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View Full Version : Help diagnosing an HTX-100, will not transmit



KK4FZM
03-25-2012, 02:57 AM
As the title states. I need help. I purchased a HTX-100 that is not 100% operable. The unit receives very well but will not transmit. When I key the mic the radio switches to tx but neither power nor swr meters indicate any change. I have tried different meters, jumper wires, antennas, and wired a different mic up (I think correctly) and nothing seems to change. I have opened up the radio and do not see any obvious mods or burnt, blown components.

I'm just a newbie trying to learn.

Thanks

KB4QAA
03-25-2012, 03:03 AM
Have you tried cleaning the Rx/Tx relay contacts?

Wet a dab of contact cleaner or alcohol on a piece of paper and gently draw it thru the contacts, holding them together as needed.

KA9JLM
03-25-2012, 07:17 AM
As the title states. I need help. I purchased a HTX-100 that is not 100% operable. The unit receives very well but will not transmit. When I key the mic the radio switches to tx but neither power nor swr meters indicate any change. I have tried different meters, jumper wires, antennas, and wired a different mic up (I think correctly) and nothing seems to change. I have opened up the radio and do not see any obvious mods or burnt, blown components.

I'm just a newbie trying to learn.

Thanks

Will it put out any power in CW ?

K7MEM
03-25-2012, 12:54 PM
Try putting it in the CW mode and keying it with a key. In the SSB mode there will not be any output until you speak into the microphone. Make sure you are connected to a dummy load, or in a nice quiet area, for the tests.

You can get a copy of the user manual and the service manual at http://www.cbtricks.com/radios/realistic/htx_100/index.htm. On my HTX-100 the high output (~15-20Watts) is a bit low, but I usually only run it in the 5 Watt mode. The 5 Watt mode is perfect for PSK-31. My home brew computer interface works fine through the microphone jack. Working cross country (i.e. Arizona - New York) is no problem.

KK4FZM
03-25-2012, 01:38 PM
No output in CW either. I downloaded the service manual this morning and will look for and clean the relay. Thanks for the tips so far guys.

KA9JLM
03-25-2012, 02:22 PM
No output in CW either. I downloaded the service manual this morning and will look for and clean the relay. Thanks for the tips so far guys.

Check the RF Output Transistor.

Transmitting with no antenna, or very bad match could have fried it.

K7MEM
03-25-2012, 05:39 PM
No output in CW either. I downloaded the service manual this morning and will look for and clean the relay. Thanks for the tips so far guys.

Don't look too long for that relay. The HTX-100 doesn't use a relay for T/R operations.

The service manual has a good, step by step, trouble shooting section. But there might be a problem working through it, if you don't have the necessary test equipment.

Did you check both the High and Low power modes? You switch between the High and Low power modes by pulling out, or pushing in, the RF Gain Control.

If neither the High and Low power modes work, yet it seems to receive fine, I would start looking at the phase locked loop section. The loop being out of lock will prevent transmitting.

You might want to look it over for odd modifications. There are mods to increase the frequency coverage, increase the power, and enhance the audio transmit section. If these mods are not done well, it could disable transmit.

KK4FZM
03-25-2012, 05:46 PM
Ok, I have checked in low and high power modes, neither work. I do not see any mods but I'm not entirely sure about that. I do not understand how to check the "phase locked loop section"? I will look at the rf out transistor after I read through the service manual and have a better understanding whats going on in here. Radio's are a new hobby for me so it is all learning.

Thanks

KC2UGV
03-25-2012, 05:50 PM
Ok, are you relying on the internal meters, or an external one?

KK4FZM
03-25-2012, 06:17 PM
External power/SWR meter. I have tried two different ones and two different jumper cables to hook them up. And I am guessing the "phase lock loop section" is the PLL? I will work through some of these tests tonight or tomorrow.

KK4FZM
03-28-2012, 12:23 PM
A small update: I built a dummy load to take place of the antenna. In this setup I can just barely see the power meter move in both SSB and CW. I'm sure it was doing this with the antenna I just could not tell. I have started to do the service manual troubleshooting and will keep you guys informed. Thanks

KD8DEY
03-28-2012, 12:29 PM
sounds like the driver is probably ok but the output is kaput
MRF-477 was unobtainium until eleflow recently developed a substitute.

http://www.ebay.com/dsc/i.html?LH_TitleDesc=1&_sacat=0&_nkw=MRF477+ELEFLOW&_osacat=0&_odkw=MRF477+ELEFLOW+HF+RF+POWER+TRANSISTOR+1pc

KA9JLM
03-28-2012, 04:13 PM
A small update: I built a dummy load to take place of the antenna. In this setup I can just barely see the power meter move in both SSB and CW. I'm sure it was doing this with the antenna I just could not tell. I have started to do the service manual troubleshooting and will keep you guys informed. Thanks

You may want to verify that you are getting B+ to the Output Transistor, and if you do, then Bubba sounds correct, on a bad output Transistor.

I would check the voltage and verify the part number, before ordering.

KK4FZM
03-28-2012, 10:23 PM
Using the transistor voltage chart. The final Q502/MRF-477 appears fine. I am following the transmitter flow chart and am at the step that requires me check test point 2. But, they failed to tell me what I should see on TP2. I am taking a break to read through this service book more.

Thanks Guys

KK4FZM
03-28-2012, 10:39 PM
BIG update!!! I was not correctly checking in CW mode. I thought the mic switch would work as a key while in CW mode but, I was wrong. I put it in CW and used a screwdriver to short the key input switch and the radio will transmit fine in CW. it beeps out of the speaker and the power meter goes full swing. (about 2watts in low or high power)

Thanks for the info so far and hopefully this info will help steer me in the correct direction.

N8XGS
03-29-2012, 12:05 AM
To test for pll lock you will have to verify which IC chip dose what, hopefully the service manual will provide that info, and it should give you voltages to test for from specific legs of of each chip. Use a volt meter to check each leg - possitive probe to the leg and neg to a point on the chassis. If your voltages are with in given tolerances it will be time to check out other components. Please do not use metal screwdrivers to do any adjusting inside of your rig or you may cause sevear damage to the rig. Good luck!

KK4FZM
03-31-2012, 02:16 AM
I have been following the service manual flow chart as best I can without some of the proper test equipment. I found that at test point 301 on the PLL board only has 4V should have 6V and a transistor Q303 has 4V on the collector and it should have 5.7V. So I think this may be the problem. My question is, is the PLL board used in CW or only SSB?

KA9JLM
03-31-2012, 03:23 AM
Chances are if it is transmitting the PLL is working.

The PLL sets your frequency on CW and SSB.

Is your power supply at 12 Volts or higher when you transmit on CW ?

I would look at the power supplies, and the RF Output driver and Output transistor voltages again.

N2KNW
04-19-2012, 12:02 AM
http://www.youtube.com/watch?v=-HL5Xvzdudk

KK4FZM
04-30-2012, 01:40 AM
Thanks guys for your help. I am slightly embarrassed to say I had a double mic issue. The original element had opened up and I replaced it. Problem solved right? Wrong, the cord has a break in the wire and I spent a lot of time diagnosing the radio when I never check the mic wiring. Anyway a totally different mic wired up to the radio got her working. At least I learned something about this radio.

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