The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

nomadradio

Have you got a link to this project?

73

nomadradio

I was unable to locate a diagram for that radio. The schematic is my starting point, whether the radio is in front of me, or across the planet.

I'll pass along my general experience concerning failures that just 'happen'.

I have accidentally bridged solder across adjacent foil pads on more than ...

nomadradio

If the MC145106 PLL chip is accessible, this means that the 18-pin Z8 CPU on the channel-selector board is also accessible.

Every NR150 I ever saw had the PLL chip and the CPU globbed together on the main pc board under a layer of hard epoxy.

This was done precisely to prevent frequency ...

nomadradio

This is not quite the same radio, but I'm pretty sure the pc board is the same.

http://www.cbtricks.com/radios/sbe/sbe_ ... /index.htm

73

nomadradio

The digits in that radio are an LED display, as in Light Emitting Diode.

Both digits are inside one chunk of plastic with sixteen pins, one row of eight on the top edge, eight on the bottom.

Desoldering it from the pc board is best done with a desoldering iron. One with a heated, hollow tip is ...

nomadradio

Half a Watt?

Time to take loose the base and emitter legs of the final transistor and see if it passes a diode test across those two.

You can leave the emitter soldered to ground and do this with only the base leg unsoldered from the pc board.

Sounds kinda like an open base to emitter junction ...

nomadradio

Wiring anything to pin 3 on the MB3756 is a mistake.

Use pin 1. It's intended to supply some current. Pin 3 is NOT. Hooking to pin #3 is the kind of misinformation that circulates the web forever, since most folks who pass it on have no idea what is inside that chip.

Hey Rick, that's a righteous ...

nomadradio

Err, a "P400" ?

Haven't found the tech info on that model yet.

Gotta figure it's got the same main pc board as a more familiar Uniden model, but I'm not sure which one that would be.

This isn't a european-standard or a 'down under' model is it?

73

nomadradio

Wait a minute, are you saying you can get receiver audio from the external speaker?

Or JUST the PA audio?

73

nomadradio

If you're going to run an amplifier, you will need to reduce the radio's carrier (dead-key) power level.

Cranked for all it's worth, the radio will dead key between 5 and 6 Watts. Too much for most ammplifiers.

But if you'll run it barefoot, by itself, this is TOTALLY WASTED EFFORT!

Yep. Won't ...

nomadradio

Umm, "SSB" and "upper channels" are NOT the same thing, really.

Now, the stock new-in-the-box Cobra 148GTL will cover ONLY the legal channels 1 through 40.

And it's a SSB radio. SSB, or Single Side Band is just a way of splitting one channel into two, sorta.

SSB tends to deliver better range ...

nomadradio

Hi KM,

Sorry about the lack of enthusiasm.

Clear, complete instructions are a really big help when you're doing a procedure the first time.

Now, if somebody (else) were to shoot some pictures or sketch the locations of what will hook where, and write up the hookup details, that might be a safe ...

nomadradio

Sure enough, this is the thread I was remembering.

Working on it......

73

nomadradio

I don't recommend messing with the driver transistor. Don't think there is much to be gained from doing that, unless it's broke.

The metal top-hat (TO-5) final transistor can be replaced with a 2SC1969.

Lining up the TO-220 final's leads with the right holes in the PC board is a pain. Especially ...

nomadradio

Hmmm. This is the point in the troubleshooting process where I grab for a 'scope probe. For the moment, I'll just guess that you don't have one handy.

Or an external speaker. The internal speaker is switched off when an external one is plugged in. If that switch contact in the external jack goes ...

nomadradio

Hello Carlos,
I am not able to offer any advice for this radio.

It has not been seen in the USA, far as I know.

If you can locate the company that imports it to Portugal, this is your best hope.

73

nomadradio

The "11Z" version of that pc board is from the very early nineties, pretty sure.

Poking about for a radio with that board in it, but no luck yet. That would be the best answer to the question, one that hasn't come loose yet.

Don't remember ever seeing those "flying" parts on the foil side of the ...

nomadradio

Westgate http://www.westgateparts.com carries both the meter lamp and the two-digit channel displays.

Not sure about the jewel knobs. Sure sounds like a Bar-Jan item to me.

73

nomadradio

I'd start with looking at the age of the radio. Around the 20 or 25-year mark some odd things begin to fail. Too bad it doesn't have an odometer like a car. The mileage is an issue, but no way to tell how many thousands of hours of running time the radio has on it.

If it says "Made in Taiwan ...

nomadradio

I can't escape the suspicion that some step in your procedure went wrong, and clobbered something.

It's pretty easy to unintentionally create a solder "bridge". If the solder glob from one foil pad spills over onto an adjacent one, this can cause unpredictable failures.

Just to start, I'd check ...

nomadradio

Uhh, "Lights" ?

If you mean the one inside the signal meter, there's only one light in there. Gotta figure you wouldn't ask if you just meant the one tiny light with just two wires, right?

Or do you mean the channel-display digits?

Have never seen an on-line walkthrough of that project. Both ...

nomadradio

As for the bigger picture, learning about what goes on inside the radio, I recommend two books written by Lou Franklin. The Screwdriver Expert's Guide is a good intro. His other title, "Understanding and Repairing CB Radios" goes into more detail.

His web site is at http://www.cbcintl.com

The ...

nomadradio

Do you have a way to test a transistor for a blown junction from base to emitter?

Time to check the driver and final both. That's what I would anticipate. That one of the two will show an open circuit from B to E.

73

nomadradio

The 2SC2028 and the 2SC1957 are pretty much interchangeable. Don't think you'll see much difference in performance.

Those two numbers were originally made by two separate, competing brands, each intended for the same market. Specs for the 1957 show a little higher power gain than the 2028, but ...

nomadradio

yamiraptor wrote: I'm going through and resolder alot of the joints and see if I might get lucky.

Always a safe bet with that radio. Let us know how it turns out.

73

nomadradio

So, you mean that it DOESN'T blow the fuse UNTIL you turn on the power switch? Important detail there.

Any chance that another truck with a really large linear in it parked alongside your truck while you were indoors? If he keyed with your antenna too close to his, that would do it.

Somebody who ...

nomadradio

Umm, you didn't hook the ground wire from the power cord to a screw in the passenger cabin, did you?

The black-coated "parkerized" screws used to hold dashboard panels in place are not suitable for a ground connection.

And if the radio's black wire is also run out to the battery, it doesn't hurt ...

nomadradio

Haven't seen a lot of that model around here. One thing I found odd was with the pc board that bolts flat against the inside of the large heat sink This is the board that the metal regulator transistors' pins are soldered to.

Other models have a brass 'eyelet' installed in each pair of holes that ...

nomadradio

Ranger USA's site used to have a 2995DX service manual in a PDF file to download. It's a 2 and a half meg file, so I'm not going to try to post it here.

Same 'linear-regulated' power supply and pc boards.

Output transistors are usually 2N3771, rated for 30 Amps each. Not the only number the ...

nomadradio

The original is a piezoelectric high-impedance "ceramic" cartridge. It can die from excess temperatures, humidity, shock, age and any or all of the above.

Mouser electronics http://www.mouser.com has some chinese-made crystal and/or ceramic cartridges. Or used to, at least.

The larger the better ...

nomadradio

My favorite is the "LC Meter II". Measures small inductances and capacitances very well.

Trouble is, it won't handle large ones; coils over 1 Henry, or electrolytic capacitors.

It's sold at http://www.aade.com

73

nomadradio

Saw some radios around here 7 or 8 years ago with that model number.

It has a unique pc board, type "EPT3000". Has an enormous modulation transformer driven by a pair of 6-Watt audio chips. Big-time high-level modulation. And no easy way to get big "swing" from a low carrier level.

No data.

No ...

nomadradio

Glad to hear it was that simple.

Congratulations.

73

nomadradio

You're forgetting the "power factor" part of the picture.

To create 120 degrees of phase shift, you'll need a capacitor with so much reactance that you won't get much power through it into a resistive load.

If it was this easy, you'd see commercially-made 3-phase adapter gadgets made this way ...

nomadradio

So long as you can still get them from RF Parts Inc for under seven bucks, the 2SC1969 is the most cost-effective upgrade by far.

Converting to a MOSFET-type final transistor is more involved, more error-prone, and the results less predictable.

The 1969 is a cousin of the original final, just ...

nomadradio

The Saturn has two ground circuits in it. The chassis is NOT connected to the negative side of the DC power supply. Each of these is a separate, er, "ground". An array of small disc capacitors is bridged across these two separate grounds to put the cabinet metal at the same RF potential as the pc ...

nomadradio

I have a suggestion.

Use a regulated supply large enough for the radio, and run the amplifier alone from the larger, unregulated supply.

The radio wil be far more sensitive to AC ripple than the amplifier, as a rule.

Your "3-phase" idea won't work the way you want it to, best I can see. Feeding ...

nomadradio

Well, let me say this about that.

A so-called "Digital Dial" will show your operating frequency while actually reading one or more of the radio's INTERNAL frequencies. A digital dial contains a frequency counter, but displays a calculated number that's NOT really the actual frequency that is fed ...

nomadradio

Most of them are not.

If you look at the radios with factory-installed amplifiers you will find that the wiring into the linear is filtered. Also, a metal shield cover separates it from the radio's interior wiring.

This is done to keep the linear from, er, "bleeding" the radio's internal ...

nomadradio

Umm for free, from here:
http://bama.edebris.com/manuals/heath/sb200/

You'll need a viewer plug-in for that type file.

Those are at http://www.lizardtech.com/download/dl_options.php?page=viewers

Or you could pay for the same info on a CD-Rom sold on Ebay.

But you probably meant "free ...

nomadradio

Latest Stryker SR-440 has one 520 driving another 520 driving two IRF520s. No big flange-mount part. At all.

Got some pics of the inside of one.. I'll dig them out and post them if anybody's interested.

73

nomadradio

just and the diode/ resistor type mod to hold my modulation/ swing the same from all levels of deadkey.......

Sorry, wrong modulator circuit. Nowhere for that diode to go. Same "low-level" AM modulator used in the President Jackson.

Every successful setup I've seen to retain peak power at ...

nomadradio

Questions, questions.

Is this a (nearly) 30 year-old President Washington with a 4-pin mike socket?

Have you ever seen it perform at full power? Or has it been like this since you first saw it?

If you hire a tech to figure it out, he's gonna ask the same questions. If he has a clue. History ...

nomadradio

This radio has turned into a real "Chicken or Egg" situation.

Even a sharp, experienced tech needs to put the wires where they belong FIRST to make measurements and identify what part of the radio has been shut down.

Or, if you could point to a radio with all the wires in place, and identify ...

nomadradio

Don't get to see the 18-channel types here in yankistan.

The 'scanner' products meant for that type radio would feed the 858 in place of the channel selector.

The flat cable was wired to feed the 'bits' directly to the pll chip's input pins. Many of the SSB base radios with that chip had a flat ...

nomadradio

Umm, you keyed your, uh, "DRIVER"!!!! ? ? ?

The keying circuit was built to tolerate only barefoot-radio drive. You have probably blown out the keying transistor that senses the radio's carrier and activates the relay.

With a light touch, the leads can be snipped flush with the body of the old ...

nomadradio

Hmmmm. "Navaho", eh?

Earliest radio with that name was a 23-channel AM base. A basic 3-knob mobile in a cabinet with an UNREGULATED power pack that came out in 1969 or 1970.

The "Navaho" name was subsequently put onto a string of other models, including some 40-channel SSB base radios from 1978 ...

nomadradio

Cool! Glad to hear nobody changed the wire colors.
Congratulations!
73

nomadradio

It's a good practice to replace the original 1 Amp-rated protection diode with one rated for more than the recommended fuse size.

A 3-Amp rectifier will probably survive reverse polarity with the proper 2-Amp fuse in line.

The original 1-Amp rectifier will not survive that 2-Amp fuse, and shorts ...

nomadradio

Best guess:

Red is power. Best source is the regulated 8 Volt or 9 Volt source in the radio.

Black is ground. Either the ground wire that comes off the mike socket, or the circuit board at the other end of that wire will work best, usually.

White is the audio out from the toy, to the audio pin ...

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