someone please crack open their late model iAM and take some detailed images of the entire RF section (from oscillator to finals), audio section and power supply section. 1 overview and several closeups on the various sections detailing resisters, caps and transistors.
i need a pic from a known iAM so i can attempt repairs to mine.
i need to be able to read the resister bands, need TR part numbers and cap part numbers.
need everyone's help in repairing this thing
the guy i got it from attempted to mod it beyond it's original design. ie: more power or asymmetric modulation or super modulation and did not know what he was doing and hosed the thing.
If it helps, I have a T.H. v5 that transmits fine with the wire antenna, so the RF section is good. It is lacking the coax connector, but as you are interested in just the RF components, it may be just what you need.
I was saving it as a parts unit. If interested in working out a trade, let me know.
what kind of trade? what would you want for it? also send pic's to my email forumsnotify at gmail
I don't have an I-AM, but recall that Tha Dood has one, 1620 Poca, WV.
This posting made me curious so I went over to the Radio System's site and read through their info on the I-AM. Couldn't find a schematic or internal pictures.
Closest thing to a schematic you can find is on the patent documentation, and that is not exactly easy to read as the numbers are blurred and the print is less than what you could get carving the road map in a stone.
RFB
Hello Pioneers of micro radio ! Ive been off the site here for a while been busy broadcasting to my yard, you know how it is when you broadcast to your yard -
I have a TH 5 radio Transmitter and am having problems with the automatic antenna tuner part of the transmitter. The tuning device which tunes for resonance does not move at all when you go to a different frequency.
Basically the transmitter frequency will change on the frequency readout, and the actual RF frequency changes but the auto antenna tuner does not function so the antenna is not peaked.
I checked voltages against a good TH 5 on the motor drive circuit, and the voltages appeared the same on both transmitters but the one in question will not function at all.
I was able to run the motor on the bad transmitter with external power to the motor so the motor is good and runs and nothing is binding in the gears. The display will not display "CAL" except for about a half second then that's it.
The transmitter works properly on the external antenna connection and all aspects of the transmitter function fine except it will not peak the output with the auto tuner as the auto tuner will not work.
Using a field strength meter I can get a nice peak if you manually move the tuning coil slugs when using and external voltage source on the tuner motor. It seems all is well on the RF side but for some reason the auto tuner will not work.
I did remove the circuit board and there were no cold solder joints as far as I could tell and also made sure the external internal antenna switch worked which it does.
I am an electronic technician trained in broadcast engineering so I have plenty of experience with radio transmitters but some times its impossible to troubleshoot equipment with out the proper documentation.
I found the outdated schmatic on the web but its next to worthless - Do any of you have experience with the tuner on the TH 5 ? There must be a problem with the reference signal to the part that runs the motor, without a wire diagram some thing like this is hard to sevice.I wrote to "I AM Radio" maybe they can supply one but if there like talking house you might as well forget it.
I can do a work around by supplying the motor on the antenna tuner with external voltage trough a DPDT toggle to reverse polarity to change directions of the tuning slugs but would like to fix this properly.
If there is any information out there that you guys know if or can give me some advice let me know..
Thanks
Radio Joe
Hello Radio Joe.
Have you double checked the unit is going into internal antenna mode when moving the antenna selector switch on the back? The front panel will indicate which mode the unit is operating in. The external antenna light on the front should not be lit when using the internal antenna ATU.
If this is ok, you may have a bad PWM IC, located next to the 4 pairs of transistors behind the motor assembly. It is an 8pin DIP IC and controls the motor through the driver transistors.
Another area to check is the sampling path. If the sample path has no signal on it, which merely is coupled from the output of the internal ATU, it won't tell the microprocessor where the tuning is and thus the microprocessor sends no commands to the PWM to move the ferrite tuning rods on the ATU assembly.
Another possibility is the RF output from the final section is not where it should be..ie too weak but there enough to be picked up by a radio or FS meter, but not enough for the sampling of the signal after it passes through the internal ATU coils.
To check this, switch the unit to external antenna mode and attach a scope or watt meter capable of reading down to 500mW.
You should see about 135mW at the external antenna jack. If it's less, like well below 100mW or even lower, something is wrong in the output network or finals or loss of voltage and current in that area.
Hope that helps.
RFB
...I'd love to maybe buy it if the price is right. My budget is $45 or less. All I need is a TH with the wire antenna. I'm not interested in hooking up an outdoor ATU at this time. I just need something that I can hook up and get my AM station going.
Hi RFB,
Thanks for the ideas, yes the switch on the back for antenna switching is working ( tested with ohm meter to make sure) and its properly soldered in also, it DOES switch from the ext antenna jack to the internal, I did swap the PWM IC with another from an old TH 2, but that transmitter was having problems too at one time with the tuner working, its my parts transmitter, so not sure if it was known good, I can pull one from another good TH 5 -
And the signal path from the antenna tuner to the chip? I dont know where that is or where to check,,, can you be a little more clear on that? I did look for cermaic disc caps thinking one was bad or not soldered in but didnt know where to check, what pin on that PWM chip does the reference RF go into?
I also saw on the bottom of the board a SMD chip right next to the area of the PWM chip, not sure what that is for but I assume has to do with the control of the antenna matcher...
When I pulled the PWM chip out I tested voltages and they were the same on the power transistors as with the chip in, and like I said, the voltages all look good compared to a good TM 5 so I assume that either the PCM chip is still bad, or there is a problem with the signal path. I bought this one used but I don't think it was ever used so must be a manuf defect - I still suspect the PWM chip or the signal path,,, if you can tell me more on where that signal comes from and goes to on the PWM chip ill start looking again - I do have a scope to trace it out...
Thank you for the input..
Oh, Just what is the number on that PWM chip, the one on the TH2 is different than on the TH 5 but looks like the same chip goofy numbers dont know what to use for cross reference..
Radio Joe
I will have to open up one of my TH5's and take a look at that chip's part number as well as trace the sampling path and get back to you on that part. The schematic, or lack thereof, requires a lot of eye squinting and cursing! But referencing that and an actual unit you can find your way around things.
The small SMD below is the PLL chip for the oscillator and it's rock is the 7.200Mhz crystal on the component side near the PWM chip.
Will return with some more info. 🙂
RFB
Thanks RFB,
I did down load the schematic and detailed circuit description off the internet with the patent information, of the original Talking House transmitter. There is more there than what I first thought but it’s confusing the way the material is presented but it’s better than nothing.
Most of the changes I think over the model numbers were in the message part of the transmitter, but I’m sure there were others. I really thank you for your help.
I am going through some vision problems right now, nothing that surgery can’t fix I guess, but anyway, always something - so this makes reading that schematic difficult.
That part number on the chip is confusing, sometimes manufactures don’t put the prefix numbers on the chips makes them hard to cross reference if you’re not working with the stuff constantly to keep up- you know how it is with coffee to drink and serious yard casting to do, those activities can take up a lot of serious time!
I’ll take another look at the transmitter and I will crack this nut and get it fixed - your sharing your know how on it is greatly appreciated. I don’t like running something that has dead sections in it with a work around - I really don’t think much can be wrong it doesn’t look like any parts are burned up or things like that.
Like I said it seems all voltages in the ATU area look good when compared to a good TH 5.Thanks again for your help.
Radio Joe
Made sure the controller chip for the ATU was good swaped from good TH5 but no luck ATU still dead, put chip from dead TH5 in good TH 5 and it worked so chip isnt it.
I then tried to check signal from the transmitter to the chip but all pins on the IC showed RF with a scope so that didnt work out, then tried a line right from the antenna through a cap to the chip on each pin to see if that made a differnce and it did not. It could be one of the driver transistors but the voltages seem to check against a good TM 5 so not sure what the deal is.
More testing ahead on this one -
Have a good one-
Radio Joe