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Author Topic: HTX-100 Need Help  (Read 1852 times)
KJ4RZY
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Posts: 3




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« on: November 15, 2012, 08:29:58 AM »

Hey guys, I have an issue with the HTX-100 that really has me confused and hope someone here can help me out with it. When keyed with the CW mode it does fine, lots of output, clean audio & when unkeyed, it reverts to receive after about 1 second. In SSB mode, it xmits fine, audio is clean, however when unkeyed, the finals pull around 2 amps & if I stuff a freq counter near the output coils I have about a 54 MHZ signal. Nothing shows on the watt meter but the receive is pretty much gone. The only way to make it quit is to switch modes to CW & key it one time. All returns to normal then. The finals have the normal 50 ma current drain in xmit, no mod condition, bias voltage is around .6 to .65v & nothing gets hot. I can see the "signal" at the finals, the TXB connection & just about anywhere around the ALC / output power set circuit. Now the REALLY weird part! It doesn't seem to do this when running SSTV through the computer. 2 different conventional power supplies, Earth ground or none makes no difference. Dummy load or antenna, same thing. If anyone has a good place to start or has run across this problem, I sure would like to hear from you !!! Thx & 73, All KJ4RZY ( ALLEN )
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N4NYY
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« Reply #1 on: November 15, 2012, 06:52:53 PM »

I had a 2510 which acted quirky. I found RF, was causing crazy transmit patterns. I was able to clean it up, but it was like 2005, so I do not recall what I did. I would try it into a dummy load to rule out RF.

Also, this one other problem drove me nuts. I would unkey, and the meter would peg for about 1/2 second. I verified on a power meter, too. I ended up finding out that the damn thing had a roger beep. Who the hell uses roger beeps? I turned it off and that was all she wrote.
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KB1GTX
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« Reply #2 on: November 16, 2012, 12:59:17 PM »

 Change R 161  330 ohm  to about 80 ohms,

It's on the driver transistor right near the final.

Also dropping the drivers bias a couple of ma to the bottom range of spec helps stop the oscillation.

Bottom left corner of this schematic, http://www.georgiacapital.net/ke4sls/htx100/pg_0061.jpg
« Last Edit: November 16, 2012, 01:33:34 PM by KB1GTX » Logged
KJ4RZY
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Posts: 3




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« Reply #3 on: November 17, 2012, 02:29:39 PM »

I had a 2510 which acted quirky. I found RF, was causing crazy transmit patterns. I was able to clean it up, but it was like 2005, so I do not recall what I did. I would try it into a dummy load to rule out RF.

Also, this one other problem drove me nuts. I would unkey, and the meter would peg for about 1/2 second. I verified on a power meter, too. I ended up finding out that the damn thing had a roger beep. Who the hell uses roger beeps? I turned it off and that was all she wrote.

Vincenzo :  Rf was one of the first things we though about, but had no evidence of it anywhere on power or cable or on mic cable. It was some problem with the ALC loop & timing of the switch xister that allowed a "cutoff spike" to shock the bias line for the finals to actually go negative when it started to oscillate.  The low pass filtering in the output of the finals prevented anything from showing up on the wattmeter, so we were scratching a lot.  After several, several hours of looking for anything out of value or leaky, we found a 22 uf  cap on the CPU output line that was leaky. Changed it & had no difference !!! Finally gave up & stiffened the bias line at the final with a 2.2 uf cap & all is now quiet! Audio is a little too high because of how the ALC loop reacts with the audio amps, but we can put up with that !!!  Roger Beeps !!!! Your kidding !!! Must have been a 11 meter wacko who had that in there!!  Anyway,  thanks again for all the suggestions.  Hope to catch you on 10 meters one day!!   73 & thanks!!   KJ4RZY    AL
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KJ4RZY
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« Reply #4 on: November 17, 2012, 02:44:14 PM »

Change R 161  330 ohm  to about 80 ohms,

It's on the driver transistor right near the final.

Also dropping the drivers bias a couple of ma to the bottom range of spec helps stop the oscillation.

Bottom left corner of this schematic, http://www.georgiacapital.net/ke4sls/htx100/pg_0061.jpg

Stan :  Great suggestion! However we had allready tried increasing the cap value on neutralizer for both finals with no change.  This thing has driven me over the edge and after a lot of hours looking for out of value caps, leaky switching diodes & or xistors, I discovered that the bias line for the finals was actually going negative when it started oscillating. Since the output filtering ( lowpass filter)  was centered around 54 MHZ, & that was what the freq counter said was the freq of osc, I went backwards through the whole ALC loop trying to find something wrong.  Nothing there. Tried running 40 ma on both finals & lowering the output levels with the Hi/Lo output adjusts & actually made it a little more sensitive to start oscillating! Finally gave up, put it all back to "spec" settings & added a 2.2 uf cap on the 2nd final bias adjust pot on the pot side of r149, 82 ohm 1/2 watt,& has not locked up again yet! Only side effect from this is a slightly overdriven audio .  Nothing excessive, just have to not get to loud into the mic.  Thanks again for the help!   73 !!    KJ4RZY    AL
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KB1GTX
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« Reply #5 on: November 17, 2012, 05:39:17 PM »

Changing the resistor on the fed back worked for me on several radios to stop that problem,
So maybe try the resistor rather than the cap?
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N4NYY
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Posts: 4758




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« Reply #6 on: November 17, 2012, 06:16:26 PM »

I had the oscillation problem and I was told to put a Mica insulator between the final and chassis. Out heatsink compound on both sides of the insulator. That seemed to work.

http://www.radioshack.com/product/index.jsp?productId=2102859
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