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Post by station8 on Oct 14, 2019 3:41:26 GMT
Hi Y'all:
Let talk about parts replacement of componets in transmitters.
What I notice and seen is that some people can not find proper parts no
Like the Ramsey tx uses a Gal 5 ( u6 ) but to let you know it's really a
Gali 5 part.
The other problem what I'm seeing is that people are NOT checking
The ft range of the componets and this will cause you create interference.
You need to find part that work only in the frequency range of your tx!.
Some circuit will have blocking capacitors to help stop certain frequency
From going through, but in most cases it does NOT work!.
Need to double check your filter after the repair to make sure
Transmitter working GREAT!.
So if you don't know what your doing the old saying is
Keep you hands out of the cookie jar!!!,
And the FCC will NOT visit you!.
Have fun with the hobby
Station 8
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Post by Boomer on Oct 16, 2019 2:42:58 GMT
Bitten by the bugI was bitten by that bug too. In the mid-2000s I got a Landmark Technologies FM stereo transmitter. This was a time before all of the inexpensive digitally tuned transmitters started to be sold out of Asia direct. The Landmark was PLL, binary rotary switch controlled, and had good audio specs, and was somewhere around $200 I think. It was common to use institutionally, like in rest homes and penal institutions. Well, I had it sitting on a window sill, with a dipole antenna stretched diagonally across the glass of the picture window and broadcasting. There was a storm outside and lightning.. normally I would have disconnected if the antenna was outside, but thought it was safe, and the lightning didn't seem too close. There was a strike nearby, and the signal was suddenly weak in a monitor radio in the room. I thought oh no, and turned it on and off, it was no use, nothing but a 15 foot signal range. Opening it up on the bench, the final was one of those blasted 4-lead devices, a black pill the size of a rice grain. Touching a probe wire to the output side of it, there was a little bit of signal to a radio, but there was more signal on the input side, so likely the output amp was blown. I wondered why they used something that was so fragile. I can see why they'd want to use something like that chip, taking less board space than a transistor, with fewer support parts, and controlled input and output specs. I guess they never thought to test it for electrostatic discharge across the output. It seemed like this bad design choice propagated to other companies, and I'm sure it hurt their reputations. I'm glad there's a fix with the 2.2 microhenry choke across the output. Did Ramsey ever do anything about the the issue, like send a choke out to buyers, or redesign their output sections? They should stay with a good old bipolar transistor output stage, something that's worked for decades, and the transistors only cost a few pennies. Here's the radio taken apart, showing the top side board, the final is under where those coils are on the lower right. Boomer
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Post by mark on Oct 16, 2019 5:05:37 GMT
The output is under those coils!? How the $%# are you supposed to get to it to replace it? And those tiny surface mounts are not fun trying to replace and easy to screw up and have to just throw it away. Yup, old fashion transistors with the few extra through hole components would not take up much space and would be more durable and very easy to replace but still I would protect from static/electrical surges like close lightening and a shock from your finger.
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Post by Boomer on Oct 16, 2019 10:39:43 GMT
Hi OldiesWMRK, well, the output chip is on the opposite side of the board from where those coils are and pretty much in the clear. You need a small tipped iron, the right tools and magnification for surface mount.
I'd only used the transmitter for a matter of hours before it went out. That was the first real broadcast, and I had a friend over and a live studio. Likely it 2005, and when it broke I just put it in a box and thought about it recently again.
I have to wonder if the ICs used are really made for use as final amps in transmitters. Usually devices made for the final stage are ruggedized, not just for electrostatic discharge, but for high SWR (which can cause the RF voltage to soar on the final), like for operating with no antenna or shorted output.
Maybe the GAL 5 is made for input amplification, RF amp stage in receivers, or as an interstage amp, not to have its output connected to an antenna? It might need even more protection than the choke, like a zener diode across the output, and a resistor.
Thanks for taking a look at it guys! I'll see what the part number is in my Landmark and if I can find a replacement.
Boomer
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Post by station8 on Oct 16, 2019 15:18:24 GMT
Howdy y'all: As being certified in surface mount technologies It's not very had as long you have a stereo scope and make sure you have A great magnifier from 10 minimum to 100x so you can see the indentifing Number on the chip, I use a hand held magnifier and made a support arm To hold in place that's the cheap way!. Boomer you need to look up and surface mount code list and this will help You out looking for the right part. If you have problems I will help you out if needed just give me I high but readable picture of part Or give me the number of the chip and I'll look for you. On the Ramsey 100 B On the rf output there is two parts shunt to ground 1) MLV5 2) Coil Gali 5 GALI-5.pdf (192.2 KB) Gali 74+ GALI-74.pdf (189.9 KB) Read the documents close on esd Hope this helps you guys out Station 8
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