If anyone can help me, I am in need of it. I have been using an SSTran AMT3000 for almost two years now, and it has been working trouble free. About two months ago, I was using it for some yardcasting, and I decided to leave it on that night, as I would usually do. About 3 am that morning, severe weather hit North Alabama, and the power went off for around an hour. That morning when I woke up, I turned on my radio and you guessed it - no audio - . My stereo since has not been working properly, neither has my SSTRAN. I started working with it, and moticed I can hear it for about 5 feet from the t, and unless I have the gain and modulation tuned maximum, I cannot hear any audio. Even then, the audio is TERRIBLE. I do not know what else to do with it, except ask here.
Thanks for the help.
Travis
Travis,
Sorry to hear of your troubles. Let's start by trying to separate the AMT-3000 systems. First, is the carrier as strong as it has been?
Second, is the audio source OK? You mentioned a problem with your stereo and if that is what you are using as an audio source for your SSTRAN perhaps that is where the problem lies.
Try feeding audio into your SSTRAN with a known good source. If it still fails to work it could be that the audio processor chip was damaged.
Try to check each major system, RF (usual carrier strength), power supply (measure the voltage), audio source (make sure it is OK), and finally suspect the processor chip.
Please post here any other information you may have and I and others will try to help.
If you think it is the processor chip, perhaps an email to Phil at SSTRAN would be in order.
Neil
Travis,
Sorry to hear of your troubles. Let's start by trying to separate the AMT-3000 systems. First, is the carrier as strong as it has been?
Second, is the audio source OK? You mentioned a problem with your stereo and if that is what you are using as an audio source for your SSTRAN perhaps that is where the problem lies.
Try feeding audio into your SSTRAN with a known good source. If it still fails to work it could be that the audio processor chip was damaged.
Try to check each major system, RF (usual carrier strength), power supply (measure the voltage), audio source (make sure it is OK), and finally suspect the processor chip.
Please post here any other information you may have and I and others will try to help.
If you think it is the processor chip, perhaps an email to Phil at SSTRAN would be in order.
Neil
Neil,
The audio source I was using was fine, and the radio I was using was also fine. The carrier, however, was not present past 5 or 10 feet from the transmitter, and the audio coud not be heard unless the Gain and Modulation was fully turned up. I also checked the P.S. and the voltage was around 18 VAC.
Does this mean I also have an RF problem?
Thanks for your advice,
Travis
Neil,
The audio source I was using was fine, and the radio I was using was also fine. The carrier, however, was not present past 5 or 10 feet from the transmitter, and the audio coud not be heard unless the Gain and Modulation was fully turned up. I also checked the P.S. and the voltage was around 18 VAC.
Does this mean I also have an RF problem?
Thanks for your advice,
Travis
Travis,
The next thing I would do in your position is to do a terminal DC voltage check on the output stage of your transmitter. To be useful you need to know the expected voltages.
Are you equipped with a digital voltmeter to measure these voltages? If so, post back here and I will post the voltages from my working unit. Let's start with the EBC voltages to ground on Q4, Q5, Q3, Q2, and Q1.
Chances are very high that if there is a problem in the stage using these transistors we can find it with the terminal voltage measurements. Let me know.
Neil
Travis,
The next thing I would do in your position is to do a terminal DC voltage check on the output stage of your transmitter. To be useful you need to know the expected voltages.
Are you equipped with a digital voltmeter to measure these voltages? If so, post back here and I will post the voltages from my working unit. Let's start with the EBC voltages to ground on Q4, Q5, Q3, Q2, and Q1.
Chances are very high that if there is a problem in the stage using these transistors we can find it with the terminal voltage measurements. Let me know.
Neil
Neil,
I do have a digital voltmeter, and it has a fresh 9 volt battery. I am very fortunate to have people like you that know about the technical side of transmitters. Also, it's hard to believe that in two weeks I will have been a member of part15.us for two years, through all the forums, and topics, it has been fun.
Travis
95.5 WBGR
www.wbgrfm.tk
Neil,
I do have a digital voltmeter, and it has a fresh 9 volt battery. I am very fortunate to have people like you that know about the technical side of transmitters. Also, it's hard to believe that in two weeks I will have been a member of part15.us for two years, through all the forums, and topics, it has been fun.
Travis
95.5 WBGR
www.wbgrfm.tk
Travis,
I didn't realize when I posted earlier that the terminal voltages are marked on the schematic for the AMT-3000 so you can get them there.
Mine measured very close to the schematic values except for Q1 C etc which is 1.97 V.
Anyway, here are my unit's voltages (DC to circuit ground)
____C___B___E
Q5 15.0 2.57 1.97
Q4 15.0 2.57 1.97
Q3 15.0 1.83 1.16
Q2 1.97 1.16 0.42
Q1 1.97 13.7 14.4
Your measurements should be fairly close to these. Be careful when taking the readings that you don't short anything with your probes. If your readings are way off that may lead to finding the problem.
Neil
Neil,
It took me a while to figure out where C,B, and E meant, but after a couple minutes I had the thing somewhat figured out. While some readings matched, others were off a good bit. Here's my results:
C B E
Q5 14.7 7.5 8.7
Q4 14.96 7.03 8.75
Q3 14.97 1.813 1.202
Q2 8.76 1.205 0.60
Q1 8.74 13.68 14.31
Maybe I'm one strp closer to getting this problem figured out
Travis
Travis,
Sorry about the confusion re EBC but you apparently figured it out.
Here's what I get from your data: The junction of R30 and R31 should bias the bases of Q4 and Q5 to about 2.6 volts however the bases are running around 7.8 volts. Also the base to emitter drop should be about +.7 volts but it is -1.2 volts. These transistors are biased off most likely due to a bad collector to base junction on one of these transistors. There is an outside chance that R31 has opened but that is rare but you should check it with an ohmmeter just in case.
Since Q4 and Q5 are essentially in parallel to DC it is not possible from the data to tell which is bad but considering that this could be storm damage the most likely "blown" transistor is Q5 since it is attached to the antenna. You may also have to replace Q4 but start with Q5. Since the modulation takes place in these transistors this could explain the bad audio you reported.
It is possible but not likely that Q2 is damaged but judging by the BE voltage and the fact that the collector is apparently drawing a controlled current it is probably OK.
The best way to replace transistors without damaging the board is to cut the leads at the body and remove the leads one at a time from the board with a soldering iron. Usually if one tries to get all three leads hot a once the board will be damaged.
The 2N2222s used here are very common and Radio Shack should stock them. Also, pick up a spool of Solder Wick or a similar product so you can clean the old solder from the board without damage. This is a braided copper flux coated wire which works much better than a "solder sucker".
This may be more detail than you want but it sure is a good learning experience....after all, you now know about EBC.
Be sure to report back when you get it working.
Neil
Neil,
I went to Radio Shack today and bought a 15 pack of 2N2222 transistors, and a spool of solder wick. I was reading in the SSTRAN manual that Q5 is a PN2222A transistor. To me, they are roughly the same size and look alike, but will the 2N2222's work?
Have a good evening,
Travis
Yes, there should be no problem.
I don't know if you know how to use the SolderWick so here goes: Clip the transistor out next to the body leaving the leads behind in the board. Remove the leads by heating with a soldering iron and pull them out one at a time with needle nose pliers. It is important that the solder is melted before you pull or the board can be damaged. Place the solder wick on top of the pad on the bottom of the board and heat it with the soldering iron pressing the wick to the pad with the iron. You should see the solder wick up leaving a clean pad and open hole. If the hole doesn't come clean, add fresh solder to the pad and repeat. Just go easy on the heat from the iron. I use a hot iron (45 watt controlled iron set to 300 degrees C) and short time...much better than a low wattage iron for a long time. It should not take more than 5 seconds per pad. The solder wick leaves a flux mess behind and if it bothers you you can remove it with a bit of rubbing or denatured alcohol. Also, watch the tinning on your iron since the wick will strip it quickly. Retin as needed. If the wick is too big (wide) then cut it with diagonal cutters lengthwise to get the width you need. This is really easy with some practice and it would be good if you could try it on a junker board first.
It is possible to use the wick from the bottom of the board without clipping the transistor leads. Once the solder is wicked, the transistor should pull from the board. I just prefer to cut the leads first especially when replacing ICs.
Neil
Neil,
I've started the trial and error expiriments. I clipped the Q5 transistor, heated the solder and removed the pins, used the solder wick and cleaned out excess solder, and installed the new transistor. I powered the unit on, and went over to a nearby radio, and there is still no carrier signal. I checked the new transistor's voltage, and It is the same as the previous transistor. Also, I tried peaking and the voltage on the trimmer, and it was still hovering around zero. This may be the cause;however, I forgot to mention that earlier. Or, could it possibly be Q2 or Q3?
Travis