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Texas star 350dx high drive keeps burning input rf choke..
- Thread starter Myst-hic
- Start date
You probably know this,
but you can only check the individual components by removing them from the circuit.
but you can only check the individual components by removing them from the circuit.
Yes, I pulled one leg..
Yes, I pulled one leg..collectors of pills are getting their 13.8 as well, as it stands I am problem solving how to raise the bias voltage, I think I will order the ceramic caps for most the board, maybe the diodes, replace from the pills outward. It's cheap insurance..
You need to check C16 and C17 capacitance values, and also to see if either one has shorted or opened .......
The cheap chinese component checker like what you find on ebay work great and are not expensive. I bought one a while back, great for checking Transistors too.
Thank you for all your insight ranch55, I have not checked them, in fact I should learn how to do that! i have them on order, including the micas, which i think 16 is..do you happen to know why c15 and 20 would be changed to a silicone diode? I ordered the caps that should be in their place just in case, was thinking of trying to bring it to schematic spec to be sure..obviously someone has been in the unit before and had the same choke problem. It is a '94 model of that helps..i did find the 5w 25ohm to be 26.2, so i ordered that as well..should be about a week, till then I will learn to check caps..
Some of the stuff from China is ok, good to know..i will look into those, maybe order tonight, my voltmeters seem to do everything but check capacitance.
The diode check on a multi meter is crude but ok for diodes. Checking resistance on a diode, same thing. I have seen transistors that check ok on a multi meter, but on a component checker, identify as the wrong component, so it's "broken" inside.
Glad to see you sticking with this.
Thank you, I hope that I get it solved, so maybe in the future someone else can benefit from the information, I had searched multiple sites, had gotten as far as I could before asking..ive fixed 3 radios all because of a lot of info, but there is not a lot on amps out there..and yes, im.poor and stubborn my friends ego and mine depend on me fixing this beautiful contraption in regards to testing o generally have a "new, good known part to reference resistance from, especially transistors and diodes, because there are 3 unknown diodes in this rig, I am left guessing, so i think I may just return it to the diagram spec capacitors later if the problem persists after testing the mica/ceramic caps. There is an aging screwdriver 1.5 hours north I could use, but he is backed up 2 months, when ALL else fails I will deliver it to him..thank you for hanging in there with me!
Update...i have changed all mica caps, starting with c16, one at a time with a test between each. Still 5.4v...all my other ceramic caps and resistors are still in transit. Further testing reveals that after keeping power on for an hour, and keying for a bit with tests (no rf at input/output) my base/ground ohms rises to 2.0ohms and the 5w 25ohm gets pretty hot to the touch. Is this normal? Bad resistor changing value due to heat? One of my larger annoyances here as I will state again is the fact that there are at least 10 components on this board that are different specs or component than is on the cb tricks schematics, different builders making variants? I can't tell if they have been replaced..solder all looked the same other than the rf choke patch done before. In regards to c17, schematic says .1 if I think, but installed is a 022k pf i think, that is an incredible difference! Do you have any ideas as to why there are so many descrepancies between my machine and the schematic?
Yep.
Engineering changes. Kinda like the difference between a car made in 2010 and the same model made five, ten or more years prior.
Best explanation I can think of is simple economics. They have some genius shopping for skidload quantities of parts they use by the thousand. The design gets adapted to that batch of capacitors, for example. When those run out, a new part takes its place and the circuit gets a tweak needed to adapt for the new part.
Another thing that has evolved decade by decade is the max drive power a Texas Star will tolerate. An amplifier from the 80s would take only half or 3/4 the power to drive it that newer amplifiers need. The reason is simple enough. When that amplifier was first designed as the "Outcom" or "Westcom" linear, there was no such thing as a dual-final CB-type radio.
Fast forward four decades and radios are just larger. Too bad the amplifier doesn't have a production date stamped on it. A complete set of year-by-year drawings that show all the changes probably doesn't exist. If it does I'll probably never see it.
73
Well that puts it on great perspective, thank you! That was a ton of information I needed...i think you just instructed me to take educated guesses to as to the diodes used, play around alittle, to see if it changes my bias voltage. The fact that you say the older amps used less power for the gain is a huge plus to me, it is a 1994 model, I consider everything made in this world after 98 or so to be junk, thus I strive to keep the antiques alive. I've seen divergents from schematics in my uniden Washington too, mainly transistors, but all those were easy to cross reference..going forward with your shared knowledge I will stick to the capacitance and type used knowing that this machine worked 15 years ago that way changing to meet the schematic is a rabbit hole I should not go down.. ok, frustration over, thank you, 73s
I'm thinking you may have 1, or both power transistors bad......
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