...?

[petehall347]

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 .

[CapLeaker]

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.

[dicky96]

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.

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.

[CapLeaker]

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.

[dicky96]

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

Oh!! The other one doesnt look too clever either!

[dicky96]

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

Pics...

[R_J]

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

[petehall347]

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

what fault sets the alarm state ? what does not work ?

[eccerr0r]

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

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

Maybe you mean some other silver alloy, but the common electronics silver solder is lower melting point.

[CapLeaker]

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

silver solder has a higher melting point than leaded 60/40 solder.

[eccerr0r]

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.

[CapLeaker]

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.

[dicky96]

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.

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!!

[CapLeaker]

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.