No Audio from D104

[blue goose]

Having a hard time with this Ebay Silver Eagle D104 here. I have limited technical abilities, so let me set the stage. I have a VOM and can solder and check components for continuity and sometimes value. (big deal) hahah but that's a start I guess. Hard to visualize/design a pc/breadboard from a schematic though..... Here is the problem: I have no audio whatsover going into my Superstar 3900 from the Silver Eagle. I have it wired right, shield and blue wire to Pin 1, white (audio) to pin 2, and black and red wires to RX and TX pins 3 and 4 on the Superstar. It keys up the radio. Battery is good. Voltage present on the pc board of the pre-amp. No audio with or without battery. My other Silver Eagle has audio even without battery, am I correct in assuming that if I could bypass the preamp and get audio directly to the radio at pin 2 it would tell me something? Is there a way to jumper around the preamp...please detail from what to where....and how can I test to see if the preamp's transistors are good? I replaced the 47 uf cap and confirmed that the pot is working (at least it changes value from 0 to whatever it is rated) Nothing looks tampered with in the base of the mic except for the cap I replaced.(I did this to a friend's D104 and his preamp started working again)The switching is a bit baffling to me,(its just the way my brain doesn't see simple things) perhaps this could be where the lack of continuity lies?????? Any help would be much appreciated guys! By the way, I have checked the mic cable, the wires from the element and even substituted the head of my good D104 which I know has a good element. No audio. What am I missing?

Mike

[Night Crawler]

Is there a way to jumper around the preamp...please detail from what to where....and how can I test to see if the preamp's transistors are good?

Remove the bottom cover of the microphone and refer to the diagram on the right [Please login or register to view this link]

Remove the green wire from the TOP of the terminal strip marked #1 and the white wire from the mic cable going to the BOTTOM of the terminal strip marked #3.

Connect those two wires together that will bypass the preamp and connect the mic element directly to the radio.

Transistor checking [Please login or register to view this link]

[blue goose]

Night Crawler,
There is no terminal strip in the base of this Silver Eagle. It has the later preamp. Thanks
Mike

[Night Crawler]

You'll have to improvise then what has to be done is to find the wire coming down the neck from the mic element going to the input of the preamp and remove it.
Then find the wire coming from the mic cable going to the output of the preamp and remove it then connect those two wires together it's possible they're the using the same color codes green and white.

[blue goose]

Two wire coming from the mic element. One goes to ground of the preamp board. The other goes to input I presume? So cut the input wire only? and leave ground?

[TheCBDoctor]

Having a hard time with this Ebay Silver Eagle D104 here. I have limited technical abilities, so let me set the stage. I have a VOM and can solder and check components for continuity and sometimes value. (big deal) hahah but that's a start I guess. Hard to visualize/design a pc/breadboard from a schematic though..... Here is the problem: I have no audio whatsover going into my Superstar 3900 from the Silver Eagle. I have it wired right, shield and blue wire to Pin 1, white (audio) to pin 2, and black and red wires to RX and TX pins 3 and 4 on the Superstar. It keys up the radio. Battery is good. Voltage present on the pc board of the pre-amp. No audio with or without battery. My other Silver Eagle has audio even without battery, am I correct in assuming that if I could bypass the preamp and get audio directly to the radio at pin 2 it would tell me something? Is there a way to jumper around the preamp...please detail from what to where....and how can I test to see if the preamp's transistors are good? I replaced the 47 uf cap and confirmed that the pot is working (at least it changes value from 0 to whatever it is rated) Nothing looks tampered with in the base of the mic except for the cap I replaced.(I did this to a friend's D104 and his preamp started working again)The switching is a bit baffling to me,(its just the way my brain doesn't see simple things) perhaps this could be where the lack of continuity lies?????? Any help would be much appreciated guys! By the way, I have checked the mic cable, the wires from the element and even substituted the head of my good D104 which I know has a good element. No audio. What am I missing?

Hi Blue Goose,

If the Mic is wired correctly then plug it into the radio. Remove the screw-on Mic Cartridge head. Stick a metal probe between two of the 3 pins at the top. If you here noise coming from the radio on Transmit, then the Mic head may be bad. I never solely rely on test equipment. A wet finger across a board or at any point will let you know if the audio section is getting to the Mic plug.....CAUTION... never do this with a Tube radio.....Ouch......

It is something simple that you are overlooking. You just have to determine if it is at the MIc head, PTT switch or the circuit board. Keep the tests simple and you can isolate the problem area. My electronics teacher always told me forget about measuring voltages...always follow the current. It has served me well over the years.

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Respectfully,

Mike

[Night Crawler]

That's right, then remove the white coming from the mic cable the one that goes to the radio from where it's connected to and hook those two wires together that will bypass any of the switches in the microphone and give a direct connection from the mic element to the radio.

[blue goose]

Did the jumpering, but still no audio.... not even a scratch. This is baffling because I have checked the wiring from the element down the neck and then switched to a known to be working head. Makes no sense.

[Night Crawler]

I had a problem like that one time and found that the audio wire in the cable going from the mic to the radio was bad.
Check it with a ohm meter for an open or short circiut.

[blue goose]

Thanks guys! Back to the "bench" I go. I knew I could get some good advice here! Will follow up and let you know what I find in the next day or two.

Mike

[Nagant]

Okay I admit I haven't read the entire post so you might have already tried this. Have you made sure the mic element is good? The easiest way to test it since I believe you stated you have a working SIlver Eagle is to swap the head from the non-operational mic to the Silver Eagle that you know is good to test it for audio on the known good stand.

[blue goose]

Yes, Nagent, I believe I stated that I had tested my already known to be good element in the first post. Tried that already. I believe like Rick said, that whatever it is is probably something simple like a broken audio wire in either the mic cord or in the handle assembly, or that mechanical switching maze . But having ohmed all that out once or twice, I thought I had ruled most of those possibilities out. Gotta go back and re-check. All these ideas are much appreciated, keep em coming!
Thanks again,
Mike

[Night Crawler]

Check the ground wire coming from the plug for the mic element for a good connection if you haven't already.

[blue goose]

Well, I finally got back to troubleshooting the D104 for a little while last evening and I am still stumped. I found the mic element to be working by connecting it directly to the CB's audio and shield pins and manually keying the radio by grounding pin 3 to chassis while using alligator test leads to directly connect audio and shield from element head's pins.(Talkback on my radio is very helpful hearing the audio instead of just watching modulation meter). I then plugged the mic head back into the stand and did the same test this time using same test leads clipped to the wires running down the stand that solder to the amp's input. (I unsoldered these for the test) Same effect: good mic audio. So wiring is good into the amp.
I checked mic cord wiring again made SURE of continuity in all wires. Then I placed the jumpers from the leads coming out of the element,around the amp, to the mic cables audio and shield wires, this time plugging in the mic connector to the CB and keying it with the mic switch. Effects: Radio keyed properly but NO AUDIO!
I then tore down my properly working Silver eagle D104 (same exact amplifier and switch) and started doing some comparing of the way the switches are wired. There are some differences!
Only 4 wires are used on my good mic: audio, shield, PTT, and a black wire from switch terminal where shield is soldered going to pin 4 of the radio. Looks like wiring from radio to switch terminals is a little different and a jumper was also added between two of the switch terminals in my working mic. The mic in question has no such jumper and has a blue wire running from switch terminal to mic pin 1 along WITH the shield. The mic wont key without this blue wire.
I then changed the switch and mic cable wiring to match the working mic and did a short test before turning out the lights last night, but still no audio! tried with and without the battery.
So this is where I am at, but I am starting to think the problem is all in the switch wiring. I tested to see if contacts were making across switch terminals when depressing PTT button using continuity function of my ohm meter.

Mike

[TheCBDoctor]

Hi,

You really need a scope or a good Multi-meter, set on AV volts (micro-volts, to follow the audio path. I would check for a bad electrolytic cap or a bad J-FET on the amplifier board. There are 2 of them. Follow the current.

Respectfully,

[blue goose]

Does anyone know a link to show a Silver Eagle amplifier's "piano switch" wiring details? This one has been modded and no way to know how it is supposed to be wired without a diagram or picture showing wires in and out I am bypassing the entire circuit and when I key up the CB using the switch in the base there is still no audio.I'm thinking the switch may be the problem because I can get audio directly to the radio using 2 alligator test leads from the element wires coming from the head and manually keying the radio by shorting pin 3 to the mic socket on the CB with a short jumper. But audio wont pass through the Silver eagle's coiled mic cord using the D104's PTT switch. Its like the switch shorts out the audio and wont let it pass.
The D104 I have does not have a terminal strip in it, it's just a PC board with a piano switch mounted on it and a battery holder. All one piece. It is the two transistor amp, maybe the later model Silver Eagle. It would help if I knew what wires are supposed to go where. I know it sounds like I am making something easy very difficult, but nothing has worked here yet. This mic was wired up for some other radio, maybe a ham radio, and came without the mic plug....just the coiled cord. I will deal with troubleshooting the amp after I am satisfied that audio is passing from the head to the CB using the PTT switch in the base of the Mic. The amp may be fine, I think this is a wiring problem.first things first is the way my simpleton mind works... hahahahh!..There needs to be a manual called " D104's for Morons " I'd be the first to buy it!

[TheCBDoctor]

Does anyone know a link to show a Silver Eagle amplifier's "piano switch" wiring details? This one has been modded and no way to know how it is supposed to be wired without a diagram or picture showing wires in and out I am bypassing the entire circuit and when I key up the CB using the switch in the base there is still no audio.I'm thinking the switch may be the problem because I can get audio directly to the radio using 2 alligator test leads from the element wires coming from the head and manually keying the radio by shorting pin 3 to the mic socket on the CB with a short jumper. But audio wont pass through the Silver eagle's coiled mic cord using the D104's PTT switch. Its like the switch shorts out the audio and wont let it pass.
The D104 I have does not have a terminal strip in it, it's just a PC board with a piano switch mounted on it and a battery holder. All one piece. It is the two transistor amp, maybe the later model Silver Eagle. It would help if I knew what wires are supposed to go where. I know it sounds like I am making something easy very difficult, but nothing has worked here yet. This mic was wired up for some other radio, maybe a ham radio, and came without the mic plug....just the coiled cord. I will deal with troubleshooting the amp after I am satisfied that audio is passing from the head to the CB using the PTT switch in the base of the Mic. The amp may be fine, I think this is a wiring problem.first things first is the way my simpleton mind works... hahahahh!..There needs to be a manual called " D104's for Morons " I'd be the first to buy it!

Most D-104 Mics come with a Schematic on the inside bottom plate. Is yours missing?

Respectfully,

[blue goose]

Not missing, just the wrong schematic for an earlier mic. with a terminal strip in the base which the Silver Eagle doesnt have. But I did find the right schematic online after all, and figured out the wiring. Completely rewired everything and put it all back together. No audio.
So I am going to start replacing components on the board one by one until I get something to happen. I inspected the board itself for cracks and breaks, but all looks good. I am going to start with a new volume pot despite the ohm meter saying it looks good. I might have been wrong. I have already replaced the 47k electrolytic.


Mike

[TheCBDoctor]

Not missing, just the wrong schematic for an earlier mic. with a terminal strip in the base which the Silver Eagle doesnt have. But I did find the right schematic online after all, and figured out the wiring. Completely rewired everything and put it all back together. No audio.
So I am going to start replacing components on the board one by one until I get something to happen. I inspected the board itself for cracks and breaks, but all looks good. I am going to start with a new volume pot despite the ohm meter saying it looks good. I might have been wrong. I have already replaced the 47k electrolytic.


Mike

Hi Mike,

First check the DC voltage on the 2 J-FETS. Then switch your digital multi-meter over to AC voltage in micro-volts, if you have an auto select that is even better. As the talk into the Mic you will see the audio show up as an average AC reading. Work your way up from the audio coming from the Mic Cartridge to the first J-FET to the 2 J_FET. You should see a gain at each step. You do not need a scope, but a scope would be better.

I suspect a bad J-FET.

Respectfully,

[Night Crawler]

The silver eagle is using two npn bi-polar transistors for the preamplifier it's the same amplifier circuit used in the original d-104 if you have to replace them a 2N3904 or 2N2222 will work you can get them at radio shack for under a dollar.
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[blue goose]

That is correct, they are the "npn" type from what I can tell. I got two 3904's today and plan on installing them hopefully this evening.. Gotta make sure that I get the pinout right, on the base, emitter, and collectors in the right holes on the board, right? Are they same as oringinals? Some are different. Guess I need to check schematic first.
I like the thought of using the meter to trace the path of the audio and see what is going on, before changing them out.

mike

[Night Crawler]

Gotta make sure that I get the pinout right, on the base, emitter, and collectors in the right holes on the board, right? Are they same as oringinals? Some are different. Guess I need to check schematic first.

That would be a very good idea you never know if their the same or not I've come across some transistors where the center pin is the collector.

There is one thing you can try it's seems that you tried eveything already but refering to the schematic I posted put a jumper between points A and B on the make/break switch that will bypass it and connect the audio from the output of the preamp directly to the mic cable.

[blue goose]

Night Crawler, I have done the by pass as you describe and still no audio. jumper between A and B which will direct output of preamp audio directly to mic cable. When i key up all is quiet.

[Night Crawler]

That mic must be possessed

[blue goose]

It sure seems so! LOL